Multi-Copy Pichia Expression Kit - FAQs

Generally, large colonies represent transformants containing pPIC6/pPIC6α integrants, while small colonies represent transformants containing pPIC6/pPIC6α non-integrants. These non-integrants have transduced the pPIC6/pPIC6α plasmid, and therefore, exhibit a low level of blasticidin resistance in the initial selection process. Upon subsequent screening, these non-integrant transformants do not retain blasticidin resistance.

When choosing a blasticidin-resistant transformant for your expression studies, we recommend that you pick blasticidin-resistant colonies from the initial transformation plate and streak them on a second YPD plate containing the appropriate concentration of blasticidin. Select transformants that remain blasticidin-resistant for further studies.

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Here are some suggestinos:

- Make sure that you have harvested cells during log-phase growth (OD <1.0 generally).
- If electroporation is being used, see the electroporator manual for suggested conditions. Vary electroporation parameters if necessary.
- Use more DNA.
- Use freshly made competent cells.
- If the LiCl transformation method is being used, try boiling the carrier DNA.

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Here are some things to consider:

- If the OD of cells that are used is too high, they will not spheroplast. Do not overgrow cells.
- Do not use old cells and make sure that they are in log phase of growth.
- Make sure to mix zymolyase well before using. Zymolyase is more of a suspension than a solution.
- Make the PEG solution fresh each time and check the pH.

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Following are the rich and minimal media used for culturing Pichia pastoris and S. cerevisiae:

Rich Media:
S. cerevisiae and Pichia pastoris
YPD (YEPD): yeast extract, peptone, and dextrose
YPDS: yeast extract, peptone, dextrose, and sorbitol

Pichia pastoris only
BMGY: buffered glycerol-complex medium
BMMY: buffered methanol-complex medium

Minimal Media (also known as drop-out media):
S. cerevisiae
SC (SD): Synthetic complete (YNB, dextrose (or raffinose or galactose), and amino acids)

Pichia pastoris
MGY: minimal glycerol medium
MD: minimal dextrose
MM: minimal methanol
BMGH: buffered minimal glycerol
BMMH: buffered minimal methanol

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Use the following high cell density protocol for pGAP clones. Feed carbon until the desired density is reached (300 to 400 g/L wet cell weight (WCW)). If the protein is well-behaved in the fermenter, increase to 300-400 g/L WCW as with methanol inducible clones. These densities can be reached in less than 48 hours of fermentation. We have fermented constitutive expressers on glycerol using these protocols with good results. Some modifications to the Fermentation Basal Salts Medium that you might want to make are:

1) Substitute 2% dextrose for the 4% glycerol in the batch medium.
2) Substitute 40% dextrose for the 50% glycerol in the fed-batch medium.
3) Feed the 40% dextrose at 12 mL/L/hr (Jim Cregg has published data on expression using several carbon sources as substrates; dextrose gave the highest levels of expression).
4) Yeast extract and peptone may be added to the medium for protein stability.

One warning: If you are working with His- strains, they remain His- after transformation with pGAPZ. Fermentation in minimal medium will require addition of histidine to the fermenter.

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No, you cannot autoclave methanol. There are two approaches to this, depending a bit on the size of the bioreactor and the volumes involved. You can either dilute to working concentration and filter-sterilize with a filter suitable for alcohols, or you can just assume that methanol is sterile (it should be) and dilute into sterile water. For the ammonium hydroxide solution, you should also not autoclave it. You can assume the 30% stock solution is sterile (nothing should live in this solution) and dilute into sterile water to the working concentration.

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The use of antibiotics is not recommended, because most antibiotics become inactivated at the low pH of the medium during Pichia fermentation. In other words, addition of antibiotics such as ampicillin or kanamycin won't hurt the fermentation process, but because of the low pH the antibiotics become inactivated or may even precipitate out. For best results, use good sterile techniques.

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You don't have to add sulfuric acid to your PTM1 salts or fermentation medium. It would serve no purpose, other than maybe help dissolve the salts.

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Yes. The cells will do fine in YPD, but there are two drawbacks: The foaming that occurs in the richer YPD is very difficult to control, and the richer medium makes it difficult to purify secreted proteins from the medium. The BMGY formulation remedies both of these problems.

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The use of mixed feeds is mainly due for "turning down" the level of expression for proteins that are troublesome for Pichia. We have generally used mixed feeds for MutS clones. The idea is to keep the culture in a state of more active growth, and thus "happier" to express proteins.

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You need not add any acid to Pichia fermentation media. A healthy culture always acidifies the medium. If the pH of the culture is increasing, it is a sign of carbon source depletion or ill health of the culture.

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It depends whether the clone is Mut+ or a MutS.

For a Mut+ clone, you should expect that initially (in the first 2-4 hours of induction), the oxygen uptake rate of the culture would be lower than that at the end of the glycerol batch phase. After the culture becomes adapted to methanol, the oxygen uptake rate will significantly increase, if the culture is healthy (i.e., not poisoned by too much methanol). One should run methanol spike tests during fermentation of Mut+ clones.

For a MutS clone, one can expect that the oxygen uptake rate will be lower than that at the end of the glycerol batch phase throughout most of the fermentation. One has to be very careful not to poison MutS clones.

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We do not offer any protocols for Pichia fermentation. Please refer to the document titled “Pichia Fermentation Guidelines” on our website.

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The following protocol has been used numerous times for Pichia pastoris. It uses a 250 mL culture that is eventually scaled down to 1 mL aliquots of each strain.

- Inoculate 10 mL YPD media with Pichia strain and grow O/N, shaking at 30 degrees C.
- In the morning, check the OD600. To get them in log phase by the afternoon, dilute cells to hit an OD600 of approximately 3.0 at 4 or 5 pm.
- When the OD600 reaches approximately 3.0, inoculate 250 mL of YPD with 250 µL of culture. The objective is to have healthy, log-phase cells in the morning at an OD600 of around 1.0.
- If the OD600 is ~1.0, spin the cells in a 1 L bottle at 3K rpm for 10 minutes.
- Gently resuspend in 250 mL cold dH20.
- Transfer to a 500 mL centrifuge bottle and spin at 3K for 10 min. Repeat.
- Resuspend in 20 mL cold 1 M sorbitol and transfer to a 50 mL conical tube.
- Spin at 3K rpm for 10 min.
- Resuspend in 1 mL 1M sorbitol, and keep on ice.
- Use 80 µL of host strain for each electroporation.

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Inclusion of 1 M sorbitol in YPD plates stabilizes electroporated cells, as they appear to be somewhat osmotically sensitive.

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PEG 4000 seems to work best for yeast transformations, although PEG 3350 has been used in-house with success.

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We recommend trying in vivo and in vitro methods to generate or isolate multi-copy inserts of your gene. It is difficult to predict beforehand which method will work better for your protein.

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We strongly recommend electroporation if you are specifically interested in isolating multi-copy integrants of your gene in Pichia. The frequency of multi-copy insertions ranges from 1 to 10%, requiring hundreds to thousands of transformants to isolate a suitable number of multi-copy clones to test for expression. Electroporation yields some of the highest transformation frequencies in Pichia and is the method of choice to isolate multi-copy integrants.

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We recommend electroporation for transformation of Pichia. Electroporation yields 10e3 to 10e4 transformants per µg of linearized DNA and does not destroy the cell wall of Pichia. If you do not have access to an electroporation device, you may use the Spheroplast Kit for Yeast(Cat. No. K172001), PEG 1000 protocol (page 78 of the manual), LiCl protocol (page 80 of the manual), or the Pichia EasyComp Transformation Kit (Cat. No. K173001). We do not recommend spheroplasting for transformation of Pichia with plasmids containing an antibiotic resistance marker. Damage to the cell wall leads to increased sensitivity to the antibiotic, causing putative transformants to die before they express the antibiotic resistance gene. In contrast, spheroplasting can be used for transformation of PichiaPink vectors because these vectors are selected using auxotrophic markers.

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Here are the different methods available for Pichia transformation:

Pichia EasyComp Transformation Kit: easy-to-use, ready-made reagents
This method produces chemically competent Pichia cells and provides a rapid and convenient alternative to electroporation. Transformation efficiency is low (transformation of 50 µl of competent cells with 3 µg of linearized plasmid DNA yields about 50 colonies), and hence it is very difficult to isolate multi-copy integrants. Higher transformation efficiencies are often obtained with frozen versus freshly prepared cells.

PEG 1000 transformation: easy, do-it-yourself protocol
It is critical to add DNA to frozen cell samples, as cell competence decreases very rapidly after the cells thaw-even when held on ice. To perform multiple transformations, it is recommended to process them in groups of six at a time. The PEG method is usually better than LiCl, but not as good as spheroplasting or electroporation for transformation. However, it is convenient for people who do not have an electroporation device. The transformation efficiency is 10e2 to 10e3 transformants per mg of DNA.

Lithium chloride transformation: easy, do-it-yourself protocol
This method is an alternative to transformation by electroporation. Competent cells must be made fresh. Transformation efficiency is 10e2 to 10e3 transformants per µg linearized DNA. Note: Lithium acetate does not work with Pichia pastoris. Use only lithium chloride.

Electroporation: easy and high efficiency, do-it-yourself protocol; does not destroy the cell wall
Competent cells must be made fresh. Transformation efficiency is 10e3 to 10e4 transformants per µg of linearized DNA.

Spheroplast Kit for Yeast (K172001): cell wall digested to allow DNA to enter the cell; the procedure involves treating cells with zymolyase to create spheroplasts.
You must determine the optimal time to treat with zymolyase by taking OD600 readings at increasing time points. Longer incubations with zymolyase result in reduced transformation efficiency. Spheroplasts are combined with DNA and then plated. Transformation efficiency is 10e3 to 10e4 transformants per µg of linearized DNA. Note: Spheroplasting is not recommended for Pichia vectors with an antibiotic resistance marker. Damage to the cell wall leads to increased sensitivity to the antibiotic, causing putative transformants to die before they express the antibiotic resistance gene. In contrast, spheroplasting can be used for transformation of PichiaPink vectors, because these vectors are selected using auxotrophic markers.

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Proteinase A is a vacuolar aspartyl protease capable of self-activation, as well as subsequent activation of additional vacuolar proteases, such as carboxypeptidase Y and proteinase B. Carobxypeptidase Y appears to be completely inactive prior to proteinase A-mediated proteolytic processing of the enzyme; proteinase B (encoded by the PrB gene of S. cerevisiae) reportedly is approximately 50% bioactive in its precursor form (i.e., the form that exists prior to proteinase A-mediated processing of the enzyme). Little is known about the proteolytic activities in Pichia pastoris. The following protease-deficient Pichia pastoris strains have been made in an attempt to inactivate or delete the homologous proteolytic activities:

SMD 1168: Pep4 gene disrupted
PichiaPink Strain 2: Pep4 gene disrupted
PichiaPink Strain 3: Prb1 gene disrupted
PichiaPink Strain 4: Prb1, Pep4 genes disrupted
The Pep4-deficient mutant is deficient in protease activity of proteinase A, carboxypeptidase Y, and has approximately one-half of proteinase B activity. The Prb1-deficient mutant is deficient in the activity of proteinase B. Finally, the Pep4/PrB-deficient strain is deficient in proteolytic activity of all three of these enzymes: proteinase A, carboxypeptidase Y, and proteinase B. These protease-deficient strains, when compared to protease wild-type Pichia strains, have been shown to be highly efficient expression systems for the production of proteolytically sensitive products.

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All of our Pichia strains are homothallic strains. This means that they actually switch mating type with each generation. In Saccharomyces strains, this would lead to the culture rapidly becoming entirely diploid. In contrast, Pichia pastoris strains mate inefficiently to form diploids. Therefore, at any given time, the cells in the population are both “a” and “alpha” mating types.

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Two genes in Pichia pastoris code for alcohol oxidase-AOX1 and AOX2. The AOX1 gene product accounts for the majority of alcohol oxidase activity in the cell. Expression of the AOX1 gene is tightly regulated and induced by methanol to very high levels. The AOX1 protein typically accounts for about 30% of the total soluble protein in cells grown on methanol. While AOX2 is about 97% homologous to AOX1, growth on methanol is much slower than with AOX1. Loss of the AOX1 gene, and thus a loss of most of the cell's alcohol oxidase activity, results in a strain with a MutS (methanol utilization slow) phenotype. A MutS strain has a mutant aox1 locus, but is wild-type for AOX2. It has reduced ability to metabolize methanol and thus exhibits poor growth on methanol medium. MutS has in the past been referred to as Mut-. Mut+ (methanol utilization plus) refers to the wild-type ability of strains to metabolize methanol as the sole carbon source. Mut+ and MutS phenotypes are used when evaluating Pichia transformants for integration of the gene of interest.

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Pichia pastoris most commonly exists in a vegetative haploid state. Upon nitrogen limitation, mating can occur and diploid cells are formed. Since cells of the same strain can readily mate with each other, P. pastoris is by definition homothallic. Relative to Saccharomyces cerevisiae, which is heterothallic, the haploid state of P. pastoris is more stable. Under nitrogen-limiting conditions, P. pastoris diploids proceed through meiosis to the production of asci containing four haploid spores.

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Upon receipt, we recommend storing Pichia strain stabs at 4 degrees C. For long-term storage, we recommend preparing a glycerol stock (in 15% glycerol) immediately upon receipt and storing at -80 degrees C. Glycerol stocks are good indefinitely (unless there are numerous freeze-thaws). When making a glycerol stock, we recommend using an overnight culture and concentrating it 2-4 fold. Spin down cells and suspend in 25-50% of the original volume with glycerol/medium. It is better to store frozen cells in fresh medium plus glycerol, rather than simply adding glycerol into the overnight culture.

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HSA will run at 55 kD on a non-reducing SDS-PAGE gel and at about 66 kDa on a reducing SDS-PAGE gel.

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Yes, you can use the ProBond system with His-tagged proteins expressed in Pichia. Here are some suggestions for using the ProBond system with Pichia supernatant:

- Adjust the pH of the Pichia supernatant to 7.5-8.0.
- Decant the supernatant from the heavy white precipitate. It is recommended to keep the precipitate for later solubilization in the rare case where the expressed protein has co-precipitated.
- Centrifuge the supernatant to remove leftover cell debris or other material that might clog the column.
- Adjust the conductivity to that of 500 mM NaCl with salt addition (may not be required since Pichia media is high salt).
- Run the column according to the instructions in the manual.

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500 units of lyticase must be used to achieve similar effects to 1 unit of zymolyase. To lyse 1 mL of Pichia cells for PCR analysis, 25 total units of lyticase were used compared to 0.05 units of zymolyase. Zymolyase is available in different purities. 20T zymolyase should be sufficient for all purposes. The further purified 100T should not be necessary.

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The lyticase for our protocol is crude lyticase. A pure preparation is more expensive and it is not necessary. We routinely use zymolyase in this protocol for lysing the cells (5 µL of a 1 mg/mL stock). This is excessive, but it works fine. Reference: BioTechniques 20:980-982, June 1996.

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Certain yeast strains secrete a protein toxin, which inhibits the growth of sensitive pathogens and yeasts. Studies have shown that production of the toxin is dependent on the presence of linear, double-stranded DNA plasmids in the killer yeasts. In the yeast Pichia pastoris, two linear double-stranded DNA plasmids have been identified. In the publication listed below, the search for toxin-producing capability in P. pastoris was conducted and no killer activity could be detected when 14 different indicator strains were tested. Reference: Banerjee and Verma (2000) Search for a Novel Killer Toxin in Yeast Pichia pastoris. Plasmid 43:181-183.

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The molecular weight of the AOX1, and the AOX2 gene product is also 72 kd each.

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No, Pichia pastoris vectors will not work in Pichia methanolica; both Pichia pastoris and Pichia methanolica vectors have promoters derived from alcohol oxidase but they are not homologous, so the Pichia pastoris vectors will not be able to integrate or replicate in Pichia methanolica. The TEF1 promoter is probably functional in Pichia methanolica.

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In the following reference, 1% casamino acids were used: Clare JJ et al. (1991) Production of mouse epidermal growth factor in yeast: high-level secretion using Pichia pastoris strains containing multiple gene copies. Gene 105(2):205-212.

In this paper, the researchers found that although Pichia grew to a similar cell density in both YP and YNB, only a very low level of mouse epidermal growth factor (0.07 µg/mL) was present in supernatants from single-copy transformants when grown in YNB, and this decreased during further incubation. By using YNB medium that had been buffered to pH 6.0 and supplemented with 1% casamino acids, secreted mEGF levels substantially increased to ~1.9 µg/mL for single-copy transformants.

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Yeasts in general are known to secrete proteases. There are some proteins specifically susceptible to proteases that have optimal activity at neutral pH. If this is the case, expression using unbuffered media may be indicated. As Pichia expression progresses in an unbuffered medium such as MMH (minimal methanol plus histidine), the pH drops to 3 or below, inactivating many neutral pH proteases. Although the acidic environment of the culture should prevent activity of neutral proteases, you may use PMSF and EDTA at a 1 mM concentration in Pichia crude supernatant (refresh the PMSF every few hours) and then monitor for protease activity. See Deutscher (1990) Guide to Protein Purification, Methods in Enzymology for details.

In contrast, it has been reported that by including 1% Casamino acids (Difco) and buffering the medium at pH 6.0, extracellular proteases were inhibited, increasing the yield of mouse epidermal growth factor. Please see Clare JJ et al. (1991) Gene 105:205-212.

Additionally, major vacuolar proteases may be a factor in degradation, particularly in fermentor cultures that have the combination of the high cell density and lysis of a small percentage of cells. Using a host strain that is defective in these proteases may help reduce degradation. SMD1168 and SMD1168H are protease-deficient Pichia strains that are defective for Pep4p, a proteinase that is required for the activation of other vacuolar proteases, such as carboxypeptidase Y and proteinase B. Please see Higgins DR and Cregg JM (1998) Pichia Protocols, Humana Press, Totowa, New Jersey. Please note that SMD1168, SMD1168H, and the Pichia Protocols book can be ordered from us.

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Under the conditions in which Pichia is fermented (aerobically), ethanol is not produced. Oxidative metabolism of methanol first produces formaldehyde, which is then converted to carbon dioxide. There is an assimilatory cycle involving formaldehyde too, but no ethanol is made in this pathway, either.

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Add 5% ammonium hydroxide solution to maintain the pH of a Pichia culture grown in shake flasks. It is used at a 28% concentrated form in fermentors. Ammonium hydroxide also acts as a nitrogen source for Pichia cells.

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There is no need for maintaining Zeocin antibiotic selection in the Pichia expression medium, since Pichia pastoris transformants are stable integrants with the gene of interest integrated into the genome.

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A secreted protein will be exposed to the glycosylation machinery and might be glycosylated if the protein contains the standard N-linked or O-linked glycosylation amino acid consensus sequence.

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The major advantage of expressing recombinant proteins as secreted proteins is that Pichia pastoris secretes very low levels of native proteins. Since there is a very low amount of protein in the minimal Pichia growth medium, this means that the secreted heterologous protein comprises the vast majority of the total protein in the medium and serves as the first step in purification of the protein.Note: A secreted protein will be exposed to the glycosylation machinery and might be glycosylated if the protein contains the standard N-linked or O-linked glycosylation amino acid consensus sequence.

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Pichia is capable of correctly assembling proteins with a quaternary structure. One of the earliest proteins to be expressed in Pichia was the Hepatitis B Surface antigen which was assembled in its natural form, the 22 nm particle. (Reference: Cregg JM et al. (1987) High-level expression and efficient assembly of hepatitis B surface antigen in the methylotrophic yeast P. Pastoris. Nat Biotechnol 5:479-485.)  In consideration of the particle assembly problem, Cregg postulated that one or more post-translational events important in the formation of particles may be slow relative to the synthesis of HBsAg protein. Therefore, he used MutS since it has a slower growth rate.

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You can supplement with 10% culture volume of a 5% methanol (in water) solution to regenerate the 0.5% methanol concentration each day.

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Zeocin antibiotic can be spread on top of YPD plates for selection of yeast if necessary. There is a report that this works well when done with 10-15 3 mm glass beads. However, it is recommended that some optimization be performed, since top-spreading may dilute the antibiotic's effectiveness.

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The alpha secretion signal is from S. cerevisiae and is a general yeast secretion signal that has been used in many species including P. pastoris, K. lactis, etc.

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The alpha “signal sequence” (which really contains both the alpha signal sequence and pro-hormone leader sequences) is cleaved 4 times by 3 different enzymes in the Pichia cell. First, near the N-terminus by signal peptidase; second, by Kex2p after the dibasic (Lys-Arg) signal slightly upstream of the multiple cloning site, and then twice by Ste13p to remove the 2 Glu-Ala repeats.

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Although the efficiency may differ from one signal to the next, in general mammalian secretion signals are functional in yeast.

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It is doubtful as to whether codon usage plays as great a role in general, as is commonly believed. Translation initiation is probably more of a rate-limiting step than elongation.
Use the following codon usage list to design your gene in the order of preference:

Glycine: GGT or GGA
Glutamic acid: GAG or GAA
Aspartic acid: GAC or GAT
Valine: GTT or GTC
Alanine: GCT or GCC
Arginine: AGA or CGT
Serine: TCT or TCC
Lysine: AAG
Asparagine: AAC
Methionine: ATG
Isoleucine: ATT or ATC
Threonine: ACT or ACC
Tryptophan: TGG
Cysteine: TGT
Tyrosine: TAC
Leucine: TTG or CTG
Phenylalanine: TTC
Glutamine: CAA or CAG
Histidine: CAC or CAT
Proline: CCA or CCT

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An OD600 of 1 is equivalent to 5 x 10e7 Pichia cells/mL. After overnight (O/N) growth from a colony pick, a Pichia culture generally reaches OD 1.3-1.5 (in 2-5 mL).

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Doubling time is 2-3.5 hrs: Pichia has a doubling time of about 2 hrs of glycerol. The yeast grow slowly at 30 degrees C and it takes at least 3 days for colonies. In practice, it takes anywhere from 3 to 7 days to get nice-sized colonies.

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The Pichia genome is similar to that of other yeast, approximately 1.5 x 107 bp (similar to S. cerevisiae) and contains 4 chromosomes (similar to S. pombe). Reference: Ohi H, Okazaki N, Uno S, Miura M, Hiramatsu R (1998) Chromosomal DNA patterns and gene stability of Pichia pastoris. Yeast 14(10):895-903.

We have clearly resolved four chromosomal bands from four Pichia pastoris (Komagataella pastoris) strains by using contour-clamped homogeneous electric field gel electrophoresis. The size of the P. pastoris chromosomal bands ranged from 1.7 Mb to 3.5 Mb, and total genome size was estimated to be 9.5 Mb to 9.8 Mb; however, chromosome-length polymorphisms existed among four strains.

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The EasySelect Pichia Expression Kit features multicopy selection with Zeocin antibiotic selection and can do almost everything the Multi-Copy Pichia Expression Kit can do. The pAO815 vector of the Multi-Copy kit is uniquely suited for in vitro multimerization. The other Multi-Copy vectors have the kanamycin resistance gene that expresses at low level (confers resistance to Geneticin in yeast).

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The P. pastoris expression system combines the benefits of expression in E. coli (high-level expression, easy scale-up, and inexpensive growth) and the advantages of expression in a eukaryotic system (protein processing, folding, and posttranslational modifications), thus allowing high-level production of functionally active recombinant protein. Pichia pastoris shares the advantages of molecular and genetic manipulations with Saccharomyces cerevisiae, and it has the added advantage of 10- to 100-fold higher heterologous protein expression levels. In S. cerevisiae, replicating plasmids are used for episomal expression whereas in Pichia pastoris, plasmids are integrated into the host chromosome.

In comparison to Saccharomyces cerevisiae, Pichia may have an advantage in the glycosylation of secreted proteins because it may not hyperglycosylate. Both Saccharomyces cerevisiae and Pichia pastoris have a majority of N-linked glycosylation of the high-mannose type; however, the length of the oligosaccharide chains added posttranslationally to proteins in Pichia (average 8-14 mannose residues per side chain) is much shorter than those in Saccharomyces cerevisiae (50-150 mannose residues). Very little O-linked glycosylation has been observed in Pichia. In addition, Saccharomyces cerevisiae core oligosaccharides have terminal alpha1,3 glycan linkages whereas Pichia pastoris does not. It is believed that the alpha1,3 glycan linkages in glycosylated proteins produced from Saccharomyces cerevisiae are primarily responsible for the hyper-antigenic nature of these proteins, making them particularly unsuitable for therapeutic use. Although not yet proven, this is predicted to be less of a problem for glycoproteins generated in Pichia pastoris, because it may resemble the glycoprotein structure of higher eukaryotes.

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Yes, you can use ProBond with His-tagged proteins expressed in Pichia. Here are some suggestions for using ProBond with Pichia supernatant:
1. Adjust pH of Pichia supernatant to 7.5-8.0.
2. Decant the supernatant from the heavy white precipitate. It is recommended to keep the precipitate for later solubilization in the rare case where the expressed protein has co-precipitated.
3. Centrifuge the supernatant to remove leftover cell debris or other material that might clog the column.
4. Adjust the conductivity to that of 500 mM NaCl with salt addition (may not be required since Pichia media is high salt).
5. Run the column according to the instructions in the manual.

Jim Cregg (Keck Graduate Institute, developer of Pichia expression system for Phillips Petroleum), Senyon Choe (head of Structural Biology at The Salk Institute) and Thermo Fisher Scientific scientists have been unable to achieve adequate protein yields with greater than 40-50% incorporation of Selenomethionine (Se-Met), and unfortunately this level is not useful for phasing of crystals for x-ray analysis. The fundamental problem for Se-Met incorporation is that Met auxotrophic strains of Pichia, unlike Met auxotrophic strains of E. coli, do not grow on Se-Met. A number of groups have even attempted second site suppression mutagenesis in order to find genetic backgrounds that are Met auxotrophic but can grow (although poorly) on Se-Met. This has not been successful. Currently, Met WT strains of Pichia incorporate too much unmodified Met into proteins to produce protein that is >90% Se-Met substituted, which appears to be necessary for adequate phasing.

Some promising references regarding this issue are:
1. Larsson, et al. Preparation and crystallization of selenomethionyl dextranase from Penicillium minioluteum expressed in Pichia pastoris. Acta Crystallogr D Biol Crystallogr. 2002 Feb;58(Pt 2):346-8.
2. Larsson, et al. Dextranase from Penicillium minioluteum: reaction course, crystal structure, and product complex. Structure (Camb). 2003 Sep;11(9):1111-21.
3. Xu, et al. Crystallization and X-ray analysis of native and selenomethionyl beta-mannanase Man5A from blue mussel, Mytilus edulis, expressed in Pichia pastoris. Acta Crystallogr D Biol Crystallogr. 2002 Mar;58(Pt 3):542-5.

Store glycerol stocks frozen at -80° C in 15% glycerol. Glycerol stocks are good indefinitely (unless there are numerous freeze-thaws). When making a glycerol stock, we recommend using an overnight culture and concentrating it 2-4 fold. Spin down cells and suspend in 25-50% of the original volume with glycerol/medium. It is better to store frozen cells in fresh medium plus glycerol, rather than simply adding glycerol into the overnight culture.

Pichia pastoris most commonly exists in a vegetative haploid state. On nitrogen limitation, mating can occur and diploid cells are formed. Since cells of the same strain can readily mate with each other, P. pastoris is by definition homothallic. Relative to Saccharomyces cerevisiae, which is heterothallic, the haploid state of P. pastoris is more stable. Under nitrogen limiting conditions P. pastoris diploids proceed through meiosis to the production of asci containing four haploid spores.

Add 0.1% (final conc.) histidine per 100-g/l wet cell weight generated. This roughly corresponds to 25 ml of 4% histidine per day. Histidine stock solution can be made as concentrated as 12%.

The use of antibiotics is not recommended because most antibiotics become inactivated at the low pH of the medium during Pichia fermentation. In other words, addition of antibiotics such as Ampicillin or Kanamycin won't hurt the fermentation process, but because of the low pH the antibiotics become inactivated or may even precipitate out. For best results, use good sterile techniques.

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All of our Pichia strains are homothallic strains. This means that they actually switch mating type with each generation. In Saccharomyces strains, this would lead to the culture rapidly becoming entirely diploid. In contrast, Pichia pastoris strains mate inefficiently to form diploids. Therefore, at any given time, the cells in the population are both a and alpha mating types.

You don't have to add sulfuric acid to your PTM1 salts or fermentation media. It would serve no purpose, other than may be help dissolve the salts.

Yes. The cells will do fine in YPD but there are two drawbacks: The foaming that occurs in the richer YPD is very difficult to control. The richer media makes it difficult to purify secreted proteins from the media. The BMGY formulation remedies both of these problems.

No acid is required for Pichia fermentation. A healthy culture always acidifies the media. If the pH of the culture is increasing it is a sign of carbon source depletion or ill health of the culture.

It depends whether the clone is a Mut+ or a MutS.

For a Mut+ you should expect that initially (in the first 2-4 hours of induction) the oxygen uptake rate of the culture would be lower than the end of glycerol batch phase. After the culture becomes adapted to methanol, the oxygen uptake rate will significantly increase, if the culture is healthy (i.e. not poisoned by too much methanol). One should run methanol spike tests during fermentation of Mut+ clones.

For a MutS one can expect that the oxygen uptake rate will be lower than the end of glycerol batch phase through out most of the fermentation. One has to be very careful not to poison MutS clones.

During the Pichia fermentation process, the nitrogen source is the ammonium hydroxide used to adjust the pH. There is no nitrogen in the basal or trace salts.

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Yes, Pichia should be done under BSL-1 conditions. BSL-1 is the lowest biosafety level.

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Our vectors have not been completely sequenced. Your sequence data may differ when compared to what is provided. Known mutations that do not affect the function of the vector are annotated in public databases.

No, our vectors are not routinely sequenced. Quality control and release criteria utilize other methods.

Sequences provided for our vectors have been compiled from information in sequence databases, published sequences, and other sources.

The pPIC3.5K, pPIC9K, and pAO815 vectors supplied in the Multi-Copy Pichia Expression Kit are also offered as standalone products (Cat. Nos. V17320, V17520, and V18020). The vector data can be accessed on the specific product pages for these vectors under "Vector information" at the bottom of the page:
- pPIC3.5K: https://www.thermofisher.com/order/catalog/product/V17320
- pPIC9K: https://www.thermofisher.com/order/catalog/product/V17520
- pAO815: https://www.thermofisher.com/order/catalog/product/V18020

Find additional tips, troubleshooting help, and resources within our Protein Expression Support Center.