Why is the actual band size on a western blot different from the predicted size of the protein?
Western blotting is based on the separation of proteins by their size on a gel. However, migration of proteins through the gel matrix is also affected by other factors, which may cause the observed band size to be different from the predicted size.
Common causes are:
-Post-translational modification; for example phosphorylation and glycosylation increase the size of the protein
-Post-translation cleavage; many proteins are synthesized as precursor proteins, and then cleaved to give the active form
-Multimers, for example dimerization of a protein. This is usually prevented under reducing conditions, although strong interactions can result in the appearance of higher bands
-Splice variants; alternative splicing may result in different sized proteins being produced from the same gene
-Relative charge; the composition of amino acids (charged vs. non-charged)
What are the standard lysis buffers used with mammalian cells for detection of protein expression by immunoprecipitation (IP) or Western blot analysis?
The most commonly used buffer is RIPA Buffer with SDS. We offer RIPA Buffer (Cat. Nos. 89900 and 89901). We also offer the Pierce IP Lysis buffer (Cat. Nos. 87787 and 87788) as well as M-PER (Cat. Nos. 78501, 78503, and 78505).
What conditions do you recommend for overnight Western transfer?
Doing an overnight Westerm transfer is not the preferred method but can be done. The power should be lowered and the buffer should be chilled or the unit should be placed in the cold room to prevent overheating. You may try an overnight transfer at 5-15 V and adjust accordingly. You may also wish to put a second membrane behind the first in order to bind any proteins that transfer through the first membrane. You can use both membranes for staining, immunoblotting, or analysis.
After transferring onto a PVDF membrane, what is the best way to store the membrane for future probing?
We recommend air drying the PVDF membrane and placing it in an envelope, preferably on top of a supported surface to keep the membrane flat. It can be stored indefinitely at ≤80 degrees C. Right before probing, we recommend re-wetting the membrane with alcohol for a few seconds, followed by a few rinses with pure water to reduce the alcohol concentration. Then proceed as normal with the blocking step.