Crosslinking is the process of chemically joining two or more molecules by a covalent bond. Crosslinking reagents contain reactive ends to specific functional groups, such as primary amines and sulfhydryls, on proteins or other molecules. The availability of several chemical groups in proteins and peptides make them targets for conjugation and for study using crosslinking methods.

Crosslinkers are used for the identification of near-neighbor protein relationships and ligand-receptor interactions. Homobifunctional, amine-reactive NHS esters or imidates, and heterobifunctional, amine-reactive, photoactivatable phenyl azides are the most commonly used crosslinkers for these applications. 

Crosslinkers also are commonly used to modify nucleic acids, drugs, and solid surfaces. The same chemistry is applied to amino acid and nucleic acid surface modification and labeling. This area of chemistry is known as bioconjugation and includes crosslinking, immobilization, surface modification, and labeling of biomolecules.

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Featured protein crosslinking categories

Homobifunctional amine-specific protein crosslinking reagents based on NHS-ester and imidoester reactive groups for selective conjugation of primary amines; available in short, long, cleavable, irreversible, membrane permeable, and cell surface varieties.

Crosslinking reagents based on maleimide and hydrazide reactive groups for conjugation and formation of covalent crosslinks 

Homobifunctional sulfhydryl-specific crosslinking reagents based on maleimide or pyridyldithiol reactive groups for selective covalent conjugation of protein and peptide thiols (reduced cysteines) to form stable thioether bonds. 

Aryl azide, diazirine, and other photo-reactive (light-activated) chemical heterobifunctional crosslinking reagents to conjugate proteins, nucleic acids and other molecular structures involved in receptor-ligand interaction complexes via two-step activation.

Heterobifunctional protein crosslinking reagents for conjugation between primary amine (lysine) and sulfhydryl (cysteine) groups of proteins and other molecules; available with different lengths and types of spacer arms.

Chemoselctive ligation refers to the use of mutually specific pairs of conjugation reagents. They are most often used for in vivo metabolic labeling. 

Check out our various types of in vivo crosslinking reagents to target cell surface or intracellular proteins and to accommodate different downstream analysis methods.

Carbodiimide crosslinking reagents, DCC and EDC (EDAC), for conjugating carboxyl groups (glutamate, aspartate, C-termini) to primary amines (lysine, N-termini) and also N-hydroxysuccinimide (NHS) for stable activation of carboxylates for amine-conjugation.