Protein modification by bis-alkylation

Conjugation by bis-alkylation using latently cross-conjugated reagents is a basis for site-specific PEGylation to the two cysteine thiols derived from a native disulfide. Known as disulfide bridging PEGylation, bis-alkylation can also be used to target histidine imidazole residues allowing for His-tag–selective PEGylation at either the N- or C-terminus of a protein. Incorporation of two histidines in a protein can also be accomplished to facilitate site-selective PEGylation by bis-alkylation at an optimal site within a protein. Other applications beyond PEGylation that can exploit the site-selectivity of bis-alkylation as a basis for conjugation include the development of antibody-drug conjugates, antibody-based mimetics, and multifunctional proteins.