Similar to any protein, antibodies have functional groups from the natural amino acids for labeling and conjugation; for example, the surface amine from Lys or N-terminal amine; the surface carboxylic acid group from Asp, Glu, or C-terminal acid; and the phenolic group from Tyr. In addition, antibodies have unique disulfide bonds at the hinge region that can be selectively cleaved and targeted for labeling. The traditional antibody labeling technologies usually take advantage of the multiple Lys groups located in the antibody. Modification of the Lys groups changes the overall pI of the antibody and may lead to higher nonspecific binding. In addition, if some of the modified or conjugated Lys residues are located at the antigen binding sites, this method may produce partially active or inactive antibody conjugates that may not bind to the antigen. At CellMosaic, we spend considerable time developing processes for labeling an antibody at a single or few predictable sites while retaining antigen binding affinity and specificity.
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