Reversing the nucleophile and electrophile for covalent affinity capture

BIOT 187

Diment D. Singh, Mark R. McCoy, Zheng Miao, Oliver L. Hsu, and Claude Meares, cfmeares@ucdavis.edu. Department of Chemistry, University of California, 1 Shields Avenue, Davis, CA 95616
Engineering the permanent formation of a receptor-ligand complex has a number of potential applications in chemistry and biology. Previously, we have used the site-directed incorporation of cysteine nucleophiles at the periphery of an antibody's binding site, paired with the chemical synthesis of weakly electrophilic ligands, to produce receptor-ligand pairs that conjugate specifically and permanently. After protein expression in Drosophila S2 cells we found that the engineered cysteine was reversibly blocked by disulfide linkage to a small thiol. Here we report that this can be used to advantage by treating the small thiol as a leaving group. Ligands bearing thiol side chains were synthesized and incubated with the antibody, with the finding that the ligands became covalently attached to the antibody within a few minutes under physiological conditions. This rapid, specific conjugation is particularly interesting for biomedical applications. Supported by NIH research grants CA016861 and CA098207.