Photolabeling the Transporter Associated with Antigen Processing

Crosslinking reagents are valuable tools used to determine the quarternary and subunit structures of proteins (1 ,2 ). Other applications for crosslinkers include the determination of protein-protein interactions, analysis of proteins in cellular membranes, and the identification of novel peptide-binding proteins (3 -5 ). Crosslinkers function by coupling reactive groups to amino acid side chains of peptides, and are divided into two groups; homobifunctional or heterobifunctional, depending on whether the available functional groups are similar or different, respectively. They can be further subdivided into groups that react either chemically or photochemically, i.e., requiring activation by ultraviolet light (UV) (6 ,7 ).