PHOTOAFFINITY-LABELING OF THE LIGAND-INTERACTING HELIX OF THE RETINOIC ACID RECEPTOR-ALPHA

Two photoaffinity-labeling probes for retinoic acid receptor (RAR) alp ha, ethyl)-3H-diazirin-3-yl)phenyl)carboxamido]benzoic acid (3DIAM) an d its para-isomer (4DIAM), were designed and synthesized. Both compoun ds possess high affinity for recombinant RAR alpha (MBP-RAR alpha/E) a nd bind covalently to its cognate ligand-binding site. The labeled sit e of MBP-RAR alpha/E with 3DIAM was determined, by the endoproteinase combination method, to be located in helix 11 of the ligand-binding do main of RAR alpha, which is the position at which the Ligand is consid ered to bind, on the basis of the reported crystal structure of the re tinoic acid/RAR gamma complex.