Methionine acts as a magnet in photoaffinity crosslinking experiments

Photoaffinity crosslinking has been utilized to probe the nature of the ligand-receptor interface for a number of G protein-coupled receptor systems. Often the photoreactive benzophenone moiety incorporated in the ligand is found to react with a methionine in the receptor. We introduced methionines one-at-a-time into the region 163-176 of the parathyroid hormone receptor, and find that crosslinking occurs to the side-chain of methionine over a range of I I amino acids. We call this the '' Magnet Effect '' of methionine. Hence, crosslinking contact points can be significantly shifted by the presence of methionine in a receptor domain. (c) 2006 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.