Cysteine mutants as chemical sensors for ligand-receptor interactions

The incorporation of cysteine residues into membrane receptors by mutagenes is has enabled the development of engineered proteins. Chemical modificatio n of the mutant receptor using a wide range of biochemical and biophysical probes has facilitated functional studies of ligand-receptor interactions. In particular, the substituted-cysteine accessibility method (SCAM) represe nts a successful example of how to probe transmembrane receptor domains aft er chemical modification of the mutants with sulfydryl-reacting molecules. We propose an extension of this methodology using site-specific affinity pr obes that react with cysteine mutants to gain reliable structural informati on on the binding of a ligand in its receptor site.