MUTAGENESIS OF HUMAN MEL(1A) MELATONIN RECEPTOR EXPRESSED IN YEAST REVEALS DOMAINS IMPORTANT FOR RECEPTOR FUNCTION

A yeast functional colorimetric assay was employed to test the effects of site-directed point mutations on the function of the human Mel(1a) melatonin receptor. Seven mutants were created in transmembrane domai ns III, V, and VII of the receptor to test the rhodopsin-based model o f melatonin recognition. Two mutants in transmembrane domains III and VI were created to investigate the mechanisms of G protein activation in the melatonin receptor. Mutations in transmembrane domain V either potentiated agonist efficiencies (H195A) or totally abolished all resp onses to tested compounds (V192T+H195A). Mutation N124A in the conserv ed NRY motif in the end of transmembrane domain III seriously impaired receptor activation. Several mutants were found to have decreased abi lity to activate functional responses, reflecting the importance of th ese residues for receptor function. These data also suggest that activ ation of the receptor involves interaction of the B-methoxy group of m elatonin with the conserved histidine H195 in transmembrane domain V. (C) 1998 Academic Press.