MODELING AND MODIFICATION OF THE BINDING-SITE OF ENDOTHELIN AND OTHERRECEPTORS

From three-dimensional models of its receptors, residues which bind th e carboxy-terminus of endothelin were predicted. This site is in a poc ket consisting of five putative transmembrane helices and includes a h istidine in the sixth helix. This residue is either phenylalanine or a sparagine in cationic neurotransmitter receptors. The histidine alkyla ting agent diethylpyrocarbonatc potently inhibited binding of [I-125]e ndothelin-1 to its receptors in bovine cerebellum, where a single popu lation of endothelin ET(B) receptors was shown to exist. From the abse nce of pH sensitivity of inhibition above pH 5 and the reversal by hyd roxylamine of inhibition, diethylpyrocarbonate is concluded to inhibit by histidine modification. Diethylpyrocarbonatc inhibited ligand bind ing to several receptors with the potency order endothelin ET(B) great er-than-or-equal-to bombesin greater-than-or-equal-to dopamine D2 grea ter-than-or-equal-to m2 muscarinic > alpha1-adrenoceptor greater-than- or-equal-to m 1 muscarinic > 5-HT2. This is consistent with histidine in the binding site of endothelin (and some other peptidergic) recepto rs and the proposed model.