A NOVEL PEPTIDE INHIBITOR OF ADENYLYL-CYCLASE (AC) - A PEPTIDE FROM TYPE-V AC DIRECTLY INHIBITS AC CATALYTIC ACTIVITY

Peptides derived from various regions of type V adenylyl cyclase (AC) were studied to determine their effect on AC catalytic activity. Out o f 10 examined, only one peptide, peptide 2 (Lys(425)-Cys(444)), signif icantly inhibited both basal and stimulated (forskolin or GTP gamma S (guanosine 5'-O-thiotriphosphate)) type VAC catalytic activity overexp ressed in CMT cells. The sequence of this peptide was taken from the f irst cytoplasmic domain of type VAC, which has a high sequence homolog y to other AC isoforms. Competition studies performed between the pept ide and the substrate ATP showed that the inhibition was noncompetitiv e. Mutation or truncation of the peptide designed to destroy its secon dary structure totally negated the inhibitory effect. This peptide als o inhibited the catalytic activity of purified types II and VAC, as we ll as that of various cells, including S49 cyc(-) cells. Our data indi cate that the peptide directly interacts with AC to inhibit catalytic activity; this provides new information regarding regions of the enzym e involved in its catalytic activation.