Structure-function studies of the tridecapeptide mating pheromone of Saccharomyces cerevisiae

An analog of α-factor, the Saccharomyces cerevisiae tridecapeptide mating pheromone (Trp-His-Trp-Leu-Gln-Leu-Lys-Pro-Gly-Gln-Pro-Met-Tyr), in which the side chains of Lys⁷ and Gln¹⁰ were covalently linked, was synthesized using solid phase methodologies. The structure of the peptide was verified by chemical analyses. Cyclo^7,10[Nle¹²]α-factor caused growth arrest and morphological alterations in S. cerevisiae MATa cells qualitatively identical to those induced by linear pheromone and was one-fourth to one-twentieth as active as the linear α-factor depending upon the S. cerevisiae strain tested. Competion binding studies were consistent with the relative activities of the linear and cyclic peptides. Hydrolysis of the cyclic peptide by the target cells did not lead to opening of the ring and was less rapid than that of linear α-factor. The α-factor antagonist des-Trp¹-[Ala³,Nle¹²]α-factor reversed the activity of the cyclic analog, and cyclo^7,10[Nle¹²]α-factor was not active at the restrictive temperature in a temperature-sensitive receptor mutant. These results support the conclusion that the cyclic α-factor occupies the same binding site within the receptor as is occupied by the natural pheromone. The cyclic α-factor represents a rare example of an agonist among covalently constrained congeners of small linear peptide messengers. Amino- and carboxy-terminus truncated peptides were derived from linear- and cyclic-α-factor using aminopeptidase M or carboxypeptidase A. Their structures were verified by chemical analyses. des-Trp¹- or des-Tyr¹³- linear or cyclic α-factor peptides showed reduced agonist activity. des-Trp¹,His²-linear or cyclic peptides were antagonists of α-factor activity. des-Nle¹²,Tyr¹³ linear or cyclic α-factor peptides exhibited synergistic activity with α-factor (increased the growth inhibition of S. cerevisiae caused by α-factor), although neither compound showed any agonist activity when tested alone. The exact mechanism of action of the synergistic peptides is still unkown.