A Covalently Constrained Congener of the Saccharomyces cerevisiae Tridecapeptide Mating Pheromone Is an Agonist
Xue, Chu Biao
Becker, Jeffrey M.
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An analog of a-factor, the Saccharomyces cerevisiae tridecapeptide mating pheromone (Trp-His-Trp-LeuGln-Leu-Lys-Pro-Gly-Gln-Pro-Met-Tyr), in which the side chains of Lys7 and Gln" were covalently linked, was synthesized using solid phase methodologies. The yield of the purified cyclic analog cyclo7~'o[Nle'21afactor was 30%, and its structure was verified by amino acid analysis, peptide sequencing, fast atom bombardment-mass spectrometry, and proton nuclear magnetic resonance spectroscopy. Cyclo7~'o[Nle'21afactor 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 afactor depending upon the S. cerevisiae strain tested. Consistent with the relative activities of the linear and cyclic peptides, binding competition studies indicated that ~y~lo~~'~[Nle'~]a-factor had approximately 20-40- fold less affinity for the a-factor receptor. 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 a-factor. The a-factor antagonist des-Trp'- [Ala3,Nle12]a-factor reversed the activity of the cyclic analog, and ~y~lo~~'~[Nle'~]a-factor was not active at the restrictive temperature in a temperature-sensitive receptor mutant. These results support the conclusion that the cyclic a-factor occupies the same binding site within the receptor as is occupied by the natural pheromone. The cyclic a-factor represents a rare example of an agonist among covalently constrained congeners of small linear peptide messengers.