Isolation and Characterization of Four Related Peptides Exhibiting alpha Factor Activity from Saccharomyces cerevisiae

Abstract

The molecular structure of a factor, a mating hormone produced by a mating type cells of Saccharomyces cerevisiae has been investigated. From culture filtrates of a cells four oligopeptides exhibiting a factor activity have been isolated. These peptides, designated as a 1, a 2 , a3, and a 4 are structurally closely related, being composed of thirteen (a1 and a3) and twelve ( a 2 and a4) amino acids, respectively. The peptides were found to be composed of the following amino acids: 2 glutamic acid or glutamine, 2 proline, 1 glycine, 1 methionine or methionine sulfoxide, 2 leucine, 1 tyrosine, 1 lysine, 1 histidine, 1 or 2 tryptophan. The tridekapeptides differ from the dodekapeptides by an additional NH2-terminal tryptophan residue. Tyrosine was identified as the C-terminal amino acid in all four peptides. a3 and a4 are oxidation products containing an internal methionine sulfoxide instead of methionine. The mechanisms which could introduce the observed heterogeneity of the peptides are discussed.In the life cycle of the yeast Saccharomyces cerevisiae the transition from the haploid to the diploid growth phase is achieved by the conjugation of two haploid cells of different mating type. This process appears to be controlled by specific regulatory factors which are now generally referred to as mating hormones or sexual hormones (for review see [l]). Haploid yeast cells belong to either one of two alternative mating types designated as a and a, each of which produces one or, probably, several hormones which are excreted into the culture medium and act specifically on cells of the opposite mating type [2-51. Thus, culture filtrates of a cells contain an activity designated as a factor which specifically inhibits cell division in cells of mating type a [2]. A corresponding a factor which is produced by a cells and acts on a cells has been recently described by several groups [4,5]. It has been shown that a factor interferes with an essential cell cycle function of the a cells arresting them at an early stage of the cycle during the G1 period [6]. As a consequence initiation of DNA synthesis and bud formation are inhibited [6,7]. Since the mating ability of haploid yeast cells is restricted to the early part of the cell cycle it has been proposed that under physiological conditions the hormones could serve to increase the fraction of competent cells in a mating mixture, thus enhancing the efficiency of conjugation [5,8].

Nuclear‐magnetic‐resonance studies on the conformations of tridecapeptide α‐mating factor from yeast Saccharomyces cerevisiae and analog peptides in aqueous solution

“…For simplicity, we use the abbreviated notations: the natural a-mating factor is denoted as (1 -13)peptide, and the des-Trp' dodecapeptide as (2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)peptide. Thus, truncated peptides are denoted with the numbering of the N-terminal and C-terminal residues.…”

“…It may readily be noted that these peptides are classified into three groups, A,, A, and B, from the spectral patterns of amide proton resonances, especially in the region 8.5 -8.0 ppm. The group B includes the inactive analogs, (3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13), (3)(4)(5)(6)(7)(8)(9)(10) and his^] (1 -13)peptide, and a number of N-H proton resonances of this group are localized around 8.4-8.3 ppm. The group A, includes active (1-n)peptides (n = 13, 12 and 10) and inactive (1 -9)peptide, and the group A, includes active (2-n)peptides ( n = 13 and 12) and inactive (2-9)peptide.…”

“…2, the N-H proton spectra of (2-13), (2 -12) and (2 -9)peptides of the group A, are remarkably similar to one another, especially in the 8.35 -8.20-ppm region. The assignments of proton resonances were therefore performed first for the shortest peptide (2)(3)(4)(5)(6)(7)(8)(9).…”

“…Masui et al have reported that the activity of a-mating factor is not affected if the N-terminal Trp' residue is deleted [7], although Shenbagamurthi et al have recently reported that the dodecapeptide is less active than a-mating factor [lo]. However, if the two residues (Trp' and His') are eliminated, the truncated peptide, (3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)peptide, shows no activity. On the other hand, the successive truncation of the C-terminal residues lowers the biological activity step by step.…”

“…The pH dependences of N-H proton chemical shifts of (2)(3)(4)(5)(6)(7)(8)(9)peptide are shown in Fig. 3.…”