Inhibition of membrane Ca2+-ATPase in vitro by mating pheromone in Rhodosporidium toruloides, a heterobasidiomycetous yeast

Identification and phylogenetic classification of eleven putative P-type calcium transport ATPase genes in the yeasts Saccharomyces cerevisiae and Schizosaccharomyces pombe

Calcium is an essential second messenger in yeast metabolism and physiology. So far, only four genes coding for calcium translocating ATPases had been discovered in yeast. The recent completion of the yeast Saccharomyces cerevisiae genome allowed us to identify six new putative Ca(++)-ATPases encoding genes. Protein sequence homology analysis and phylogenetic classification of all putative Ca(++)-ATPase gene products from the yeasts Saccharomyces cerevisiae and Schizosaccharomyces pombe reveal three clusters of homologous proteins. Two of them comprises seven proteins which might belong to a new class of P-type ATPases of unknown subcellular location and of unknown physiological function.

Fungal lipopeptide mating pheromones: a model system for the study of protein prenylation

In a variety of fungal species, mating between haploid cells is initiated by the action of peptide pheromones. The identification and characterization of several fungal pheromones has revealed that they have common structural features classifying them as lipopeptides. In the course of biosynthesis, these pheromones undergo a series of posttranslational processing events prior to export. One common modification is the attachment of an isoprenoid group to the C terminus of the pheromone precursor. Genetic and biochemical investigations of this biosynthetic pathway have led to the elucidation of genes and enzymes which are responsible for isoprenylation of other polypeptides including the nuclear lamins, several vesicular transport proteins, and the oncogene product Ras. The alpha-factor of Saccharomyces cerevisiae serves as a model for studying the biosynthesis, export, and bioactivity of lipopeptide pheromones. In addition to being isoprenylated with a farnesyl group, the alpha-factor is secreted by a novel peptide export pathway utilizing a yeast homolog of the mammalian multidrug resistance P-glycoprotein. The identification of putative lipopeptide-encoding loci within other fungi, including the human immunodeficiency virus-associated opportunistic pathogen Cryptococcus neoformans and the plant pathogen Ustilago maydis, has stimulated much interest in understanding possible roles for pheromones in fungal proliferation and pathogenicity. Knowledge of variations within the processing, export, and receptor-mediated signal transduction pathways associated with different fungal lipopeptide pheromones will continue to provide insights into similar mechanisms which exist in higher eukaryotes.

Inhibition of membrane Ca2(+)-ATPase of Saccharomyces cerevisiae by mating pheromone alpha-factor in vitro

Plasma membrane Ca2(+)-ATPase of Saccharomyces cerevisiae was solubilized and partially purified by calmodulin-affinity chromatography. The activity of Ca2(+)-ATPase isolated from MATa cells was inhibited by physiological concentrations of the mating pheromone alpha-factor in a dose-dependent manner. The enzyme prepared from a receptor-deficient sterile mutant cells (delta ste-2) was similarly inhibited by alpha-factor, but the enzyme from MAT alpha cells was resistant to the mating pheromone. We suggest that the inhibition may be involved in the alpha-factor-induced increase of Ca2+ uptake reaction of MATa cells.

Interaction with phospholipids of a membrane thiol peptidase that is essential for the signal transduction of mating pheromone in Rhodosporidium toruloides

Interaction with phospholipids of a membrane thiol peptidase [referred to as trigger peptidase (TPase), T. Miyakawa et al. (1987) J. Bacteriol. 169, 1626-1631] that plays a key role in the signalling of a lipopeptidyl mating pheromone at the cell surface of pheromone-target cell (mating type a) of Rhodosporidium toruloides was studied. The activity of highly purified TPase which requires phospholipids was restored by reconstitution of the enzyme into liposomes prepared with phospholipids extracted from the yeast cell. The presence of Ca2+ was essential for both the reconstitution process and the catalytic reaction of TPase. Triton X-100 mixed micelles containing phospholipids also activated the enzyme. The specificity and stoichiometry of activation by phospholipids was investigated by determination of TPase in the presence of mixed micelles that contained defined classes and numbers of phospholipid molecules in the Triton X-100 micelles. It was demonstrated that TPase is activated by mixed micelles containing 2-6 molecules of phosphatidylserine or phosphatidylethanolamine. Other phospholipids of the membranes of this organism, such as phosphatidylcholine and phosphatidylglycerol, had little effect on activation, indicating that the amino group of the phospholipids may be required for the function of TPase. Direct evidence for the interaction of TPase and Triton X-100/phosphatidylserine mixed micelles was obtained by molecular sieve chromatography on Sephacryl S-200. These data established that a phospholipid bilayer is not a requirement for TPase activation, and that the purified enzyme can be activated by a relatively small number of phospholipid molecules of specific classes.