title: Sxa2 is a serine carboxypeptidase that degrades extracellular P-factor in the fission yeast Schizosaccharomyces pombe.
abstract: Stimulating the fission yeast Schizosaccharomyces pombe with mating pheromones brings about responses that lead to cell conjugation. Persistent stimulation does not, however, induce a continuous response as the cells become desensitized to the presence of the pheromone. One mechanism that contributes to desensitization in M-cells is the release of a carboxypeptidase that inactivates the extracellular P-factor pheromone. Production of the carboxypeptidase requires a functional sxa2 gene. In this study, we report the first molecular characterization of the Sxa2 protein and provide direct evidence that it is the carboxypeptidase that degrades P-factor. Sxa2 is synthesized as a precursor that undergoes an internal cleavage event catalysed by a protease with specificity for basic residues. This generates a series of catalytically active N-terminal fragments and an inactive C-terminal fragment. Cleavage is essential for activation of the carboxypeptidase and, although the C-terminal fragment is inactive, it is required for the N-terminal fragment to attain activity.
authors.affiliation: Department of Biological Sciences, University of Warwick, Coventry CV4 7AL, UK.
authors.forename: G
authors.initials: G
authors.lastname: Ladds
authors.forename: J
authors.initials: J
authors.lastname: Davey
mesh_terms: D000595:Amino Acid Sequence; D000908:Antibodies, Fungal; D002268:Carboxypeptidases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D004587:Electrophoresis, Agar Gel; D005656:Fungal Proteins; D015966:Gene Expression Regulation, Fungal; D006031:Glycosylation; D006639:Histidine / Q000276:immunology / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation; D010675:Pheromones / Q000378:metabolism*; D021382:Protein Sorting Signals / Q000378:metabolism*; D012568:Schizosaccharomyces / Q000201:enzymology* / Q000235:genetics; D029702:Schizosaccharomyces pombe Proteins; D017422:Sequence Analysis, DNA; D014157:Transcription Factors / Q000378:metabolism*
chemical_list: D000908:Antibodies, Fungal; D005656:Fungal Proteins; D010675:Pheromones; D021382:Protein Sorting Signals; D029702:Schizosaccharomyces pombe Proteins; D014157:Transcription Factors; C085847:map2 protein, S pombe; D006639:Histidine; D002268:Carboxypeptidases; C109436:Sxa2 protein, S pombe; C022633:serine carboxypeptidase