A novel protease from yeast with specificity towards paired basic residues

Abstract

Paired basic residues have been observed as sites of proteolytic processing of prohormones in a wide range of eukaryotic species1–3. This strongly suggests that proteases exhibiting specificity towards paired basic residues may be involved in prohormone processing, but candidate enzymes have not so far been identified. Yeast Saccharomyces cerevisiae α-cells synthesize and secrete α-mating factor, a peptide of 13 amino acids4,5, the processing of which from a larger precursor involves cleavage at paired basic residues (-Lys-Arg-)3,6. We have therefore used them as a simple model system for the study of prohormone processing and report here the identification, in cell lysates, of a novel protease which specifically recognizes and cleaves the peptide bonds between consecutive basic residues. The purified enzyme, which we have called pro-pheromone-convertase Y, has a molecular weight (MW) of around 43,000. It cleaves various peptide substrates at paired basic residues, but not at single basic residues, implying it is distinct from trypsin-like proteases. Its unique substrate specificity suggests the enzyme may be involved in propheromone processing in vivo.