Substrate specificity of proteinase yscA from saccharomyces cerevisiae.

Proteinase yscA is an intracellular aspartic proteinase located in the lysosome-like vacuole of the yeast cell. The specificity towards denatured protein substrates was determined by separation and identification of cleavage products after digestions with proteinase yscA, and compared to that obtained with pepsin used under similar conditions. Proteinase yscA is more selective towards the peptide bonds it cleaves than pepsin, but shows the same preference for large hydrophobic residues on both sides of the cleaved bond as pepsin and lysosomal cathepsin D. Phe, Leu and Glu are favoured in substrate subsite P1 and Phe, Ile, Leu and Ala in P'1, whereas Val is unfavoured in P'1. The implications for the role of proteinase yscA as hydrolase maturase are discussed.