Proteinase yscD (oligopeptidase yscD)

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Abstract
The yeast PRD1 gene, encoding proteinase yscD, was cloned by complementation of the prd1‐6 point mutation. Sequencing of the gene revealed an open reading frame of 2.136 kb, encoding a protein of 712 amino acids with a calculated molecular mass of 81.8 kDa. The sequence HEGLG beginning at residue 501 represents the HEXXH motif, unique for the zinc metallo‐peptidases. Sequence comparison revealed complete identity of the proteinase yscD gene with a recently published open reading frame of yeast chromosome III. We found 34.8% identity between proteinase yscD and rat metalloendopeptidase (thimet oligopeptidase, EP 24.15). Proteinase yscD hydrolyzes several chromogenic and fluorogenic peptides that are substrates of thimet oligopeptidase. N‐[1‐(RS)‐carboxy‐3‐phenylpropyl]‐Ala‐Ala‐Phe‐p‐aminobenzoic acid, a compound designed as specific inhibitor of EP 24.15, is also a strong inhibitor of the yeast enzyme. Proteinase yscD is a non‐vacuolar enzyme. 3–5% of the total enzyme activity can be detected in the intermembrane space of mitochondria. In a mutant carrying a deletion of the PRD1 gene no proteinase yscD activity is detectable in the cytoplasm and in mitochondria of these cells. They do not show any grossly altered phenotype but exhibit a decrease in the intracellular degradation of peptides. This suggests a function of proteinase yscD in the late stages of protein degradation.