Penicillopepsin: 2.8 a Structure, Active Site Conformation and Mechanistic Implications

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Abstract
Penicillopepsin is an acid protease produced by the mold Penicillium janthinellum at pH’s less than 4.1 (1). Enzyme production occurs after the mycelial growth has ceased and sporulation has begun (2). The specificity and catalytic mechanism of penicillo-pepsin are very similar to those of porcine pepsin (3). The two active site aspartic acid residues, Asp-32 and Asp-215, occur in peptide sequences of at least eight amino acid residues which are almost identical in penicillopepsin, pepsin and chymosin (1,4–10). In addition, there is an overall 32% identity of amino acid sequence between penicillopepsin and porcine pepsin; a tentative sequence alignment of these two enzymes is given in Table I using this sequence numbering of porcine pepsin (5). These facts indicate that the fungal enzyme penicillopepsin is an evolutionary homologue of the mammalian acid proteases.