Complete Amino Acid Sequence of a Zinc Metalloendoprotease from Streptomyces caespitosus

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Abstract
We determined the complete amino acid sequence of a zinc metalloendoprotease from Streptomyces caespitosus (ScNP). Peptide fragments obtained by digestion of Rcm‐ScNP with trypsin, ScNP and endoproteinase Asp‐N were purified by reverse‐phase HPLC and their amino acids were analyzed using an automatic sequencer. ScNP consisted of a single polypeptide chain of 132 amino acid residues with one disulfide bond between residues 99 and 112 (M, 14376). Thus, the number of amino acid residues determined for this enzyme is much lower than the number of residues previously reported for metalloendoproteases. The amino acid sequence indicated that although ScNP has the zinc‐binding motif, His‐Glu‐Xaa‐Xaa‐His, which is found at the active site of most zinc metalloendoproteases, it does not share overall significant similarity to the sequences of other zinc metalloendoproteases. Moreover, an analysis of the X‐ray structure of ScNP at 0.2–nm resolution (Kirisu et al., unpublished results) revealed that Asp93, together with two histidine residues in the zinc‐binding motif (His83 and His87) and a water molecule, is a zinc ligand. We propose that ScNP, which bears the HEXXHXXGXXD motif, represents a novel subfamily of zinc‐containing metalloendoproteases.