Abstract
A novel staphylolytic enzyme, ALE-1, is a glycylglycine endopeptidase produced by Staphylococcus capitis EPK1. ALE-1 possesses seven histidines. Chemical modification studies using diethylpyrocarbonate and iodoacetic acid suggested that a histidine or tyrosine residue(s) in the molecule is important for the organism's staphylolytic activity. All of the histidine residues, one tyrosine, and one aspartic acid residue in the N-terminally truncated ALE-1 (DeltaN-term ALE-1) were systematically altered by site-directed mutagenesis, and the enzyme activities and metal contents of the variants were measured. Our studies indicated that His-150, His-200, His-231, His-233, and Asp-154 are essential for the enzyme activity of DeltaN-term ALE-1. Except for His-150 and Asp-154, all of these amino acids were located within the 38-amino-acid region conserved among 11 proteins, including 5 staphylolytic endopeptidases. Inductively coupled plasma-mass spectrometric analysis of DeltaN-term ALE-1 revealed that it contains one atom of zinc per molecule. Measurement of the zinc content of the mutant DeltaN-term ALE-1 suggested that His-150 and -233 are important for zinc binding; their loss in these variant enzymes coincided with the loss of staphylolytic activity. These results strongly suggest that ALE-1 is a novel member of zinc metalloproteases.