The Streptococcus thermophilus protein Wzh functions as a phosphotyrosine phosphatase.

Amino acid residues that are important for metal binding and catalysis in Gram-positive phosphotyrosine phosphatases were identified in the Wzh protein of Streptococcus thermophilus MR-1C by using sequence comparisons. A His-tagged fusion Wzh protein was purified from Escherichia coli cultures and tested for phosphatase activity against synthetic phosphotyrosine and phosphoserine-threonine peptides. Purified Wzh released 2316.5 ± 138.7 pmol PO4·min(-1)·μg(-1) from phosphotyrosine peptide-1 and 2345.7 ± 135.2 pmol PO4·min(-1)·μg(-1) from phosphotyrosine peptide-2. The presence of the phosphotyrosine phosphatase inhibitor sodium vanadate decreased purified Wzh activity by 45%-50% at 1 mmol·L(-1), 74%-84% at 5 mmol·L(-1), and by at least 88% at 10 mmol·L(-1). Purified Wzh had no detectable activity against the phosphoserine-threonine peptide. These results clearly establish that S. thermophilus MR-1C Wzh functions as a phosphotyrosine phosphatase that could function to remove phosphate groups from proteins involved in exopolysaccharide biosynthesis, including the protein tyrosine kinase Wze and priming glycosyltransferase.