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Relation between the flexibility of the WPD loop and the activity of the catalytic domain of protein tyrosine phosphatase SHP‐1
Author(s) -
Yang Jian,
Niu Tianqi,
Zhang Aihua,
Mishra Ashwini K.,
Zhao Zhizhuang Joe,
Zhou G. Wayne
Publication year - 2001
Publication title -
journal of cellular biochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.028
H-Index - 165
eISSN - 1097-4644
pISSN - 0730-2312
DOI - 10.1002/jcb.1265
Subject(s) - protein tyrosine phosphatase , chemistry , phosphatase , dephosphorylation , alanine , tyrosine , residue (chemistry) , cysteine , mutant , biochemistry , phosphorylation , stereochemistry , enzyme , amino acid , gene
The conserved WPD loop of protein tyrosine phosphatases play an important role in the catalytic activity and the invariant aspartate residue acts as a general acid/base catalyst in the dephosphorylation reaction. In our previous report, we have demonstrated that the catalytic activities of the PTPs are influenced by the flexibility and stability of the WPD loop in its active “open” conformation [Yang et al., 1998]. Phosphatases with a more flexible WPD loop generally have higher specific activity. In this report, we modify the WPD loop of SHP‐1 by alanine‐scan mutation of the residues flanking the loop and measure their effects on the catalytic activity of the phosphatase. We show that the S418A, V424A, S426A, E427A, and P428A mutants increase the phosphatase activity, possibly due to the increased flexibility of the WPD loop, whereas the L417A, L417G and P425A mutants decrease its phosphatase activity. In addition, we propose that the two‐proline residues in the WPD loop (Pro 420 and Pro 425 in SHP‐1) work as pivotal points through a conserved hydrophobic network and allows residues between the pivotal points to have maximum flexibility in enhancing the phosphatase activity. Furthermore, our data suggest that the hydrolysis of the phosphoryl‐cysteine intermediate, not its formation, is the rate‐limiting step with p ‐nitrophenyl phosphate as the substrate while both the steps are rate‐limiting with phosphotyrosine as the substrate. J. Cell. Biochem. 84: 47–55, 2002. © 2001 Wiley‐Liss, Inc.