The catalytic role of Cys124 in the dual specificity phosphatase VHR.

G Zhou,J M Denu,L Wu,J E Dixon

doi:10.1016/s0021-9258(18)46898-6

G Zhou, J M Denu + Show 2 more

Open Access

https://doi.org/10.1016/s0021-9258(18)46898-6

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Abstract

The recombinant human Vaccinia virus H1-related protein tyrosine phosphatase, (VHR PTPase) possesses intrinsic Tyr and Thr/Ser phosphatase activities. Both activities were abolished by a single amino acid substitution, C124S. When VHR was incubated with a 32P-labeled phosphotyrosine-containing substrate and then rapidly denatured, enzyme-associated 32P was evident following SDS-polyacrylamide gel electrophoresis. The formation of 32P-labeled protein could be blocked in the presence of an unlabeled substrate. VHR-associated 32P was sensitive to iodine but insensitive to pyridine and hydroxylamine. The catalytically inactive C124S mutant would not form a 32P-labeled enzyme. Furthermore, VHR phosphatase could be selectively inactivated by the alkylating agent iodoacetate. The inactivation resulted from the specific covalent modification of Cys124. Collectively these results suggest that a thiol-phosphate enzyme intermediate is formed when Cys124 of VHR accepts a phosphate from the substrate. Our results also demonstrate that the dual specificity phosphatases and the tyrosine-specific PTPases employ similar catalytic mechanisms.

Highlights

Collec- trap and two-hybrid protein interaction screening, a human tively these results suggest that a thiol-phosphate en- dual specificity protein phosphatase that interacts with cdk2 zyme intermediateis formed when Cys’” VofHR accepts has been identified by two independent groups
Balance of tyrosine phosphorylation is a result of interplay Outside of the conserved protein tyrosine phosphatase signabetween protein tyrosine phosphatases (PTPases) and protein ture motif, HCXXGXXRSfI’, the dual specificity phosphatases tyrosine kinases [3, 4]
Phosphatase Activities-Amino acid sequence alignment suggests that VHR is a dual specificity phosphatase capable of dephosphorylatingbothphosphotyrosine and phosphothreoninelserine-containing substrates [20].As shown in Fig. 2, purified recombinant VHR hydrolyzed the phosphate monoester from Raytid(ephosphotyrosine) and Kemptide

Summary

EXPERIMENTAL PROCEDURES

Materials-p-Nitrophenylphosphate (pNPP),’S-Sepharose,Q-Sephatute and National Institutes of Health Grants NIDDKD 18849 and rose, phenylmethylsulfonylfluoride, and iodoacetatewere from Sigma. Depaoli-Roach of Indiana University School of Medicine, Indianapolis, IN) were phosphorylated a t 30 "C for 30 min in a 100-pl reaction mixture containing 50 mM Ms-HCl, pH 7.6, 150 mM NaCI, 10 mM MgCl,, 0.1 mM [Y-~'P]ATP(60 pCi/nmol) and 30 ng of casein kinase I1 Peptide KRPSQRHGSKY (UOM-81,University of Michigan) was labeled a t 30 "C for 30min in a 120-111 reaction mixture containing 20 mM Ms-HCI, pH7.4, 10 mM MgCI,, 20 p~ [y3*P1ATP(100 pCi/nmol), 50 n~ TPA, 0.3 m~ CaCI,, 80 ng/ml phosphatidylserine, and 1pl of protein kinase C Mass Analysis, and Sequencing of lodoacetate-modifid Peptide-VHR (6.0 nmol) was incubated with 1.6 m~ of ['4Cliodoacetate (18.6 mCi/mmol) in buffer C in a total volume of 140 pl a t 25 "C. The radioactive peptides were subjected to laser desoption mass analysis and amino acid sequencing analysis. 20% of the product of each cycle was counted for radioactivity and the remainder of the sample subjected to amino acid analysis

RESULTS

Iodoacetate Inactivates VHR by CovalentModification of

DISCUSSION