High resolution structure of the phosphatase VHZ explains unexpected substrate specificity, and suggests the presence of metavanadate at the active site

VHZ, a recently discovered phosphatase expressed in most fetal tissues and associated with several types of cancer, had been classified as a dual specificity phosphatase (DUSP23). However, screening assays of VHZ with 360 phosphopeptides has revealed a number of peptide phosphotyrosine substrates, but no activity toward phosphothreonine or phosphoserine substrates. A 1.1 Å crystal structure of VHZ bound to vanadate shows that VHZ has a deep and narrow active site that is more characteristic of protein‐tyrosine phosphatases rather than dual‐specificity phosphatases. Together, these results suggest that VHZ's designation should be reconsidered. The vanadate species in the active site is unusual, with no discernable electron density observed between the VO 3 unit and apical ligands. This structure suggests a stabilized metavanadate, a previously unobserved mode of vanadate inhibition. A mechanism is proposed explaining the strong potency of vanadate as an inhibitor of these phosphatases under conditions where non‐inhibitory polyvanadate species dominate in solution. (Funding from NIH GM47297)