Crystal Structure of the Catalytic Subunit of Human Protein Phosphatase 1 and its Complex with Tungstate

Protein phosphatase 1 (PP1) is a serine/threonine protein phosphatase that is essential in regulating diverse cellular processes. Here we report the crystal structure of the catalytic subunit of human PP1 γ1and its complex with tungstate at 2.5 Å resolution. The anomalous scattering from tungstate was used in a multiple wavelength anomalous dispersion experiment to derive crystallographic phase information. The protein adopts a single domain with a novel fold, distinct from that of the protein tyrosine phosphatases. A di-nuclear ion centre consisting of Mn 2+and Fe 2+is situated at the catalytic site that binds the phosphate moiety of the substrate. Proton-induced X-ray emission spectroscopy was used to identify the nature of the ions bound to the enzyme. The structural data indicate that dephosphorylation is catalysed in a single step by a metal-activated water molecule. This contrasts with other phosphatases, including protein tyrosine phosphatases, acid and alkaline phosphatases which form phosphoryl-enzyme intermediates. The structure of PP1 provides insight into the molecular mechanism for substrate recognition, enzyme regulation and inhibition of this enzyme by toxins and tumour promoters and a basis for understanding the expanding family of related phosphatases which include PP2A and PP2B (calcineurin).