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 re port the crystal structure of the catalytic subunit of human PP1(71) a nd its complex with tungstate at 2.5 Angstrom resolution. The anomalou s scattering from tungstate was used in a multiple wavelength anomalou s dispersion experiment to derive crystallographic phase information. The protein adopts a single domain with a novel fold, distinct from th at of the protein tyrosine phosphatases. A di-nuclear ion centre consi sting of Mn2+ and Fe2+ is situated at the catalytic site that binds th e phosphate moiety of the substrate. Proton-induced X-ray emission spe ctroscopy was used to identify the nature of the ions bound to the enz yme. The structural data indicate that dephosphorylation is catalysed in a single step by a metal-activated water molecule. This contrasts w ith 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 enzym e by toxins and tumour promoters and a basis for understanding the exp anding family of related phosphatases which include PP2A and PP2B (cal cineurin). (C) 1995 Academic Press Limited