%0 Journal Article
%T Crystal structures of a purple acid phosphatase, representing different steps of this enzyme's catalytic cycle
%A Gerhard Schenk
%A Tristan W Elliott
%A Eleanor Leung
%A Lyle E Carrington
%A Nata£¿a Miti£¿
%A Lawrence R Gahan
%A Luke W Guddat
%J BMC Structural Biology
%D 2008
%I BioMed Central
%R 10.1186/1472-6807-8-6
%X Red kidney bean purple acid phosphatase is a heterovalent enzyme with an Fe(III)Zn(II) center in the active site. Two new structures with bound sulfate (2.4 £¿) and fluoride (2.2 £¿) provide insight into the pre-catalytic phase of its reaction cycle and phosphorolysis. The sulfate-bound structure illustrates the significance of an extensive hydrogen bonding network in the second coordination sphere in initial substrate binding and orientation prior to hydrolysis. Importantly, both metal ions are five-coordinate in this structure, with only one nucleophilic ¦̀-hydroxide present in the metal-bridging position. The fluoride-bound structure provides visual support for an activation mechanism for this ¦̀-hydroxide whereby substrate binding induces a shift of this bridging ligand towards the divalent metal ion, thus increasing its nucleophilicity.In combination with kinetic, crystallographic and spectroscopic data these structures of red kidney bean purple acid phosphatase facilitate the proposal of a comprehensive eight-step model for the catalytic mechanism of purple acid phosphatases in general.At least one-third of enzymes characterized require metal ions to function. Roles include electron transfer reactions, oxidations and a plethora of hydrolytic processes [1]. The majority of these enzymes require one or two metal ions for functionality but more complex multinuclear metal clusters also occur. Amongst metalloenzymes binuclear hydrolases form a diverse family with biological functions including signal transduction and cell cycle progression, nucleotide homeostasis and bone metabolism [2-9]. Members of this group of enzymes have evolved into targets for the development of chemotherapeutic agents.Binuclear metallohydrolases employ variants of the same basic mechanism to catalyze esterolysis of a large number of substrates, in some cases under inversion of stereochemistry, and in others without [2,8,10-13]. In the latter (e.g. alkaline phosphatase [13]) a covalently modifi
%U http://www.biomedcentral.com/1472-6807/8/6