Bioinformatic Analysis of Helicobacter pylori XGPRTase: A Potential Therapeutic Target

Background: Xanthine–guanine phosphoribosyltransferase (XGPRTase) is an enzyme of purine nucleotide salvage synthesis. The gpt gene of Helicobacter pylori has been annotated as encoding an XGPRTase and proposed as essential for survival of the bacterium in vitro. The aims of this work were to investigate the structure of H. pylori XGPRTase and to compare the key features of the enzyme to other phosphoribosyltransferases employing computational, modelling, and bioinformatic tools. Materials and Methods: XGPRTase activity was measured in the cytosolic fraction of H. pylori by 31P-nuclear magnetic resonance spectroscopy, and also in recombinant XGPRTase produced by a cell-free expression system. Bioinformatics was employed to analyze the phylogeny of XGPRTase, and a structural model of the XGPRTase was built using threading techniques. The observed interactions of purine phosphoribosyltransferases with immucillin-GP were used to study the theoretical interactions of H. pylori XGPRTase with this transition-state analog. Results: It was demonstrated that the gpt gene of H. pylori encodes a functional XGPRTase enzyme. Analyses of the XGPRTase sequence showed that the enzyme is significantly divergent from equivalent mammalian enzymes. Modelling served to identify specific features of the enzyme and key residues involved in catalysis. Conclusions: The H. pylori XGPRTase is structurally similar to other phosphoribosyltransferase enzymes, but there were significant differences between the hood domain of H. pylori XGPRTase and other purine salvage phosphoribosyltransferases. Significant differences were found between the interactions of the H. pylori and human enzymes with a purine phosphoribosyltransferase inhibitor.