Interference of Sulphonate Buffering Agents with E. coli Hypoxanthine-Guanine Phosphoribosyltransferase Active Site Functioning: A Crystallographic and Enzymological Study

The investigation of the structure–function relationship in hypoxanthine-guanine phosphoribosyltransferases (HGPRT) is a direction that is relevant for the development of drugs and approaches of enzymatic synthesis of modified nucleosides and nucleotides. This research paper is dedicated to the investigation of binding of sulphonate molecules, such as HEPES (4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid) in the active sites of HGPRT and similar proteins. We report the crystal structure of HGPRT from Escherichia coli (EcoHGPRT) in a complex with HEPES. In the obtained X-ray structure, a HEPES molecule binds to the active site in a position that mimics one of the HGPRT substrates, namely phosphoribosylpyrophosphate (PRPP). Enzymological study has shown that HEPES is an inhibitor of EcoHGPRT, along with two structurally similar molecules, namely MES and PIPES. Comparison of the observed EcoHGPRT/HEPES complex to other reported structures in the context of inhibition study results provides an opportunity to explore the variety of binding modes of HEPES and similar molecules and to discuss the structure–function relationship in this enzyme and similar proteins.