title: Slow ligand-induced conformational switch increases the catalytic rate in Plasmodium falciparum hypoxanthine guanine xanthine phosphoribosyltransferase.
abstract: P. falciparum (Pf) hypoxanthine guanine xanthine phosphoribosyltransferase (HGXPRT) exhibits a unique mechanism of activation where the enzyme switches from a low activity (unactivated) to a high activity (activated) state upon pre-incubation with substrate/products. Xanthine phosphoribosylation by unactivated PfHGXPRT exhibits a lag phase, the duration of which reduces with an increase in concentration of the enzyme or substrate, PRPP·Mg(2+). Activated PfHGXPRT does not display the lag phase and exhibits a ten-fold drop in the Km value for PRPP·Mg(2+). These observations suggest the involvement of ligand-mediated oligomerization and conformational changes in the process of activation. The dipeptide Leu-Lys in the PPi binding site of human and T. gondii HG(X)PRT that facilitates PRPP·Mg(2+) binding by isomerization from trans to cis conformation is conserved in PfHGXPRT. Free energy calculations using the well-tempered metadynamics technique show the ligand-free enzyme to be more stable when this dipeptide is in the trans conformation than in the cis conformation. The high rotational energy barrier observed for the conformational change from experimental and computational studies permits delineation of the activation mechanism.
authors.affiliation: Molecular Biology and Genetics Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bangalore 560064, India. hb@jncasr.ac.in.
authors.forename: Sourav
authors.initials: S
authors.lastname: Roy
authors.forename: Tarak
authors.initials: T
authors.lastname: Karmakar
authors.forename: Vasudeva S
authors.initials: VS
authors.lastname: Prahlada Rao
authors.forename: Lakshmeesha K
authors.initials: LK
authors.lastname: Nagappa
authors.forename: Sundaram
authors.initials: S
authors.lastname: Balasubramanian
authors.forename: Hemalatha
authors.initials: H
authors.lastname: Balaram
mesh_terms: D001665:Binding Sites; D002384:Catalysis; D020134:Catalytic Domain; D004789:Enzyme Activation; D006801:Humans; D007700:Kinetics; D008024:Ligands; D008958:Models, Molecular; D008968:Molecular Conformation; D062105:Molecular Docking Simulation; D056004:Molecular Dynamics Simulation; D009154:Mutation; D010430:Pentosyltransferases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D010963:Plasmodium falciparum / Q000201:enzymology* / Q000235:genetics; D011485:Protein Binding; D011487:Protein Conformation; D013329:Structure-Activity Relationship
chemical_list: D008024:Ligands; D010430:Pentosyltransferases; C083867:hypoxanthine-guanine-xanthine phosphoribosyltransferase