title: Single tryptophan of disordered loop from Plasmodium falciparum purine nucleoside phosphorylase: involvement in catalysis and microenvironment.
abstract: Among various tropical diseases, malaria is a major life-threatening disease caused by Plasmodium parasite. Plasmodium falciparum is responsible for the deadliest form of malaria, so-called cerebral malaria. Purine nucleoside phosphorylase from P. falciparum is a homohexamer containing single tryptophan residue per subunit that accepts inosine and guanosine but not adenosine for its activity. This enzyme has been exploited as drug target against malaria disease. It is important to draw together significant knowledge about inherent properties of this enzyme which will be helpful in better understanding of this drug target. The enzyme shows disorder to order transition during catalysis. The single tryptophan residue residing in conserved region of transition loop is present in purine nucleoside phosphorylases throughout the Plasmodium genus. This active site loop motif is conserved among nucleoside phosphorylases from apicomplexan parasites. Modification of tryptophan residue by N-bromosuccinamide resulted in complete loss of activity showing its importance in catalysis. Inosine was not able to protect enzyme against N-bromosuccinamide modification. Extrinsic fluorescence studies revealed that tryptophan might not be involved in substrate binding. The tryptophan residue localised in electronegative environment showed collisional and static quenching in the presence of quenchers of different polarities.
authors.affiliation: Division of Biochemistry, CSIR-Central Drug Research Institute, Chattar Manzil Palace, M. G. Road, Lucknow, U.P. 226001, India.
authors.forename: Manish Kumar
authors.initials: MK
authors.lastname: Suthar
authors.forename: Anita
authors.initials: A
authors.lastname: Verma
authors.forename: Pawan Kumar
authors.initials: PK
authors.lastname: Doharey
authors.forename: Shiv Vardan
authors.initials: SV
authors.lastname: Singh
authors.forename: Jitendra Kumar
authors.initials: JK
authors.lastname: Saxena
mesh_terms: D000595:Amino Acid Sequence; D000817:Anilino Naphthalenesulfonates / Q000737:chemistry; D001974:Bromosuccinimide / Q000737:chemistry; D002384:Catalysis; D020134:Catalytic Domain; D017124:Conserved Sequence; D004789:Enzyme Activation; D008969:Molecular Sequence Data; D010963:Plasmodium falciparum / Q000201:enzymology* / Q000235:genetics; D011485:Protein Binding; D017433:Protein Structure, Secondary; D015800:Protozoan Proteins / Q000737:chemistry*; D011683:Purine-Nucleoside Phosphorylase / Q000737:chemistry* / Q000235:genetics; D055672:Static Electricity; D014364:Tryptophan / Q000737:chemistry* / Q000235:genetics
chemical_list: D000817:Anilino Naphthalenesulfonates; D015800:Protozoan Proteins; D014364:Tryptophan; D011683:Purine-Nucleoside Phosphorylase; D001974:Bromosuccinimide