title: Connecting Active-Site Loop Conformations and Catalysis in Triosephosphate Isomerase: Insights from a Rare Variation at Residue 96 in the Plasmodial Enzyme.
abstract: Despite extensive research into triosephosphate isomerases (TIMs), there exists a gap in understanding of the remarkable conjunction between catalytic loop-6 (residues 166-176) movement and the conformational flip of Glu165 (catalytic base) upon substrate binding that primes the active site for efficient catalysis. The overwhelming occurrence of serine at position 96 (98% of the 6277 unique TIM sequences), spatially proximal to E165 and the loop-6 residues, raises questions about its role in catalysis. Notably, Plasmodium falciparum TIM has an extremely rare residue--phenylalanine--at this position whereas, curiously, the mutant F96S was catalytically defective. We have obtained insights into the influence of residue 96 on the loop-6 conformational flip and E165 positioning by combining kinetic and structural studies on the PfTIM F96 mutants F96Y, F96A, F96S/S73A, and F96S/L167V with sequence conservation analysis and comparative analysis of the available apo and holo structures of the enzyme from diverse organisms.
authors.affiliation: Molecular Biophysics Unit, Indian Institute of Science, Bangalore, 560012, India.
authors.forename: Vidhi
authors.initials: V
authors.lastname: Pareek
authors.affiliation: Molecular Biophysics Unit, Indian Institute of Science, Bangalore, 560012, India.
authors.forename: Moumita
authors.initials: M
authors.lastname: Samanta
authors.affiliation: Centre for Ecological Sciences, Indian Institute of Science, Bangalore, 560012, India.
authors.forename: Niranjan V
authors.initials: NV
authors.lastname: Joshi
authors.affiliation: Molecular Biology and Genetics Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bangalore, 560064, India.
authors.forename: Hemalatha
authors.initials: H
authors.lastname: Balaram
authors.affiliation: Molecular Biophysics Unit, Indian Institute of Science, Bangalore, 560012, India.
authors.forename: Mathur R N
authors.initials: MR
authors.lastname: Murthy
authors.affiliation: Molecular Biophysics Unit, Indian Institute of Science, Bangalore, 560012, India. pb@mbu.iisc.ernet.in.
authors.forename: Padmanabhan
authors.initials: P
authors.lastname: Balaram
mesh_terms: D000595:Amino Acid Sequence; D002384:Catalysis; D020134:Catalytic Domain; D017124:Conserved Sequence; D014644:Genetic Variation; D009154:Mutation; D010963:Plasmodium falciparum / Q000201:enzymology* / Q000235:genetics*; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D014305:Triose-Phosphate Isomerase / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*
chemical_list: D014305:Triose-Phosphate Isomerase
keywords: enzyme catalysis; isomerization; sequence conservation; structure-activity relationships; triosephosphate isomerase