title: Different contribution of conserved amino acids to the global properties of triosephosphate isomerases.
abstract: It is generally assumed that the amino acids that exist in all homologous enzymes correspond to residues that participate in catalysis, or that are essential for folding and stability. Although this holds for catalytic residues, the function of conserved noncatalytic residues is not clear. It is not known if such residues are of equal importance and have the same role in different homologous enzymes. In humans, the E104D mutation in triosephosphate isomerase (TIM) is the most frequent mutation in the autosomal diseases named "TPI deficiencies." We explored if the E104D mutation has the same impact in TIMs from four different organisms (Homo sapiens, Giardia lamblia, Trypanosoma cruzi, and T. brucei). The catalytic properties were not significantly affected by the mutation, but it affected the rate and extent of formation of active dimers from unfolded monomers differently. Scanning calorimetry experiments indicated that the mutation was in all cases destabilizing, but the mutation effect on rates of irreversible denaturation and transition-state energetics were drastically dependent on the TIM background. For instance, the E104D mutation produce changes in activation energy ranging from 430 kJ mol(-1) in HsTIM to -78 kJ mol(-1) in TcTIM. Thus, in TIM the role of a conserved noncatalytic residue is drastically dependent on its molecular background. Accordingly, it would seem that because each protein has a particular sequence, and a distinctive set of amino acid interactions, it should be regarded as a unique entity that has evolved for function and stability in the organisms to which it belongs.
authors: Departamento de Bioquímica y Biología Estructural, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, México D.F, México.
authors: Yolanda
authors: Y
authors: Aguirre
authors: Nallely
authors: N
authors: Cabrera
authors: Beatriz
authors: B
authors: Aguirre
authors: Ruy
authors: R
authors: Pérez-Montfort
authors: Alejandra
authors: A
authors: Hernandez-Santoyo
authors: Horacio
authors: H
authors: Reyes-Vivas
authors: Sergio
authors: S
authors: Enríquez-Flores
authors: Marietta Tuena
authors: MT
authors: de Gómez-Puyou
authors: Armando
authors: A
authors: Gómez-Puyou
authors: Jose M
authors: JM
authors: Sanchez-Ruiz
authors: Miguel
authors: M
authors: Costas
mesh_terms: D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D017124:Conserved Sequence; D018360:Crystallography, X-Ray; D019277:Entropy; D004795:Enzyme Stability; D016829:Giardia lamblia / Q000201:enzymology; D006801:Humans; D007700:Kinetics; D008958:Models, Molecular; D058767:Protein Unfolding; D015800:Protozoan Proteins / Q000737:chemistry* / Q000235:genetics; D040681:Structural Homology, Protein; D014305:Triose-Phosphate Isomerase / Q000737:chemistry* / Q000235:genetics; D014346:Trypanosoma brucei brucei / Q000201:enzymology; D014349:Trypanosoma cruzi / Q000201:enzymology
chemical_list: D015800:Protozoan Proteins; D014305:Triose-Phosphate Isomerase
keywords: free-energy barriers; homologous enzymes; kinetic stability; protein denaturation; transition-state plasticity