title: Crosstalk between the subunits of the homodimeric enzyme triosephosphate isomerase.
abstract: Homodimeric triosephosphate isomerase (TIM) from Trypanosoma cruzi (TcTIM) and T. brucei (TbTIM) are markedly similar in amino acid sequence and three-dimensional structure. In their dimer interfaces, each monomer has a Cys15 that is surrounded by loop3 of the adjoining subunit. Perturbation of Cys15 by methylmethane thiosulfonate (MMTS) induces abolition of catalysis and structural changes. In the two TIMs, the structural arrangements of their Cys15 are almost identical. Nevertheless, the susceptibility of TcTIM to MMTS is nearly 100-fold higher than in TbTIM. To ascertain the extent to which the characteristics of the interface Cys depend on the dynamics of its own monomer or on those of the adjacent monomer, we studied MMTS action on mutants of TcTIM that had the interface residues of TbTIM, and hybrids that have only one interfacial Cys15 (C15ATcTIM-wild type TbTIM). We found that the solvent exposure of the interfacial Cys depends predominantly on the characteristics of the adjoining monomer. The maximal inhibition of activity induced by perturbation of the sole interface Cys in the C15ATcTIM-TbTIM hybrid is around 60%. Hybrids formed with C15ATcTIM monomers and catalytically inert TbTIM monomers (E168DTbTIM) were also studied. Their activity drops by nearly 50% when the only interfacial Cys is perturbed. These results in conjunction with those on C15ATcTIM-wild type TbTIM hybrid indicate that about half of the activity of each monomer depends on the integrity of each of the two Cys15-loop3 portions of the interface. This could be another reason of why TIM is an obligatory dimer.
authors.affiliation: Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Apartado Postal 70243, 04510 México, D. F., Mexico.
authors.forename: Viviana
authors.initials: V
authors.lastname: Zomosa-Signoret
authors.forename: Beatriz
authors.initials: B
authors.lastname: Aguirre-López
authors.forename: Gloria
authors.initials: G
authors.lastname: Hernández-Alcántara
authors.forename: Ruy
authors.initials: R
authors.lastname: Pérez-Montfort
authors.forename: Marietta Tuena
authors.initials: MT
authors.lastname: de Gómez-Puyou
authors.forename: Armando
authors.initials: A
authors.lastname: Gómez-Puyou
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D003545:Cysteine / Q000737:chemistry*; D019281:Dimerization; D007700:Kinetics; D008741:Methyl Methanesulfonate / Q000031:analogs & derivatives* / Q000737:chemistry / Q000494:pharmacology; D016297:Mutagenesis, Site-Directed; D025941:Protein Interaction Mapping / Q000379:methods; D020836:Protein Structure, Quaternary; D014305:Triose-Phosphate Isomerase / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D014346:Trypanosoma brucei brucei / Q000201:enzymology*; D014349:Trypanosoma cruzi / Q000201:enzymology*
chemical_list: C014674:methyl methanethiosulfonate; D008741:Methyl Methanesulfonate; D014305:Triose-Phosphate Isomerase; D003545:Cysteine