1
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Díaz-Mazariegos S, Cabrera N, Perez-Montfort R. Three unrelated and unexpected amino acids determine the susceptibility of the interface cysteine to a sulfhydryl reagent in the triosephosphate isomerases of two trypanosomes. PLoS One 2018; 13:e0189525. [PMID: 29342154 PMCID: PMC5771576 DOI: 10.1371/journal.pone.0189525] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2017] [Accepted: 11/27/2017] [Indexed: 11/23/2022] Open
Abstract
Proteins with great sequence similarity usually have similar structure, function and other physicochemical properties. But in many cases, one or more of the physicochemical or functional characteristics differ, sometimes very considerably, among these homologous proteins. To better understand how critical amino acids determine quantitative properties of function in proteins, the responsible residues must be located and identified. This can be difficult to achieve, particularly in cases where multiple amino acids are involved. In this work, two triosephosphate isomerases with very high similarity from two related human parasites were used to address one such problem. We demonstrate that a seventy-fold difference in the reactivity of an interface cysteine to the sulfhydryl reagent methylmethane sulfonate in these two enzymes depends on three amino acids located far away from this critical residue and which could not have been predicted using other current methods. Starting from previous observations with chimeric proteins involving these two triosephosphate isomerases, we developed a strategy involving additive mutant enzymes and selected site directed mutants to locate and identify the three amino acids. These three residues seem to induce changes in the interface cysteine in reactivity by increasing (or decreasing) its apparent pKa. Some enzymes with four to seven mutations also exhibited altered reactivity. This study completes a strategy for identifying key residues in the sequences of proteins that can have applications in future protein structure-function studies.
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Affiliation(s)
- Selma Díaz-Mazariegos
- Departamento de Bioquímica y Biología Estructural, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Ciudad de México, México
| | - Nallely Cabrera
- Departamento de Bioquímica y Biología Estructural, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Ciudad de México, México
| | - Ruy Perez-Montfort
- Departamento de Bioquímica y Biología Estructural, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Ciudad de México, México
- * E-mail:
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2
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Olivares-Illana V, Riveros-Rosas H, Cabrera N, Tuena de Gómez-Puyou M, Pérez-Montfort R, Costas M, Gómez-Puyou A. A guide to the effects of a large portion of the residues of triosephosphate isomerase on catalysis, stability, druggability, and human disease. Proteins 2017; 85:1190-1211. [PMID: 28378917 DOI: 10.1002/prot.25299] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2016] [Revised: 03/14/2017] [Accepted: 03/27/2017] [Indexed: 12/11/2022]
Abstract
Triosephosphate isomerase (TIM) is a ubiquitous enzyme, which appeared early in evolution. TIM is responsible for obtaining net ATP from glycolysis and producing an extra pyruvate molecule for each glucose molecule, under aerobic and anaerobic conditions. It is placed in a metabolic crossroad that allows a quick balance of the triose phosphate aldolase produced by glycolysis, and is also linked to lipid metabolism through the alternation of glycerol-3-phosphate and the pentose cycle. TIM is one of the most studied enzymes with more than 199 structures deposited in the PDB. The interest for this enzyme stems from the fact that it is involved in glycolysis, but also in aging, human diseases and metabolism. TIM has been a target in the search for chemical compounds against infectious diseases and is a model to study catalytic features. Until February 2017, 62% of all residues of the protein have been studied by mutagenesis and/or using other approaches. Here, we present a detailed and comprehensive recompilation of the reported effects on TIM catalysis, stability, druggability and human disease produced by each of the amino acids studied, contributing to a better understanding of the properties of this fundamental protein. The information reviewed here shows that the role of the noncatalytic residues depend on their molecular context, the delicate balance between the short and long-range interactions in concerted action determining the properties of the protein. Each protein should be regarded as a unique entity that has evolved to be functional in the organism to which it belongs. Proteins 2017; 85:1190-1211. © 2017 Wiley Periodicals, Inc.
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Affiliation(s)
- Vanesa Olivares-Illana
- Laboratorio de Interacciones Biomoleculares y Cáncer. Instituto de Física, Universidad Autónoma de San Luis Potosí, SLP, 78290, México
| | - Hector Riveros-Rosas
- Departamento de Bioquímica, Facultad de Medicina, Universidad Nacional Autónoma de México, Ciudad de México, 04510, México
| | - Nallely Cabrera
- Departamento de Bioquímica y Biología Estructural, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Ciudad de México, 04510, México
| | - Marietta Tuena de Gómez-Puyou
- Departamento de Bioquímica y Biología Estructural, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Ciudad de México, 04510, México
| | - Ruy Pérez-Montfort
- Departamento de Bioquímica y Biología Estructural, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Ciudad de México, 04510, México
| | - Miguel Costas
- Laboratorio de Biofisicoquímica, Departamento de Fisicoquímica, Facultad de Química, Universidad Nacional Autónoma de México, Ciudad de México, 04510, México
| | - Armando Gómez-Puyou
- Departamento de Bioquímica y Biología Estructural, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Ciudad de México, 04510, México
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3
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López-Castillo LM, Jiménez-Sandoval P, Baruch-Torres N, Trasviña-Arenas CH, Díaz-Quezada C, Lara-González S, Winkler R, Brieba LG. Structural Basis for Redox Regulation of Cytoplasmic and Chloroplastic Triosephosphate Isomerases from Arabidopsis thaliana. FRONTIERS IN PLANT SCIENCE 2016; 7:1817. [PMID: 27999583 PMCID: PMC5138414 DOI: 10.3389/fpls.2016.01817] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/04/2016] [Accepted: 11/18/2016] [Indexed: 05/04/2023]
Abstract
In plants triosephosphate isomerase (TPI) interconverts glyceraldehyde 3-phosphate (G3P) and dihydroxyacetone phosphate (DHAP) during glycolysis, gluconeogenesis, and the Calvin-Benson cycle. The nuclear genome of land plants encodes two tpi genes, one gene product is located in the cytoplasm and the other is imported into the chloroplast. Herein we report the crystal structures of the TPIs from the vascular plant Arabidopsis thaliana (AtTPIs) and address their enzymatic modulation by redox agents. Cytoplasmic TPI (cTPI) and chloroplast TPI (pdTPI) share more than 60% amino acid identity and assemble as (β-α)8 dimers with high structural homology. cTPI and pdTPI harbor two and one accessible thiol groups per monomer respectively. cTPI and pdTPI present a cysteine at an equivalent structural position (C13 and C15 respectively) and cTPI also contains a specific solvent accessible cysteine at residue 218 (cTPI-C218). Site directed mutagenesis of residues pdTPI-C15, cTPI-C13, and cTPI-C218 to serine substantially decreases enzymatic activity, indicating that the structural integrity of these cysteines is necessary for catalysis. AtTPIs exhibit differential responses to oxidative agents, cTPI is susceptible to oxidative agents such as diamide and H2O2, whereas pdTPI is resistant to inhibition. Incubation of AtTPIs with the sulfhydryl conjugating reagents methylmethane thiosulfonate (MMTS) and glutathione inhibits enzymatic activity. However, the concentration necessary to inhibit pdTPI is at least two orders of magnitude higher than the concentration needed to inhibit cTPI. Western-blot analysis indicates that residues cTPI-C13, cTPI-C218, and pdTPI-C15 conjugate with glutathione. In summary, our data indicate that AtTPIs could be redox regulated by the derivatization of specific AtTPI cysteines (cTPI-C13 and pdTPI-C15 and cTPI-C218). Since AtTPIs have evolved by gene duplication, the higher resistance of pdTPI to redox agents may be an adaptive consequence to the redox environment in the chloroplast.
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Affiliation(s)
- Laura M. López-Castillo
- Laboratorio Nacional de Genómica para la Biodiversidad, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico NacionalIrapuato Guanajuato, Mexico
- Departamento de Biotecnología y Bioquímica, CINVESTAV Unidad IrapuatoIrapuato Guanajuato, Mexico
| | - Pedro Jiménez-Sandoval
- Laboratorio Nacional de Genómica para la Biodiversidad, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico NacionalIrapuato Guanajuato, Mexico
| | - Noe Baruch-Torres
- Laboratorio Nacional de Genómica para la Biodiversidad, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico NacionalIrapuato Guanajuato, Mexico
| | - Carlos H. Trasviña-Arenas
- Laboratorio Nacional de Genómica para la Biodiversidad, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico NacionalIrapuato Guanajuato, Mexico
| | - Corina Díaz-Quezada
- Laboratorio Nacional de Genómica para la Biodiversidad, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico NacionalIrapuato Guanajuato, Mexico
| | - Samuel Lara-González
- División de Biología Molecular, Instituto Potosino de Investigación Científica y Tecnológica A.C.San Luis Potosí, Mexico
| | - Robert Winkler
- Departamento de Biotecnología y Bioquímica, CINVESTAV Unidad IrapuatoIrapuato Guanajuato, Mexico
| | - Luis G. Brieba
- Laboratorio Nacional de Genómica para la Biodiversidad, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico NacionalIrapuato Guanajuato, Mexico
- *Correspondence: Luis G. Brieba
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4
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Labastida-Polito A, Garza-Ramos G, Camarillo-Cadena M, Zubillaga RA, Hernández-Arana A. Complex kinetics and residual structure in the thermal unfolding of yeast triosephosphate isomerase. BMC BIOCHEMISTRY 2015; 16:20. [PMID: 26334568 PMCID: PMC4558838 DOI: 10.1186/s12858-015-0049-2] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/24/2015] [Accepted: 08/19/2015] [Indexed: 11/10/2022]
Abstract
BACKGROUND Saccharomyces cerevisiae triosephosphate isomerase (yTIM) is a dimeric protein that shows noncoincident unfolding and refolding transitions (hysteresis) in temperature scans, a phenomenon indicative of the slow forward and backward reactions of the native-unfolded process. Thermal unfolding scans suggest that no stable intermediates appear in the unfolding of yTIM. However, reported evidence points to the presence of residual structure in the denatured monomer at high temperature. RESULTS Thermally denatured yTIM showed a clear trend towards the formation of aggregation-prone, β-strand-like residual structure when pH decreased from 8.0 to 6.0, even though thermal unfolding profiles retained a simple monophasic appearance regardless of pH. However, kinetic studies performed over a relatively wide temperature range revealed a complex unfolding mechanism comprising up to three observable phases, with largely different time constants, each accompanied by changes in secondary structure. Besides, a simple sequential mechanism is unlikely to explain the observed variation of amplitudes and rate constants with temperature. This kinetic complexity is, however, not linked to the appearance of residual structure. Furthermore, the rate constant for the main unfolding phase shows small, rather unvarying values in the pH region where denatured yTIM gradually acquires a β-strand-like conformation. It appears, therefore, that the residual structure has no influence on the kinetic stability of the native protein. However, the presence of residual structure is clearly associated with increased irreversibility. CONCLUSIONS The slow temperature-induced unfolding of yeast TIM shows three kinetic phases. Rather than a simple sequential pathway, a complex mechanism involving off-pathway intermediates or even parallel pathways may be operating. β-strand-type residual structure, which appears below pH 8.0, is likely to be associated with increased irreversible aggregation of the unfolded protein. However, this denatured form apparently accelerates the refolding process.
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Affiliation(s)
- Ariana Labastida-Polito
- Área de Biofisicoquímica, Departamento de Química, Universidad Autónoma Metropolitana-Iztapalapa, San Rafael Atlixco 186, Iztapalapa, D.F. 09340, Mexico.
| | - Georgina Garza-Ramos
- Departamento de Bioquímica, Facultad de Medicina, Universidad Nacional Autónoma de México, Coyoacán, D.F. 04510, Mexico.
| | - Menandro Camarillo-Cadena
- Área de Biofisicoquímica, Departamento de Química, Universidad Autónoma Metropolitana-Iztapalapa, San Rafael Atlixco 186, Iztapalapa, D.F. 09340, Mexico.
| | - Rafael A Zubillaga
- Área de Biofisicoquímica, Departamento de Química, Universidad Autónoma Metropolitana-Iztapalapa, San Rafael Atlixco 186, Iztapalapa, D.F. 09340, Mexico.
| | - Andrés Hernández-Arana
- Área de Biofisicoquímica, Departamento de Química, Universidad Autónoma Metropolitana-Iztapalapa, San Rafael Atlixco 186, Iztapalapa, D.F. 09340, Mexico.
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Zinsser VL, Hoey EM, Trudgett A, Timson DJ. Biochemical characterisation of triose phosphate isomerase from the liver fluke Fasciola hepatica. Biochimie 2013; 95:2182-9. [DOI: 10.1016/j.biochi.2013.08.014] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2013] [Accepted: 08/07/2013] [Indexed: 11/29/2022]
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Zinsser VL, Farnell E, Dunne DW, Timson DJ. Triose phosphate isomerase from the blood flukeSchistosoma mansoni: Biochemical characterisation of a potential drug and vaccine target. FEBS Lett 2013; 587:3422-7. [DOI: 10.1016/j.febslet.2013.09.022] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2013] [Revised: 09/04/2013] [Accepted: 09/11/2013] [Indexed: 11/26/2022]
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Lara-González S, Estrella-Hernández P, Ochoa-Leyva A, Del Carmen Portillo-Téllez M, Caro-Gómez LA, Figueroa-Angulo EE, Salgado-Lugo H, Miranda Ozuna JFT, Ortega-López J, Arroyo R, Brieba LG, Benítez-Cardoza CG. Structural and thermodynamic folding characterization of triosephosphate isomerases from Trichomonas vaginalis reveals the role of destabilizing mutations following gene duplication. Proteins 2013; 82:22-33. [PMID: 23733417 DOI: 10.1002/prot.24333] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2012] [Revised: 05/01/2013] [Accepted: 05/03/2013] [Indexed: 11/07/2022]
Abstract
We report the structures and thermodynamic analysis of the unfolding of two triosephosphate isomerases (TvTIM1 and TvTIM2) from Trichomonas vaginalis. Both isoforms differ by the character of four amino acids: E/Q 18, I/V 24, I/V 45, and P/A 239. Despite the high sequence and structural similarities between both isoforms, they display substantial differences in their stabilities. TvTIM1 (E18, I24, I45, and P239) is more stable and less dissociable than TvTIM2 (Q18, V24, V45, and A239). We postulate that the identities of residues 24 and 45 are responsible for the differences in monomer stability and dimer dissociability, respectively. The structural difference between both amino acids is one methyl group. In TvTIMs, residue 24 is involved in packing α-helix 1 against α-helix 2 of each monomer and residue 45 is located at the center of the dimer interface forming a "ball and socket" interplay with a hydrophobic cavity. The mutation of valine at position 45 for an alanine in TvTIM2 produces a protein that migrates as a monomer by gel filtration. A comparison with known TIM structures indicates that this kind of interplay is a conserved feature that stabilizes dimeric TIM structures. In addition, TvTIMs are located in the cytoplasm and in the membrane. As TvTIM2 is an easily dissociable dimer, the dual localization of TvTIMs may be related to the acquisition of a moonlighting activity of monomeric TvTIM2. To our knowledge, this is the simplest example of how a single amino acid substitution can provide alternative function to a TIM barrel protein.
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Affiliation(s)
- Samuel Lara-González
- IPICYT, División de Biología Molecular, Camino a la Presa San José 2055, San Luis Potosí, San Luis Potosí, México, CP 78216
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Moraes J, Arreola R, Cabrera N, Saramago L, Freitas D, Masuda A, da Silva Vaz I, Tuena de Gomez-Puyou M, Perez-Montfort R, Gomez-Puyou A, Logullo C. Structural and biochemical characterization of a recombinant triosephosphate isomerase from Rhipicephalus (Boophilus) microplus. INSECT BIOCHEMISTRY AND MOLECULAR BIOLOGY 2011; 41:400-409. [PMID: 21396445 DOI: 10.1016/j.ibmb.2011.02.009] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/22/2008] [Revised: 02/17/2011] [Accepted: 02/28/2011] [Indexed: 05/30/2023]
Abstract
Triosephosphate isomerase (TIM) is an enzyme with a role in glycolysis and gluconeogenesis by catalyzing the interconversion between glyceraldehyde 3-phosphate and dihydroxyacetone phosphate. This enzyme has been used as a target in endoparasite drug development. In this work we cloned, expressed, purified and studied kinetic and structural characteristics of TIM from tick embryos, Rhipicephalus (Boophilus) microplus (BmTIM). The Km and Vmax of the recombinant BmTIM with glyceraldehyde 3-phosphate as substrate, were 0.47 mM and 6031 μmol min⁻¹ mg protein⁻¹, respectively. The resolution of the diffracted crystal was estimated to be 2.4 Å and the overall data showed that BmTIM is similar to other reported dimeric TIMs. However, we found that, in comparison to other TIMs, BmTIM has the highest content of cysteine residues (nine cysteine residues per monomer). Only two cysteines could make disulfide bonds in monomers of BmTIM. Furthermore, BmTIM was highly sensitive to the action of the thiol reagents dithionitrobenzoic acid and methyl methane thiosulfonate, suggesting that there are five cysteines exposed in each dimer and that these residues could be employed in the development of species-specific inhibitors.
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Affiliation(s)
- Jorge Moraes
- Laboratório de Química e Função de Proteínas e Peptídeos and Unidade de Experimentação Animal-RJ, CBB, UENF, Avenida Alberto Lamego 2000, Horto, Campos dos Goytacazes, RJ, CEP 28015-620, Brazil
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9
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García-Torres I, Cabrera N, Torres-Larios A, Rodríguez-Bolaños M, Díaz-Mazariegos S, Gómez-Puyou A, Perez-Montfort R. Identification of amino acids that account for long-range interactions in two triosephosphate isomerases from pathogenic trypanosomes. PLoS One 2011; 6:e18791. [PMID: 21533154 PMCID: PMC3078909 DOI: 10.1371/journal.pone.0018791] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2010] [Accepted: 03/18/2011] [Indexed: 11/18/2022] Open
Abstract
For a better comprehension of the structure-function relationship in proteins it is necessary to identify the amino acids that are relevant for measurable protein functions. Because of the numerous contacts that amino acids establish within proteins and the cooperative nature of their interactions, it is difficult to achieve this goal. Thus, the study of protein-ligand interactions is usually focused on local environmental structural differences. Here, using a pair of triosephosphate isomerase enzymes with extremely high homology from two different organisms, we demonstrate that the control of a seventy-fold difference in reactivity of the interface cysteine is located in several amino acids from two structurally unrelated regions that do not contact the cysteine sensitive to the sulfhydryl reagent methylmethane sulfonate, nor the residues in its immediate vicinity. The change in reactivity is due to an increase in the apparent pKa of the interface cysteine produced by the mutated residues. Our work, which involved grafting systematically portions of one protein into the other protein, revealed unsuspected and multisite long-range interactions that modulate the properties of the interface cysteines and has general implications for future studies on protein structure-function relationships.
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Affiliation(s)
- Itzhel García-Torres
- Departamento de Bioquímica y Biología Estructural, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Circuito Exterior S/N, Ciudad Universitaria, México DF, Mexico
| | - Nallely Cabrera
- Departamento de Bioquímica y Biología Estructural, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Circuito Exterior S/N, Ciudad Universitaria, México DF, Mexico
| | - Alfredo Torres-Larios
- Departamento de Bioquímica y Biología Estructural, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Circuito Exterior S/N, Ciudad Universitaria, México DF, Mexico
| | - Mónica Rodríguez-Bolaños
- Departamento de Bioquímica y Biología Estructural, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Circuito Exterior S/N, Ciudad Universitaria, México DF, Mexico
| | - Selma Díaz-Mazariegos
- Departamento de Bioquímica y Biología Estructural, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Circuito Exterior S/N, Ciudad Universitaria, México DF, Mexico
| | - Armando Gómez-Puyou
- Departamento de Bioquímica y Biología Estructural, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Circuito Exterior S/N, Ciudad Universitaria, México DF, Mexico
| | - Ruy Perez-Montfort
- Departamento de Bioquímica y Biología Estructural, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Circuito Exterior S/N, Ciudad Universitaria, México DF, Mexico
- * E-mail:
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Banerjee M, Balaram H, Joshi NV, Balaram P. Engineered dimer interface mutants of triosephosphate isomerase: the role of inter-subunit interactions in enzyme function and stability. Protein Eng Des Sel 2011; 24:463-72. [DOI: 10.1093/protein/gzr005] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
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11
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Tellez LA, Blancas-Mejia LM, Carrillo-Nava E, Mendoza-Hernández G, Cisneros DA, Fernández-Velasco DA. Thermal Unfolding of Triosephosphate Isomerase from Entamoeba histolytica: Dimer Dissociation Leads to Extensive Unfolding. Biochemistry 2008; 47:11665-73. [DOI: 10.1021/bi801360k] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Luis A. Tellez
- Laboratorio de Fisicoquímica e Ingeniería de Proteínas, Departamento de Bioquímica, Facultad de Medicina, and Departamento de Fisicoquímica, Facultad de Química, Universidad Nacional Autónoma de México, Apdo. Postal 70-159, 04510 México, DF
| | - Luis M. Blancas-Mejia
- Laboratorio de Fisicoquímica e Ingeniería de Proteínas, Departamento de Bioquímica, Facultad de Medicina, and Departamento de Fisicoquímica, Facultad de Química, Universidad Nacional Autónoma de México, Apdo. Postal 70-159, 04510 México, DF
| | - Ernesto Carrillo-Nava
- Laboratorio de Fisicoquímica e Ingeniería de Proteínas, Departamento de Bioquímica, Facultad de Medicina, and Departamento de Fisicoquímica, Facultad de Química, Universidad Nacional Autónoma de México, Apdo. Postal 70-159, 04510 México, DF
| | - Guillermo Mendoza-Hernández
- Laboratorio de Fisicoquímica e Ingeniería de Proteínas, Departamento de Bioquímica, Facultad de Medicina, and Departamento de Fisicoquímica, Facultad de Química, Universidad Nacional Autónoma de México, Apdo. Postal 70-159, 04510 México, DF
| | - David A. Cisneros
- Laboratorio de Fisicoquímica e Ingeniería de Proteínas, Departamento de Bioquímica, Facultad de Medicina, and Departamento de Fisicoquímica, Facultad de Química, Universidad Nacional Autónoma de México, Apdo. Postal 70-159, 04510 México, DF
| | - D. Alejandro Fernández-Velasco
- Laboratorio de Fisicoquímica e Ingeniería de Proteínas, Departamento de Bioquímica, Facultad de Medicina, and Departamento de Fisicoquímica, Facultad de Química, Universidad Nacional Autónoma de México, Apdo. Postal 70-159, 04510 México, DF
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