The role of electrostatics in TrxR electron transfer mechanism: A computational approach.
Thioredoxin reductase (TrxR) is an important enzyme in the control of the intracellular reduced redox environment. It transfers electrons from NADPH to several molecules, including its natural partner, thioredoxin. Although there is a generally accepted model describing how the electrons are transferred along TrxR, which involves a flexible arm working as a "shuttle," the molecular details of such mechanism are not completely understood. In this work, we use molecular dynamics simulations with Poisson-Boltzmann/Monte Carlo pKa calculations to investigate the role of electrostatics in the electron transfer mechanism. We observed that the combination of redox/protonation states of the N-terminal (FAD and Cys59/64) and C-terminal (Cys497/Selenocysteine498) redox centers defines the preferred relative positions and allows for the flexible arm to work as the desired "shuttle." Changing the redox/ionization states of those key players, leads to electrostatic triggers pushing the arm into the pocket when oxidized, and pulling it out, once it has been reduced. The calculated pKa values for Cys497 and Selenocysteine498 are 9.7 and 5.8, respectively, confirming that the selenocysteine is indeed deprotonated at physiological pH. This can be an important advantage in terms of reactivity (thiolate/selenolate are more nucleophilic than thiol/selenol) and ability to work as an electrostatic trigger (the "shuttle" mechanism) and may be the reason why TrxR uses selenium instead of sulfur. Proteins 2016; 84:1836-1843. © 2016 Wiley Periodicals, Inc.
Centro de Química e Bioquímica, Departamento de Química e Bioquímica, Faculdade de Ciências, Universidade de Lisboa, 1749-016, Lisboa, Portugal.
Vitor H
VH
Teixeira
Centro de Química e Bioquímica, Departamento de Química e Bioquímica, Faculdade de Ciências, Universidade de Lisboa, 1749-016, Lisboa, Portugal.
Ana Sofia C
AS
Capacho
Centro de Química e Bioquímica, Departamento de Química e Bioquímica, Faculdade de Ciências, Universidade de Lisboa, 1749-016, Lisboa, Portugal.
Miguel
M
Machuqueiro
D020816:Amino Acid Motifs; D003067:Coenzymes / Q000737:chemistry*; D003545:Cysteine / Q000737:chemistry*; D004579:Electron Transport; D004583:Electrons; D005182:Flavin-Adenine Dinucleotide / Q000737:chemistry*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D056004:Molecular Dynamics Simulation; D009010:Monte Carlo Method; D009154:Mutation; D010084:Oxidation-Reduction; D016012:Poisson Distribution; D000072417:Protein Domains; D017433:Protein Structure, Secondary; D017279:Selenocysteine / Q000737:chemistry*; D055672:Static Electricity; D054481:Thioredoxin Reductase 1 / Q000737:chemistry*; D014867:Water / Q000737:chemistry
D003067:Coenzymes; D014867:Water; D017279:Selenocysteine; D005182:Flavin-Adenine Dinucleotide; C516124:TXNRD1 protein, human; D054481:Thioredoxin Reductase 1; D003545:Cysteine
cofactor; disulfide; electron transfer; electrostatic; ionization; pH; selenocystein; shuttle; thiol; thioredoxin reductase