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Anthrax Edema Factor: An Ion-Adaptive Mechanism of Catalysis with Increased Transition-State Conformational Flexibility

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Autor(es):
Jara, Gabriel E. ; Martinez, Leandro
Número total de Autores: 2
Tipo de documento: Artigo Científico
Fonte: Journal of Physical Chemistry B; v. 120, n. 27, p. 6504-6514, JUL 14 2016.
Citações Web of Science: 1
Resumo

Edema Factor (EF) is one of three major toxins of anthrax. EF is an adenylyl cyclase that disrupts cell signaling by accelerating the conversion of ATP into cyclic-AMP. EF has a much higher catalytic rate than that of mammalian adenylyl cyclases (mACs). Crystal structures were obtained for mACs and EF, but the molecular basis for different catalytic activities remained poorly understood. In particular, the arrangement of the active site in EF is unclear in what concerns the number of ions present and the conformation of the substrate. Here, we use quantum mechanics-molecular mechanics simulations to estimate the free-energy profiles for the reaction catalyzed by EF and a mAC. We found that EF catalysis is possible, and faster than that of mACs, in both one and two Mg2+-ion-binding modes, providing adaptive plasticity to host-cell environments. In both enzymes, the reaction mechanisms are highly associative. However, mechanistic differences exist. In the mAC, the nucleophile oxygen (ATP-O3') is consistently coordinated to one of the Mg2+ ions, increasing its acidity. In EF, on the other hand, this coordination is eventual and not essential for the reaction to proceed. The persistent coordination of O3' to the ion is favored in mACs by a greater ion partial charge. In EF, the reduced acidity of the O3' oxygen is compensated by the presence of the His351 residue for proton abstraction. As proton transfer in EF does not require persistent attachment of the substrate to an ion, the substrate (ATP) and transition state display greater conformational flexibilities. These greater flexibilities allow the sampling of lower energy conformations and might represent an entropic advantage for catalytic efficiency. (AU)

Processo FAPESP: 13/05475-7 - Métodos computacionais de otimização
Beneficiário:Sandra Augusta Santos
Linha de fomento: Auxílio à Pesquisa - Temático
Processo FAPESP: 13/22360-9 - Estudo computacional do mecanismo de conversão de ATP a AMP-cíclico catalisada pelo fator de edema do antraz
Beneficiário:Gabriel Ernesto Jara
Linha de fomento: Bolsas no Brasil - Pós-Doutorado
Processo FAPESP: 10/16947-9 - Estrutura, dinâmica e função em proteínas: simulação computacional e desenvolvimento de algoritmos
Beneficiário:Leandro Martinez
Linha de fomento: Auxílio à Pesquisa - Regular
Processo FAPESP: 13/08293-7 - CECC - Centro de Engenharia e Ciências Computacionais
Beneficiário:Munir Salomao Skaf
Linha de fomento: Auxílio à Pesquisa - Centros de Pesquisa, Inovação e Difusão - CEPIDs