Avaliação in silico da tioredoxina redutase como alvo para terapia anti-tumoral
Year: 2012
Type: dissertation
Abstract: Thioredoxin reductase (TrxR) is a crucial enzyme in cellular protection by reducing oxygen rective species. Its function depends on the transfer of reductive equivalents from NADPH to thioredoxin (Trx) by creating several dissulfide bonds along the opposite way. The protein presents two main redox centres: the N-terminal close to FAD group and the C-terminal whith the pair Cys497/Sec498, responsible for Trx coupling. Using a shuttle effect, C-terminal redox center is flexible enough to bring reductive equivalentes from the N-terminal redox center almost 20 A apart. The reduction of several electrophilic substracts is possible since the enzyme presents a highly reactive selenocystein at this catalytic site. At different moments of its catalytic cycle, the general reactivities of Sec498 and Cys497 were studied by determining their p Ka values. The deprotonated species are the real nucleophilic agent and the p Ka values of these residues define the amount of thiolate/selenolate available at physiologic pH., Molecular Dynamics Simulations and p Ka value calculations were performed varying some protonation/redox features of FAD, Cys59/Cys64, Cys497/Sec498 and also histidin residues. MD Simulations with oxidized Sec498 through a Trx dissulfide bond or a potential inhibitor were also performed. By introducing this auranofin derived inhibitor, we studied its mechanism and its effect on Cys497p Ka, a pivotal residue in TrxR regeneration. The p Ka calculations were performed using linear response aproximation (LRA) with Poisson- Boltzmann and Monte Carlo. In all systems we followed the distance profiles between N and C-terminal redox centres. The system with a reduced N-terminal and an oxidised C-terminal presented the shortest distance. These results are in accordance with the known mechanism and shows an aproximation between the two centres whenever there is a need to transfer electrons. Cys497 p Ka values when coupled with Trx or the inhibitor are quite similar, while Sec498 p Ka is significantly lower. The expected difference between Cys497 and Sec498 p Ka values represents a significant difference in the ionized species availability and therefore in its reactivity for substrate.
Author: Ana Sofia Cardoso Capacho
Language: Portuguese
Subfield: Drug Discovery
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W2167367093