Conformational Substates Modulate Hydride Transfer in Dihydrofolate Reductase

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• 作者：Ian F. Thorpe and Charles L. Brooks III
• 刊名：Journal of the American Chemical Society
• 出版年：2005
• 出版时间：September 21, 2005
• 年：2005
• 卷：127
• 期：37
• 页码：12997 - 13006
• 全文大小：330K
• 年卷期：v.127,no.37(September 21, 2005)
• ISSN：1520-5126

文摘

In earlier studies of the hydride-transfer reaction catalyzed by dihydrofolate reductase (DHFR)we identified features of the protein correlated with variations in the reaction barrier. We extend the scopeof those studies by carrying out potential of mean force (PMF) simulations to determine the hydride-transferbarrier in the wild-type protein as well as the G121V and G121S mutants. While our prior studies focusedon the reactant state, our current work addresses the full reaction pathway and directly probes the reactiveevent. The free energy barriers and structural ensembles resulting from these PMF calculations exhibit thesame trends reported in our previous work. Fluctuations present in these simulations also exhibit trendsassociated with differences in the hydride-transfer barrier height. Moreover, vibrational modes anticipatedto promote hydride transfer exhibit larger amplitudes in simulations that generate lowered barriers. Theresults of our study indicate that discrete basins (substates) on a potential energy landscape of the enzymegive rise to distinct hydride-transfer barriers. We suggest that the long-range effects of mutations at position121 within DHFR are mediated by differentially preorganized protein environments in the context of distinctsubstate distributions, with concomitant changes to the dynamic properties of the enzyme.