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首页> 外文期刊>Proceedings of the National Academy of Sciences of the United States of America >Identification of the proton pathway in bacterial reaction centers: Replacement of Asp-M17 and Asp-L210 with Asn reduces the proton transfer rate in the presence of Cd~2+
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Identification of the proton pathway in bacterial reaction centers: Replacement of Asp-M17 and Asp-L210 with Asn reduces the proton transfer rate in the presence of Cd~2+

机译：鉴定细菌反应中心中的质子途径：用Asn替代Asp-M17和Asp-L210可降低存在Cd〜2 +时的质子转移速率

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摘要

The reaction center (RC) from Rhodobacter sphaeroides converts light into chemical energy through the reduction and protonation of a bound quinone molecule QB (the secondary quinone electron acceptor). We investigated the proton transfer pathway by mea- Suring the proton-coupled electron transfer, kAB~(2) [Q_AQ_B' + H+ → Q_A(Q_BH)-] in native and mutant RCs in the absence and presence of Cd~2+. Previous work has shown that the binding of Cd~2+ decreases k_AB(2) in native RCs ≈100-fold. The preceding paper shows that bound Cd~2+ binds to Asp-H 124. His-H 126, and His-H 128. This region represents the entry point for protons. In this work we investigated the proton transfer pathway connecting the entry point with Q_B by searching for mutations that greatly affect k_AB(2) (≥10-fold) in the presence of Cd2+, where k~AB(2) is limited by the proton transfer rate (k_H). Upon mutation of Asp-L210 or Asp-M17 to Asn, k_H decreased from ≈60 s-1 to ≈e7 s-1, which shows the important role that Asp-L210 and Asp-M17 play in the proton transfer chain. By comparing the rate of proton transfer in the mutants with that in native RCs in the absence of Cd2+ we conclude that alternate proton transfer path- ways. which have been postulated, are at least 103-fold less effective.
机译：球形球形红细菌的反应中心（RC）通过结合的醌分子QB（次级醌电子受体）的还原和质子化将光转换为化学能。我们通过测量在不存在和存在Cd〜2 +的情况下在天然和突变RC中的质子耦合电子传递kAB〜（2）[Q_AQ_B'+ H +→Q_A（Q_BH）-]来研究质子传递途径。先前的研究表明，Cd〜2 +的结合降低了天然RC中的k_AB（2）≈100倍。前面的论文表明，结合的Cd〜2 +与Asp-H 124，His-H 126和His-H 128结合。该区域表示质子的进入点。在这项工作中，我们通过寻找在Cd2 +存在下对k_AB（2）（≥10倍）产生重大影响的突变来研究连接入口点与Q_B的质子传递途径，其中k〜AB（2）受质子限制传输速率（k_H）。当Asp-L210或Asp-M17突变为Asn时，k_H从≈60s-1降低到≈e7s-1，这表明Asp-L210和Asp-M17在质子转移链中起着重要的作用。通过比较在没有Cd2 +的情况下突变体中的质子转移速率与天然RC中的质子转移速率，我们得出了替代的质子转移途径的结论。假定的效果至少要低103倍。

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