Tuning of the H-transfer coordinate in primitive versus well-evolved enzymes
Tuning of the H-transfer coordinate in primitive versus well-evolved enzymes
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DOI：
10.1002/cphc.200800067
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发表时间：
2008-05-02
期刊：
影响因子：
2.9
通讯作者：
Kohen, Amnon
中科院分区：
文献类型：
--
作者：
Yahashiri, Atsushi;Howell, Elizabeth E.;Kohen, Amnon
考察了由原始酶催化的h转移反应的性质，并将其与由成熟（高度进化）酶催化的相同反应进行了比较。这些发现是用两种不同的理论模型来评估的。隧道修正模型[1-3]表明，成熟酶催化的反应具有广泛的隧道作用，而原始酶催化的反应没有隧道作用。另一方面，Marcus-like模型[2-5]表明，原始酶催化的反应具有较差的重组反应坐标，而成熟酶则将反应坐标调整为接近完美的重组。后一种解释并不表明隧穿的程度，但它确实解决了使反应坐标达到隧穿构象的体系准备水平。重要的是，研究结果表明，与原始酶相比，成熟酶已经进化到催化具有显著隧道贡献的反应，或者具有完美重组的h隧道反应坐标（分别使用隧道校正或马库斯样模型）。本研究比较了本征动力学同位素效应（KIEs）的温度依赖性。近年来，这种方法已被建立为酶促反应中化学步骤（在这种情况下是h转移）性质的关键探针。[2,3,6 - 13]该工具的一个独特之处在于，它不需要对所研究的系统进行完整的动力学检查，因为它直接报告了所讨论的化学步骤的性质。据报道，许多高度进化的催化h转移的酶都具有温度不相关的KIEs，这一现象表明，这些酶已经进化到使供体和受体达到一个完美的供-受体距离（DAD）以进行h隧道。[2,3,6 - 8,14 - 17]通常，在非生理条件下（例如低温或突变[5,14]），相同的酶呈现温度依赖性的KIEs。因此，测试系统内在KIE的温度依赖性，提供了一种方法来区分涉及不同程度的隧道和/或不同水平的重组的系统（根据这两种理论方法）。虽然“进化”一词意味着原始酶不会像进化良好的酶那样拥有完美的DAD，但在目前的研究之前，这一点还没有得到验证。
The nature of an H-transfer reaction catalyzed by a primitive enzyme is examined and compared to the same reaction catalyzed by a mature (highly evolved) enzyme. The findings are evaluated using two different theoretical models. The tunneling correction model [1–3] suggests that the reaction catalyzed by the mature enzyme involves extensive tunneling, while that of the primitive enzyme involves no tunneling contribution. Marcus-like models,[2–5] on the other hand, suggest that the reaction catalyzed by the primitive enzyme has a poorly reorganized reaction coordinate, while the mature enzyme has tuned the reaction coordinate to near perfect reorganization. The latter interpretation does not indicate the degree of tunneling, but it does address the level of system preparation that brings the reaction coordinate to the tunneling conformation. Importantly, the findings indicate that, in contrast to the primitive enzyme, the mature one has evolved to catalyze a reaction with asignificant tunneling contribution or with a perfectly reorganized reaction coordinate for H-tunneling (using tunneling-correction or the Marcus-like models, respectively).The current study compares the temperature dependence of intrinsic kinetic isotope effect (KIEs). This method has been established in recent years as a critical probe for the nature of the chemical step (H-transfer in this case) in enzymatic reactions.[2, 3, 6–13] One of the unique features of this tool is that it circumvents the need for complete kinetic examination of the system under study as it directly reports on the nature of the chemical step in question. Temperature-independent KIEs have been reported for many highly evolved enzymes catalyzing H-transfer, and it has been suggested that this phenomenon indicates that these enzymes have evolved to bring the donor and acceptor to a perfect donor–acceptor distance (DAD) for H-tunneling.[2, 3, 6–8, 14–17] Typically, under non-physiological conditions (eg low temperature [8] or following a mutation [5, 14]), the same enzymes present temperaturedependent KIEs. Thus, testing the temperature dependence of the intrinsic KIE of a system, provides a means to differentiate between systems that involve different degrees of tunneling and/or different levels of reorganization (according to these two theoretical approaches). While the term evolved implies that primitive enzymes would not have as perfect a DAD as their well-evolved counterparts, this has not been tested prior to the current study.