ADDITIVITY OF MUTATIONAL EFFECTS IN PROTEINS
ADDITIVITY OF MUTATIONAL EFFECTS IN PROTEINS
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DOI：
10.1021/bi00489a001
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发表时间：
1990-09-18
期刊：
影响因子：
2.9
通讯作者：
WELLS, JA
中科院分区：
文献类型：
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作者：
WELLS, JA
1990年5月29日收到的修订手稿e几乎所有蛋白质结合功能的能量学是一系列分子相互作用的顶峰。例如，通过点突变去除单个分子接触会导致过渡态稳定的自由能(通常为0.5-5千卡/摩尔)、蛋白质-蛋白质相互作用(Laskowski等人，1983,1989；Ackers&Smith，1985)或蛋白质稳定性[参见Matthews(1987)]的相对较小的下降(通常为5-20千卡/摩尔)。因此，有可能通过许多接触点的突变来调节蛋白质的功能。事实上，设计大的功能变化通常需要一个以上的功能残基的突变。现在有一个巨大的数据库，当单个突变体组合在一起时，自由能变化的结果。对这些数据的回顾表明，在大多数情况下，来自单个突变的自由能变化的总和几乎等于在多个突变中测量的自由能变化。然而，有两个主要的例外情况下，这种简单的可加性被打破。第一种是突变残基通过直接接触或通过静电相互作用或结构扰动间接相互作用，从而使它们不再独立发挥作用。第二种是突变导致反应的机制或限速步骤发生变化。值得注意的是，这里讨论的加法效应不会改变它们各自反应的分子性。当反应的分子性改变时[如比较一个连接底物的结合自由能(AB)与两个片段的总和(A+B)]，可能会由于熵效应而导致与简单加和性的巨大偏差(Jencks，1981)。虽然这里的重点是酶的活性，但从影响蛋白质-蛋白质相互作用、蛋白质-DNA识别或蛋白质稳定性的突变可能得出类似的结论。文中还给出了一些实例和应用。
Revised Manuscript Received May 29, 1990 e energetics of virtually all binding functions in proteins is the culmination of a set of molecular interactions. For example, removal of a single molecular contact by a point mutation causes relatively small reductions (typically 0.5—5 kcal/mol) in the free energy of transition-state stabilization [for reviews see Fersht (1987) and Wells and Estell (1988)], protein-protein interactions (Laskowski et al., 1983, 1989; Ackers & Smith, 1985), or protein stability [for review see Matthews (1987)] compared to the overall free energy asso-ciated with these functional properties (usually 5-20 kcal/mol). Thus, it is possibleto modulate protein function by mutation at many contact sites. In fact, to design large changes in function will often require mutation of more than one functional residue.There is now a large data base for free energy changes that result when single mutants are combined. A review of these data shows that, in the majority of cases, the sum of the free energy changes derived from the single mutations is nearly equal to the free energy change measured in the multiple mutant. However, there are two major exceptions where such simple additivity breaks down. The first is where the mutated residues interact with each other, by direct contact or indirectly through electrostatic interactions or structural perturbations, so that they no longer behave independently. The second is where the mutation causes a change in mechanism or rate-limiting step of the reaction. It is important to note that the additive effects discussed here do not change the molecularity of their respective reactions. When the molecularity of the reaction changes [as in comparing the free energy of binding of one linked substrate (AB) versus the sum of two fragments (A plus B)], large deviations from simple additivity can result from entropic effects (Jencks, 1981). Although thefocus here is on enzyme activity, similar conclusions may be drawnfrom mutations affecting protein-protein interactions, protein-DNA recognition, or protein stability. Some practical examples and applications are discussed.