Tokuriki Nobuhiko, Tawfik Dan S
Department of Biological Chemistry, Weizmann Institute of Science, Rehovot 76100, Israel.
Nature. 2009 Jun 4;459(7247):668-73. doi: 10.1038/nature08009.
Most protein mutations, and mutations that alter protein functions in particular, undermine stability and are therefore deleterious. Chaperones, or heat-shock proteins, are often implicated in buffering mutations, and could thus facilitate the acquisition of neutral genetic diversity and the rate of adaptation. We examined the ability of the Escherichia coli GroEL/GroES chaperonins to buffer destabilizing and adaptive mutations. Here we show that mutational drifts performed in vitro with four different enzymes indicated that GroEL/GroES overexpression doubled the number of accumulating mutations, and promoted the folding of enzyme variants carrying mutations in the protein core and/or mutations with higher destabilizing effects (destabilization energies of >3.5 kcal mol(-)(1), on average, versus approximately 1 kcal mol(-)(1) in the absence of GroEL/GroES). The divergence of modified enzymatic specificity occurred much faster under GroEL/GroES overexpression, in terms of the number of adapted variants (>or=2-fold) and their improved specificity and activity (>or=10-fold). These results indicate that protein stability is a major constraint in protein evolution, and buffering mechanisms such as chaperonins are key in alleviating this constraint.
大多数蛋白质突变，尤其是那些改变蛋白质功能的突变，会破坏稳定性，因此是有害的。伴侣蛋白，即热休克蛋白，常常与缓冲突变有关，因而可能促进中性遗传多样性的获得以及适应速率。我们研究了大肠杆菌GroEL/GroES伴侣蛋白缓冲不稳定和适应性突变的能力。在此我们表明，用四种不同的酶在体外进行的突变漂移表明，GroEL/GroES的过表达使累积突变的数量增加了一倍，并促进了携带蛋白质核心突变和/或具有更高去稳定化效应（平均去稳定化能量>3.5千卡摩尔(-1)，而在没有GroEL/GroES的情况下约为1千卡摩尔(-1)）的酶变体的折叠。就适应变体的数量（>或=2倍）及其提高的特异性和活性（>或=10倍）而言，在GroEL/GroES过表达的情况下，修饰酶特异性的分化发生得要快得多。这些结果表明，蛋白质稳定性是蛋白质进化中的一个主要限制因素，而诸如伴侣蛋白的缓冲机制是缓解这一限制的关键。
