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首页> 外文期刊>Proceedings of the National Academy of Sciences of the United States of America >Retroevolution of λ Cro toward a stable monomer
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Retroevolution of λ Cro toward a stable monomer

机译：λCro向稳定单体的逆进化

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摘要

The Cro protein from bacteriophage λ has a dimeric α+β fold that evolved from an ancestral all-α monomer. The sequence mutations responsible for this dramatic structural evolution are unknown. Here we use analysis of sequence alignments to show that Ala-33, a small side chain in the hydrophobic "ball-and-socket" dimer interface of λ Cro, was a much larger tryptophan side chain at a previous point in evolution. The retroevolutionary λ Cro-A33W mutant shows a 10-fold reduction in dimerization affinity relative to the wild type as well as a large increase in monomer thermal stability (ΔT_m > 10℃), apparently due to partial filling of the hydrophobic socket from within the same monomer. An additional mutation in the dimer interface, F58D, almost completely abolishes detectable dimerization while maintaining the high monomer stability. The secondary structure content of the monomerized versions of λ Cro is similar to that of the wild-type protein, and the tertiary structure of the monomer appears relatively well defined. These results (ⅰ) support a model in which the ball-and-socket dimer interface of λ Cro was created by altered volume mutations within a limited branch of the Cro lineage and (ⅱ) suggest the possibility that the evolution of the α+β dimer from an all-α monomer proceeded through an α+β monomer intermediate.
机译：来自噬菌体λ的Cro蛋白具有从祖先全α单体进化而来的二聚体α+β折叠。导致这种剧烈的结构进化的序列突变是未知的。在这里，我们使用序列比对分析显示，Ala-33是λCro的疏水性“球窝”二聚体界面中的小侧链，在进化的前一个点是较大的色氨酸侧链。相对于野生型，逆向进化型λCro-A33W突变体的二聚化亲和力降低了10倍，单体热稳定性也大大提高了（ΔT_m> 10℃），这显然是由于疏水窝从内部部分填充而引起的。相同的单体。二聚体界面中的另一个突变F58D几乎完全消除了可检测的二聚化，同时保持了较高的单体稳定性。 λCro的单体化形式的二级结构含量与野生型蛋白质相似，单体的三级结构看起来相对较好。这些结果（ⅰ）支持一个模型，其中λCro的球窝二聚体界面是通过在Cro谱系的有限分支内改变体积突变而创建的，并且（ⅱ）暗示了α+β进化的可能性来自全α单体的二聚体通过α+β单体中间体进行。

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