Bridgham Jamie T, Carroll Sean M, Thornton Joseph W
Center for Ecology and Evolutionary Biology, University of Oregon, Eugene, OR 97403, USA.
Science. 2006 Apr 7;312(5770):97-101. doi: 10.1126/science.1123348.
According to Darwinian theory, complexity evolves by a stepwise process of elaboration and optimization under natural selection. Biological systems composed of tightly integrated parts seem to challenge this view, because it is not obvious how any element's function can be selected for unless the partners with which it interacts are already present. Here we demonstrate how an integrated molecular system-the specific functional interaction between the steroid hormone aldosterone and its partner the mineralocorticoid receptor-evolved by a stepwise Darwinian process. Using ancestral gene resurrection, we show that, long before the hormone evolved, the receptor's affinity for aldosterone was present as a structural by-product of its partnership with chemically similar, more ancient ligands. Introducing two amino acid changes into the ancestral sequence recapitulates the evolution of present-day receptor specificity. Our results indicate that tight interactions can evolve by molecular exploitation-recruitment of an older molecule, previously constrained for a different role, into a new functional complex.
根据达尔文理论，复杂性是在自然选择下通过逐步的细化和优化过程演化而来的。由紧密整合的部分组成的生物系统似乎对这一观点提出了挑战，因为除非与之相互作用的伙伴已经存在，否则不清楚任何元素的功能如何能够被选择。在这里，我们展示了一个整合的分子系统——类固醇激素醛固酮与其伙伴盐皮质激素受体之间的特定功能相互作用——是如何通过逐步的达尔文过程演化而来的。通过祖先基因复活，我们表明，早在激素演化之前，受体对醛固酮的亲和力就作为其与化学性质相似、更古老的配体相互作用的结构副产物而存在。在祖先序列中引入两个氨基酸变化概括了当今受体特异性的演化。我们的结果表明，紧密的相互作用可以通过分子利用——将一个以前因不同作用而受到限制的较老分子招募到一个新的功能复合体中——而演化。
