Institute of Evolutionary Biology and Environmental Studies, University of Zurich, Zurich, Switzerland.
Adv Exp Med Biol. 2012;751:29-52. doi: 10.1007/978-1-4614-3567-9_2.
Since the last decade of the twentieth century, systems biology has gained the ability to study the structure and function of genome-scale metabolic networks. These are systems of hundreds to thousands of chemical reactions that sustain life. Most of these reactions are catalyzed by enzymes which are encoded by genes. A metabolic network extracts chemical elements and energy from the environment, and converts them into forms that the organism can use. The function of a whole metabolic network constrains evolutionary changes in its parts. I will discuss here three classes of such changes, and how they are constrained by the function of the whole. These are the accumulation of amino acid changes in enzyme-coding genes, duplication of enzyme-coding genes, and changes in the regulation of enzymes. Conversely, evolutionary change in network parts can alter the function of the whole network. I will discuss here two such changes, namely the elimination of reactions from a metabolic network through loss of function mutations in enzyme-coding genes, and the addition of metabolic reactions, for example through mechanisms such as horizontal gene transfer. Reaction addition also provides a window into the evolution of metabolic innovations, the ability of a metabolism to sustain life on new sources of energy and of chemical elements.
自 20 世纪最后十年以来，系统生物学已经能够研究基因组规模的代谢网络的结构和功能。这些系统包含数百到数千种维持生命的化学反应。这些反应中的大多数都是由基因编码的酶催化的。代谢网络从环境中提取化学元素和能量，并将其转化为生物体可以利用的形式。整个代谢网络的功能限制了其各部分的进化变化。我将在这里讨论三类这样的变化，以及它们是如何受到整体功能的限制的。这些变化包括酶编码基因中氨基酸变化的积累、酶编码基因的重复以及酶的调控变化。相反，网络部分的进化变化可以改变整个网络的功能。我将在这里讨论其中两种变化，即通过酶编码基因突变导致功能丧失而从代谢网络中消除反应，以及添加代谢反应，例如通过水平基因转移等机制。反应添加还为代谢创新的进化提供了一个窗口，即新陈代谢在新的能源和化学元素来源上维持生命的能力。
