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首页> 外文期刊>Proceedings of the National Academy of Sciences of the United States of America >A compromise required by gene sharing enables survival: Implications for evolution of new enzyme activities
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A compromise required by gene sharing enables survival: Implications for evolution of new enzyme activities

机译：基因共享所需的折衷方案可实现生存：对新酶活性进化的启示

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摘要

Evolution of new enzymatic activities is believed to require a period of gene sharing in which a single enzyme must serve both its original function and a new function that has become advan-tageogs to the organism. Subsequent gene duplication allows one copy to maintain the original function, while the other diverges to optimize the new function. The physiological impact of gene sharing and the constraints imposed by the need to maintain the original activity during the early stages of evolution of a new activity have not been addressed experimentally. We report here an investigation of the evolution of a new activity under circumstances in which both the original and the new activity are critical for growth. Glutamylphosphate reductase (ProA) has a very low promiscuous activity with N-acetylglutamylphosphate, the normal substrate for ArgC (N-acetylglutamylphosphate reductase). A mutation that changes Glu-383 to Ala increases the promiscuous activity by 12-fold but decreases the original activity by 2,800-fold. The impairment in Pro and Arg synthesis results in 14-fold over-expression of E383A ProA, providing sufficient N-acetylglu-tamylphosphate reductase activity to allow a strain lacking ArgC to grow on glucose. Thus, reaching the threshold level of NAGP reductase activity required for survival required both a structural mutation and overexpression of the enzyme. Notably, overexpres-sion does not require a mutation in the regulatory region of the protein; amino acid limitation attributable to the poor catalytic abilities of E383A ProA causes a physiological response that results in overexpression.
机译：据信，新酶活性的进化需要一段基因共享期，在此期间，一种酶必须既发挥其原始功能，又发挥新的功能，而新功能已成为生物的优势。随后的基因复制使一个拷贝可以维持原始功能，而另一个则可以分散以优化新功能。尚未通过实验解决基因共享的生理影响以及在新活动进化的早期阶段必须维持原始活动所施加的限制。我们在这里报告了一项新活动的演变情况调查，其中原始活动和新活动都对增长至关重要。谷氨酰磷酸还原酶（ProA）与ArgC的正常底物N-乙酰谷氨酰磷酸（N-乙酰谷氨酰磷酸还原酶）的混合活性非常低。将Glu-383更改为Ala的突变可将混杂活性提高12倍，但将原始活性降低2800倍。 Pro和Arg合成中的损伤导致E383A ProA过量表达14倍，从而提供了足够的N-乙酰基-戊基-氨基磷酸磷酸还原酶活性，以使缺乏ArgC的菌株在葡萄糖上生长。因此，达到生存所需的阈值水平的NAGP还原酶活性既需要结构突变又需要酶的过表达。值得注意的是，过表达并不需要蛋白质调节区域的突变。由于E383A ProA催化能力差而导致的氨基酸限制导致生理反应，导致过表达。

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