Metabolic networks are complex cellular systems dependent on the interactions among, and regulation of, the enzymes in the network. Although there is great diversity of types of enzymes that make up metabolic networks, the models meant to understand the possible evolutionary outcomes following duplication neglect specifics about the enzyme, pathway context, and cellular constraints. To illuminate the mechanisms that shape the evolution of biochemical pathways, I functionally characterize the consequences of gene duplication of an enzyme family that performs multiple subsequent enzymatic reactions (a multistep enzyme) in the corticosteroid pathway in primates. The products of the corticosteroid pathway (aldosterone and cortisol) are steroid hormones that regulate metabolism and stress response in tetrapods. These steroid hormones are synthesized by a multistep enzyme Cytochrome P450 11B (CYP11B) that performs subsequent steps on different carbon atoms of the steroid derivatives. Through ancestral state reconstruction and in vitro characterization, I find that the primate ancestor of the CYP11B1 and CYP11B2 paralogs had moderate ability to synthesize both cortisol and aldosterone. Following duplication in Old World primates, the CYP11B1 homolog specialized on the production of cortisol, whereas its paralog, CYP11B2, maintained its ability to perform multiple subsequent steps as in the ancestral pathway. Unlike CYP11B1, CYP11B2 could not specialize on the production of aldosterone because it is constrained to perform earlier steps in the corticosteroid synthesis pathway to achieve the final product aldosterone. These results suggest that enzyme function, pathway context, along with tissue-specific regulation, both play a role in shaping potential outcomes of metabolic network elaboration.

中文翻译：

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通过多步酶在灵长类动物中精心设计皮质类固醇合成途径。

代谢网络是复杂的细胞系统，依赖于网络中酶之间的相互作用和调节。尽管构成代谢网络的酶种类繁多，但这些模型旨在了解重复后可能的进化结果，忽略了有关酶、途径背景和细胞限制的细节。为了阐明塑造生化途径进化的机制，我在功能上表征了在灵长类动物的皮质类固醇途径中执行多个后续酶促反应（多步酶）的酶家族基因复制的后果。皮质类固醇途径的产物（醛固酮和皮质醇）是调节四足动物新陈代谢和应激反应的类固醇激素。这些类固醇激素由多步酶细胞色素 P450 11B (CYP11B) 合成，该酶对类固醇衍生物的不同碳原子执行后续步骤。通过祖先状态重建和体外表征，我发现 CYP11B1 和 CYP11B2 旁系同源物的灵长类祖先具有合成皮质醇和醛固酮的中等能力。在旧世界灵长类动物中复制后，CYP11B1 同源物专门用于产生皮质醇，而其旁系同源物 CYP11B2 保持其执行多个后续步骤的能力，就像在祖先途径中一样。与 CYP11B1 不同，CYP11B2 不能专门生产醛固酮，因为它受限于在皮质类固醇合成途径中执行较早的步骤以实现最终产物醛固酮。