Department of Molecular, Cellular and Developmental Biology, University of Colorado Boulder, Boulder, CO 80309.
Cooperative Institute for Research in Environmental Sciences, University of Colorado Boulder, Boulder, CO 80309.
Proc Natl Acad Sci U S A. 2019 Nov 26;116(48):24164-24173. doi: 10.1073/pnas.1915569116. Epub 2019 Nov 11.
PdxB (erythronate 4-phosphate dehydrogenase) is expected to be required for synthesis of the essential cofactor pyridoxal 5'-phosphate (PLP) in Surprisingly, incubation of the ∆ strain in medium containing glucose as a sole carbon source for 10 d resulted in visible turbidity, suggesting that PLP is being produced by some alternative pathway. Continued evolution of parallel lineages for 110 to 150 generations produced several strains that grow robustly in glucose. We identified a 4-step bypass pathway patched together from promiscuous enzymes that restores PLP synthesis in strain JK1. None of the mutations in JK1 occurs in a gene encoding an enzyme in the new pathway. Two mutations indirectly enhance the ability of SerA (3-phosphoglycerate dehydrogenase) to perform a new function in the bypass pathway. Another disrupts a gene encoding a PLP phosphatase, thus preserving PLP levels. These results demonstrate that a functional pathway can be patched together from promiscuous enzymes in the proteome, even without mutations in the genes encoding those enzymes.
PdxB（磷酸甘油酸 4-羟丙酮脱氢酶）预计是合成必需辅酶吡哆醛 5'-磷酸（PLP）所必需的。令人惊讶的是，将 ∆ 菌株在仅含葡萄糖作为唯一碳源的培养基中培养 10 天导致可见的浊度，表明 PLP 是通过某些替代途径产生的。平行谱系的持续进化 110 到 150 代产生了几个在葡萄糖中生长健壮的菌株。我们鉴定了一个由混杂酶组成的 4 步旁路途径，该途径恢复了 JK1 菌株中 PLP 的合成。JK1 中的突变都不在新途径中编码酶的基因中。两个突变间接增强了 SerA（3-磷酸甘油酸脱氢酶）在旁路途径中执行新功能的能力。另一个突变破坏了编码 PLP 磷酸酶的基因，从而保持 PLP 水平。这些结果表明，即使在编码这些酶的基因没有突变的情况下，也可以从蛋白质组中的混杂酶中拼凑出功能性途径。
