Polyhydroxyalkanoates (PHAs) are renewably-derived, microbial polyesters composed of hydroxy acids (HAs). Demand for sustainable plastics alternatives, combined with the unfavorable thermal properties exhibited by some PHAs, motivates the discovery of novel PHA-based materials. Incorporation of α-substituted HAs yields thermostable PHAs; however, the reverse β-oxidation (rBOX) pathway, the canonical pathway for HA production, is unable to produce these monomers because it utilizes thiolases with narrow substrate specificity. Here, we present a thiolase-independent pathway to two α-substituted HAs, 3-hydroxyisobutyric acid (3HIB) and 3-hydroxy-2-methylbutyric acid (3H2MB). This pathway involves the conversion of glucose to various branched acyl-CoAs and ultimately to 3HIB or 3H2MB. As proof of concept, we engineered Escherichia coli for the specific production of 3HIB and 3H2MB from glucose at titers as high as 66 ± 5 mg/L and 290 ± 40 mg/L, respectively. Optimizing this pathway for 3H2MB production via a novel byproduct recycle increased titer by 60%. This work illustrates the utility of novel pathway design HA production leading to PHAs with industrially relevant properties.

中文翻译：

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大肠杆菌中葡萄糖产生 α-取代的 3-羟基酸


聚羟基脂肪酸酯 （PHA） 是由羟基酸 （HA） 组成的可再生衍生的微生物聚酯。对可持续塑料替代品的需求，加上一些 PHA 表现出的不利热性能，推动了基于 PHA 的新型材料的发现。掺入 α 取代的 HA 可产生热稳定的 PHA;然而，逆β氧化 （rBOX） 途径（HA 产生的经典途径）无法产生这些单体，因为它利用了底物特异性较窄的硫代酶。在这里，我们提出了一种不依赖硫代酶的途径，通向两种α取代的 HAs，即 3-羟基异丁酸 （3HIB） 和 3-羟基-2-甲基丁酸 （3H2MB）。该途径涉及葡萄糖转化为各种支链酰基辅酶 A，并最终转化为 3HIB 或 3H2MB。作为概念验证，我们设计了大肠杆菌，用于从葡萄糖中特异性产生 3HIB 和 3H2MB，滴度分别高达 66 ± 5 mg/L 和 290 ± 40 mg/L。通过一种新的副产品回收来优化 3H2MB 生产的这一途径，将滴度提高了 60%。这项工作说明了新型途径设计 HA 生产的效用，导致具有工业相关特性的 PHA。