3-Hydroxy-3-methylbutyrate (HMB) is a five-carbon branch-chain hydroxy acid currently used as a dietary supplement to treat sarcopenia and exercise training. However, its current production relies on conventional chemical processes which require toxic substances and are generally non-sustainable. While bio-based syntheses of HMB have been developed, they are dependent on biotransformation of its direct precursors which are generally costly. Therefore, in this work, we developed a synthetic HMB biosynthetic pathway that enables HMB production from renewable resources. This novel HMB biosynthesis employs heterologous enzymes from mevalonate pathway and myxobacterial iso-fatty acid pathway for converting acetyl-CoA to HMB-CoA. Subsequently, HMB-CoA is hydrolyzed by a thioesterase to yield HMB. Upon expression of this pathway, our initial strain produced 660 mg/L of HMB from glucose in 48 hours. Through optimization of coenzyme A removal from HMB-CoA and genetic operon structure, our final strain achieved HMB production titer of 17.7 g/L in glucose minimal media using a bench-top bioreactor. This engineered strain was further demonstrated to produce HMB from other renewable carbon sources such as xylose, glycerol, and acetate. The results from this work provided a flexible and environmentally benign method for producing HMB.

中文翻译：

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代谢工程大肠杆菌从头生物合成 3-羟基-3-甲基丁酸酯作为抗分解代谢补充剂


3-羟基-3-甲基丁酸（HMB）是一种五碳支链羟基酸，目前用作治疗肌肉减少症和运动训练的膳食补充剂。然而，其目前的生产依赖于传统的化学工艺，需要有毒物质并且通常是不可持续的。虽然 HMB 的生物基合成方法已经开发出来，但它们依赖于其直接前体的生物转化，而这种生物转化通常成本高昂。因此，在这项工作中，我们开发了一种合成 HMB 生物合成途径，可以利用可再生资源生产 HMB。这种新颖的 HMB 生物合成采用来自甲羟戊酸途径和粘细菌异脂肪酸途径的异源酶将乙酰辅酶 A 转化为 HMB-辅酶 A。随后，HMB-CoA被硫酯酶水解产生HMB。表达该途径后，我们的初始菌株在 48 小时内从葡萄糖产生 660 mg/L 的 HMB。通过优化从 HMB-CoA 和遗传操纵子结构中去除辅酶 A，我们的最终菌株使用台式生物反应器在葡萄糖基本培养基中实现了 17.7 g/L 的 HMB 生产滴度。该工程菌株被进一步证明可以从木糖、甘油和乙酸盐等其他可再生碳源生产 HMB。这项工作的结果提供了一种灵活且环保的 HMB 生产方法。