Aims: Characterization of the role of CaiC in the biotransformation of trimethylammonium compounds into l(−)‐carnitine in Escherichia coli.Methods and Results: The caiC gene was cloned and overexpressed in E. coli and its effect on the production of l(−)‐carnitine was analysed. Betaine:CoA ligase and CoA transferase activities were analysed in cell free extracts and products were studied by electrospray mass spectrometry (ESI‐MS). Substrate specificity of the caiC gene product was high, reflecting the high specialization of the carnitine pathway. Although CoA‐transferase activity was also detected in vitro, the main in vivo role of CaiC was found to be the synthesis of betainyl‐CoAs. Overexpression of CaiC allowed the biotransformation of crotonobetaine to l(−)‐carnitine to be enhanced nearly 20‐fold, the yield reaching up to 30% (with growing cells). Higher yields were obtained using resting cells (up to 60%), even when d(+)‐carnitine was used as substrate.Conclusions: The expression of CaiC is a control step in the biotransformation of trimethylammonium compounds in E. coli.Significance and Impact of the Study: A bacterial betaine:CoA ligase has been characterized for the first time, underlining its important role for the production of l‐carnitine with Escherichia coli.
目的:研究 CaiC 在大肠杆菌将三甲基
铵化合物
生物转化为 l(-)-肉碱过程中的作用: 克隆 caiC
基因并在大肠杆菌中过表达,分析其对 l(-)-肉碱生产的影响。分析了细胞游离
提取物中
甜菜碱:CoA 连接酶和 CoA 转移酶的活性,并通过电喷雾质谱(ESI-MS)对产物进行了研究。caiC
基因产物的底物特异性很高,反映了肉碱途径的高度专业化。虽然在体外也检测到了 CoA 转移酶活性,但发现 CaiC 在体内的主要作用是合成
甜菜碱酰-CoAs。过量表达 CaiC 使
巴豆甜菜碱向 l(-)-肉碱的
生物转化提高了近 20 倍,产量高达 30%(生长细胞)。即使使用 d(+)-肉碱作为底物,静止细胞也能获得更高的产量(高达 60%): 结论:CaiC 的表达是大肠杆菌对三甲基
铵化合物进行
生物转化的一个控制步骤: 该研究首次鉴定了一种细菌
甜菜碱:CoA 连接酶,强调了它在大肠杆菌生产
左旋肉碱过程中的重要作用。