Altering glycolipid structure by genetic engineering of Starmerella bombicola is a recently started research topic and worthy alternative to the unsuccessful selective feeding strategies conventionally applied to reach this goal. One question to be addressed when expressing heterologous proteins in S. bombicola is the activity of the subsequent biosynthetic enzymes toward such modified substrates. In this scope, we studied the substrate specificity of the UDP-glucosyltransferases UgtA1 and UgtB1, responsible for the stepwise synthesis of sophorolipids from a hydroxylated fatty acid, and that of the acetyltransferase, responsible for acetylation of the sophorolipid molecule. All enzymes showed specificity toward a C18:1 chained acceptor and both glucosyltransferases were highly selective toward the UDP-glucose donor. Severe product inhibition of the glucosyltransferases explains the limited accumulation of sophorolipid intermediates by earlier created single deletion mutants of S. bombicola. Finally, a more detailed study of the acetylation of sophorolipid intermediates sheds light on the enzymatic cascade during synthesis.
通过星形芽孢杆菌的
基因工程改变
糖脂结构是最近开始的研究课题,也是传统选择性喂养策略的可行替代方案。在星形芽孢杆菌中表达异源蛋白时,需要解决的一个问题是后续
生物合成酶对这种修饰底物的活性。在这个范围内,我们研究了
UDP-
葡萄糖基转移酶UgtA1和UgtB1的底物特异性,它们负责从羟基
脂肪酸逐步合成
槐糖脂,以及乙酰转移酶的底物特异性,负责
槐糖脂分子的乙酰化。所有酶都表现出对C18:1链状受体的特异性,两种
葡萄糖基转移酶对
UDP-
葡萄糖供体都有很高的选择性。
葡萄糖基转移酶的严重产物抑制解释了星形芽孢杆菌早期产生的单缺失突变体中
槐糖脂中间体的有限积累。最后,对
槐糖脂中间体的乙酰化进行了更详细的研究,揭示了合成过程中的酶促级联反应。