Division of Medicinal Chemistry, College of Pharmacy, Department of Chemistry and Biochemistry, and Institute of Cellular & Molecular Biology, University of Texas at Austin, Austin, Texas 78712, USA.
J Am Chem Soc. 2010 Mar 10;132(9):2901-3. doi: 10.1021/ja910223x.
Spinosyn A is a polyketide-derived macrolide produced by Saccharopolyspora spinosa and is an active ingredient in several commercial insecticides. It is glycosylated by a tri-O-methylated rhamnose at C-9 and a forosamine at C-17. Previous studies indicated that the rhamnose methyltransferases are encoded by the spnH, spnI, and spnK genes. To verify the functions of these methyltransferases and to study how they are coordinated to achieve the desired level of methylation of rhamnose, we studied the catalytic properties of the spnH, spnI, and spnK gene products and validated their roles in the permethylation process of spinosyn A. Our data reported herein firmly established that SpnH, SpnI, and SpnK are the respective rhamnose 4'-, 2'-, and 3'-O-methyltransferase. Investigation of the order of the methylation events revealed that only one route catalyzed by SpnI, SpnK, and SpnH in sequence is productive for the permethylation of the rhamnose moiety. Moreover, the completion of rhamnose permethylation is likely achieved by the proper control of the expression levels of the methyltransferase genes involved. These results set the stage for future exploitation of the spinosyn biosynthetic pathway to produce targeted spinosyn derivatives and, perhaps, new analogues.
Spinosyn A 是一种由多杀菌素产生的聚酮类大环内酯，是几种商业杀虫剂的有效成分。它在 C-9 位被三-O-甲基化的鼠李糖和 C-17 位的福来糖所糖基化。先前的研究表明，鼠李糖甲基转移酶由 spnH、spnI 和 spnK 基因编码。为了验证这些甲基转移酶的功能以及研究它们如何协调以达到所需的鼠李糖甲基化水平，我们研究了 spnH、spnI 和 spnK 基因产物的催化特性，并验证了它们在 spinosyn A 全甲基化过程中的作用。我们在此报告的研究数据确凿地证明了 SpnH、SpnI 和 SpnK 分别是鼠李糖 4'、2' 和 3'-O-甲基转移酶。对甲基化事件顺序的研究表明，只有 SpnI、SpnK 和 SpnH 依次催化的一条途径对鼠李糖部分的全甲基化是有产物生成的。此外，鼠李糖全甲基化的完成可能是通过适当控制相关甲基转移酶基因的表达水平来实现的。这些结果为未来利用多杀菌素生物合成途径生产靶向多杀菌素衍生物甚至可能是新类似物奠定了基础。
