Amide N-glycosylation by Asm25, an N-glycosyltransferase of ansamitocins.

Peiji Zhao, Linquan Bai, Juan Ma, Ying Zeng, Lei Li, Yirong Zhang, Chunhua Lu, Huanqin Dai, Zhaoxian Wu, Yaoyao Li, Xuan Wu, Gang Chen, Xiaojiang Hao, Yuemao Shen, Zixin Deng, Heinz G Floss

Index: Chem. Biol. 15(8) , 863-74, (2008)

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Abstract

Ansamitocins are potent antitumor maytansinoids produced by Actinosynnema pretiosum. Their biosynthesis involves the initial assembly of a macrolactam polyketide, followed by a series of postpolyketide synthase (PKS) modifications. Three ansamitocin glycosides were isolated from A. pretiosum and fully characterized structurally as novel ansamitocin derivatives, carrying a beta-D-glucosyl group attached to the macrolactam amide nitrogen in place of the N-methyl group. By gene inactivation and complementation, asm25 was identified as the N-glycosyltransferase gene responsible for the macrolactam amide N-glycosylation of ansamitocins. Soluble, enzymatically active Asm25 protein was obtained from asm25-expressing E. coli by solubilization from inclusion bodies. Its optimal reaction conditions, including temperature, pH, metal ion requirement, and Km/Kcat, were determined. Asm25 also showed broad substrate specificity toward other ansamycins and synthetic indolin-2-ones. To the best of our knowledge, this represents the first in vitro characterization of a purified antibiotic N-glycosyltransferase.