期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2015
卷号：112
期号：50
页码：E6844-E6851
DOI：10.1073/pnas.1512976112
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：SignificancePolyketides are a class of diverse natural products with well-documented bioactivity and medicinal importance. Enzymes known as aromatase/cyclases (ARO/CYCs) catalyze regiospecific cyclization and aromatization during type II polyketide biosynthesis. Understanding how ARO/CYCs catalyze cyclization and aromatization is critical for developing strategies for engineering biosynthetic pathways. This is the first study, to our knowledge, to use X-ray crystallography, bioinformatic and structural analysis, and in vitro functional assays to critically compare a reducing di-domain ARO/CYC (BexL) and a nonreducing di-domain ARO/CYC (StfQ). Together, these results fill in a missing link in the structural enzymology of polyketide biosynthesis and will have a direct effect on future biosynthetic engineering efforts and bioinformatic analysis of type II PKS gene clusters. Aromatic polyketides make up a large class of natural products with diverse bioactivity. During biosynthesis, linear poly-{beta}-ketone intermediates are regiospecifically cyclized, yielding molecules with defined cyclization patterns that are crucial for polyketide bioactivity. The aromatase/cyclases (ARO/CYCs) are responsible for regiospecific cyclization of bacterial polyketides. The two most common cyclization patterns are C7-C12 and C9-C14 cyclizations. We have previously characterized three monodomain ARO/CYCs: ZhuI, TcmN, and WhiE. The last remaining uncharacterized class of ARO/CYCs is the di-domain ARO/CYCs, which catalyze C7-C12 cyclization and/or aromatization. Di-domain ARO/CYCs can further be separated into two subclasses: "nonreducing" ARO/CYCs, which act on nonreduced poly-{beta}-ketones, and "reducing" ARO/CYCs, which act on cyclized C9 reduced poly-{beta}-ketones. For years, the functional role of each domain in cyclization and aromatization for di-domain ARO/CYCs has remained a mystery. Here we present what is to our knowledge the first structural and functional analysis, along with an in-depth comparison, of the nonreducing (StfQ) and reducing (BexL) di-domain ARO/CYCs. This work completes the structural and functional characterization of mono- and di-domain ARO/CYCs in bacterial type II polyketide synthases and lays the groundwork for engineered biosynthesis of new bioactive polyketides.
