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Appl. Environ. Microbiol. doi:10.1128/AEM.01012-08
Copyright (c) 2008, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Selective removal of the aberrant extender units by a type II thioesterase for the efficient FR-008/candicidin biosynthesis in Streptomyces sp. FR-008

Laboratory of Microbial Metabolism, and School of Life Science & Biotechnology, Shanghai Jiaotong University, Shanghai 200030, China; School of Pharmacy, Shanghai Jiaotong University, Shanghai 200240, China

^* To whom correspondence should be addressed. Email: hczhou{at}sjtu.edu.cn. bailq{at}sjtu.edu.cn. zxdeng{at}sjtu.edu.cn.

	Abstract

Gene fscTE, encoding a putative type II thioesterase (TEII), was associated with FR-008/candicidin gene cluster. Deletion of fscTE reduced approximately 90 % of the FR-008/candicidin production, while the production level was well restored when fscTE was added back to the mutant in trans. FscTE was unable to compensate the release of the maturely elongated-polyketide as site-directed inactivation of the type I thioesterase (TEI) totally abolished FR-008/candicidin production. Direct biochemical analysis of FscTE in parallel with its homologue TylO from tylosin biosynthetic pathway demonstrated their remarkable preferences of acyl-thioesters, i.e. propionyl-SNAC over methylmalonyl-SNAC and acetyl-SNAC over malonyl-SNAC, and thus concluded that TEII could maintain effective polyketide biosynthesis by selectively removing the nonelongatable residues bound to ACPs. Over-expression of FscTE under the strong constitutive ermE*p promoter in the wild-type strain did not suppress FR-008/candicidin formation, which confirmed its substrate specificity in vivo. Furthermore, successful complementation of the fscTE mutant was obtained with fscTE and tylO, whereas no complementation was detected with NRPS TEII tycF and srfAD, reflecting distinctively substrate specificities of TEIIs from either PKSs or NRPSs.