Journal
JOURNAL OF STRUCTURAL BIOLOGY
Volume 194, Issue 3, Pages 368-374Publisher
ACADEMIC PRESS INC ELSEVIER SCIENCE
DOI: 10.1016/j.jsb.2016.03.014
Keywords
Short-chain dehydrogenase/reductase (SDR); Reductase domain; NRPS; Gating loop; Catalytic loop
Funding
- Council of Scientific and Industrial Research, India [BSC0302]
- Science and Engineering Research Board (SERB), India
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The termination module of nonribosomal peptide synthetases (NRPS) and polyketide synthases (PKS) off-loads the final product as an acid (occasionally also accompanied by cyclization) upon hydrolysis by employing thioesterase domains (TE-domains). Reductase domains (R-domains) of short-chain dehydrogenase/reductase (SDR) family offer an alternative offloading mechanism by reducing 4'-phosphopantetheine (4'-PPant) arm-tethered peptidyl chain, a thioester, to an aldehyde or an alcohol. Recent studies have highlighted their functional importance, for instance in the glycopeptidolipid (GPL) biosynthesis of Mycobacterium smegmatis, where the resulting alcoholic group is the site for subsequent modifications such as glycosylations. The mechanistic understanding of how these R-domains function in the context of multi-modular NRPS and PKS is poorly understood. In this study, conformational differences in functionally important loops, not reported previously, were identified in a new crystal form of R-domain which may be relevant to functioning in the context of assembly-line NRPS and PKS enzymology. Here, we propose a concerted loop movement model that allows gating of cofactor binding to these enzymes, enabling the release of the final product only after the substrate has reached the active site during biosynthesis, and therefore distinct from a canonical single domain SDR family of enzymes. (C) 2016 Elsevier Inc. All rights reserved.
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