{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,6]],"date-time":"2026-10-06T09:29:23Z","timestamp":1791278963673,"version":"4.1.0"},"reference-count":19,"publisher":"American Chemical Society (ACS)","issue":"29","license":[{"start":{"date-parts":[[2015,7,8]],"date-time":"2015-07-08T00:00:00Z","timestamp":1436313600000},"content-version":"vor","delay-in-days":365,"URL":"https:\/\/pubs.acs.org\/page\/policy\/authorchoice_termsofuse.html"}],"funder":[{"DOI":"10.13039\/100000002","name":"National Institutes of Health","doi-asserted-by":"publisher","award":["GM 087934"],"award-info":[{"award-number":["GM 087934"]}],"id":[{"id":"10.13039\/100000002","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/100000002","name":"National Institutes of Health","doi-asserted-by":"publisher","award":["GM022172"],"award-info":[{"award-number":["GM022172"]}],"id":[{"id":"10.13039\/100000002","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/100000002","name":"National Institutes of Health","doi-asserted-by":"publisher","award":["GM106112"],"award-info":[{"award-number":["GM106112"]}],"id":[{"id":"10.13039\/100000002","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/100000928","name":"Welch Foundation","doi-asserted-by":"publisher","award":["F-1712"],"award-info":[{"award-number":["F-1712"]}],"id":[{"id":"10.13039\/100000928","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":[],"published-print":{"date-parts":[[2014,7,23]]},"abstract":"<jats:title>Abstract<\/jats:title>\n                  <jats:p>Many modular polyketide synthases harbor one or more redox-inactive domains of unknown function that are highly homologous to ketoreductase (KR) domains. A newly developed tandem equilibrium isotope exchange (EIX) assay has now established that such \u201cKR0\u201d domains catalyze the biosynthetically essential epimerization of transient (2R)-2-methyl-3-ketoacyl-ACP intermediates to the corresponding (2S)-2-methyl-3-ketoacyl-ACP diastereomers. Incubation of [2-2H]-(2R,3S)-2-methyl-3-hydroxypentanoyl-SACP ([2-2H]-3b) with the EryKR30 domain from module 3 of the 6-deoxyerythronolide B synthase, and the redox-active, nonepimerizing EryKR6 domain and NADP+ resulted in time- and cofactor-dependent washout of deuterium from 3b, as a result of EryKR30-catalyzed epimerization of transiently generated [2-2H]-2-methyl-3-ketopentanoyl-ACP (4). Similar results were obtained with redox-inactive PicKR30 from module 3 of the picromycin synthase. Four redox-inactive mutants of epimerase-active EryKR1 were engineered by mutagenesis of the NADPH binding site of this enzyme. Tandem EIX established that these EryKR10 mutants retained the intrinsic epimerase activity of the parent EryKR1 domain. These results establish the intrinsic epimerase activity of redox-inactive KR0 domains, rule out any role for the NADPH cofactor in epimerization, and provide a general experimental basis for decoupling the epimerase and reductase activities of a large class of PKS domains.<\/jats:p>","DOI":"10.1021\/ja5056998","type":"journal-article","created":{"date-parts":[[2014,7,8]],"date-time":"2014-07-08T18:05:59Z","timestamp":1404842759000},"page":"10190-10193","source":"Crossref","is-referenced-by-count":39,"title":["Elucidation\nof the Cryptic Epimerase Activity of Redox-Inactive\nKetoreductase Domains from Modular Polyketide Synthases by Tandem\nEquilibrium Isotope Exchange"],"prefix":"10.1021","volume":"136","author":[{"given":"Ashish","family":"Garg","sequence":"first","affiliation":[{"name":"Brown University , Box H, , , ,","place":["Providence, Rhode Island, United States, 02912-9108"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Xinqiang","family":"Xie","sequence":"additional","affiliation":[{"name":"Brown University , Box H, , , ,","place":["Providence, Rhode Island, United States, 02912-9108"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Adrian","family":"Keatinge-Clay","sequence":"additional","affiliation":[{"name":"the University of Texas at Austin , , 1 University Station A5300 , , ,","place":["Austin, Texas, United States, 78712-0165"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Chaitan","family":"Khosla","sequence":"additional","affiliation":[{"name":"Stanford University , , , ,","place":["Stanford, California, United States, 94305"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"David E.","family":"Cane","sequence":"additional","affiliation":[{"name":"Brown University , Box H, , , ,","place":["Providence, Rhode Island, United States, 02912-9108"]}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"316","published-online":{"date-parts":[[2014,7,8]]},"reference":[{"key":"2026090201004851800_cit1","article-title":"Methods in\nEnzymology","volume-title":"Complex enzymes in microbial natural\nproduct biosynthesis, part B: polyketides, aminocoumarins and carbohydrates","author":"Hopwood","year":"2009"},{"key":"2026090201004851800_cit2a","doi-asserted-by":"crossref","first-page":"737","DOI":"10.1016\/j.str.2006.01.009","volume":"14","author":"Keatinge-Clay","year":"2006","journal-title":"Structure"},{"key":"2026090201004851800_cit2b","doi-asserted-by":"crossref","first-page":"898","DOI":"10.1016\/j.chembiol.2007.07.009","volume":"14","author":"Keatinge-Clay","year":"2007","journal-title":"Chem. 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