Structural highlights
Publication Abstract from PubMedSpinosyns A and D (spinosad), like many other complex polyketides, are tailored near the end of their biosyntheses through the addition of sugars. SpnG, which catalyzes their 9-OH rhamnosylation, is also capable of adding other monosaccharides to the spinosyn aglycone (AGL) from TDP-sugars; however, the substitution of UDP-d-glucose for TDP-d-glucose as the donor substrate is known to result in a >60000-fold reduction in k(cat). Here, we report the structure of SpnG at 1.65 A resolution, SpnG bound to TDP at 1.86 A resolution, and SpnG bound to AGL at 1.70 A resolution. The SpnG-TDP complex reveals how SpnG employs N202 to discriminate between TDP- and UDP-sugars. A conformational change of several residues in the active site is promoted by the binding of TDP. The SpnG-AGL complex shows that the binding of AGL is mediated via hydrophobic interactions and that H13, the potential catalytic base, is within 3 A of the nucleophilic 9-OH group of AGL. A model for the Michaelis complex was constructed to reveal the features that allow SpnG to transfer diverse sugars; it also revealed that the rhamnosyl moiety is in a skew-boat conformation during the transfer reaction. Structural Studies of the Spinosyn Rhamnosyltransferase, SpnG.,Isiorho EA, Liu HW, Keatinge-Clay AT Biochemistry. 2012 Feb 14;51(6):1213-22. Epub 2012 Feb 3. PMID:22283226[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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