کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
2185170 | 1095963 | 2011 | 13 صفحه PDF | دانلود رایگان |
![عکس صفحه اول مقاله: Structural and Functional Analysis of C2-Type Ketoreductases from Modular Polyketide Synthases Structural and Functional Analysis of C2-Type Ketoreductases from Modular Polyketide Synthases](/preview/png/2185170.png)
The process by which α-stereocenters of polyketide intermediates are set by modular polyketide synthases (PKSs) when condensation is not immediately followed by reduction is mysterious. However, the reductase-incompetent ketoreductase (KR) from the third module of 6-deoxyerythronolide B synthase has been proposed to operate as a racemase, aiding in the epimerization process that reverses the orientation of the α-methyl group of the polyketide intermediate generated by the ketosynthase to the configuration observed in the 6-deoxyerythronolide B final product. To learn more about the epimerization process, the structure of the C2-type KR from the third module of the pikromycin synthase, analogous to the KR from the third module of 6-deoxyerythronolide B synthase, was determined to 1.88 Å resolution. This first structural analysis of this KR-type reveals differences from reductase-competent KRs such as that the site NADPH binds to reductase-competent KRs is occluded by side chains and the putative catalytic tyrosine possesses more degrees of freedom. The active-site geometry may enable C2-type KRs to align the thioester and β-keto groups of a polyketide intermediate to reduce the pKa of the α-proton and accelerate its abstraction. Results from in vivo assays of engineered PKSs support that C2-type KRs cooperate with epimer-specific ketosynthases to set the configurations of substituent-bearing α-carbons.
Research Highlights
► The first structure of a C2-type KR at 1.88 Å resolution.
► Functional assays of engineered PKSs support C2-type KRs as racemases.
► Racemization mechanism of C2-type KRs is proposed.
Journal: Journal of Molecular Biology - Volume 410, Issue 1, 1 July 2011, Pages 105–117