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Publication Abstract from PubMed

Human UDP-alpha-d-glucose-6-dehydrogenase (hUGDH) displays hysteresis because of a slow isomerization from an inactive state (E*) to an active state (E). Here we show that the structure of E* constrains hUGDH in a conformation that favors feedback inhibition at physiological pH. The feedback inhibitor UDP-alpha-d-xylose (UDP-Xyl) competes with the substrate UDP-alpha-d-glucose for the active site. Upon binding, UDP-Xyl triggers an allosteric switch that changes the structure and affinity of the intersubunit interface to form a stable but inactive horseshoe-shaped hexamer. Using sedimentation velocity studies and a new crystal structure, we show that E* represents a stable conformational intermediate between the active and feedback-inhibited conformations. Because the allosteric switch occludes the cofactor and substrate binding sites in the inactive hexamer, the intermediate conformation observed in the crystal structure is consistent with the E* transient observed in relaxation studies. Steady-state analysis shows that the E* conformation enhances the affinity of hUGDH for the allosteric inhibitor UDP-Xyl by 8.6-fold (Ki = 810 nM). We present a model in which the constrained quaternary structure permits a small effector molecule to leverage a disproportionately large allosteric response.

Hysteresis in Human UDP-Glucose Dehydrogenase Is Due to a Restrained Hexameric Structure That Favors Feedback Inhibition.,Kadirvelraj R, Custer GS, Keul ND, Sennett NC, Sidlo AM, Walsh RM Jr, Wood ZA Biochemistry. 2014 Dec 30;53(51):8043-51. doi: 10.1021/bi500594x. Epub 2014 Dec, 18. PMID:25478983^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.