Hysteresis in human UDP-glucose dehydrogenase is due to a restrained hexameric structure that favors feedback inhibition.
Biochemistry
; 53(51): 8043-51, 2014 Dec 30.
Article
en En
| MEDLINE
| ID: mdl-25478983
ABSTRACT
Human UDP-α-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-α-d-xylose (UDP-Xyl) competes with the substrate UDP-α-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.
Texto completo:
1
Bases de datos:
MEDLINE
Asunto principal:
Uridina Difosfato Glucosa Deshidrogenasa
Límite:
Humans
Idioma:
En
Revista:
Biochemistry
Año:
2014
Tipo del documento:
Article
País de afiliación:
Estados Unidos