Role of a dynamic loop in cation activation and allosteric regulation of recombinant porcine fructose-1,6-bisphosphatase.
A disordered loop (loop 52-72, residues 52-72) in crystal structures of fructose-1,6-bisphosphatase (FBPase) has been implicated in regulatory and catalytic phenomena by studies in directed mutation. A crystal structure of FBPase in a complex with three zinc cations and the products fructose 6-phosphate (F6P) and phosphate (Pi) reveals loop 52-72 for the first time in a well-defined conformation with strong electron density. Loop 52-57 interacts primarily with the active site of its own subunit. Asp68 of the loop hydrogen bonds with Arg276 and a zinc cation located at the putative potassium activation site. Leu56 and Tyr57 of the loop pack against hydrophobic residues from two separate subunits of FBPase. A mechanism of allosteric regulation of catalysis is presented, in which AMP, by binding to its allosteric pocket, displaces loop 52-72 from the active site. Furthermore, the current structure suggests that both the alpha- and beta-anomers of F6P can be substrates in the reverse reaction catalyzed by FBPase. Mechanisms of catalysis are proposed for the reverse reaction in which Asp121 serves as a catalytic base for the alpha-anomer and Glu280 serves as a catalytic base for the beta-anomer.
Choe
J Y
JY
Department of Biochemistry and Biophysics, Iowa State University, Ames 50011, USA.
Poland
B W
BW
Fromm
H J
HJ
Honzatko
R B
RB
D000494:Allosteric Regulation; D000818:Animals; D001665:Binding Sites; D002413:Cations, Divalent / Q000378:metabolism; D018360:Crystallography, X-Ray; D004789:Enzyme Activation; D005635:Fructosediphosphates / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D008024:Ligands; D008956:Models, Chemical; D008958:Models, Molecular; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000737:chemistry* / Q000378:metabolism*; D013552:Swine; D015032:Zinc / Q000378:metabolism
D002413:Cations, Divalent; D005635:Fructosediphosphates; D008024:Ligands; D011994:Recombinant Proteins; D015032:Zinc; C029063:fructose-1,6-diphosphate