title: Mechanism of displacement of a catalytically essential loop from the active site of mammalian fructose-1,6-bisphosphatase.
abstract: AMP triggers a 15° subunit-pair rotation in fructose-1,6-bisphosphatase (FBPase) from its active R state to its inactive T state. During this transition, a catalytically essential loop (residues 50-72) leaves its active (engaged) conformation. Here, the structures of Ile(10) → Asp FBPase and molecular dynamic simulations reveal factors responsible for loop displacement. The AMP/Mg(2+) and AMP/Zn(2+) complexes of Asp(10) FBPase are in intermediate quaternary conformations (completing 12° of the subunit-pair rotation), but the complex with Zn(2+) provides the first instance of an engaged loop in a near-T quaternary state. The 12° subunit-pair rotation generates close contacts involving the hinges (residues 50-57) and hairpin turns (residues 58-72) of the engaged loops. Additional subunit-pair rotation toward the T state would make such contacts unfavorable, presumably causing displacement of the loop. Targeted molecular dynamics simulations reveal no steric barriers to subunit-pair rotations of up to 14° followed by the displacement of the loop from the active site. Principal component analysis reveals high-amplitude motions that exacerbate steric clashes of engaged loops in the near-T state. The results of the simulations and crystal structures are in agreement: subunit-pair rotations just short of the canonical T state coupled with high-amplitude modes sterically displace the dynamic loop from the active site.
authors.affiliation: Department of Biochemistry, Biophysics, and Molecular Biology, 4206 Molecular Biology Building, Iowa State University , Ames, Iowa 50011-3260, United States.
authors.forename: Yang
authors.initials: Y
authors.lastname: Gao
authors.forename: Cristina V
authors.initials: CV
authors.lastname: Iancu
authors.forename: Susmith
authors.initials: S
authors.lastname: Mukind
authors.forename: Jun-Yong
authors.initials: JY
authors.lastname: Choe
authors.forename: Richard B
authors.initials: RB
authors.lastname: Honzatko
mesh_terms: D000249:Adenosine Monophosphate / Q000737:chemistry / Q000378:metabolism; D000818:Animals; D001665:Binding Sites; D002384:Catalysis; D020134:Catalytic Domain; D004789:Enzyme Activation; D006597:Fructose-Bisphosphatase / Q000737:chemistry* / Q000378:metabolism; D056004:Molecular Dynamics Simulation; D017433:Protein Structure, Secondary; D034421:Sus scrofa / Q000235:genetics* / Q000378:metabolism
chemical_list: D000249:Adenosine Monophosphate; D006597:Fructose-Bisphosphatase