title: Inherent conformational flexibility of F1-ATPase α-subunit.
abstract: The core of F1-ATPase consists of three catalytic (β) and three noncatalytic (α) subunits, forming a hexameric ring in alternating positions. A wealth of experimental and theoretical data has provided a detailed picture of the complex role played by catalytic subunits. Although major conformational changes have only been seen in β-subunits, it is clear that α-subunits have to respond to these changes in order to be able to transmit information during the rotary mechanism. However, the conformational behavior of α-subunits has not been explored in detail. Here, we have combined unbiased molecular dynamics (MD) simulations and calorimetrically measured thermodynamic signatures to investigate the conformational flexibility of isolated α-subunits, as a step toward deepening our understanding of its function inside the α3β3 ring. The simulations indicate that the open-to-closed conformational transition of the α-subunit is essentially barrierless, which is ideal to accompany and transmit the movement of the catalytic subunits. Calorimetric measurements of the recombinant α-subunit from Geobacillus kaustophilus indicate that the isolated subunit undergoes no significant conformational changes upon nucleotide binding. Simulations confirm that the nucleotide-free and nucleotide-bound subunits show average conformations similar to that observed in the F1 crystal structure, but they reveal an increased conformational flexibility of the isolated α-subunit upon MgATP binding, which might explain the evolutionary conserved capacity of α-subunits to recognize nucleotides with considerable strength. Furthermore, we elucidate the different dependencies that α- and β-subunits show on Mg(II) for recognizing ATP.
authors.affiliation: Instituto de Química Universidad Nacional Autónoma de México, Circuito Exterior, Ciudad Universitaria, México 04630, D.F., Mexico.
authors.forename: Otto
authors.initials: O
authors.lastname: Hahn-Herrera
authors.affiliation: Instituto de Química Universidad Nacional Autónoma de México, Circuito Exterior, Ciudad Universitaria, México 04630, D.F., Mexico.
authors.forename: Guillermo
authors.initials: G
authors.lastname: Salcedo
authors.affiliation: Catalan Institution for Research and Advanced Studies (ICREA), Passeig Lluís Companys 23, 08010 Barcelona, Spain; Departament de Fisicoquímica, Facultat de Farmàcia, Universitat de Barcelona, Barcelona, Spain.
authors.forename: Xavier
authors.initials: X
authors.lastname: Barril
authors.affiliation: Instituto de Química Universidad Nacional Autónoma de México, Circuito Exterior, Ciudad Universitaria, México 04630, D.F., Mexico. Electronic address: egarciah@unam.mx.
authors.forename: Enrique
authors.initials: E
authors.lastname: García-Hernández
mesh_terms: D002151:Calorimetry; D056004:Molecular Dynamics Simulation; D011487:Protein Conformation; D021122:Protein Subunits / Q000737:chemistry; D006180:Proton-Translocating ATPases / Q000737:chemistry*; D013816:Thermodynamics
chemical_list: D021122:Protein Subunits; D006180:Proton-Translocating ATPases
keywords: Conformational flexibility; F(O)F(1)-ATP synthase; Isothermal titration calorimetry; Molecular dynamics simulation; Noncatalytic subunit