title: Quaternary structure of the oxaloacetate decarboxylase membrane complex and mechanistic relationships to pyruvate carboxylases.
abstract: The oxaloacetate decarboxylase primary Na(+) pump (OAD) is an essential membrane protein complex that functions in the citrate fermentation pathway of some pathogenic bacteria under anaerobic conditions. OAD contains three different subunits: Oad-α, a biotinylated extrinsic protein that catalyzes the α-ketodecarboxylation of oxaloacetate; Oad-γ, a structural bitopic membrane protein whose cytosolic tail (named as Oad-γ') binds tightly to Oad-α; and Oad-β, a multispan transmembrane α-helical protein that constitutes the Na(+) channel. How OAD is organized structurally at the membrane and what the molecular determinants are that lead to an efficient energy coupling mechanism remain elusive. In the present work, we elucidate the stoichiometry of the native complex as well as the low resolution structure of the peripheral components of OAD (Oad-α and Oad-γ') by small angle x-ray scattering. Our results point to a quaternary assembly similar to the pyruvate carboxylase complex organization. Herein, we propose a model in which the association in pairs of Oad-α dimers, mediated by Oad-γ, results in the acquisition of a functional oligomeric state at the bacterial membrane. New structural insights for the conformational rearrangements associated with the carboxylbiotin transfer reaction within OAD are provided.
authors.affiliation: Biomolecular Research, Paul Scherrer Institut, 5232 Villigen, Switzerland.
authors.forename: Monica
authors.initials: M
authors.lastname: Balsera
authors.forename: Ruben M
authors.initials: RM
authors.lastname: Buey
authors.forename: Xiao-Dan
authors.initials: XD
authors.lastname: Li
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics; D002262:Carboxy-Lyases / Q000737:chemistry* / Q000235:genetics; D008565:Membrane Proteins / Q000737:chemistry* / Q000235:genetics; D020836:Protein Structure, Quaternary; D017433:Protein Structure, Secondary; D011766:Pyruvate Carboxylase / Q000737:chemistry* / Q000235:genetics; D014734:Vibrio cholerae / Q000201:enzymology* / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; D008565:Membrane Proteins; D002262:Carboxy-Lyases; C021916:oxaloacetate decarboxylase; D011766:Pyruvate Carboxylase