title: Nucleotide dependence of the dimerization of ATP binding cassette nucleotide binding domains.
abstract: ATP-binding cassette proteins are ubiquitously present throughout all known genomes. Their basic functional unit possesses two transmembrane domains and two nucleotide-binding domains. The nucleotide-binding domains are responsible for ATP binding and hydrolysis, and their 3-dimensional structure is conserved across ATP-binding cassette proteins. Binding of ATP produces nucleotide-binding domain dimerization, a step necessary for hydrolysis. However, the possibility that nucleotide-binding domains bind and/or hydrolyze nucleotide triphosphates different from ATP has not been explored in detail. Here, we studied that possibility using M. jannaschii MJ0796, a prototypical ATP-binding cassette nucleotide-binding domain. We found that nucleotide-binding domain dimerization occurs as a result of binding to the natural nucleotide triphosphates ATP, GTP, CTP and UTP, and also to the analog ATP-γ-S. All the natural nucleotide triphosphates are hydrolyzed at similar rates, whereas ATP-γ-S is not hydrolyzed. We also found that the non-hydrolyzable ATP analog AMP-PNP, frequently assumed to produce the nucleotide-bound conformation, failed to elicit nucleotide-binding domain dimerization. Our results raise the possibility that not all the nucleotide binding sites of nucleotide-binding domains are occupied by ATP under physiological conditions, and that ATP is not always the nucleotide hydrolyzed to dissociate the nucleotide-binding domain dimers.
authors.affiliation: Department of Cell Physiology and Molecular Biophysics, Texas Tech University Health Sciences Center, Lubbock, TX 79430-6551, USA.
authors.forename: Gregory A
authors.initials: GA
authors.lastname: Fendley
authors.affiliation: Center for Membrane Protein Research, Texas Tech University Health Sciences Center, Lubbock, TX 79430-6551, USA; Department of Cell Biology and Biochemistry, Texas Tech University Health Sciences Center, Lubbock, TX 79430-6540, USA.
authors.forename: Ina L
authors.initials: IL
authors.lastname: Urbatsch
authors.affiliation: Department of Cell Physiology and Molecular Biophysics, Texas Tech University Health Sciences Center, Lubbock, TX 79430-6551, USA; Center for Membrane Protein Research, Texas Tech University Health Sciences Center, Lubbock, TX 79430-6551, USA.
authors.forename: Roger B
authors.initials: RB
authors.lastname: Sutton
authors.affiliation: School of Natural Sciences, University of California, Merced, 4225 N. Hospital Road, Atwater, CA 95301, USA.
authors.forename: Maria E
authors.initials: ME
authors.lastname: Zoghbi
authors.affiliation: Department of Cell Physiology and Molecular Biophysics, Texas Tech University Health Sciences Center, Lubbock, TX 79430-6551, USA; Center for Membrane Protein Research, Texas Tech University Health Sciences Center, Lubbock, TX 79430-6551, USA. Electronic address: g.altenberg@ttuhsc.edu.
authors.forename: Guillermo A
authors.initials: GA
authors.lastname: Altenberg
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism*; D001665:Binding Sites; D006868:Hydrolysis; D009154:Mutation; D000072417:Protein Domains; D055503:Protein Multimerization
chemical_list: D018528:ATP-Binding Cassette Transporters; C434961:MJ0796 protein, Methanococcus jannaschii; D000255:Adenosine Triphosphate
keywords: ABC protein; ATPase; Dimer; Motor domain; Tryptophan fluorescence