title: N-terminal domain of the V-ATPase a2-subunit displays integral membrane protein properties.
abstract: V-ATPase is a multisubunit membrane complex that functions as nanomotor coupling ATP hydrolysis with proton translocation across biological membranes. Recently, we uncovered details of the mechanism of interaction between the N-terminal tail of the V-ATPase a2-subunit isoform (a2N(1-402)) and ARNO, a GTP/GDP exchange factor for Arf-family small GTPases. Here, we describe the development of two methods for preparation of the a2N(1-402) recombinant protein in milligram quantities sufficient for further biochemical, biophysical, and structural studies. We found two alternative amphiphilic chemicals that were required for protein stability and solubility during purification: (i) non-detergent sulfobetaine NDSB-256 and (ii) zwitterionic detergent FOS-CHOLINE®12 (FC-12). Moreover, the other factors including mild alkaline pH, the presence of reducing agents and the absence of salt were beneficial for stabilization and solubilization of the protein. A preparation of a2N(1-402) in NDSB-256 was successfully used in pull-down and BIAcore™ protein-protein interaction experiments with ARNO, whereas the purity and quality of the second preparation in FC-12 was validated by size-exclusion chromatography and CD spectroscopy. Surprisingly, the detergent requirement for stabilization and solubilization of a2N(1-402) and its cosedimentation with liposomes were different from peripheral domains of other transmembrane proteins. Thus, our data suggest that in contrast to current models, so called "cytosolic" tail of the a2-subunit might actually be embedded into and/or closely associated with membrane phospholipids even in the absence of any obvious predicted transmembrane segments. We propose that a2N(1-402) should be categorized as an integral monotopic domain of the a2-subunit isoform of the V-ATPase.
authors.affiliation: Center for Systems Biology, Program in Membrane Biology and Division of Nephrology, Simches Research Center, Massachusetts General Hospital and Department of Medicine, Harvard Medical School, Boston, Massachusetts 02114, USA.
authors.forename: Maria
authors.initials: M
authors.lastname: Merkulova
authors.forename: Mary
authors.initials: M
authors.lastname: McKee
authors.forename: Phat Vinh
authors.initials: PV
authors.lastname: Dip
authors.forename: Gerhard
authors.initials: G
authors.lastname: Grüber
authors.forename: Vladimir
authors.initials: V
authors.lastname: Marshansky
mesh_terms: D000818:Animals; D002942:Circular Dichroism; D003902:Detergents / Q000494:pharmacology; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism / Q000648:ultrastructure; D006801:Humans; D008081:Liposomes; D008565:Membrane Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D008623:Mercaptoethanol / Q000494:pharmacology; D046529:Microscopy, Electron, Transmission; D010713:Phosphatidylcholines / Q000737:chemistry / Q000378:metabolism; D011485:Protein Binding; D011489:Protein Denaturation; D017510:Protein Folding; D017434:Protein Structure, Tertiary; D021122:Protein Subunits / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D012995:Solubility / Q000187:drug effects; D025262:Vacuolar Proton-Translocating ATPases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
chemical_list: D003902:Detergents; D008081:Liposomes; D008565:Membrane Proteins; D010713:Phosphatidylcholines; D021122:Protein Subunits; D011994:Recombinant Proteins; D008623:Mercaptoethanol; C024990:asolectin; D025262:Vacuolar Proton-Translocating ATPases