title: Crosslinking between alpha and beta subunits defines the orientation and spatial relationship of some of the transmembrane helices of the proton-translocating pyridine nucleotide transhydrogenase of Escherichia coli.
abstract: The proton-translocating pyridine nucleotide transhydrogenase of Escherichia coli is composed of two types of subunits, alpha and beta, organized as an alpha(2)beta(2) tetramer. The protein contains three recognizable domains, of which domain II is the transmembrane region of the molecule containing the pathway for proton translocation. Domain II is composed of four transmembrane helices at the carboxyl-terminus of the alpha subunit and either eight or nine transmembrane helices at the amino-terminal region of the beta subunit. We have introduced pairs of cysteine residues into a cysteine-free transhydrogenase by site-directed mutagenesis. Disulfide bond formation between some of these cysteine residues occurred spontaneously or on treatment with cupric 1, 10-phenanthrolinate. Analysis of crosslinked products confirmed that there are nine transmembrane helices in the domain II region of the beta subunit. The proximity to one another of several of the transmembrane helices was determined. Thus, helices 2 and 4 are close to helix 6 (nomenclature of Meuller and Rydström, J. Biol. Chem. 274, 19072-19080, 1999), and helix 3 and the carboxyl-terminal eight residues of the alpha subunit are close to helix 7. In the alpha(2)beta(2) tetramer, helices 2 and 4 of one alpha subunit are close to the same pair of transmembrane helices of the other alpha subunit, and helix 6 of one beta subunit is close to helix 6 of the other beta subunit.
authors.affiliation: Department of Biochemistry and Molecular Biology, University of British Columbia, 2146 Health Sciences Mall, Vancouver, British Columbia, V6T 1Z3, Canada. pbragg@interchange.ubc.ca
authors.forename: P D
authors.initials: PD
authors.lastname: Bragg
authors.forename: C
authors.initials: C
authors.lastname: Hou
mesh_terms: D000595:Amino Acid Sequence; D004591:Electrophoresis, Polyacrylamide Gel; D004926:Escherichia coli / Q000201:enzymology*; D017136:Ion Transport; D008969:Molecular Sequence Data; D008970:Molecular Weight; D009250:NADP Transhydrogenases / Q000737:chemistry / Q000378:metabolism*; D011522:Protons
chemical_list: D011522:Protons; D009250:NADP Transhydrogenases