The DCCD-binding polypeptide alone is insufficient for proton translocation through F0 in membranes of Escherichia coli

Anomalous effect of uncouplers on respiratory chain-linked transhydrogenation in Escherichia coli membranes: evidence for a localized proton pathway?

Energization of the pyridine nucleotide transhydrogenase in everted membrane vesicles from Escherichia coli JM83 was compared with the process in vesicles of the same strain transformed with the plasmid pDC21 overexpressing this enzyme. Proton translocation was assayed by the quenching of the fluorescence of the probe quinacrine. Agents able to discharge transmembrane proton gradients such as nigericin and the uncouplers 3,3',4',5-tetrachlorosalicylanilide and carbonyl cyanide m-chlorophenylhydrazone inhibited ATP-dependent transhydrogenation of NADP by NADH and discharged transmembrane proton gradients generated by transhydrogenation of AcNAD by NADPH, by oxidation of NADH, and by hydrolysis of ATP. This was observed in everted membrane vesicles of both strains JM83 and JM83pDC21. These strains differed significantly in the response of the NADH oxidation-dependent transhydrogenase. This reaction was inhibited by nigericin and uncouplers in membrane vesicles of JM83 but there was little inhibition or the reaction was stimulated in JM83pDC21, in spite of the discharge of the NADH oxidation-generated proton gradient measured by quinacrine fluorescence in the latter strain. It is proposed that the transhydrogenase is energized by direct or local (nonbulk phase) proton translocation in membranes of this strain. Uncouplers might facilitate these routes but would not discharge them. The generality of these observations was shown using other strains. NADH oxidase activity was severalfold lower in membrane vesicles of JM83pDC21 compared with JM83. The levels of ubiquinone and cytochromes, and the activities of NADH dehydrogenases I and II, and of cytochrome oxidase, were similar in the two strains. It is concluded that the NADH oxidase activity of JM83pDC21 is low because of the reduced rate of collision between electron-transferring complexes of the respiratory chain due to the large amount of transhydrogenase protein in the membranes of this strain. The large amount of transhydrogenase favors direct, nonbulk phase proton transfer. Transhydrogenase activity was stimulated by Ca2+, Mg2+, or Mn2+.

Topological analysis of the pyridine nucleotide transhydrogenase of Escherichia coli using proteolytic enzymes

The pyridine nucleotide transhydrogenase of Escherichia coli has an alpha 2 beta 2 structure (alpha: Mr, 54,000; beta: Mr, 48,700). Hydropathy analysis of the amino acid sequences suggested that the 10 kDa C-terminal portion of the alpha subunit and the N-terminal 20-25 kDa region of the beta subunit are composed of transmembranous alpha-helices. The topology of these subunits in the membrane was investigated using proteolytic enzymes. Trypsin digestion of everted cytoplasmic membrane vesicles released a 43 kDa polypeptide from the alpha subunit. The beta subunit was not susceptible to trypsin digestion. However, it was digested by proteinase K in everted vesicles. Both alpha and beta subunits were not attacked by trypsin and proteinase K in right-side out membrane vesicles. The beta subunit in the solubilized enzyme was only susceptible to digestion by trypsin if the substrates NADP(H) were present. NAD(H) did not affect digestion of the beta subunit. Digestion of the beta subunit of the membrane-bound enzyme by trypsin was not induced by NADP(H) unless the membranes had been previously stripped of extrinsic proteins by detergent. It is concluded that binding of NADP(H) induces a conformational change in the transhydrogenase. The location of the trypsin cleavage sites in the sequences of the alpha and beta subunits were determined by N- and C-terminal sequencing. A model is proposed in which the N-terminal 43 kDa region of the alpha subunit and the C-terminal 30 kDa region of the beta subunit are exposed on the cytoplasmic side of the inner membrane of E. coli. Binding sites for pyridine nucleotide coenzymes in these regions were suggested by affinity chromatography on NAD-agarose columns.

Bacterial adenosine 5'-triphosphate synthase (F1F0): purification and reconstitution of F0 complexes and biochemical and functional characterization of their subunits

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Conformational interactions between alpha and beta subunits in the F1 ATPase of Escherichia coli as shown by chemical modification of uncA401 and uncD412 mutant enzymes

In contrast to wild-type F1 adenosine triphosphatase, the beta subunits of soluble ATPase from Escherichia coli mutant strains AN120 (uncA401) and AN939 (uncD412) were not labeled by the fluorescent thiol-specific reagents 5-iodoacetamidofluorescein, 2-(4'-iodoacetamidoanilino)naphthalene-6-sulfonic acid or 4-[N-(iodoacetoxy)ethyl-N-methyl]amino-7-nitrobenzo-2-oxa-1,3-diazole. The mutation in the alpha subunit (uncA401) of F1 ATPase thus influences the accessibility of the single cysteinyl residue in the beta subunit. Following reaction of ATPase with 4-chloro-7-nitrobenzo-2-oxa-1,3-diazole or N,N'-dicyclohexylcarbodiimide, the alpha and beta subunits of the uncA401, but not of the uncD412 mutant F1 ATPase were intensely labeled by a fluorescent thiol reagent. The mutation in the beta subunit (uncD412) thus influences the accessibility of the cysteinyl residues in the alpha subunit. In other work [Stan-Lotter, H. and Bragg, P.D. (1986) Arch. Biochem. Biophys. 248] we have shown that 4-chloro-7-nitrobenzo-2-oxa-1,3-diazole and 2-(4'-iodoacetamidoanilino)naphthalene-6-sulfonic acid react with a different beta subunit from that labeled by N,N'-dicyclohexylcarbodiimide. This asymmetry with respect to modification by 4-chloro-7-nitrobenzo-2-oxa-1,3-diazole and N,N'-dicyclohexylcarbodiimide was seen in both mutant enzymes. In addition, the modification of one beta subunit of the uncA401 F1 ATPase induced the previously unreactive sulfhydryl group of another beta subunit to react with 2-(4'-iodoacetamidoanilino-naphthalene-6-sulfonic acid. These results provide evidence for at least three types of conformational interactions of the major subunits of F1 ATPase: from alpha to beta, from beta to alpha, and from beta to beta. As in wild-type ATPase, labeling of membrane-bound unc mutant ATPase by a fluorescent thiol reagent modified the alpha subunits. This suggests that a conformational change of yet a different type occurs when the enzyme binds to the membrane.

Thiol modification as a probe of conformational forms of the F1 ATPase of Escherichia coli and of the structural asymmetry of its beta subunits

The sulfhydryl groups of soluble and membrane-bound F1 adenosine triphosphatase of Escherichia coli were modified by reaction with the fluorescent thiol reagents 5-iodoacetamidofluorescein, 2-[(4'-iodoacetamido)anilino]naphthalene-6-sulfonic acid 4-[N-(iodoacetoxy)ethyl-N-methyl]amino-7-nitrobenzo-2-oxa-1,3-d iaz ole and 2-[(4'-maleimidyl)anilino]naphthalene-6-sulfonic acid. Whereas gamma and delta subunits were always labeled by these reagents, the beta subunit reacted preferentially in the soluble enzyme, and the alpha subunit in the membrane-bound enzyme. This suggests that the soluble enzyme undergoes a conformational change on binding to the membrane. The three beta subunits of the soluble ATPase did not react with chemical reagents in a similar manner. One beta subunit was cross-linked to the epsilon subunit on treatment of the ATPase with 1-ethyl-3-[3-(dimethyl-amino)propyl]carbodiimide, as observed previously by Lötscher et al. [Biochemistry (1984) 23, 4134-4140]. A second beta subunit, which did not cross-link to the epsilon subunit, was modified preferentially by the fluorescent thiol reagents and by 4-chloro-7-nitrobenzo-2-oxa-1,3-diazole. The third beta subunit was less chemically reactive than the others. Both alpha and beta subunits of the soluble 4-chloro-7-nitrobenzo-2-oxa-1,3-diazole-modified enzyme were labeled by the fluorescent thiol reagents. Thus, the modified enzyme, which is inactive, probably has a different conformation from the native soluble ATPase.

The DCCD-reactive aspartyl-residue of subunit C from the Escherichia coli ATP-synthase is important for the conformation of F0

The effect of various point mutations in subunits a and and c of the E. coli ATP-synthase was characterized. In each of the mutants there was no F0-dependent H+-conduction, but still an ATPase-activity comparable to wildtype activities. In addition, the subunit b could be extracted from the mutant's F0 but not from the F0 of wildtype. The effects are interpreted as a change in the conformation of F0 caused by the different mutations.

Evidence for the involvement of coupling factor B in the H+ channel of the mitochondrial H+-ATPase

Membrane energization by ATP has been measured in vesicles containing purified bovine heart mitochondrial H+-ATPase (ATP synthase) with the voltage-sensitive dye oxonol VI. The dithiol chelator, Cd2+, and the thiol oxidant, copper o-phenanthroline, produced discharge of the membrane potential when added at the steady state and inhibited its establishment when added prior to energization by ATP. These effects, which were reversed by dithiothreitol, were not accompanied by an increase in the nonspecific H+ permeability of the membrane. Passive H+ conduction in proteoliposomes containing F0 (hydrophobic segment of ATP synthase) was assayed by the quenching of 9-aminoacridine fluorescence after establishing a K+ diffusion potential. This conductance was blocked by Cd2+, an inhibitor of coupling factor B (FB). Labeling of F0 with 115Cd2+ at the concentrations that inhibited the F0 conductance followed by gel electrophoresis yielded a single radioactive band with a molecular weight corresponding to FB, the presence of which in the F0 preparation was confirmed by immunoblot staining. The data offer strong evidence that FB is an essential component of the H+ channel of F0, because H+ conduction through the channel is inhibited by chemical modification of FB.

Use of lambda unc transducing bacteriophages in genetic and biochemical characterization of H+-ATPase mutants of Escherichia coli

The eight subunits of the H+-ATPase of Escherichia coli are coded by the genes of the unc operon, which maps between bglB and asnA. A collection of unc mutations were transferred via P1 transduction into a strain in which lambda cI857 S7 was inserted into bglB. The lambda phage was induced, and asnA+ transducing phage that carried unc were selected. Transducing phage carrying mutations in the uncA, B, D, E, and F genes were used for complementation analysis with a collection of unc mutants, including mutants which had been reported previously but not genetically characterized. Some mutations gave a simple complementation pattern, indicating a single defective gene, whereas other mutations gave more complex patterns. Two mutants (uncE105 and uncE107) altered in the proteolipid (omega) subunit of F0 were not complemented by any of the lambda unc phage, even though both mutants had a fully functional F1 ATPase and therefore normal A and D genes. Hence, only limited conclusions can be drawn from genetic complementation alone, since it cannot distinguish normal from abnormal genes in certain classes of unc mutants. The lambda unc phage proved to be essential in characterizing several mutants defective in F0-mediated H+ translocation. The unc gene products were overproduced by heat induction of the lysogenized lambda unc phage to determine whether all the F0 subunits were in the membrane. Two mutants that gave a simple complementation pattern, indicative of one defective gene, did not assemble a three-subunit F0. The uncB108 mutant was shown to lack the chi subunit of F0 but to retain psi and omega. Trace amounts of an altered omega subunit and normal amounts of chi and psi were found in the uncE106 mutant. A substitution of aspartate for glycine at residue 58 of the protein was determined by DNA sequence analysis of the uncE gene cloned from the lambda uncE106 phage DNA. One of the omega-defective, noncomplementing mutants (uncE107) was shown to retain all three F0 subunits. The uncE gene from this mutant was also sequenced to confirm an asparagine-for-aspartate substitution at position 61 (the dicyclohexylcarbodiimide-binding site) of the omega subunit.

Interaction of Escherichia coli F1-ATPase with dicyclohexylcarbodiimide-binding polypeptide

Antibody raised against the N,N'-dicyclohexylcarbodiimide (DCCD)-binding polypeptide of Escherichia coli bound to the cytoplasmic surface of the cell membrane. A weak reaction was seen with everted vesicles of the thermophile PS3. Rat-liver mitochondrial membranes did not react with the antibody. Reaction of the isolated DCCD-binding polypeptide with the antibody was prevented by oxidation of methionine residues or cleavage of the polypeptide with cyanogen bromide. Modification of the arginine residues of the DCCD-binding polypeptide did not affect interaction with the antibody. Purified F1-ATPase of E. coli bound to the isolated DCCD-binding polypeptide as shown by solid-phase radioimmune assay. Binding involved the alpha and/or beta subunits of F1 and the arginine residues of the polar central region of the DCCD-binding polypeptide. Our results are consistent with a looped arrangement of the DCCD-binding polypeptide in the membrane in which the carboxyl- and amino-terminal regions of the molecule are at the periplasmic surface and the polar central region, interacting with F1, is at the cytoplasmic surface of the cell membrane.

Membrane topology of ATP synthase from bovine heart mitochondria and Escherichia coli

The polypeptides exposed to lipids in the membranous F0 sector of the mitochondrial and Escherichia coli ATP synthases were labelled with radioactive photoreactive lipids. Highly resolving gel electrophoretic conditions were used in order to separate all the eighteen components forming the bovine heart mitochondrial enzyme. The hydrophobic labelling was performed on fully active and inhibitor-sensitive ATP synthases. In the mitochondrial enzyme prepared according to Serrano et al. (1976) [J. Biol. Chem. 251, 2453-2461] seven polypeptides of Mr 30500; 11500; 10500; 10000; 9500; 8500 and 4500 were labelled. The major amount of radioactivity was associated with the 30500-Mr component, which is thought to be the adenine nucleotide carrier. In the preparation of Galante et al., (1979) which almost completely lacks this component [J. Biol. Chem. 254, 12372-12378] nine polypeptides of Mr 25000; 21000; 11500; 10500; 10000; 9500; 9200; 8500 and 4500 were labelled. In the ATPase synthase from E. coli the major amount of labelling was associated with subunit b and only a minor portion with subunit c.