H+-ATPase of Escherichia coli. An uncE mutation impairing coupling between F1 and Fo but not Fo-mediated H+ translocation.

The uncE114 mutation from Escherichia coli strain KI1 (Nieuwenhuis, F. J. R. M., Kanner, B. I., Gutnick, D. L., Postma, P. W., and Van Dam, K. (1973) Biochim. Biophys. Acta 325, 62-71) was characterized after transfer to a new genetic background. A defective H+-ATPase complex is formed in strains carrying the mutation. Based upon the genetic complementation pattern of other unc mutants by a lambda uncE114 transducing phage, and complementation of uncE114 recipients by an uncE+ plasmid (pCP35), the mutation was concluded to lie in the uncE gene. The uncE gene codes for the omega subunit ("dicyclohexylcarbodiimide binding protein") of the H+-ATPase complex. The mutation was defined by sequencing the mutant gene. The G----C transversion found results in a substitution of Glu for Gln at position 42 of the omega subunit in the Fo sector of the H+-ATPase. The substitution did not significantly impair H+ translocation by Fo or affect inhibition of H+ translocation by dicyclohexylcarbodiimide. Wild-type F1 was bound by uncE114 Fo with near normal affinity, but the functional coupling between F1 and Fo was disrupted. The uncoupling was indicated by an H+-leaky membrane, even when saturating levels of wild-type F1 were bound. Disassociation of F1 from Fo under conditions of assay did partially contribute to the H+ leakiness, but the major contributor to the high H+ conductance was Fo with bound F1. The F1 bound to uncE114 membranes exhibited normal ATPase activity, but ATP hydrolysis was uncoupled from H+ translocation and was resistant to inhibition by dicyclohexylcarbodiimide. The F1 isolated from the uncE114 mutant was modified with partial loss of coupling function. However, this modification did not account for the uncoupled properties of the mutant Fo described above, since these properties were retained after reconstitution of mutant membrane (Fo) with wild-type F1.

A phenylalanine for serine substitution in the beta subunit of Escherichia coli F1-ATPase affects dependence of its activity on divalent cations.

A mutant (KF11) of Escherichia coli H+-translocating ATPase (F1-F0) has a single point mutation in the beta subunit of F1 that has lost 90% of its Mg2+-dependent ATPase activity (Kanazawa, H., Horiuchi, Y., Takagi, M., Ishino, Y., and Futai, M. (1980) J. Biochem. (Tokyo) 88, 695-703). The mutation was mapped at about the 500th nucleotide residue from the 5' end of the beta subunit gene by a genetic recombination test on the physical map of the cistron coding for the beta subunit. The mutant allele of KF11 (uncD11) was cloned on a hybrid plasmid (pKF11) via DNA isolated from a lambda uncD11 transducing phage. Restriction fragments of pKF11 containing the estimated mutation site were subjected to polyacrylamide gel electrophoresis under conditions where strands were separated into single strands. The two strands of a DNA segment, which was shown to carry an altered base, showed anomalous migration compared with those from the wild-type fragment. The results confirmed the result of mapping of the altered site by genetic tests. On the basis of these results, the nucleotide sequence of the mutated gene was determined, and a single base change of the 524th cytosine to thymine resulting in a phenylalanine for serine substitution at residue 174 of the beta subunit was found. This result, together with results on the altered properties of F1 from KF11 reported previously, indicates that residue 174 is essential for the Mg2+-dependent ATPase activity of F1 but not for the Ca2+-dependent ATPase activity.

Mutations altering aspartyl-61 of the omega subunit (uncE protein) of Escherichia coli H+ -ATPase differ in effect on coupled ATP hydrolysis.

Mutations in the H+-translocating ATPase complex (F1F0) of Escherichia coli have been described in which aspartyl-61 of the omega subunit ( uncE protein) is substituted by either glycine ( uncE105 ) or asparagine ( uncE107 ). Either substitution blocks the H+-translocation activity of the F0 sector of the complex. Here we report a difference in the effects of the two substitutions on the coupled ATPase activity of F1 bound to F0. Wild-type F1 was bound to the F0 of either mutant with affinities comparable to wild-type. The ATPase activity of F1 bound to uncE107 F0 was inhibited by 50%, whereas that bound to uncE105 F0 was not inhibited. Complementation studies with a pBR322-derived plasmid that carried the E gene of the unc operon only indicated that a single mutation in the host strain was responsible for the respective phenotypes. In mutants complemented by the uncE + plasmid, restoration of wild-type biochemical properties was only partial and may be attributed to a mixing of wild-type and mutant omega subunits in a hybrid F0 complex. The activity of membrane-bound F1 was less inhibited in the uncE +/ uncE107 hybrid. Paradoxically, complementation of uncE105 by the uncE + plasmid resulted in substantial inhibition of the activity of membrane-bound F1. The results indicate that a glycine-versus-asparagine substitution for aspartyl-61 must lead to altered conformations of omega and that these differences in conformation are important in the coupling between the F0 and F1 sectors of the complex.

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.

H+-ATPase of Escherichia coli uncB402 mutation leads to loss of chi subunit of subunit of F0 sector.

The uncB402 mutation in Escherichia coli results in formation of an H+-ATPase complex that is defective in energy-transducing capacity. The mutation, originally described by Butlin et al. (Butlin, J.D., Cox, G.B., and Gibson, F. (1973) Biochim. Biophys. Acta 292, 366-375), alters the F0 sector of the H+-ATPase complex. Here, we show that uncB402 is an amber-suppressible, chain-terminating mutation that results in loss of the chi subunit from F0. This was demonstrated in crude membrane fractions after overproduction of the ATPase complex by heat induction of a lambda transducing phage carrying the unc operon of uncB402. The lambda-uncB402 DNA was used as a template in an in vitro transcription-translation system. A synthesis product that may correspond to the truncated form of the chi subunit was observed. Despite the absence of chi, the F1-ATPase was still bound to the membrane, although more weakly than in wild type. The omega subunit of F0 ("dicyclohexylcarbodiimide-binding protein") shows normal reactivity with dicyclohexylcarbodiimide, indicating that at least this portion of F0 integrates properly in the membrane in the absence of the chi subunit. The F0 of uncB402 was not functional in H+ translocation activity. This was shown by direct H+ flux measurements with crude membrane vesicles that were treated with guanidine to disrupt the binding of F1 to F0. Secondly, a method was developed for isolation of F0 from F1-depleted membranes. The F0 from uncB402 was shown to have less than 5% the proton-translocase activity of wild type F0 when reconstituted into liposomes. Although the uncB402 mutant shows these defects, the question of whether the chi subunit plays a direct role in F1-binding or H+ translocation remains open, since the loss of chi may lead to subtle changes in the assembly of the other F0 subunits. Analysis of other mutants should permit a more definitive assignment of function.

Subunits of the H+-ATPase of Escherichia coli. Overproduction of an eight-subunit F1F0-ATPase following induction of a lambda-transducing phage carrying the unc operon.

The proton-translocating ATPase complex (F1F0) of Escherichia coli was purified after inductin of a lambda-transducing phage (lambda asn5) carrying the ATPase genes of th unc operon. ATPase activity of membranes prepared from the induced lambda-unc lysogen was 6-fold greater than the activity of membranes prepared from strains lacking the unc-transducing phage, confirming the report of Kanazawa et al. (1979) Proc. Natl. Acad. Sci. U. S. A. 76, 1126-1130). The F1F0-ATPase complex was purified in comparable yield from either enriched membranes or control membranes using a modification of the procedure reported by Foster and Fillingame ((1979) J. Biol. Chem. 254, 8230-8236). EAch of the eight subunits that had been reported as components of the F1F0 complex from wild type E. coli was overproduced in the lambda-unc lysogen. All eight subunits co-purified in the same stoichiometric proportion as in the complex purified from wild type E. coli. We conclude that all eight subunits are likely coded by the small segment of chromosomal DNA carried by the lambda-transducing phage. These experiments provide the first evidence that all eight polypeptides are authentic subunits of the ATPase complex rather than contaminants that fortuitously co-purify.