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

Abstract

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.