ABSTRACTAtpI, a membrane protein encoded by many bacterialatpoperons, is reported to be necessary forc-ring oligomer formation during assembly of some ATP synthase complexes. We investigated chaperone functions of AtpI and compared them to those of AtpZ, a protein encoded by a gene upstream ofatpIthat has a role in magnesium acquisition at near-neutral pH, and of SpoIIIJ and YqjG, two YidC/OxaI/Alb3 family proteins, in alkaliphilicBacillus pseudofirmusOF4. A strain with a chromosomal deletion ofatpIgrew nonfermentatively, and its purified ATP synthase had ac-ring of normal size, indicating that AtpI is not absolutely required for ATP synthase function. However, deletion ofatpI, but notatpZ, led to reduced stability of the ATP synthase rotor, reduced membrane association of the F1domain, reduced ATPase activity, and modestly reduced nonfermentative growth on malate at both pH 7.5 and 10.5. BothspoIIIJandyqjG, but notatpIoratpZ, complemented a YidC-depletedEscherichia colistrain. Consistent with such overlapping functions, single deletions ofspoIIIJoryqjGin the alkaliphile did not affect membrane ATP synthase levels or activities, but functional specialization was indicated by YqjG and SpoIIIJ showing respectively greater roles in malate growth at pH 7.5 and 10.5. Expression ofyqjGwas elevated at pH 7.5 relative to that at pH 10.5 and in ΔspoIIIJstrains, but it was lower than constitutivespoIIIJexpression. Deletion ofatpZcaused the largest increase among the mutants in magnesium concentrations needed for pH 7.5 growth. The basis for this phenotype is not yet resolved.
The Regulatory C-Terminal Domain of Subunit of FoF1 ATP Synthase Is Dispensable for Growth and Survival of Escherichia coli
