The essential arginine residue at position 210 in the a subunit of the Escherichia coli ATP synthase can be transferred to position 252 with partial retention of activity

Abstract

The substitution of arginine at position 210 in the a subunit of Escherichia coli F0F1-ATPase by either lysine or alanine causes dominance in complementation tests with a chromosomal c subunit mutation. Reversal of dominance was achieved for the a R210K mutation but not for the a R210A mutation by the presence of an aspartic acid residue at position 50 or at position 252 in the a subunit. It was concluded that position 210 in putative helix 4 of a previously proposed model of the a subunit is close to position 252 in putative helix 5 and to position 50 in putative helix 1. The juxtaposition of residues 252 and 210 was also indicated by the observation that the double mutant a R210Q/Q252R was partially functional. A revertant of the partially functional double mutant, isolated on succinate medium, was found to contain a third mutation resulting in Pro-204 in the a subunit being replaced by threonine. That the revertant phenotype was due to the a P204T change was confirmed by site-directed mutagenesis. ATP synthesis in the revertant strain was at near normal levels as judged by growth yield experiments, but the revertant strain was unable to pump protons in response to ATP hydrolysis.