Significance of Leu and Ser in the βDELSEED-loop of Escherichia coli ATP synthase.

The current study investigated the significance of βLeu-382 and βSer-383 residues in the highly conserved βDELSEED-loop of Escherichia coli ATP synthase. E. coli wild type and mutant enzymes were inhibited by the honeybee venom peptide melittin, which is a known ATP synthase inhibitor. The wild type enzyme was fully inhibited by melittin. Melittin-induced inhibitory profiles of single mutants βL382A/R/Q/D/E and βS383A/R/Q/D/E followed the pattern of wild-type enzymes with 7% to 30% residual activity. Double mutants βL382A/βS383A, βL382E/βS383E, and βL382R/βS383R retained 30%, 80%, and 78% residual activity, respectively. Variable loss of oxidative phosphorylation was observed in mutant enzymes, which was also reflected in the comparative growth of wild type and mutant E. coli strains. Double mutant enzymes βL382E/βS383E and βL382R/βS383R showed significant resistance to the melittin-induced inhibition. Wild type and mutant E. coli strains showed variable loss of growth in the presence of melittin. Indicial growth loss of E. coli strains and inhibition of isolated ATP synthase suggested that βLeu-382 and βSer-383 are vital for the function of enzyme. Individual loss of βLeu-382 and βSer-383 does not affect the melittin-induced inhibition. However, loss of both βLeu-382 and βSer-383 obstructs the inhibition suggesting loss of peptide binding at the βDELSEED-loop of ATP synthase.