F1FO-ATP synthase is the primary source of cellular energy production in most living organisms. Malfunction of this enzyme is implicated in diseases. There are many functional motifs in and around the catalytic sites of this enzyme. One of them is the highly conserved α-subunit VISIT-DG sequence that is close to the Pi binding subdomain. The questions arise "Are they involved in Pi binding? Or are they there simply for the structural integrity of the catalytic sites?" Here, αIle-346and αIle-348, two important residues of the conserved VISIT-DG sequence, are discussed. Each residue was mutated to A/R/D/Q. Growth assays in limiting glucose media and on succinate plates suggests αIle-346 and αIle-348 are critical for the normal enzymatic function (oxidative phosphorylation). And the biochemical assays do suggest both αI-346 and αI-348 are required to maintain catalytic site, involved in Pi binding indirectly, but αI-348 plays more important role than αI-346.

The role of αPhe-291 residue in phosphate binding by Escherichia coli F1F0-ATP synthase was examined. X-ray structures of bovine mitochondrial enzyme suggest that this residue resides in close proximity to the conserved βR246 residue. Herein, we show that mutations αF291D and αF291E in E. coli reduce the ATPase activity of F1F0 membranes by 350-fold. Yet, significant oxidative phosphorylation activity is retained. In contrast to wild-type, ATPase activities of mutants were not inhibited by MgADP-azide, MgADP-fluoroaluminate, or MgADP-fluoroscandium. Whereas, 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole (NBD-Cl) inhibited wild-type ATPase essentially completely, ATPase in mutants was inhibited maximally by ∼75%, although reaction still occurred at residue βTyr-297, proximal to αPhe-291 in the phosphate-binding pocket. Inhibition characteristics supported the conclusion that NBD-Cl reacts in βE (empty) catalytic sites, as shown previously by X-ray structure analysis. Phosphate protected against NBD-Cl inhibition in wild-type but not in mutants. In addition, our data suggest that the interaction of αPhe-291 with phosphate during ATP hydrolysis or synthesis may be distinct.