Catalysis and energy coupling of H(+)-ATPase (ATP synthase): molecular biological approaches

The molecular biological approach has provided important information for understanding the F0F1 H(+)-ATPase. This article focuses on our recent results on the catalytic site in the beta subunit, and the roles of alpha/beta subunit interaction and amino/carboxyl terminal interaction of the gamma subunit in energy coupling. Extensive mutagenesis of the beta subunit revealed that beta Lys-155, beta Thr-156, beta Glu-181 and beta Arg-182 are essential catalytic residues. beta Glu-185 is not absolutely essential, but a carboxyl residue may be necessary at this position. A pseudo-revertant analysis positioned beta Gly-172, beta Ser-174, beta Glu-192 and beta Val-198 in the proximity of beta Gly-149. The finding of the roles of beta Gly-149, beta Lys-155, and beta Thr-156 emphasized the importance of the glycine-rich sequence (Gly-X-X-X-X-Gly-Lys-Thr/Ser, E. coli beta residues between beta Gly-149 and beta Thr-156) conserved in many nucleotide binding proteins. The A subunits of vacuolar type ATPases may have a similar catalytic mechanism because they have conserved glycine-rich and Gly-Glu-Arg (corresponding to beta Gly-180-beta Arg-182) sequences. The results of these mutational studies are consistent with the labeling of beta Lys-155 and beta Lys-201 with AP3-PL, and of beta Glu-192 with DCCD [15]. The DCCD-binding residue of a thermophilic Bacillus corresponds to beta Glu-181, an essential catalytic residue discussed above. The defective coupling of the beta Ser-174-->Phe mutant was suppressed by the second mutation alpha Arg-296-->Cys, indicating the importance of alpha/beta interaction in energy coupling. The gamma subunit, especially its amino/carboxyl interaction, seems to be essential for energy coupling between catalysis and transport judging from studies on gamma Met-23-->Lys or Arg mutation and second-site mutations which suppressed the gamma Lys-23 mutation. Thus the conserved gamma Met-23 is not absolutely essential but is located in the important region for amino/carboxyl interaction for energy coupling.