Catalytic and structural importance of Gly-454, Tyr-455, and Leu-456 in the carboxy-terminal region of Escherichia coli F1-ATPase alpha subunit.

Monoclonal antibody alpha110 recognizes Leu-456 in the alpha subunit of the Escherichia coli F1-ATPase. Binding of this antibody to the alpha subunit or mutation of this residue to Pro caused enhancement of the ATPase activity, suggesting that this residue is involved in the catalytic mechanism of this molecule (H. Kanazawa et al. (1995) Arch. Biochem. Biophys. 317, 348-356). Leu-456 together with Gly-454 and Tyr-455 are the only residues in the carboxy-terminal 75 amino acids conserved among various species, suggesting that these three residues play important roles in catalysis by the ATPase. Here, we introduced site-directed mutations into these residues. Not only L456P but also G454L, Y455K, Y455L, and L456N mutations caused enhancement of the ATPase activity. Surprisingly, Y455V, L456H, and L456S caused assembly defects of F1 subunits on the membrane. Reconstitution of the alpha betagamma complex from the wild-type beta and gamma subunits with the mutant alpha subunit (L4gamma6P) exhibited enhanced ATPase activity. Addition of delta or epsilon fused to glutathione S-transferase which are functionally similar to the delta and epsilon subunits, respectively, to the reconstituted F1-ATPase did not cause significant enhancement of its activity. Decreased interaction between alpha and beta subunits with the L456P mutation was detected by the yeast two-hybrid system. According to the deduced three-dimensional structure of the bovine a subunit, Leu-456, Gly-454, and Tyr-455 are included in a small alpha helix. These results suggest that this alpha helix affects interaction of the alpha subunit with the beta subunit but not with delta or epsilon, which may be important for the catalytic mechanism and F1 assembly.