BETA-GAMMA SUBUNIT INTERACTION IS REQUIRED FOR CATALYSIS BY H-ATPASE (ATP SYNTHASE) - BETA-SUBUNIT AMINO-ACID REPLACEMENTS SUPPRESS A GAMMA-SUBUNIT MUTATION HAVING A LONG UNRELATED CARBOXYL-TERMINUS()

The mechanisms of energy coupling and catalytic cooperativity are not yet understood for H+-ATPase (ATP synthase). An Escherichia coli gamma subunit frameshift mutant (downstream of Thr-gamma 277) could not gro w by oxidative phosphorylation because both mechanisms were defective (Iwamoto, A., Miki, J., Maeda, M., and Futai, M., (1990) J. Biol, Chem , 265, 5043-5048). The defect(s) of the gamma frameshift was obvious, because the mutant subunit had a carboxyl terminus comprising 16 resid ues different from those in the wild type. However, in this study, we surprisingly found that an Arg-beta 52 --> Cys or Gly-beta 150 --> Asp replacement could suppress the deleterious effects of the gamma frame shift. The membranes of the two mutants (gamma frameshift/Cys-beta 52 with or without a third mutation, Val-beta 77 --> Ala) exhibited incre ased oxidative phosphorylation, together with 70-100% of the wild type ATPase activity. Similarly, the gamma frameshift/Asp-beta 150 mutant could grow by oxidative phosphorylation, although this mutant had low membrane ATPase activity. These results suggest that the beta subunit mutation suppressed the defects of catalytic cooperativity and/or ener gy coupling in the gamma mutant, consistent with the notion that confo rmational transmission between the two subunits is pertinent for this enzyme.