F1-ATPase changes its conformations upon phosphate release

Motor proteins, myosin, and kinesin have gamma-phosphate sensors in the switch H loop that play key roles in conformational changes that support motility. Here we report that a rotary motor, F-1-ATPase, also changes its conformations upon phosphate release. The tryptophan mutation was introduced into Arg-333 in the beta subunit of F-1-ATPase from thermophilic Bacillus PS3 as a probe of conformational changes. This residue interacts with the switch II loop (residues 308-315) of the beta subunit in a nucleotide-bound conformation. The addition of ATP to the mutant F-1 subcomplex alpha(3)beta(R333W)(3)gamma caused transient increase and subsequent decay of the Trp fluorescence. The increase was caused by conformational changes on ATP binding. The rate of decay agreed well with that of phosphate release monitored by phosphate-binding protein assays. This is the first evidence that the beta subunit changes its conformation upon phosphate release, which may share a common mechanism of exerting motility with other motor proteins.