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Hiroyuki Noji

Publications and source records attributed to Hiroyuki Noji.

22 records · Page 2Linked to original sources
PubMed2002

Stepping rotation of F(1)-ATPase with one, two, or three altered catalytic sites that bind ATP only slowly.

F(1)-ATPase is an ATP hydrolysis-driven motor in which the gamma subunit rotates in the stator cylinder alpha(3)beta(3). To know the coordination of three catalytic beta subunits during catalysis, hybrid F(1)-ATPases, each containing one, two, or three "slow" mutant beta subunits that bind ATP very slowly, were prepared, and the rotations were observed with a single molecule level. Each hybrid made one, two, or three steps per 360 degrees revolution, respectively, at 5 microm ATP where the wild-type enzyme rotated continuously without step under the same observing conditions. The observed dwell times of the steps are explained by the slow binding rate of ATP. Except for the steps, properties of rotation, such as the torque forces exerted during rotary movement, were not significantly changed from those of the wild-type enzyme. Thus, it appears that the presence of the slow beta subunit(s) does not seriously affect other normal beta subunit(s) in the same F(1)-ATPase molecule and that the order of sequential catalytic events is faithfully maintained even when ATP binding to one or two of the catalytic sites is retarded.

Adenosine Triphosphate↗
PubMed2002

F1-ATPase changes its conformations upon phosphate release.

Motor proteins, myosin, and kinesin have gamma-phosphate sensors in the switch II loop that play key roles in conformational changes that support motility. Here we report that a rotary motor, F1-ATPase, also changes its conformations upon phosphate release. The tryptophan mutation was introduced into Arg-333 in the beta subunit of F1-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 F1 subcomplex alpha3beta(R333W)3gamma 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.

Adenosine Diphosphate↗