Conformational dynamics monitored by His-179 and His-200 of isolated thermophilic F1-ATPase beta subunit which reside at the entrance of the 'conical tunnel' in holoenzyme.

When monitored by 1H NMR at various pH values, most of the C-2 proton signals from 12 His residues of the isolated beta subunit of thermophilic F1-ATPase (TF1) could be separately observed. Two of them were assigned to His-179 and His-200 which reside at the entrance of a 'conical tunnel' to reach catalytic site in the crystal structure of F1-ATPase. His-200 gave doublet, suggesting that this region is not a rigid alpha-helix in the isolated beta subunit. The binding of Mg.AMP-PNP changed the chemical shifts of His-179 and His-200 significantly. Although His-119 located at the opposite side of the conical tunnel was not affected by the nucleotide-binding, it contributed to the stability of beta subunit and the efficiency of the catalysis of the holoenzyme.