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Small-angle X-ray scattering studies of Mg.AT(D)P-induced hexamer to dimer dissociation in the reconstituted alpha 3 beta 3 complex of ATP synthase from thermophilic bacterium PS3

1991; Elsevier BV; Volume: 266; Issue: 18 Linguagem: Inglês

10.1016/s0021-9258(18)98980-5

1083-351X

M. Harada, Yuji Ito, Masa H. Sato, Osamu Aono, Shigeo Ohta, Y Kagawa,

Protein Structure and Dynamics

The a3D3 complex of ATP synthase obtained from a thermophilic bacterium PS3 was isolated and found to show the ATPase activity (Kagawa, Y., Ohta, S., and Otawara-Hamamoto, Y. (1989) FEBS Lett.249, 67-69).The structure and the nucleotide binding effects of the a3D3 complex were investigated by means of small-angle x-ray scattering and high performance liquid chromatography.The scattering profile from the a3D3 complex was explained with a model in which the complex is made of an ellipsoid qf revolution with the axes of 121.8, 121.8, and 72.0A having an elliptic@ hollow cavity with the axes of 35.4,35.4,and 72.0 A. By the addition of Mg*AT(D)P, significant changes in the scattering profile were observed, in which*the radius of gyration decreased from 44 to 35 A. This change was found by gel filtration to be caused by the dissociation reaction from the a3D3 hexamer to the a@ dimer.The dissociation of the a3D3 complex was not induced by unhydrolyzable ATP analogue, nor by Pi, Mg2+, and Pi + Mg2+.The structure of the dimer was well explained by the triaxial ellipsoidal model with the axes of 105.2, 39.4, and 108.2 A. The dissociation into the dimer is considered to be related to the ATPase activity because the AT(D)P-induced dissociation is observed only in the presence of Mg2+ ions.Adenosine triphosphate synthase (ATPase) is an enzyme that uses transmembrane proton motive force to play a role in ATP synthesis and hydrolysis (1).It is composed of a proton channel portion, Fo, and a catalytic portion, F1 (2, 3).The enzyme can be purified from various sources, but ATPase from the thermophilic bacterium PS3 (TF,F,)' is unique because its catalytic portion (TF,) shows considerable stability against both heat and dissociating agents.This stability is useful to perform various physicochemical studies, and it is also valuable for investigating the effects of nucleotide binding on the F1 complex because an active F, complex can be reconstituted without adding ATP and Mg2+ ions (4).The TF, portion is composed of five subunits with a stoichiometry