J. Biol. Chem., Vol. 266, Issue 18, 11455-11460, Jun, 1991
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
M Harada, Y Ito, M Sato, O Aono, S Ohta and Y Kagawa
Institute for Solid State Physics, University of Tokyo, Japan.
The alpha 3 beta 3 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 alpha 3 beta 3 complex
were investigated by means of small-angle x-ray scattering and high
performance liquid chromatography. The scattering profile from the alpha 3
beta 3 complex was explained with a model in which the complex is made of
an ellipsoid of revolution with the axes of 121.8, 121.8, and 72.0 A having
an elliptical 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 alpha 3 beta 3 hexamer to the alpha beta dimer. The
dissociation of the alpha 3 beta 3 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.
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