Evidence for major structural changes in the Manduca sexta midgut V-1 ATPase due to redox modulation - A small angle X-ray scattering study

The shape and overall dimensions of the oxidized and reduced form of the V- 1 ATPase from Manduca sexta were investigated by synchrotron radiation x-ra y solution scattering. The radius of gyration of the oxidized and reduced c omplex differ noticeably, with dimensions of 6.20 +/- 0.06 and 5.84 +/- 0.0 6 nm, respectively, whereas the maximum dimensions remain constant at 22.0 +/- 0.1 nm. Comparison of the low resolution shapes of both forms, determin ed ab initio, indicates that the main structural alteration occurs in the h ead piece, where the major subunits A and B are located, and at the bottom of the stalk. In conjunction with the solution scattering data, decreased s usceptibility to tryptic digestion and tryptophan fluorescence of the reduc ed V-1 molecule pro vide the first strong evidence for major structural cha nges in the V-1 ATPase because of redox modulation.