Evidence for major structural changes in the Manduca sexta midgut V₁ 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 V₁ ATPase from Manduca sexta were investigated by synchrotron radiation x-ray solution scattering. The radius of gyration of the oxidized and reduced complex differ noticeably, with dimensions of 6.20 ± 0.06 and 5.84 ± 0.06 nm, respectively, whereas the maximum dimensions remain constant at 22.0 ± 0.1 nm. Comparison of the low resolution shapes of both forms, determined ab initio, indicates that the main structural alteration occurs in the head 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 susceptibility to tryptic digestion and tryptophan fluorescence of the reduced V₁ molecule provide the first strong evidence for major structural changes in the V₁ ATPase because of redox modulation.