X-ray scattering studies of Methylophilus methylotrophus (sp W(3)A(1)) electron-transferring flavoprotein - Evidence for multiple conformational states and an induced fit mechanism for assembly with trimethylamine dehydrogenase

Small angle x-ray solution scattering has been used to generate a low resol ution, model-independent molecular envelope structure for electron-transfer ring flavoprotein (ETF) from Methylophilus methylotrophus (sp. W(3)A(1)). A nalysis of both the oxidized and 1-electron-reduced (anionic flavin semiqui none) forms of the protein revealed that the solution structures of the pro tein are similar in both oxidation states. Comparison of the molecular enve lope of ETF from the x-ray scattering data with previously determined struc tural models of the protein suggests that ETF samples a range of conformati ons in solution. These conformations correspond to a rotation of domain II with respect to domains I and III about two flexible "hinge" sequences that are unique to M. methylotrophus ETF, The x-ray scattering data are consist ent with previous models concerning the interaction of M. methylotrophus ET F with its physiological redox partner, trimethylamine dehydrogenase. Our d ata reveal that an "induced fit" mechanism accounts for the assembly of the trimethylamine dehydrogenase-ETF electron transfer complex, consistent wit h spectroscopic and modeling studies of the assembly process.