Small-angle X-ray scattering studies of tryptophan synthase from Escherichia coli and its alpha and beta 2 subunits.
The alpha and beta 2 subunits of tryptophan synthase were investigated by small-angle X-ray scattering. The molecular parameters are: radius of gyration, alpha: 1.95 nm, beta 2: 3.01 nm; maximum particle diameter, alpha: 5.8 nm, beta 2: 10.5 nm; and hydrated volume, alpha: 60 nm3, beta 2 160 nm3. The shape of the alpha subunit can best be described by a circular cylinder, slightly tapered at one end. An elongated elliptical cylinder with its cross section larger in the middle than at the ends was found to be a model equivalent in scattering to the beta 2 subunits. The alpha 2 beta 2 enzyme complex was found to have a radius of gyration of 4.01 nm, a maximum length of 13.5 nm, and a hydrated volume of 270 nm3. No satisfactory fit of the scattering data was obtainable by mere apposition of the models of the alpha and beta 2 subunits. Two cylinders overlapping laterally fit the experimental data considerably better, suggesting changes in the conformation of the subunits on forming the alpha 2 beta 2 complex.
D001426:Bacterial Proteins / Q000302:isolation & purification; D004926:Escherichia coli / Q000201:enzymology*; D008958:Models, Molecular; D010446:Peptide Fragments / Q000302:isolation & purification; D012542:Scattering, Radiation; D014367:Tryptophan Synthase / Q000302:isolation & purification*; D014965:X-Rays
D001426:Bacterial Proteins; D010446:Peptide Fragments; D014367:Tryptophan Synthase