title: Leucine/isoleucine/valine-binding protein contracts upon binding of ligand.
abstract: Small-angle x-ray scattering and computer modeling have been used to study the effects of ligand binding to the leucine/isoleucine/valine-binding protein, an initial component of the high-affinity active transport system for branched-chain aliphatic amino acids in Escherichia coli. Measurements were made with no ligand present and with either L-leucine or L-valine present. Upon binding of either leucine or valine, there is a decrease in the radius of gyration, from 23.2 +/- 0.2 to 22.2 +/- 0.2 A, and in the maximum particle dimension, from 82 +/- 3 to 73 +/- 3 A. The x-ray structure of the unbound form has been determined and gives a radius of gyration and a maximum dimension consistent with the values found for the solution structure in this study (Sack, J. S., Saper, M. A., and Quiocho, F. A. (1989) J. Mol. Biol. 206, 171-191). The reduction in the radius of gyration and maximum dimension upon ligand binding can be accounted for by a substrate-induced cleft closure in a combined "hinge-twist" motion. Modeling of the substrate-bound state was done by comparison of this protein with another periplasmic binding protein (L-arabinose-binding protein), which possesses a similar two-lobe structure and for which the x-ray structure is known in its ligand-bound form.
authors.affiliation: Isotope and Nuclear Chemistry Division, Los Alamos National Laboratory, New Mexico 87545.
authors.forename: G A
authors.initials: GA
authors.lastname: Olah
authors.forename: S
authors.initials: S
authors.lastname: Trakhanov
authors.forename: J
authors.initials: J
authors.lastname: Trewhella
authors.forename: F A
authors.initials: FA
authors.lastname: Quiocho
mesh_terms: D001426:Bacterial Proteins; D002352:Carrier Proteins / Q000737:chemistry* / Q000378:metabolism; D029968:Escherichia coli Proteins; D007930:Leucine / Q000378:metabolism; D008024:Ligands; D008958:Models, Molecular; D014633:Valine / Q000378:metabolism; D014961:X-Ray Diffraction
chemical_list: D001426:Bacterial Proteins; D002352:Carrier Proteins; D029968:Escherichia coli Proteins; D008024:Ligands; C488923:LivJ protein, E coli; C028332:leucine-isoleucine-valine binding protein, bacteria; D007930:Leucine; D014633:Valine