Leucine_Binding_Protein_Contracts_Upon_Binding_Ligand_J_biol_Chem_268(22)_16241-247_Olah_(1993)

Leucine_Binding_Protein_Contracts_Upon_Binding_Ligand_J_biol_Chem_268(22)_16241-247_Olah_(1993)

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THE JOURNAL OF BIOLOGICAL CHEMISTRY Vol. 268, No. 22, Issue of August 5, pp. 16241-16247, 1993 Printed in U.S.A. Leucine/IsoleucineNaline-binding Protein Contracts upon Binding of Ligand* (Received for publication, January 29, 1993, and in revised form, April 21, 1993) Glenn A. OlahS, Sergei TrakhanovO, Jill Trewhella, and Florante A. QuiochoO From the Isotope and Nuclear Chemistry Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 and the §Howard Hughes Medical Institute, Houston, Texas 77030 Small-angle x-ray scattering and computer modeling have been used to study the effects of ligand binding to the leucinelisoleucinelvaline-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 bind- ing of either leucine or valine, there is a decrease in the radius of gyration, from 23.2 * 0.2 to 22.2 2 0.2 A, and ip the maximum particle dimension, from 82 3 to 73 3 A. The x-ray structure of the unbound form has been de- termined and gives a radius of gyration and a maximum dimension consistent with the values found for the so- lution structure in this study (Sack, J. S., Saper, M. A, and Quiocho, F. (1989) J. Mol. Biol. 206, 171-191). The reduction in the radius of gyration and maximum di- mension 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 pro- tein), which possesses a similar two-lobe structure and for which the x-ray structure is known in its ligand- bound form. ~ leucine/isoleucine/valine-binding protein (LIVBP)l (M, = 36,700) is a member of a family of binding proteins found in the periplasm of Gram-negative bacteria. These are essen- tial components of high-affinity osmotic shock-sensitive uptake systems for a wide variety of low molecular weight compounds such as sugars, amino acids, peptides, oxyanions, and other nutrients (Sack et al., 1989a; Wilson and Smith, 1978; Furlong, 1987). The binding initiate translocation of these var- ious compounds by recognizing and specifically binding them. Actual across cytoplasmic membrane is achieved by other protein components embedded in the mem- brane that preferentially interact corresponding li- gatedbindingprotein.Thebindingproteinshave also been implicated in process of bacterial chemotaxis, in which they serve initial receptors (Adler, 1975; Macnab, 1987). W-7405-ENG-36, Department of EnergyIOffice of Health and Environ- * This work was supported in part by Department of Energy Contract mental Research Project KP-04-01-00-0 (to J. T.), National Insti- tutes of Health and Welch Foundation grants (to F. A. Q.). The costs of Publication of this article were defrayed in part by the payment of page in accordance with 18 U.S.C.
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Leucine_Binding_Protein_Contracts_Upon_Binding_Ligand_J_biol_Chem_268(22)_16241-247_Olah_(1993)

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