Abstract
The technique of small angle x-ray scattering has been employed to study the effect of sugars on the radius of gyration of the L-arabinose-binding protein, a component of the high affinity L-arabinose transport system in Escherichia coli. We find that the binding of L-arabinose to the "sugar-free" protein in solution causes a 0.94 +/- 0.33 A decrease in the radius of gyration while D-glucose, a nonbinder, produces no such effect. The radius of gyration calculated from the complete atomic co-ordinates of the crystal structure of L-arabinose-binding protein (solved with bound L-arabinose) corresponds to the experimentally determined value for the radius of gyration in the presence of L-arabinose. This reduction in radius of gyration can be best accounted for in terms of a substrate-induced cleft closure in which one lobe rotates relative to the other lobe. A compute modeling study indicates that a rotation of 18 degrees about a hinge deep in the base of the sugar-binding cleft between the two domains would produce the observed decrease in the radius of gyration. The findings (Newcomer, M. E., Gilliland, G. L., and Quiocho, F. A. (1981) J. Biol. Chem. 256, 13213-13222) that the L-arabinose molecule embedded in the cleft between two domains is completely inaccessible to the solvent is consistent with a closing of the cleft between the two lobes.
Highlights
The technique of small angle x-ray scattering has globular domains [2, 3] and the sugar-binding site is located beenemployed to studythe effect of sugars on the deep in thceleft formed by the asymmetric contributiofnrosm radius of gyration of the L-arabinose-binding protein, the two domains [4, 5]
The radius of gyration calculated from the complete atomic co-ordinatesof thecrystal structure ofL-arabinose-binding protein from low angle x-ray scattering measurements and comparisons with model calculations that in solution the binding of sugar induces a decrease in the radius of gyration which is consistentwitha closing of thesubstrate-binding cleft
L -Arabinose-binding Protein a n d Binding Assay-L-Arabinosebinding proteinwas purified from E . coli B/r strainUP1041 according to the procedure of Parsons and Hogg [8]
Summary
Vol 256, No 24, issue of December 25, pp. 13218-13222, 1981 Printed tn U .S. A. The technique of small angle x-ray scattering has globular domains [2, 3] and the sugar-binding site is located beenemployed to studythe effect of sugars on the deep in thceleft formed by the asymmetric contributiofnrosm radius of gyration of the L-arabinose-binding protein, the two domains [4, 5]. These dominant structural features a component of thehigh affinity L-arabinose transport presage the picture that habsegun to emerge for the liganded system in Escherichia coli. A computer modeling study indicates that a rotation of18’ aboutahingedeepinthebaseofthe sugar-binding cleft between the two domains would
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