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F A Quiocho

Publications and source records attributed to F A Quiocho.

At least 127 records · Page 7Linked to original sources
PubMed1981

L-Arabinose-binding protein-sugar complex at 2.4 A resolution. Stereochemistry and evidence for a structural change.

The L-arabinose molecule (in the C1 pyranose chair conformation) has been fitted to the electron density corresponding to the bound sugar in the 2.4 A resolution Fourier map of the L-arabinose-binding protein. The sugar molecule is buried in the cleft between the two lobes of the bilobate protein. All sugar hydroxyls are hydrogen-bonded to side chain residues: beta-OH(1) to Lys-10 and Asp-90, OH(2) to Lys-10, OH(3) to Asn-205 and Glu-14 (possibly via a water molecule), and OH(4) to Asn-232. Lys-10, Glu-14, and Asp-90 are associated with one domain while Asn-205 and Asn-232 are lodged in the other. Protein structural change accompanying binding is indicated by the inaccessibility of the bound L-arabinose to the aqueous environment.

Arabinose↗
PubMed1981

The radius of gyration of L-arabinose-binding protein decreases upon binding of ligand.

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.

Arabinose↗
PubMed1980

The structure of D-galactose-binding protein at 4.1 A resolution looks like L-arabinose-binding protein.

The structure of D-galactose-binding protein, a receptor for both high affinity active transport system and chemotaxis in Escherichia coli, has been solved at 4.1 A resolution using three heavy atom derivatives. The molecule is ellipsoidal with dimensions of about 65 X 35 X 35 A. The overall shape of the molecule and the indication that the molecule consists of two domains separated by a cleft are reminiscent of the structure of L-arabinose-binding protein.

Arabinose↗
PubMed1980

Concerning the structure of 7 alpha,15 beta-dichloro-5 alpha-cholest-8(14)-en-3 beta-ol, a novel inhibitor of cholesterol biosynthesis.

Treatment of 3 beta-p-bromobenzoyloxy-14 alpha,15 alpha-epoxy-5 alpha-cholest-7-ene with gaseous HCl in chloroform at -25 degrees C gave 3 beta-p-bromobenzoyloxy-7 alpha,15 beta-dichloro-5 alpha-cholest-8(14)-ene in 93% yield. The structure of the latter compound was unequivocally established by the results of X-ray crystallographic analysis.

Cholesterol↗
PubMed1979

Location of the sugar-binding site of L-arabinose-binding protein. Sugar derivative syntheses, sugar binding specificity, and difference Fourier analyses.

The sugar-binding site of the L-arabinose-binding protein, an essential component of the high affinity L-arabinose uptake system in Escherchia coli, is located deep in a cleft formed by the asymmetric contributions from both of the two similar domains. The site was unambiguously identified with the electron-rich substrate analog 6-bromo-6-deoxy-D-galactose in a difference Fourier analysis. The observation that the original native structure might have been solved with bound L-arabinose necessitated the synthesis of a heavy atom analog, its structure consistent with the known sugar-binding specificity of the protein. Difference Fourier maps (3.5 A) of crystals soaked in 46 mM analog showed a peak 3.5 times background, which is attributed to the -CH2Br moiety of the analog. Superposition of a difference map onto a 2.8-A native electron density map indicated that the difference peak is 6 to 7 A from the reactive single cysteine (Cys-64) and partially coincident with an "extraneous" density found in the native map. This "extraneous" peak was previously attributed to a bound L-arabinose molecule, and its presence accounts for the early failures of difference Fourier analyses of crystals soaked in or co-crystallized with L-arabinose to locate the sugar-binding site.

Arabinose↗
PubMed1977

The interaction of tetraiodofluorescein with creatine kinase.

The dye 2',4',5',7'-tetraiodofluorescein is a potent inhibitor of creatine kinase (ATP:creatine N-phosphotransferase, EC 2.7.3.2) with an apparent competitive inhibition constant with respect to MgATP2- of 2.6 - 10(-5) M. The association of the dye with the enzyme elicited a red shift in the dye's spectrum, indicative of a binding site less polar than water. The dye binds to the enzyme with an equilibrium constant of dissociation of 1.7 - 10(-5) M. MgATP or MgADP competes for the dye-binding site. Creatine binds to creatine kinase-tetraiodofluorescein complex to form a ternary complex and further causes a blue-shift in the spectrum of the bound dye. The binding of the dye to fully active creatine kinase causes conformational change that was monitored by enzyme-bound 2-mercuri-4-nitrophenol, a conformation-dependent "reporter group".

Binding Sites↗
PubMed1977

Synthesis an crystal structure of 3beta-p-bromobenzoyloxy-14alpha, 15alpha-epoxy-5alpha-cholest-7-ene.

The chemical synthesis of 3beta-bromobenzoyloxy-14alpha, 15alpha-epoxy-5alpha-cholest-7-ene is described. Single crystal structral analysis was employed to unambiguously determine the location and absolute configuration of the epoxide moiety in the 3beta-p-bromobenzoyloxy-14alpha, 15alpha-epoxy-5alpha-cholest-7-ene. The space group of the crystal was P1, with unit cell parameters: a=10.873 A, b=13.841 A, c=11.037 A, alpha=75.19 degrees, beta=78.79 degrees, gamma=101.57 degrees, and two molecules per unit cell. Intitial phases were derived from the two bromine atoms. Least squares refinements on all non-hydrogen atoms were carried out to a final unweighted R value of 0.10 and weighted R value of 0.04. The epoxide ring was located at the 14, 15 position and was found to extend to the alpha side of the molecule. Molecular measurements for asymmetry parameters of the sterol nuceus indicate that ring A has a symmetrical chair conformation and ring B has a half chair conformation due to the double bond at C(7). Ring C has a fairly distorted chair conformation due to the trigonal C(8) on one sie and the almost planar 5-membered ring on the other. Ring D has the 17alpha-envelope conformation.

Cholestenes↗