ESR and fluorescence studies on the adenine binding site of lectins using a spin-labeled analogue.

The techniques of electron spin resonance (ESR) and fluorescence spectroscopy have been used to study the interaction of a spin-labeled analogue of adenine, N6-(2,2,6,6-tetramethyl-1-oxypiperidin-4-yl)adenine (I), with several plant lectins. While most adenine derivatives enhanced lectin-induced fluorescence of 1,8-anilinonaphthalenesulfonic acid by binding to a separate, adenine-specific site [Roberts, D.D., & Goldstein, I.J. (1982) J. Biol. Chem. 257, 11274-11277], the spin label I caused a decrease in this fluorescence with certain lectins. ESR showed the ligand to interact strongly with lectins from lima bean (Phaseolus lunatus), Dolichos biflorus, and Phaseolus vulgaris (PHA); however, no binding was observed with Griffonia simplicifolia isolectins A4 and B4, soybean agglutinin, or Amphicarpaea bracteata lectins. The spin label was highly immobilized by each of these proteins (2T magnitude of = 68 G). Apparent affinities of the spin label for the lectins decreased in the order lima bean lectin greater than PHA erythroagglutinin greater than PHA leukoagglutinin greater than D. biflorus. Spin-labeled adenine appeared to bind specifically to the adenine binding site of D. biflorus and PHA leukoagglutinin, as demonstrated by total abolition of the ESR spectrum of bound spin label by adenine. PHA erythroagglutinin and lima bean lectin bound the analogue with apparent dissociation constants of 5 X 10(-5) and 3.2 X 10(-5) M, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Binding of N-acetylgalactosamine-specific lectins to spin-labeled galactosamine derivatives.

Legume seed lectins specific for N-acetyl-alpha-D-galactosaminyl end groups from Amphicarpaea bracteata, lima bean, Griffonia simplicifolia, Dolichos biflorus, and soybean were compared with respect to binding of several spin-labeled derivatives of D-galactosamine by electron spin resonance and precipitin inhibition analysis. Spin-label II [methyl 2-[[(2,2,5,5-tetramethyl-1-oxopyrrolidin-3-yl) carbonyl]amino]-2-deoxy-alpha-D-galactopyranoside], spin-label III [1-(methyl 2-deoxy-alpha-D-galactopyranosid-2-yl)-3-(2,2,6, 6-tetramethyl-1-oxypiperidin-4-yl)-2-thiourea], and spin-label IV [1-[4-[[(methyl 2-deoxy-alpha-D-galactopyranosid-2-yl)amino]carbonyl]phenyl]-3-(2, 2,6-tetramethyl-1-oxypiperidin-4-yl)-2-thiourea] contain 2-N-(oxypiperidinyl) or 2-N-(oxypyrrolidinyl) substituents varying in length and polarity of the linker arm between the glycoside and nitroxide ring. Spin-labels II and III were found to bind very weakly to all the lectins tested (Kd greater than or equal to 1.0 mM). Spin-label IV, containing a planar, nonpolar 2-N-phenyl group, was bound very strongly (Kd = 0.1-0.4 mM) and was moderately immobilized (2T parallel = 48-56 G) by all lectins except that from D. biflorus. Notably, the affinity of spin-label IV to lima bean lectin was 18-fold greater than that for methyl N-acetyl-alpha-galactosaminide. These results suggest that when the bulky oxypiperidinyl moiety lies in a position close to the sugar ring, it interferes with binding; in the cases where a phenyl group spacer exists, the aromatic ring in some cases actually enhances binding.(ABSTRACT TRUNCATED AT 250 WORDS)

Probing the topography of lectins with site-specific spin-labeled glycosides.

Three new spin-labeled glycosides, spin-label I [1-[4-(beta-D-galactopyranosyloxy)phenyl]-3-(2,2,6,6-tetramethyl-1 -oxypiperidin-4-yl)-2-thiourea], spin-label II (2,2,6,6-tetramethyl-1-oxypiperidin-4-yl alpha-D-galactopyranoside), and spin-label III [1-(methyl 2-deoxy-alpha-D-galactopyranosid-2-yl)-3-(2,2,6,6- tetramethyl-1-oxypiperidin-4-yl)-2-thiourea], were investigated as structural probes of Griffonia simplicifolia I isolectins (GS I) A4 and B4, respectively, by electron spin resonance (ESR) and inhibition of guaran isolectin precipitation. The p-aminophenyl beta-galactoside spin-label I was strongly immobilized by the B4 isolectin (Kd = 0.42 mM; 2T parallel = 54.0 +/- 0.3 G), while binding to the A4 isolectin was so weak (KI congruent to 2 mM) that binding was undetectable by ESR. The preference for the B4 isolectin was indicative of a more extended hydrophobic binding locus adjacent to the carbohydrate-specific binding site. The alpha-galactosyl spin-label II bound slightly more strongly to the A4 than to the B4 isolectin, as evidenced in both Kd values and particularly by differences in the degree of immobilization (2T parallel = 53.5 vs. 51.5 G, respectively). The 2-N-substituted methyl galactoside spin-label III was so poor an inhibitor of both isolectins (KI congruent to 1-2 mM) that ESR detection of the bound complex was not feasible. In all cases above, the spin-labels were displaced by specific monosaccharide haptens.

Synthesis of N-acetyllactosamine containing a D-[6-3H]galactopyranosyl group.

A simple and convenient method for the introduction of radiolabel onto C-6' of N-acetyllactosamine is described. 1-N-Benzyl-3-O-beta-D-galactopyranosyl-D-arabinosylamine (1) was synthesized from 3-O-beta-D-galactopyranosyl-D-arabinose as described by Lee and Lee. Compound 1 was oxidized with D-galactose oxidase, and the product reduced with KB3H4 to introduce the label at C-6'. After dilution with unlabeled material, the N-benzyl-3-O-beta-D-[6-3H]galactopyranosyl-D-arabinosylamine was converted into 2-(benzylamino)-2-deoxy-4-O-D-[6-3H]galactopyranosyl-D-glucononitrile , which was subjected to simultaneous hydrogenolysis of the benzylamino and nitrile groups. N-Acetylation of the amino group as described by Alais and Veyrières afforded the crystalline title compound in 63% yield.

Synthesis of alpha- and beta-glycosides containing spin labels, as probes for studies of carbohydrate-protein interaction.

Nitroxide spin-labeled alpha-D-glycopyranosides were synthesized in good yield and in a highly stereoselective manner by reaction of per-O-benzyl-alpha-D-glycopyranosyl bromides with 2,2,6,6-tetramethyl-4-piperidinol under the bromide ion-catalyzed conditions devised by Lemieux et al. After hydrogenolysis, the deblocked intermediates were oxidized to give the desired, spin-labeled alpha-D-glycopyranosides. Nitroxide spin-labeled beta-D-glycopyranosides, as well as a beta-maltoside, were synthesized by standard methods. The synthesis is also described of 2-amino-2-deoxy-D-glucose and -D-galactose derivatives having a spin label at C-2, and of the spin-labeled compound 1-[4-(beta-D-galactopyranosyloxy)phenyl]-3-(2,2,6,6-tetramethylpiperidin-1-oxyl -4-yl)-2-thiourea.