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Thermodynamic and kinetic analysis of carbohydrate binding to the basic lectin from winged bean (Psophocarpus tetragonolobus)

Khan, MI and Sastry, MV and Surolia, Avadhesha (1986) Thermodynamic and kinetic analysis of carbohydrate binding to the basic lectin from winged bean (Psophocarpus tetragonolobus). In: Journal of Biological Chemistry, 261 (7). pp. 3013-3019.

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A basic lectin (pI approximately 10.0) was purified to homogeneity from the seeds of winged bean (Psophocarpus tetragonolobus) by affinity chromatography on Sepharose 6-aminocaproyl-D-galactosamine. The lectin agglutinated trypsinized rabbit erythrocytes and had a relative molecular mass of 58,000 consisting of two subunits of Mr 29,000. The lectin binds to N-dansylgalactosamine, leading to a 15-fold increase in dansyl fluorescence with a concomitant 25-nm blue shift in the emission maximum. The lectin has two binding sites/dimer for this sugar and an association constant of 4.17 X 10(5) M-1 at 25 degrees C. The strong binding to N-dansylgalactosamine is due to a relatively positive entropic contribution as revealed by the thermodynamic parameters: delta H = -33.62 kJ mol-1 and delta S0 = -5.24 J mol-1 K-1. Binding of this sugar to the lectin shows that it can accommodate a large hydrophobic substituent on the C-2 carbon of D-galactose. Studies with other sugars indicate that a hydrophobic substituent in alpha- conformation at the anomeric position increases the affinity of binding. The C-4 and C-6 hydroxyl groups are critical for sugar binding to this lectin. Lectin difference absorption spectra in the presence of N-acetylgalactosamine indicate perturbation of tryptophan residues on sugar binding. The results of stopped flow kinetics with N- dansylgalactosamine and the lectin are consistent with a simple one- step mechanism for which k+1 = 1.33 X 10(4) M-1 s-1 and k-1 = 3.2 X 10(- 2) s-1 at 25 degrees C. This k-1 is slower than any reported for a lectin-monosaccharide complex so far. The activation parameters indicate an enthalpically controlled association process.

Item Type: Journal Article
Publication: Journal of Biological Chemistry
Publisher: The American Society for Biochemistry and Molecular Biology
Additional Information: Copyright of this article belongs to The American Society for Biochemistry and Molecular Biology.
Department/Centre: Division of Biological Sciences > Molecular Biophysics Unit
Date Deposited: 27 Jan 2010 09:54
Last Modified: 19 Sep 2010 05:42
URI: http://eprints.iisc.ac.in/id/eprint/22660

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