Thermodynamics of the binding of galactopyranoside derivatives to the basic lectin from winged bean (Psophocarpus tetrogonolobus)

Schwarz, FP and Puri, K and Surolia, A (1991) Thermodynamics of the binding of galactopyranoside derivatives to the basic lectin from winged bean (Psophocarpus tetrogonolobus). In: Journal of Biological Chemistry, 266 (36). pp. 24344-24350.

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Abstract

The thermodynamics of the binding of D-galactopyranoside (Gal), 2-acetamido-2-deoxygalactopyranoside (GalNAc), methyl-alpha-D-galactopyranoside, and methyl-beta-D-galactopyranoside to the basic agglutinin from winged bean (WBAI) in 0.02 M sodium phosphate and 0.15 M sodium chloride buffer have been investigated from 298.15 to 333.15 K by titration calorimetry and at the denaturation temperature by differential scanning calorimetry (DSC). WBAI is a dimer with two binding sites. The titration calorimetry yielded single-site binding constants ranging from 0.56 +/- 0.14 x 10(3) M-1 for Gal at 323.15 K to 7.2 +/- 0.5 x 10(3) M-1 for GalNAc at 298.15 K and binding enthalpies ranging from -28.0 +/- 2.0 kJ mol-1 for GalNAc at 298.15 K to -14.3 +/- 0.1 kJ mol-1 for methyl-beta-D-galactopyranoside at 322.65 K. The denaturation transition consisted of two overlapping peaks over the pH range 5.6-7.4. Fits of the differential scanning calorimetry data to a two-state transition model showed that the low temperature transition (341.6 +/- 0.4 K at pH 7.4) consisted of two domains unfolding as a single entity while the higher temperature transition (347.8 +/- 0.6 K at pH 7.4) is of the remaining WBAI dimer unfolding into two monomers. Both transitions shift to higher temperatures and higher calorimetric enthalpies with increase in added ligand concentration at pH 7.4. Analysis of the temperature increase as a function of added ligand concentration suggests that one ligand binds to the two domains unfolding at 341.6 +/- 0.6 K and one ligand binds to the domain unfolding at 347.8 +/- 0.6 K.

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:	21 May 2010 06:07
Last Modified:	19 Sep 2010 06:01
URI:	http://eprints.iisc.ac.in/id/eprint/27524

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