The D-galactose specific lectin of field bean (Dolichos lablab) seed binds sugars with extreme negative cooperativity and half-of-the-sites binding.

Devavratha, H. Rao and Gowda, L. R. (2012) The D-galactose specific lectin of field bean (Dolichos lablab) seed binds sugars with extreme negative cooperativity and half-of-the-sites binding. Archives of Biochemistry and Biophysics, 524. pp. 85-92.

PDF Archives of Biochemistry and Biophysics, Volume 524, Issue 2, 15 August 2012, Pages 85-92.pdf - Published Version Restricted to Registered users only Download (920kB) | Request a copy

Abstract

The field bean (Dolichos lablab) lectin designated as PPO-haemagglutinin (DLL-II) is bifunctional, exhibiting both polyphenol oxidase and haemagglutinating activity. The lectin is unusual in that it binds galactose (Gal), lactose (Lac) and N-acetylgalactosamine (GalNAc) only in the presence of (NH4)2SO4 and exhibits negative cooperativity and half-of-the-sites binding. Circular dichroism, isothermal titration calorimetry and fluorescence quenching were used to assess the sugar binding in the presence of (NH4)2SO4. Comparison of the near-UV CD spectra with and without bound sugar revealed ligand induced conformational changes. The intrinsic fluorescence quenching data indicate that DLL-II exhibits weak binding to Gal in the presence of (NH4)2SO4 with a stoichiometry of one bound ligand per dimer. ITC data fitted using a two sets of sites binding model presented a similar picture. The Ka’s for Gal, Lac and GalNAc in the presence of (NH4)2SO4 were 0.16 ± 0.002, 0.21 ± 0.004 and 8.45 ± 0.78 (�10�3) M�1 respectively. The Hill plot for the binding of these sugars to DLL-II was curvilinear with a tangent slope <1.0 indicating negative cooperativity. DLL-II thus exhibits half-of-the-site binding, an extreme form of negative cooperativity in which the second ligand does not bind at all. This is the first report of a legume lectin, exhibiting half-of-the-sites binding.

Item Type:	Article
Uncontrolled Keywords:	Hill plot ,Ligand binding, N-Acetylgalactosamine Isothermal titration calorimetry, Curvilinear Scatchard plot Stoichiometry
Subjects:	600 Technology > 08 Food technology > 16 Nutritive value > 03 Proteins 600 Technology > 08 Food technology > 22 Legumes-Pulses
Divisions:	Food Safety Analytical Quality Control Lab Protein Chemistry and Technology
Depositing User:	Food Sci. & Technol. Information Services
Date Deposited:	27 Aug 2012 04:30
Last Modified:	25 Sep 2018 06:58
URI:	http://ir.cftri.res.in/id/eprint/10955

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