The enzymatic lectin of field bean (Dolichos lablab): Salt assisted lectin–sugar interaction.

Devavratha, H. Rao and Yashavanth, L. Vishweshwaraiah and Lalitha, R. Gowda (2012) The enzymatic lectin of field bean (Dolichos lablab): Salt assisted lectin–sugar interaction. Phytochemistry, 83. pp. 7-14.

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Abstract

Field bean seed contains a Gal/GalNAc lectin (DLL-II) that exhibits associated polyphenol oxidase (PPO) activity and does not bind to its sugar specific affinity matrix. The molecular basis for this lack of binding is not known. The DLL-II gene was therefore cloned and its sequence analyzed. A conserved aromatic residue in the sugar binding site required for a stacking interaction with the apolar backbone of Gal is replaced by His in DLL-II, which explains the lack of binding. However, specific sugar binding is achieved by including (NH4)2SO4 in the buffer. Interestingly two other salts of the Hofmeister series, K2HPO4 and Na2SO4 also assist binding to immobilized galactose. In the presence of (NH4)2SO4 the surface hydrophobicity of DLL-II and dissociation constant for 8-anilino 1-naphthalene sulfonic acid were enhanced three fold. This increased surface hydrophobicity in the presence of salt is probably the cause for assisted sugar binding in legume lectins that lack aromatic stacking interactions. Accordingly, two other lectins which lack the conserved aromatic residue show similar salt assisted binding. The salt concentrations required for Gal/GalNAc binding are not physiologically relevant in vivo, suggesting that the role of DLL-II per se in the seed is primarily that of a PPO purportedly for plant defense.

Item Type:	Article
Uncontrolled Keywords:	ANS binding, Fluorescence, Lectin-ELISA Protein sequence, Surface hydrophobicity
Subjects:	500 Natural Sciences and Mathematics > 04 Chemistry and Allied Sciences > 29 Protein Chemistry 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:	06 Nov 2012 11:01
Last Modified:	28 Aug 2018 06:36
URI:	http://ir.cftri.res.in/id/eprint/10990

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