The Role of Histidine in D-Galactose Binding lectin of Legumes

Pradeep, Parihar (2010) The Role of Histidine in D-Galactose Binding lectin of Legumes. [Student Project Report]

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Abstract

This Dissertation / Report is the outcome of investigation carried out by the creator(s) / author(s) at the department/division of Central Food Technological Research Institute (CFTRI), Mysore mentioned below in this page.

Item Type:	Student Project Report
Additional Information:	Field bean (Dolichos lablab) seed lectin is a heterotetramer of molecular mass 120,000 Da, consisting of 2a (30,087 Da) and 2β (29,808 Da) subunits. It was purified to homogeneity using D-galactose affinity chromatography. During purification it was observed that the protein bound to the D-galactose matrix only in the presence of 1.5M (NH4)2SO4 and eluted with buffer minus (NH4)2SO4. This was unusual as commonly in affinity binding the bound protein is eluted with free ligand in the buffer. Therefore to understand this unusual behavior of this lectin the multiple alignment of this lectin with other Gal/GalNAc binding lectin was done. Most galactose binding legume lectins have aromatic residues (F, Y or W) in the sugar binding site. These lectins bind to the galactose sepharose column in the absence of (NH4)2SO4. The aromatic residues stack perfectly against the C-3, C-4, C-5 and C-6 apolar patch of the B face galactose. The field bean lectin is not having the aromatic residue, at the sugar binding site instead it is replaced by a His residue which could account for the unusual binding property of this lectin. Histidine can also stack against galactose. However in DLL histidine is in a polar environment and therefore will be charged. The presence of (NH4)2SO4 reduce the dielectric constant around histidine favoring the stacking against galactose, which explain the unusual behavior. Further to compare this unusual sugar binding property of this lectin with other lectins with similar sugar binding site residues, two other lectins P. glalbellus lectin and P. lunatus lectin which are having similar sugar binding site were selected for the galactose affinity binding study. They share 70% sequence homology and are having hisidine residue in place of aromatic residue as in D. lablab lectin. These lectins also showed similar binding property as that of field bean lectin. This clearly reveals the role of His in unusual sugar binding property of lectins and supports our assumption of involvement of His in sugar stacking in the presence of apolar environment.
Uncontrolled Keywords:	Field bean; Dolichos lablab; Lectins; D-galactose affinity chromatography;
Subjects:	500 Natural Sciences and Mathematics > 04 Chemistry and Allied Sciences > 13 Carbohydrate Chemistry 600 Technology > 08 Food technology > 22 Legumes-Pulses
Divisions:	Protein Chemistry and Technology
Depositing User:	Food Sci. & Technol. Information Services
Date Deposited:	21 Jul 2010 05:54
Last Modified:	28 Dec 2011 10:16
URI:	http://ir.cftri.res.in/id/eprint/9585

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