Document Detail

Structural basis for the energetics of jacalin-sugar interactions: promiscuity versus specificity.
MedLine Citation:
PMID:  15733927     Owner:  NLM     Status:  MEDLINE    
Jacalin, a tetrameric lectin, is one of the two lectins present in jackfruit (Artocarpus integrifolia) seeds. Its crystal structure revealed, for the first time, the occurrence of the beta-prism I fold in lectins. The structure led to the elucidation of the crucial role of a new N terminus generated by post-translational proteolysis for the lectin's specificity for galactose. Subsequent X-ray studies on other carbohydrate complexes showed that the extended binding site of jacalin consisted of, in addition to the primary binding site, a hydrophobic secondary site A composed of aromatic residues and a secondary site B involved mainly in water-bridges. A recent investigation involving surface plasmon resonance and the X-ray analysis of a methyl-alpha-mannose complex, had led to a suggestion of promiscuity in the lectin's sugar specificity. To explore this suggestion further, detailed isothermal titration calorimetric studies on the interaction of galactose (Gal), mannose (Man), glucose (Glc), Me-alpha-Gal, Me-alpha-Man, Me-alpha-Glc and other mono- and oligosaccharides of biological relevance and crystallographic studies on the jacalin-Me-alpha-Glc complex and a new form of the jacalin-Me-alpha-Man complex, have been carried out. The binding affinity of Me-alpha-Man is 20 times weaker than that of Me-alpha-Gal. The corresponding number is 27, when the binding affinities of Gal and Me-alpha-Gal, and those of Man and Me-alpha-Man are compared. Glucose (Glc) shows no measurable binding, while the binding affinity of Me-alpha-Glc is slightly less than that of Me-alpha-Man. The available crystal structures of jacalin-sugar complexes provide a convincing explanation for the energetics of binding in terms of interactions at the primary binding site and secondary site A. The other sugars used in calorimetric studies show no detectable binding to jacalin. These results and other available evidence suggest that jacalin is specific to O-glycans and its affinity to N-glycans is extremely weak or non-existent and therefore of limited value in processes involving biological recognition.
A Arockia Jeyaprakash; G Jayashree; S K Mahanta; C P Swaminathan; K Sekar; A Surolia; M Vijayan
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't     Date:  2005-01-18
Journal Detail:
Title:  Journal of molecular biology     Volume:  347     ISSN:  0022-2836     ISO Abbreviation:  J. Mol. Biol.     Publication Date:  2005 Mar 
Date Detail:
Created Date:  2005-02-28     Completed Date:  2005-04-07     Revised Date:  2006-11-15    
Medline Journal Info:
Nlm Unique ID:  2985088R     Medline TA:  J Mol Biol     Country:  England    
Other Details:
Languages:  eng     Pagination:  181-8     Citation Subset:  IM    
Molecular Biophysics Unit, Indian Institute of Science, Bangalore 560 012, India.
Data Bank Information
Bank Name/Acc. No.:
PDB/1WS4;  1WS5
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MeSH Terms
Adjuvants, Immunologic* / chemistry,  metabolism
Artocarpus / chemistry
Carbohydrate Metabolism
Carbohydrates* / chemistry
Crystallography, X-Ray
Models, Molecular
Molecular Sequence Data
Plant Lectins* / chemistry,  metabolism
Protein Conformation*
Protein Subunits / chemistry,  metabolism
Reg. No./Substance:
0/Adjuvants, Immunologic; 0/Carbohydrates; 0/Plant Lectins; 0/Protein Subunits; 0/jacalin

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