A Mesorhizobium lipopolysaccharide (LPS) specific lectin (CRL) from the roots of nodulating host plant, Cicer arietinum

A 30 kDa rabbit erythrocyte agglutinating glycoprotein isolated and characterized from the roots of Cicer arietinum and designated as cicer root lectin (CRL). Hemagglutination activity of CRL is strongly inhibited by cell surface LPS of nodulating cicer specific Rhizobium. CRL agglutinates mesorhizobial cells and not Escherichia coli or yeast cells. It binds to immobilized LPS of cicer specific Rhizobium only. The primary structure of CRL as predicted by peptide mass fingerprinting by MALDI-TOF (matrix-assisted laser desorption/ionization-time of flight) indicated ∼54% amino acid sequence homology with C. arietinum seedling lectin (Accession no. gi/3204123) and ∼26% with C. arietinum (Accession no. gi/110611256), and Pisum sativum (Accession nos. gi/230612, gi/6729956, gi/126148) lectins. These suggested CRL to be a member of vegetative tissue lectin. Circular dichroism analysis indicated that the secondary structure of CRL consists of 48% β-sheets, 26% random coils, and 11% α-helix. CRL has six isoforms of closely associated molecular mass with differential acidic pI of 5.30, 5.20, 5.15, 5.05, 5.00, 4.80. Identity of these isoforms was confirmed from their binding with cicer specific Rhizobium LPS. All the isoforms of CRL are differentially glycosylated as identified by deglycosylation and monosaccharide analysis using high-performance anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD). All these results suggest that unlike other plant lectins CRL is a LPS-binding lectin.