Purification of Cajanus cajan root lectin and its interaction with rhizobial lipopolysaccharide as studied by different spectroscopic techniques

A lectin present in roots of Cajanus cajan seedlings was isolated and purif ied by affinity chromatography. Sugar specificity assayed by hemagglutinati on-inhibition activity indicated that lectin belongs to glucose/ mannose-sp ecific group. The root lectin was found to be mannose-specific from the sec ond day onwards as it was reconfirmed by specific elution of different days ' sample from mannose agarose matrix. The maximum interaction of lectin wit h goat IgM was obtained in 10-day-old sample, indicating the highest crude lectin content. Lectin (total amount of eluted protein) from different days soil sample showed a maximum amount in 10-day-old sample. For further stud ies, the lectin has been isolated from the roots of 10-day C. cajan seedlin gs and purified on mannose-CL agarose column by affinity chromatography. Le ctin was found to be a dimer of 18.5-kDa subunit as revealed by SDS-PAGE. T ryptophan quenching fluorescence was studied for C. cajan root lectin. Seco ndary structure C. cajan root lectin as studied by circular dichroism. was found to be a typical beta -pleated sheet structure. The interaction of pur ified root lectin with C. cajan-specific rhizobial lipopolysaccharide and i ts inhibition by specific and nonspecific sugars was demonstrated by fluore scence and circular dichroism. Results discussed in this paper were studied for the first time by different spectroscopic methods, suggesting that C. cajan root lectin-lipopolysaccharide interaction is specific. (C) 2001 Else vier Science.