On the specificity of carbohydrate-lectin recognition: the interaction of a lectin from Ricinus communis beans with simple saccharides and concanavalin A

Podder, Sunil K. ; Surolia, Avadhesha ; Bachhawat, Bimal K. (1974) On the specificity of carbohydrate-lectin recognition: the interaction of a lectin from Ricinus communis beans with simple saccharides and concanavalin A European Journal of Biochemistry, 44 (1). pp. 151-160. ISSN 0014-2956

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Official URL: http://onlinelibrary.wiley.com/doi/10.1111/j.1432-...

Related URL: http://dx.doi.org/10.1111/j.1432-1033.1974.tb03468.x

Abstract

A galactose-specific protein (RC1) isolated from Ricinus communis beans was found to give a precipitin reaction with concanavalin A. Its carbohydrate content amounted to 8-9% of the total protein and was found to be rich in mannose. The interaction of RC1 with galactose and lactose was measured in 0.05 M phosphate buffer containing 0.2 M NaCl (pH 6.8) by the method of conventional equilibrium dialysis. From the analysis of the binding data according to Scatchard method the association constant (Ka) at 5°C was calculated as 3.8 mM−1 and 1.2 mM−1 for lactose and galactose, respectively. In both cases the number of binding sites per molecule of RC1 with molecular weight of 120000 was found to be 2. From the temperature-dependent Ka values for the binding of lactose, the values of -5.7 kcal/mol and -4.3 cal×mol−1×K−1 were calculated for ΔH and ΔS, respectively. The addition of concanavalin A to RC1 or vice versa led to the formation of the insoluble complex RC1·ConA4 containing one molecule of RC1 and one molecule of tetrameric concanavalin A (ConA4) which could be dissociated upon addition of concanavalin A-specific sugars. The complex formation results in a time-dependent appearance of turbidity in the time range from 10s to 10 min. From the measurement of the time-dependent appearance and disappearance of the turbidity the formation (kf) and dissociation (kd) rate constants were calculated as 3 mM−1×s−1 and 0.07 ks−1 respectively. The ratio kf/kd (43μM −1), that corresponds to the association constant of complex RC1·ConA4, is higher than that of mannoside·ConA4 and thereby suggests that protein-protein interaction contributes significantly in stabilising glycoprotein·lectin complexes. The relevance of this finding to the understanding of the chemical specificities that are involved in a model cell-lectin interaction is discussed.

Item Type:Article
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