A spectroscopic analysis of the interaction between MEGA10 and Concanavalin A

Abstract

The binding of MEGA10 with Concanavalin A (Con A) at pH 7.4 and pH 5 have been studied using steady-state and time-resolved fluorescence, dynamic light scattering (DLS) and Circular Dichroism(CD). Downward curving Stern-Volmer plots suggested the existence of tryptophan residues exposed in the protein surface and other tryptophans extensively buried within the protein. The major proportion of protein tryptophan groups are not involved in MEGA10 interaction. The pH significantly influences the affinity of MEGA10 to Con A, with it being stronger at pH 7.4 than at pH 5.0. It is inferred from the thermodynamic analysis of the binding constant dependencewith temperature that van derWaals and hydrogen bonds are the predominant forces in the interaction of MEGA10with lectin. In time-resolved fluorescence experiments, the decay curveswere well fitted to three exponential patterns. The mean lifetime at pH 7.4 systematically decreased with increasing MEGA10 concentration, whereas this parameter at pH 5 is practically constant, indicating greater protein structure alterations at pH 7.4 than at pH 5 after surfactant association, and they were corroborated by circular dichroismmeasurements. Anisotropy complementary studies detail that Con A undergoes motion restrictions because of the association with surfactant. The attachment of MEGA10 to Con A was confirmed by dynamic light scattering.