Specific interaction of the legume lectins, concanavalin a and peanut agglutinin, with phycocyanin

In a recent study, we found that jacalin, a T-antigen specific lectin could interact with phycocyanin (PC) in a carbohydrate-independent manner. We show here that concanavalin A and peanut agglutinin too can interact with PC, although the nature of the interaction is distinctly different from that for jacalin. The legume lectins bind PC weaker in the presence of their specific carbohydrate ligands. Like jacalin, the legume lectins too interact with PC via two distinct sites. Higher ionic strengths resulted in a weakening of the interaction at site 1 and did not affect the interaction at site 2, clearly indicating that the interactions involve charged residues at the former and hydrophobic interactions at the latter site. The implications for the use of these lectin-PC complexes in photodynamic therapy and other clinical applications are discussed.