Modulation of the pharmacological effects of enzymatically-active PLA(2 )by BTL-2, an isolectin isolated from the Bryothamnion triquetrum red alga

BACKGROUND: An interaction between lectins from marine algae and PLA(2 )from rattlesnake was suggested some years ago. We, herein, studied the effects elicited by a small isolectin (BTL-2), isolated from Bryothamnion triquetrum, on the pharmacological and biological activities of a PLA(2 )isolated from rattlesnake venom (Crotalus durissus cascavella), to better understand the enzymatic and pharmacological mechanisms of the PLA(2 )and its complex. RESULTS: This PLA(2 )consisted of 122 amino acids (approximate molecular mass of 14 kDa), its pI was estimated to be 8.3, and its amino acid sequence shared a high degree of similarity with that of other neurotoxic and enzymatically-active PLA(2)s. BTL-2 had a molecular mass estimated in approximately 9 kDa and was characterized as a basic protein. In addition, BTL-2 did not exhibit any enzymatic activity. The PLA(2 )and BTL-2 formed a stable heterodimer with a molecular mass of approximately 24–26 kDa, estimated by molecular exclusion HPLC. In the presence of BTL-2, we observed a significant increase in PLA(2 )activity, 23% higher than that of PLA(2 )alone. BTL-2 demonstrated an inhibition of 98% in the growth of the Gram-positive bacterial strain, Clavibacter michiganensis michiganensis (Cmm), but only 9.8% inhibition of the Gram-negative bacterial strain, Xanthomonas axonopodis pv passiflorae (Xap). PLA(2 )decreased bacterial growth by 27.3% and 98.5% for Xap and Cmm, respectively, while incubating these two proteins with PLA(2)-BTL-2 inhibited their growths by 36.2% for Xap and 98.5% for Cmm. PLA(2 )significantly induced platelet aggregation in washed platelets, whereas BTL-2 did not induce significant platelet aggregation in any assay. However, BTL-2 significantly inhibited platelet aggregation induced by PLA(2). In addition, PLA(2 )exhibited strong oedematogenic activity, which was decreased in the presence of BTL-2. BTL-2 alone did not induce oedema and did not decrease or abolish the oedema induced by the 48/80 compound. CONCLUSION: The unexpected results observed for the PLA(2)-BTL-2 complex strongly suggest that the pharmacological activity of this PLA(2 )is not solely dependent on the presence of enzymatic activity, and that other pharmacological regions may also be involved. In addition, we describe for the first time an interaction between two different molecules, which form a stable complex with significant changes in their original biological action. This opens new possibilities for understanding the function and action of crude venom, an extremely complex mixture of different molecules.