Comparison of the nature of interactions of two sialic acid specific lectins Saraca indica and Sambucus nigra with N-acetylneuraminic acid by spectroscopic techniques

The present paper deals with the isolation and purification of a new sialic acid binding lectin from the seed integument of Saraca indica (Ashok) and the purified lectin was designated Saracin II. Comparative studies on the interactions of saracin II and another sialic acid specific lectin Sambucus nigra agglutinin (SNA) with N-acetylneuraminic acid (NANA) were made using UV-vis absorption, steady state and time resolved fluorescence along with circular dichroism (CD) spectroscopy to reveal the nature and mechanisms of binding of these two lectins with NANA. The experimental observations obtained from UV-vis, steady state and time resolved fluorescence measurements demonstrated that SNA-NANA system formed relatively stronger ground state complex than saracin II-NANA pair. CD measurements further substantiated the propositions made from steady state and time resolved spectroscopic investigations. It was inferred that during interaction of SNA with NANA, the lectin adopted a relatively looser conformation with the extended polypeptide structures leading to the exposure of the hydrophobic cavities which favoured stronger binding with NANA.