Abstract :Contrary to earlier views where carbohydrates were thought of merely as sources of food, energy and structural materials we now know that they provide cells with their individuality and recognition patterns that crucially regulate their social behavior including their growth and differentiation. Our recognition that it is indeed so is largely due to the advent of a class of proteins called lectins that bind carbohydrates selectively much as antibodies bind with antigens and enzymes to their substrates. Though originally discovered in plants they are found in all forms of life. Lectins by binding to specific carbohydrate receptor at the surface of the cell mediate cell- cell adhesion, cell signaling, immune response etc. As all the biologic activities of lectins stem from their carbohydrate recognition abilities structural studies on them particularly of their binding sites have become an object of intense scientific scrutiny.
Structurally there are six families of plant lectins-jelly roll, haevin domains, β- prism I and II, β-trefoil and cyanovirin folds. My talk will be focused on some features of carbohydrate recognition by lectins exhibiting jelly roll and β-prism I folds. In general their binding sites exist as shallow depressions on the surface of the proteins which often involve interactions through one of the surface of the ologosacharide. While the specificity for the interactions is provided by hydrogen bonding directly between the atoms in the sugars and the amino acid side chains in the combining site of the lectins, van der waals, stacking and OH-∏ interactions contribute significantly to the affinity of binding. Water mediated hydrogen bonds between the sugar and the binding site are crucial in some instances for modulating the affinity. Also, variation in the size and shape of the loops in the combining sites of lectins is used for discriminating between apparently similar monosaccharide structures. Post-translational proteolysis and distortion of the pyranose ring in the bound conformation will be the other unprecedented findings in this area that will be discussed.
About the Speaker : Prof. Avadhesha Surolia (Born 03 December 1947) is an eminent Glycobiologist at Indian Institute of Science (IISc), Bangalore. Presently, he is an Honorary Professor at the Molecular Biophysics Unit (MBU), IISc and holds the prestigious Bhatnagar Fellowship of the Council of Scientific and Industrial Research (CSIR), India. He is internationally recognized for his seminal contributions on lectin structure and interactions, orientation and dynamics of cell surface carbohydrate receptors and protein folding, diabetes, anti-malarials and anti-cancer agents based on curcumin, flavonoids, etc. In addition, neuropathic pain, neurodegenerative disorders and the link between immunity and obsessive compulsive disorder are other areas of his current interest. He has been a recipient of several prestigious National and International awards.