Protein-carbohydrate interactions

Abstract

Carbohydrates are ubiquitous in nature and have become the focus of much scientific investigation. The proteins which recognise carbohydrates have become widely used in the areas of cell and molecular biology. Protein - carbohydrate interactions have been probed by theoretical, structural and thermodynamic techniques. The lectins are a class of carbohydrate binding proteins which bind carbohydrates through non covalent interactions such as hydrogen bonds and van der Waals interactions. In addition to these interactions, other factors play an important role in determining affinity such as carbohydrate conformation, solvent reorganisation and changes in the protein binding site. The legume lectin concanavalin A specifically recognises mannose and glucose terminal residues. The thermodynamics of concanavalin A binding to carbohydrates has been well documented. Concanavalin A binds the core trimannoside and pentasaccharide of the biantennary glycan found on mammalian cell surfaces with a high affinity. This thesis describes the structural basis of carbohydrate binding by con A, through the interpretation of crystal structures of concanavalin A bound with α1-2 mannobiose, methyl α1-2 mannobioside, the core pentasaccharide of the biantennary glycan and fructose. The structural information obtained from these structures is related to thermodynamic information available and unravels the importance of the role played by carbohydrate conformation, solvent reorganisation and statistical population of ligand in determining affinity. This work helps to develop an understanding of the physical basis of carbohydrate recognition.