It is now clear that carbohydrates play a vital role in biological communication. Highly specific glycoconjugates on cell surfaces display information regarding the type, location, developmental stage, and disease state of cells. This information is """"""""read"""""""" by a specialized group of proteins, the lectins. Protein-carbohydrate interactions are key in the early stages of a range of bacterial, viral, parasitic and mycoplasmal infections, as the pathogen recognizes and adheres to its host. Other human disease states including the metastatic distribution of malignancies are also mediated by lectin-carbohydrate recognition motifs. Carbohydrate mimics, which would bind tightly to specific lectins and inhibit recognition and adhesion of pathogens, would therefore represent a whole new class of therapeutic agents. The primary impediment to the development of therapeutic carbohydrate mimics is specificity. While carbohydrate-mediated recognition is ubiquitous, only eight monosaccharides are transferred in mammalian biochemistry. Before carbohydrate-based treatment modalities can be realized, paradigms for installing specificity into mimics must be developed. We propose to investigate the aspects of protein-carbohydrate interactions relevant to specificity. Our fundamental design is to obtain detailed energetic data regarding the formation of protein-carbohydrate interactions, and analyze this information in terms of structure of the bound complex. We will use microcalorimetry, a well developed technique but one which has only recently been applied to biological systems, to measure the important thermodynamic parameters of protein-carbohydrate complexes, including deltaG, deltaH, deltaS, and deltaCp. We will make use of high-field magnetic resonance techniques to obtain structural information regarding the bound form of the carbohydrate and, where possible, the protein. We will make use of transfer of nuclear Overhauser effects, paramagnetic contributions to spin-lattice relaxation times, and three bond carbon- hydrogen coupling constants to obtain this information. As model systems, we will examine several plant and microbial lectins which all bind similar oligomannose epitopes. We will utilize all of this information to direct the synthesis of specifically modified carbohydrates to begin preparing highly modified species which bind tightly and specifically to only a single lectin.
