Proposed are studies of the process by which structures of carbohydrates of cellular glycoproteins are determined. The subcellular events leading to the covalent addition and modification of complex carbohydrates on glycoproteins are known to be important in cellular interactions including the regulation of cell growth and differentiation. Alterations in these processes are implicated in cancer. Our system uses fetal hybridomas, lymphomas, hybridomas and plasmacytomas which make subcellular, membrane bound, and secreted IgM and IgG. These cells are representative of various stages of differentiation. We are using high field NMR and conventional carbohydrate chemistry to determine carbohydrate structures at each of the glycosylation sites on IgM and IgG. We are also studying carbohydrates on IgM produced by two groups of mutant cell lines. The first group produces IgM with a normal polypeptide molecular weight but with three levels of processing of the carbohydrate. The second group includes mutants which produce IgM with deletions in various constant domains. IgM secreted by the latter mutants has an altered protein structure. We can thus determine the consequences of alterations in the protein on carbohydrate processing. Finally, we are studying the subcellular events of glycoprotein synthesis and processing for membrane bound and soluble glycoproteins. Our goal is to understand how a cell determines the structure of carbohydrates on glycoproteins and how these events vary for membrane bound and secreted glycoproteins.
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