We will continue to study carbohydrate-protein interactions using the cloned carbohydrate-recognition domains of rat serum and liver mannose- binding proteins (MBP) as well as isolated alligator hepatic lectin (AHL). NBP is important in the pre-immune defense against invaders. AHL, though similar to other hepatic lectins, show interesting differences in binding specificity and in subunit size and organization. AHL will be cloned so that the peptide sequence can be compared with other hepatic lectins, and further biochemical, physical studies can be performed. Throughout these studies, the glycoside cluster effect and mapping of the binding sites will be the major foci. The glycoside cluster effect is unique for binding of carbohydrate ligands, and warrants thorough understanding. It can also be beneficial for designing agents for carbohydrate-mediated targeting or prevention of harmful binding such as microbial or viral infection. For this purpose, a series of clustered glycosides, varying in the glycoside spacing and the aglycon lengths will be systematically synthesized. Synthetic glycopeptides containing alkyl glycosides of different aglycon lengths attached to a peptide of different lengths will be condensed. We also plan to examine epitopic structure of Burmuda grass antigen (BG-60) which causes allergic reactions in some individuals. We will attempt to elucidate unequivocally the major oligosaccharide structure in this antigen, and try to map the relative importance of the sugar and amino residues involved in the interaction with the IgE. Although Fuc(alpha)3GlcNAc may be an important segment, other part of the oligosaccharide from the antigen are most likely to be required for the binding to IgE. Glycopeptides possessing structures similar to the BG-60 oligosaccharide will be isolated from various sources or synthesized. chemical or enzymatic trimming of these glycopeptides yields simpler structures. We have detected a unique endo-alpha1,6-mannosidase activity in the jack bean alpha-mannosidase preparations, and will attempt to isolate this enzyme, which will be extremely useful for structural determination of Asn-linked glycosides. We will design substrates for the enzymes of this type based on energy transfer or quenching of fluorescence.
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