Proteins containing convalenty linked carbohydrate play vital roles in the biology of cells, being abundantly represented among secretory products as well as cell surface and basement membrane constituents. The carbohydrate units, with their great potential for diversity, have been implicated in recognition phenomena involving the interaction of cells with each other as well as with substrata and circulating molecules and therefore have relevance to disease processes ranging from neoplasia to diabetes. It is the objective of this research proposal to continue our studies on the structure of the glycoprotein components of cell surfaces and basement membranes, to evaluate their biological role in defined model systems and to pursue our exploration of the biochemical basis of the diabetic renal filtration defect. Furthermore, we will investigate the structure of the sulfated carbohydrate units which we recently detected in thyroglobulins. The carbohydrate chains of glomerular basement membrane and lens capsule components, including heparan sulfate proteoglycan, entactin and type IV collagen, will be defined. In regard to the proteoglycan, particular attention will be given to the distribution of sulfate groups, nature of the core protein and antigenicity as well as binding reactivities of various regions of the molecule; moreover an assessment of anticoagulant activity of the heparan sulfate chains will be made and structural alterations in the diabetic state will be evaluated. Cell-basement membrane interactions will be studied in our lens capsule model system and a search for a type IV collagen receptor on lens cells will be made; the role of the Glc-Gal-Hyl units of collagen in the binding of cells to basement membranes will be evaluated. The disposition of macromolecular components will be probed with immunochemical procedures from both faces of the lens capsule and this basement membrane will also be used to study the migration of polymorphonuclear leukocytes through basement membranes. Thyroid cells will be employed for the study of cell surface glycoprotein structure and cell-cell interactions. Included in these investigations will be the thyrotropin receptor and GP-3, a major carbohydrate rich component. The effect of polarity inversion on the surface distribution of glycoproteins will be evaluated and the role of glycoconjugates on interactions leading to follicle formation will be explored. Studies on the sulfated N-linked carbohydrate units of calf and human thyroglobulins should extend our understanding of this prohormone's structure.
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