MECHANISMS OF PROTEOGLYCAN/COLLAGEN INTERACTIONS

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Proteoglycan-collagen interactions are ubiquitous in most vertebrate tissues and likely play key roles in cell adhesion, migration, and extracellular matrix (ECM)assembly and function. Although the biochemistry of the binding between the cell surface or secreted proteoglycans and collagens is incompletely understood, a primarily electrostatic, non-specific basis for their interactions has been proposed. However, by electron microscopy this laboratory has observed heparin binding to specific regions on type I collagen monomers and fibrils, and using affinity coelectrophoresis has shown that high affinity collagen-binding domains comprise only a small fraction of the heparin molecule. These results favor the hypothesis that high affinity heparin-type I collagen binding depends more upon unique, sparsely represented domains or sequences within the glycosaminoglycan and protein, than upon site-independent electrostatic interactions. To test the above hypothesis, first, the collagen-binding sites of heparin will be isolated and their abundance, size, sequence, and binding selectivity for other ECM molecules will be determined by affinity coelectrophoresis (ACE) and other biochemical approaches. Second, the putative heparin-binding regions of type I collagen will be confirmed by studying the interactions of heparin with a) recombinant type I collagens in which D-period segments have either been deleted or inserted in multiple copies, or in altered positions, and b) with "mini collagen" peptides carrying known type I collagen sequences. Last, the identified interactive domains of heparin and type I collagen will be tested in cell interactions with type i collagen and with other ECM molecules. These studies will define the biochemistry and function of one of the most abundant of cell-matrix interactions, and contribute to the understanding and treatment of diseases such as cancer which involve abnormal cell adhesion and migration within the ECM.