Proteoglycan 4 (PRG4) is a mucin-like glycoprotein that is a key synovial fluid constituent, functioning as a cartilage boundary lubricant. PRG4 has been suggested to exist as a supramolecular structure. The objectives of this thesis were to (1) characterize the supramolecular structure of recombinant human PRG4 (rhPRG4) and its dependency on concentration, (2) elucidate the molecular forces underlying the formation of the supramolecular structure, and (3) assess the lubricating ability of the

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... upramolecular structure. rhPRG4's ability to form a supramolecular structure and reduce friction was concentration dependent. Arginine (0.2M) disrupted the formation of the supramolecular structure of rhPRG4 and diminished its lubricating ability. Conversely, 20 mM calcium enhanced the formation of rhPRG4 supramolecular structure and enhanced its lubricating ability. These results suggest non-covalent interactions mediate rhPRG4's supramolecular structure, shown here to exist for the first time, which in turn is a functionally (lubrication) determinant property.