The macromolecular structure of type-VI collagen. Formation and stability of filaments.

Type-VI collagen microfilaments were directly isolated from human amnion without using strong denaturing reagents. The microfilaments were characterized by electron microscopy, SDS/PAGE and immunoprecipitation. There was no evidence of other components bound to the isolated filaments and no covalent bonds between adjacent tetramers. The association between tetramers was further analyzed by studying the affinity between globular domains and the helix of type-VI collagen. Solid-phase-binding assays and conventional column chromatography showed that the globular domains have a high affinity for each other and for the helices of type-VI collagen, indicating that filaments may be assembled and stabilized in the absence of additional components. Hyaluronan did not stabilize the filaments nor facilitate the assembly of tetramers into filaments. The interaction between domains was also studied after modifying the sugar moieties of type-VI collagen globular domains and monomeric triple-helical domains. The oligosaccharides are involved in helix-helix interactions but not in interactions of the globular domains with each other or with the triple helix.