Abstract. Type IV collagen incubated at elevated temperatures in physiologic buffers self-associates (a) via its carboxy-terminal (NC1) domain, (b) via its aminoterminal (7S) domain, and (c) laterally; and it forms a network. When examined with the technique of rotary shadowing, isolated domain NC1 was found to bind along the length of type IV collagen to four distinct sites located at intervals of âą100 nm each. The same 100-nm distance was observed in domain NC1 of intact type IV collagen bound along the length of the collagen molecules during initial steps of network formation and in complete networks. The presence of anti-NC1 Fab fragments in type IV collagen solutions inhibited lateral association and network formation in rotary shadow images. During the process of selfassociation type IV collagen develops turbidity; addition of isolated domain NC1 inhibited the development of turbidity in a concentration-dependent manner. These findings indicate that domain NC1 of type IV collagen plays an important role in the process of selfassociation and suggest that alterations in the structure of NC1 may be partially responsible for impaired functions of basement membranes in certain pathological conditions. T YPE IV collagen is one of the exclusive macromolecular components of basement membranes (11). Structurally, it consists of three a-chains [tIl(IV)2-t12(IV)] and has in its monomeric form a molecular weight of 500,000 (1, 5). When compared to the a-chains of the other collagen types, the a-chains of type IV collagen are of higher molecular weight and contain along their length many short interruptions of the GIy-X-Y repeating unit (9, 18). Therefore, type IV collagen has multiple short non-triple-helical domains along its length and also has a large globular domain (NC1) l at its carboxy-terminal end (22).Type IV collagen molecules have the ability to selfassemble by interacting via their carboxy termini (NC1) (22), via their amino termini (7S) (22), and laterally (26). The end product of these interactions is a closed network, as visualized with the rotary shadowing technique (26). Pepsintreated type IV collagen molecules which lack their globular NC1 domain are not able to form networks (26). This observation suggested that the carboxy-terminal globule might play an important role in type IV collagen self-assembly. In this study, we present evidence that domain NC1 is critically involved in lateral association and network formation of type IV collagen.1. Abbreviation used in this paper: NC1, noncollagenous domain 1 (carboxy terminal) of type IV collagen.
Materials and Methods
Preparation of l~pe I V CollagenThe source of type IV collagen was the Engelbreth-Holm-Swarn (EHS) tumor (16) grown subcutaneously in mice which were rendered lathyritic by the addition of 0.25 % I~-aminopropionitrile fumarate (Sigma Chemical Co., St. Louis, MO) in their drinking water. Type IV collagen was isolated by a modification of previously described methods (4, 12). Briefly, the tissue was extracted first with 3.4 M NaCI in 0.05 M ...