Gel Formation from the Type IV Collagen Isolated from Bovine Lens Capsule in Guanidine-HCl and Dithiothreitol

Type IV collagen was prepared from bovine lens capsule by acetic acid extraction, followed by purification including DEAE-Sephacel chromatography and dialysis. The type IV collagen solution became viscous and eventually gelated upon dialysis against 2 M guanidine-HCl and 10 mM dithiothreitol. Gelation was not observed for heat-denatured type IV collagen, suggesting that collagenous conformation may be required for the gelation. A reducing agent, dithiothreitol, was essential for the gelation of type IV collagen in 2 M guanidine-HCl. An optimal concentration of guanidine-HCl for the gelation lays between 1.5 and 2.5 M: gelation did not occur at 1 M or lower and at 3 M or higher, although the circular dichroism spectrum characteristic of the collagenous triple-helix was not changed in 3 M guanidine-HCl. This suggests that an appropriate change in conformation of the type IV collagen at a region other than the triple-helical region or/and partial dissociation of complexed type IV collagen aggregates may drive intermolecular interactions of the type IV collagen leading to polymerization and eventually to gelation. To our knowledge, this is the first report that the type IV collagen alone has the ability to form a rigid gel. The assembled structure of the type IV collagen in gel form might be related to the skeletal architecture of basement membrane(s).