Fragility of Reconstituted Type V Collagen Fibrils with the Chain Composition of α1(V)α2(V)α3(V) Respective of the D-Periodic Banding Pattern

The triple-helical domains of two subtypes of type V collagen were prepared from human placenta, one with the chain composition of [alpha 1(V)](2)alpha 2(V) (Vp112) and the other with the chain composition of alpha 1(V)alpha 2(V)alpha 3(V) (Vp123) with limited pepsin treatment. In order to characterize the triple-helical domain of the type Vp123 collagen molecule, the reconstituted aggregate structure formed from the pepsin-treated collagen was compared by using transmission electron microscopy. The diameter of the fibrils reconstituted from types pepsin-treated type Vp123 collagen and type Vp112 collagen was highly uniform and less than the D-periodicity at all the temperatures examined, suggesting that the major triple-helical domain of both subtypes has a potency to limit their lateral growth. Both fibrils were approximately 45 nm in width and showed the D-periodic banding pattern along their axes at 34 degrees C. In contrast to type Vp112, the reconstituted type Vp123 fibrils showed no banding pattern along their axes when they were reconstituted at 37 degrees C. The banded fibrils once reconstituted from type Vp123 at 34 degrees C tend to lose their characteristic pattern within 60 min when they were incubated at 37 degrees C. One explanation is that a slightly higher content of hydrophobic residues of type Vp123 collagen than those of type V112p collagen augmented the intermolecular interaction that disturbs the D-periodicity governed essentially by electrostatic interactions. Taken together with recent data in Col5a3 gene-targeted mice, the results suggest that type V123 collagen exists not only as a periodic banded fibril but also as nonfibrillar meshwork structures.