Structural polymorphism of collagen type I–heparin cofibrils

Abstract

We report on the coexistence of 2 different supramolecular polymorphic forms of pepsin-digested collagen type I fibrils reconstituted in vitro in the presence of heparin. Detailed structural analysis using transmission electron microscopy and scanning force microscopy shows a hierarchy involving 3 different structural levels and banding patterns in the system: asymmetric segment longspacing (SLS) fibrils and symmetric segments with an average periodicity (AP) of 250–260 nm, symmetric fibrous longspacing (FLS IV) nanofibrils with AP of 165 nm, and cofibrils exhibiting an asymmetric D-periodicity of 67 nm with a striking resemblance to the native collagen type I banding pattern. The intercalation of the high negatively charged heparin in the fibrils is suggested as being the main trigger for the hierarchical formation of the polymorphic structures. We propose a model explaining the unexpected presence of a symmetric and asymmetric form in the system and the principles governing the symmetric or asymmetric fate of the molecules