Modeling and characterization of the amino propeptide of collagen α1(XI), a regulatory domain in collagen fibrillar architecture

Connective tissues such as cartilage, tendon, skin, bone, and arteries are composite biomaterials that contain predominantly water, collagen, proteoglycans and hyaluronic acid. Like any composite material, the components themselves and their interactions dictate the properties of the material. Fibrillar collagens are the principal structural molecules of the connective tissues and require regulated assembly and growth. Previous work from our lab indicates that the amino propeptide (Npp) domain of collagen type XI α1 chain regulates fibril diameter growth. Npp is a globular domain that is thought to sterically hinder the dense packing assembly of collagen molecules in fibrils. This mechanism of regulating collagen fibril assembly may be more complex than steric hindrance. We hypothesize that the Npp domain has a more dynamic role in establishing the structure/function relationship of collagen fibrils in connective tissues. In this study, the molecular structure of Npp was predicted by modeling. The model predicted putative binding sites for heparan sulfate and divalent cations. These predicted binding sites were evaluated empirically by fluorescence spectroscopy and surface plasmon resonance.