Collagen fibrillar structure and hierarchies

Tim J Wess

doi:10.1007/978-0-387-73906-9_3

Collagen is most commonly found in animals as long, slender generally cylindrical fibrillar structures with tapered ends that are most easily recognized by a 65-67 nm axial periodicity. Collagen fibrils are substantial constituents of skin, tendon, bone, ligament, cornea, and cartilage, where the fundamental tensile properties of the fibril are finely tuned to serve bespoke biomechanical, and less well understood structural signaling roles. Many of these properties derive from the structural organization within a fibril, where the axial and lateral organization and topology of the collagen molecules ensure strong intermolecular interactions and cross-linkage. The presence of different collagen types within a single fibril is a structural prerequisite in many tissues. However, the necessity for heterotypic fibrillar structures may point to fine tuning of the structural properties in a composite, such as fibril size regulation, dispersion of crystallinity, and interfibrillar communication. Furthermore the specific properties of an individual tissue also rely on the suprafibrillar architecture at the mesoscopic level. The chapter will discuss current information about fibrillar structure from both homo-and heterotypic fibrils from a structural and biochemical viewpoint. Fibrils rich in collagen I, II and III will be considered as will the contribution of minor fibrillar and FACIT collagens. The molecular organization in both axial and lateral senses will be reviewed for both helicoidal and quasi crystalline fibrillar structures. Current models that account for the dynamic behavior of collagen segments within the fibril will be reviewed and the basis for order and disorder within the fibril discussed. The discrete size and polydispersity of fibrils will be discussed in terms of tissue properties and characteristics. The surface features of fibrils will be considered which conveniently leads to the possible features of interfibrillar interactions. The overall properties and morphology of a fibril are as important as its internal organization. For example, the fibril surface is a complex area that contains collagen molecules and a variety of proteoglycans. These dictate the interaction between fibrils and specify the environment of partner macromolecules. They are also important in restricting fibril growth and permitting fusion to occur. The defined diameter (or distribution of fibril diameters) and overall slender tapering of collagen fibrils has significance in determining the macroscopic mechanical properties of the tissues. The variety of local suprafibrillar and resultant architectures such as bundles, felt work, lamellae and fibers that are evidenced in tissues will be discussed. © 2008 Springer Science+Business Media, LLC.

Collagen fibrillar structure and hierarchies

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