Solid-State NMR Studies of Collagen Structure and Dynamics in Isolated Fibrils and in Biological Tissues

Collagen is the most abundant protein on earth. Having a unique amino acid sequence featuring a high content of glycine. proline and hydroxyproline residues, the collagen alpha-chains form a slightly twisted left-handed polyproline-II-type helix with three amino acids per turn. Three such alpha-chains form the collagen triple helix, which is the basic building block for collagen fibrils that are characterized by very high tensile strength. Collagen fibrils form basic structures of the extracellular matrix of many biological tissues such as bone, skin, cartilage. teeth, blood vessels tendon and many others. Since collagen is neither water soluble nor does it form highly ordered crystals, a significant amount of information about isolated and tissue collagen has been acquired by solid-state NMR techniques over the last 30 years. This review will provide an overview of solid-state NMR applications to study structural and dynamical features of collagen. The discussed examples include static and magic-angle spinning NMR studies on isolated collagen fibrils as well as solid-state NMR applications on the dynamics of collagen in biological tissues such as cartilage and bone. Finally, the interaction of water with collagen fibrils will be discussed as the molecular basis for magnetic resonance imaging techniques on the orientation of collagen fibrils in biological tissues.