Fibrous proteins: New structural and functional aspects revealed

Coiled-coil proteins, Collagen, and elastomers together comprise an important subset of the fibrous proteins. The former group-the a-fibrous coiled-coil proteins-are widely distributed in nature and, indeed, the characteristic heptad motif has been recognized as an oligomerisation motif in fibril-forming collagens. This volume has selected a number of the a-fibrous proteins for detailed discussion, including intermediate filament proteins, the spectrin super-family, and fibrin/fibrinogen. Of particular interest is the growing realization that the design principles governing the structures of these coiled-coil proteins are now largely discernible and can be specified with a high degree of confidence, due in large part to the wealth of crystal structure data now available. Within the connective tissues covered in this volume, two constituents of defining importance mechanically are the collagen fibrils/networks and the elastic fibers. Crystal structures of collagen peptides have been published and are described. The effects of the precise sequence of the distinct constituent triplets on molecular conformation have also become clearer. The ultrastructures of connective tissues are largely defined by the spatial arrangement of the collagen fibrils and networks, and this is elucidated here in some detail. The elastic fibers with their elastin cores and fibrillin-containing microfibril palisades are also described. A theme underlying all of the proteins discussed in this volume is the significantly increased effort to characterize the structures and functions of mutants. Some of these occur naturally and lead to various disease states, while others have been genetically engineered in order to study design principles.