2Department of Biochemistry, College of Wisconsin, Madison, Wisconsin 53706
Summary
INTRODUCTION
The classes of collagen embody the classical fibrillar and network-forming collagens, the FACITs (fibril-associated collagens with interrupted triple helices), MACITs (membrane-associated collagens with interrupted triple helices), and MULTIPLEXINs (a number of triple-helix domains and interruptions). It’s noteworthy that, though the three polypeptide chains within the triple helix of every collagen kind could be similar, heterotrimeric triple helices are extra prevalent than are homotrimeric triple helices. Collagen sorts, their distribution, composition, and pathology are listed in Desk 1.
STRUCTURE OF THE COLLAGEN TRIPLE HELIX
On the premise of X-ray crystal constructions of proline-rich CRPs, and in accordance with an early proposal relating to the helical pitch of pure triple helices (23), Okuyama and coworkers (24) postulated that the right common helical pitch for pure collagen is 7/2. The entire ensuing constructions have a 7/2 helical pitch (20.0-Å axial repeat), in distinction to the ten/3 helical pitch (28.6-Å axial repeat) predicted for pure collagen by fiber diffraction (17). Particularly, the helical pitch may very well be 10/3 in proline-poor areas and seven/2 in proline-rich areas.
UNDERSTANDING TRIPLE-HELIX STRUCTURE AND STABILITY
Understanding how such properties are derived from the basic structural unit of collagen, the triple helix, necessitates a complete data of the mechanisms underlying triple-helix construction and stability. These traits embody thermal stability, mechanical energy, and the power to interact in particular interactions with different biomolecules. The very important significance of collagen as a scaffold for animals calls for a manifold of important traits.
HIGHER-ORDER COLLAGEN STRUCTURE
The self-assembly processes concerned in collagen fibrillogenesis are of monumental significance to ECM pathology and correct animal improvement (see sidebar for a dialogue of how collagen self-assembly may be directed away from deleterious protein aggregates). Particular person TC monomers self-assemble into the macromolecular fibers which are important elements of tissues and bones. In vivo collagen has a hierarchical construction (Determine 2).
MECHANICAL PROPERTIES OF COLLAGEN FIBRILS
An evaluation by Buehler (102) of the mechanical properties of collagen fibrils means that nature has chosen a size for the TC monomer that maximizes the robustness of the assembled collagen fibril through environment friendly vitality dissipation. Simulations point out that TC monomers both longer or shorter than ~300 nm (which is the size of a kind I collagen triple helix) would type collagen fibrils with much less favorable mechanical properties.
COLLAGENOUS BIOMATERIALS
The heterologous manufacturing of collagen is made problematic by the problem of incorporating posttranslational modifications, equivalent to that resulting in the important Hyp residues (Determine 6), and by the necessity to use advanced expression methods (125). Bovine collagen is available and helpful for some biomedical functions, but it surely suffers from heterogeneity, potential immunogenicity, and lack of structural integrity throughout the isolation course of. These challenges underscore the necessity for artificial sources of collagen-like proteins and fibrils.