Collagen fibril self-assembly

Fibrils self-assemble in the extracellular space, as desaibed in Section 9.03.2.1. Only later, this stmcture is stabilized and mechanically reinforced by chemical cross-links between the molecules. For a recent review on cross-linking in collagen, see Avery and Bailey. There are different types of cross-links that... 

Fig. 1 Examples of enzyme-controlled supramolecular polymerisation from the biological world (a) formation of collagen fibrils, (b) dynamic self-assembly of actin filaments, and (c) formation of microtubules...

Kadler K, Hojima Y, Prockop DJ (1987) Assembly of collagen fibrils de novo by cleavage of the type I pC-collagen with procollagen C-proteinase. Assay of critical concentration demonstrates that collagen self-assembly is a classical example of an entropy-driven process. J Biol Chem 262 15696-15701... 

Self-assembly of collagen molecules into fibrils, with subsequent cross-linking. 

Since fibril assembly can be regarded in part as a spontaneous self-assembly process, the limitation of fibril size could be ascribed to a physical equilibrium between soluble procollagen molecules and the growing insoluble fibril. Fibril-forming collagens are synthesized as precursor... 

Blaschke, U. K., Eikenberry, E. F., Hulmes, D. J. S., Galla, H. J., and Bruckner, P. (2000). Collagen XI nucleates self-assembly and limits lateral growth of cartilage fibrils./. Biol. Chem. 275, 10370-10378. 

Figure 5.3. Turbidity-time curve illustrating collagen self-assembly.Turbidity-time curve illustrating lag phase, during which small linear and lateral aggregates form, and growth phase, during which unit fibers form that rapidly grow into fibers. The plateau is characteristic of termination of fibril growth.

Figure 5.7. Diagram showing role of N- and C-propeptides in collagen self-assembly. The procollagen molecule is represented by a straight line with bent (N-propeptide) and circular (C-propeptide) regions. Initial linear and lateral aggregation is promoted by the presence of both the N- and C-propeptides. In the presence of both propeptides lateral assembly is limited and the fibrils are narrow. Removal of the N-propeptide results in lateral assembly of narrow fibrils removal of the C-propeptide results in additional lateral growth of fibrils. As indicated in the diagram, the presence of the N- and C-propeptides physically interferes with fibril formation.

Figure 7.6. Effective mechanical fibril length versus fibril segment length. Plot of effective fibril length in pm determined from viscous stress-strain curves for rat tail tendon and self-assembled collagen fibers versus fibril segment length. The correlation coefficient (R2) for the line shown is 0.944 (see Silver et al., 2003).

Figure 7.9. Relationship between mechanical properties and fibril length (L) for self-assembled collagen fibers. Plot of UTS (A) and elastic slope (B) versus L in im for self-assembled type I collagen fibers stretched in tension at strain rate of 50%/min. Points with fibril lengths less than 20 pm are for uncrosslinked self-assembled type I collagen fibers and the points above 20 pm are for crosslinked fibers. The correlation coefficient for the best fit line is given by R2.

The procollagen molecule is secreted from the cell, and the extension propeptides are excised by two specific procollagen peptidases to form the tropocollagen molecule. The removal of the peptides (Mr = 20,000 and 35,000) allows the tropocollagen molecules to self-assemble to form fibrils. This assembly is regulated to some extent by the cells and by other extracellular components to produce the wide variety of structures found in collagen fibers. 

Collagen molecules undergo self-assembly by lateral associations into fibrils and fibers and are able, therefore, along with other biological functions, to ensure the mechanical support of the connective tissue. Collagen also plays an important role in many bioadhesion processes. Collagen molecules bound to implant materials enhance adhesion of epidermal cells to the surfaces of biomaterials and prevent implant failure. 

Fibril A self-assembled group of collagen molecules. 

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