Collagens, network-forming assembly

Network-forming collagens Types IV and VII form a three-dimensional mesh, rather than distinct fibrils (Figure 4.4). For example, type IV molecules assemble into a sheet or meshwork that constitutes a major part of basement membranes. [Note Basement membranes are thin, sheet-like structures that provide mechanical support for adjacent cells, and function as a semipermeable filtration barrier for macromolecules in organs such as the kidney and the lung.]... 

There are several self-assembling macromolecules that are of interest to us in this text. They include (1) collagen, the primary structural material found in the extracellular matrix (2) actin, a component of the cell cytoskeleton that is involved in cell locomotion and in formation of the thin filaments of muscle (3) microtubules, which are involved in cell mitosis, movement, and organelle movement and finally (4) fibrinogen, which forms fibrin networks that minimize bleeding from cut vessels. Self-assembly is important in these systems because the function of these macromolecules can be modified via processes that increase the molecular axial ratio and hence decrease the solubility. 

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