Collagen, type structural model

Figure 4.9. Bead models used to simulate macromolecular structures. The drawing shows a model used to simulate a collagen molecule with a single bend at an angle a. Each molecule is represented by a series of N beads of diameter d that are separated by a distance rv. (A) through (D) illustrate the typical shapes observed for collagen type I by rotary electron microscopy. The molecule depicted has a total length of 300 nm.

Examination of the model reveals that every third residue, which must lie near the center of the triple helix, can be only glycine (Figure 6.13a). Any side chain would be too bulky. Formation of the individual helices of the collagen type is also favored by the presence of or hydroxyproline in the tropocollagen molecule. A repetitive theme in the sequence is of the form Gly - X - Y, where X is often proline and Y is proline or hydroxyproline. However, other residues are sometimes tolerated in these positions. Like silk fibroin, collagen is a good example of how a particular kind of repetitive sequence dictates a particular structure. 

The three-dimensional organization of type 1 collagen molecules within a fibril has been the subject of extensive research over the past 40 years [Fraser et al., 1983 Katz and li, 1972,1973a, b, 1981 Miller, 1976 Ramachandran, 1967 Yamuchi et al, 1986]. Many structural models have been proposed based on... 

Figure 6 Model of type VI collagen assembly. Two type VI collagen molecules assemble with 30 nm overlap " with two pairs of disulfide bonds between cysteines, one in collagenous domain and another in the C-terminal globular domain.Two dimers form a tetramer with disulfide bonds presumably in the a3(VI) chains. The tetramers assemble into the long beaded filamentous structure with 105nm periodicity.

Siebold, B., Qian, R., Glanville, R. W., Hofmann, H., Deutzmann, R., and Khun, K. (1987). Construction of a model for the aggregation and cross linking region (7S domain) of Type IV collagen based upon an evaluation of the primary structure of the alphal and alpha2 chains in this region. Eur. J. Biochem. 168, 569-575. 

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