Collagen macromolecule

Nishihara T., Doty P. 1958. The Sonic Fragmentation of Collagen Macromolecules. Proceeding National Academic Sciences 44, 411-417. 

There are pyridine cross-links between the parallel chains of collagen of bone mass, namely, between the lysine amino acid residues (PYD), and between the lysine and hydroxylysine residues (DPD). They are found in nonhelical terminal (N- and C-terminal) regions of collagen macromolecules—telopeptides. They are the final products of the biodegradation of collagen excreted to urine in the kidneys. 

The existence of these subunits establishes with certainty that intramolecular cross-links exist between the individual chains of the collagen macromolecule. Isolation of even larger components from insoluble collagens (Veis et al, 1960, 1961) establishes that in mature collagen inter-molecular cross-links are also present. 

In addition to the hydrogen bonding which stabilises the triple helix, a variety of links are formed between adjacent molecules within the fibrillar structure. In particular, covalent bonds are formed between the ends of one collagen macromolecule in what is termed the telopeptide region and the helical structure of an adjacent one. 

The reactions involved in the chrome-tanning process are those of coordination complexes. They involve the interaction between charged carboxyl groups on the collagen macromolecule and polynuclear chromium(III) coordination compounds. The most widely used chrome-tanning material is 33% basic chromium(III) sulfate produced industrially by reducing sodium dichromate with sulfur dioxide. 

The detailed spatial structure has been worked out using X-ray diffraction data, together with the clue that glycine occupies every third position. The main structural features of the collagen macromolecule are shown in Figure 27.5. 

Figure 27.5 Arrangement of the polypeptide chains in the collagen macromolecule...

Figure 27.6 Aggregation of collagen macromolecules to form a striated fibril - the quarter staggered arrangement...

Later, many research groups demonstrated the ability of nucleation of HA crystals onto collagen through a chemical interaction of carboxylate groups of collagen macromolecules [138-140]. All the reports suggested that the nucleation process... 

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