Biomedical Engineering Reference
In-Depth Information
Okuyama model
1
1
1
1
1
1
1
1
7
20.1 Å
7
7
7
7
7
7
6
6
6
6
6
6
6
6
5
5
5
60.2 Å
60.2 Å
5
20.1 Å
5
5
5
4
4
4
4
4
4
4
4
3
3
3
3
3
3
3
20.1 Å
20.1 Å
2
2
2
2
2
2
2
1
1
1
1
1
A
C
B
7/1-Helix with
60.2 Å pitch length
Triple helix with
20.1 Å repeating unit
Radial projection of 7/2-helix
Figure 1.34
The three-chain configuration proposed for
collagen by Okuyama [216]. Courtesy of Kenji Okuyama.
The triple-helix motif has now been identified in proteins other than collagens,
and it has been established as being important in many specific biological interac-
tions as well as being a structural element. Triple-helix binding domains consist of
linear sequences along the helix, making them amenable to description by simple
model peptides. Advances, principally through the study of peptide models, have led
to an enhanced understanding of the structure and function of the collagen triple
helix. In particular, the first crystal structure has clearly shown the highly ordered
hydration network that is critical for stabilizing both the molecular conformation
and the interactions between triple helices.
Collagen is almost unique among proteins in its use of triple helical secondary
structure. Collagen is also unique among animal proteins in its high content of
hydroxyproline, which is formed as a post-translational modification of prolines,
which are incorporated in the Y position of
Gly
-X-Y triplets. The analysis of collagen
structure emphasizes the dominance of enthalpy and hydrogen bonding in the
stabilization of the triple helix [217-230].
1.3.7.1
Molecular Structure
There are 29 types of collagens known. Over 90% of the collagens in the body,
however, are of types I, II, III, and IV.
•
Collagen I
- skin, tendon, vascular, ligature, organs, bone (main component of
bone);
•
Collagen II
- cartilage (main component of cartilage);
