Collagen triple helix helical twists

Figure 1.31 Cartoon depiction of the right-handed collagen triple helix. Depiction emphasises how three polypeptides in Left-handed Pn helical conformations associate to form the triple helical structure wherein each polypeptide adopts a gentle right-handed rope-like twist in order to maximise stabilising inter-chain hydrogen bond interactions. Structure is also stabilised by a sheath of ordered water molecules of solvation (illustration from Voet, Voet Pratt, 1999 [Wiley], Fig. 6-17).

Collagen is composed of three left-handed polypeptide helices that are twisted around each other to form a right-handed triple helix (Figure 5.26). Type I collagen molecules, found in teeth, bone, skin, and tendons, are about 300 nm long and approximately 1.5 nm wide. (There are 20 major families of collagen molecules. Approximately 90% of the collagen found in humans is type I.)... 

The three individual collagen chains are themselves helices that differ from the a-helix. They are twisted around each other in a superhelical arrangement to form a stiff rod. This triple helical molecule is called tropocollagen it is 300 nm (3000 A) long and 1.5 nm (15 A) in diameter. The three strands are held together... 

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