A Section of Collagen

Collagen is a triple helix that is right-handed. Each strand is a Polyproline II helix. Those helices are left-handed. Collagen is rich in Proline and Hydroxyproline. These are colored dark blue, when the structure changes to wireframe. The central part of the collagen structure illustrates that Proline is not necessary for a PPII helix.

Sequence dependent conformational variations of collagen triple-helical structure.
Kramer RZ, Bella J, Mayville P, Brodsky B, Berman HM.
Nat Struct Biol. 1999 May;6(5):454-7.

(PubMed)

1bkv (PDB)