Hi there,

P and G are not compatible with alpha helix structure (right handed helix 3.613) . The collagen triple helice (right handed superhelix) is not made of alpha type helices, it's made of type 2 helix (left handed helix).

Hi there,

P and G are not compatible with alpha helix structure (right handed helix 3.613) . The collagen triple helice (right handed superhelix) is not made of alpha type helices, it's made of type 2 helix (left handed helix).

Dear Aizaz Ul Haq ,

Due to the bulky (side chain) groups of Prolines and hydroxyprolines (and sometimes stretches of charged amino acids) this type of helix, originally found in collagen, is often called an extended helix also known as a polyProline helix or a left-handed polyProline II helix (PPII, poly-Pro II). The hydrogen bond donors needed to form the well-known collagen triple helix are the peptide NH groups of glycine residues.

See for more info about poly-Proline-II helices:

Article Polyproline-II Helix in Proteins: Structure and Function

Chapter Characterization of helical junction zones in gelatin networ...

Chapter Characterization of helical structures in gelatin networks a...

For more info about the collagen structure:

Shoulders, M. D., & Raines, R. T. (2009). Collagen Structure and Stability. Annual Review of Biochemistry, 78, 929-58.

http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.505.5611&rep=rep1&type=pdf

Best regards.

Proline does not found in alpha helical structure of the proteins,since it has special cyclic structure ( it is an imino acid not amino acid )m this type of secondary structure has specific width and specific number of amino acids residues / turn. Therefore proline is consider as alpha helical breaker. and for glycine it is too small to be present within this type of secondary structure. Collagen has specific triple helical structure, which is much wider than alpha helix .Proline within this structure is usually present as hydroxy proline & its structure is suitable for this triple helical structure & in fact it is essential to form this structure of collagen, as is the presence of glycine since there is no steric hindrance in this case.