Alpha-helix kinked by presence of Proline

This is a membrane spanning alpha-helix from bacteriorhodopsin. The Proline residue is colored green. Notice the kink in the helix. It creates a discontinuity in the H-bonding pattern. The Proline does not have an NH hydrogen for H-bonding, so the CO (colored Pink) bends away to find another partner.

Model for the structure of Bacteriorhodopsin based on high-resolution Electron Cryo-microscopy
Henderson, R., Baldwin, J.M., Ceska, T.A., Zemlin, F., Beckmann, E., Downing, K.H.
(1990) J.Mol.Biol. 213: 899-929

(PubMed)

1brd (PDB)