Here is another 10 residue alpha-helix. What do you observe about the H-bonding in this helix?
The culprit. Complete alpha-helix. Proline lacks an amide proton when found within proteins. This precludes H-bonding between it and hydrogen bond acceptors, and typically restricts the Pro residue to the first 4 positions of an alpha-helix. Positioning a Pro after position four, as in the helix you are viewing, results in the exposure of two backbone carbonyl oxygen atoms. These exposed atoms often serve as important sites for ligand binding. The helix shown here from the muscle protein Actin is fairly straight. In many instances, however, Pro induces a pronounced kink in the helix; this often aids in the packing of long helices in globular proteins.
Complete alpha-helix. Proline lacks an amide proton when found within proteins. This precludes H-bonding between it and hydrogen bond acceptors, and typically restricts the Pro residue to the first 4 positions of an alpha-helix. Positioning a Pro after position four, as in the helix you are viewing, results in the exposure of two backbone carbonyl oxygen atoms. These exposed atoms often serve as important sites for ligand binding. The helix shown here from the muscle protein Actin is fairly straight. In many instances, however, Pro induces a pronounced kink in the helix; this often aids in the packing of long helices in globular proteins.
Proline lacks an amide proton when found within proteins. This precludes H-bonding between it and hydrogen bond acceptors, and typically restricts the Pro residue to the first 4 positions of an alpha-helix. Positioning a Pro after position four, as in the helix you are viewing, results in the exposure of two backbone carbonyl oxygen atoms. These exposed atoms often serve as important sites for ligand binding. The helix shown here from the muscle protein Actin is fairly straight. In many instances, however, Pro induces a pronounced kink in the helix; this often aids in the packing of long helices in globular proteins.