Chapter 27: Amino Acids, Peptides and Proteins

α-Helices

•  α-helices (shown in magenta) are so named because the amide backbone of the peptide is arranged in a right-handed spiral.
• The side chains are typically arranged pointing out and away from that spiral.
• The α-helix is stabilised by hydrogen-bonding between the carbonyl oxygen C=O and amide N-H units situated four residues away.
• A set of 3D JSMOL images of human insulin chains A and B are shown below.
• The top pair of images shown both the A and the B chains. The amino acids in the α-helices can be highlighted on the right.
• The lower pair of images show only the α-helix of the B chain.

Jmol._Canvas2D (Jmol) "window0"[x]	Jmol._Canvas2D (Jmol) "window1"[x]	Highlight alpha helix
α-helices in the A and B chains of human insulin

 

Jmol._Canvas2D (Jmol) "window2"[x]	Jmol._Canvas2D (Jmol) "window3"[x]	Highlight alpha helix
α-helix in the B chain of human insulin

• In the 3D JMOL image of the α-helix in the B chain, you can see the spiral by manipulating the image to look along the central core of the spiral, where the external arrangement of the side chains becomes obvious.
• You should also look at the hydrogen-bonding between the carbonyl oxygen C=O and amide N-H units situated four residues away in this helix.

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© Dr. Ian Hunt, Department of Chemistry