a-helices (shown in red) 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 a-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 CHIME images of human insulin chains A and B are shown below.
The top pair of images shown both the A and the B chains with the amino
acids in the a-helices highlighted on
the right.
The lower pair of images show only the a-helix
of the B chain.
a-helices
reset
a-helices in
the A and B chains of human insulin
a-helices H-bonds reset
a-helix in
the B chain of human insulin
In the 3D CHIME image of the a-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.
