Chapter 27: Amino Acids, Peptides and Proteins
b
-Sheets
b
-pleated sheets (shown in yellow) are so named because the amide backbone of the peptide is arranged in a "zig-zag".
The side chains are typically arranged on each side of the sheet.
b
-sheets are usually stabilised by hydrogen-bonding between a carbonyl oxygen
C=O
on one strand with an amide
N-H
units on
another
strand.
A set of 3D CHIME images of human insulin chains B and D are shown below.
The top pair of images shown both the complete B and D chains with the amino acids in the
b
-sheet highlighted on the right.
The lower pair of images focus on the
b
-sheet portions of the B and D chains (note this is only a short
b
-sheet of 3 amino acid residues).
b
-sheet
reset
b
-sheets in the B and D chains of human insulin
b
-sheet
reset
Close-up of the
b
-sheets in the B and D chains of human insulin
In the close-up 3D CHIME image of th
e
b
-sheets
in the B and chains, twist the image to see the alternate arrangement of the side chains
.
This is an example of
anti-parallel
sheets since the C termini (as indicated by the arrowheads) are at opposite ends of the sheets.
