Chapter 27: Amino Acids, Peptides and Proteins

β-Sheets

• β-pleated sheets (shown in orange)  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.
•  β-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 JMOL 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 acid backbone in the β-sheet highlighted on the right.
• The lower pair of images focus on the β-sheet portions of the B and D chains (note this is only a short β-sheet of 3 amino acid residues).

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β-sheets in the B and D chains of human insulin

 

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Close-up of the β-sheets in the B and D chains of human insulin

• In the close-up 3D JMOL image of the β-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.

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