Protein Secondary Structure Section G
Beta SHEET
Beta sheets are also held together by hydrogen bonds between the Hydrogen on the Nitrogen and another amide carbonyl oxygen of the peptide bonds but between chains of the backbone rather than along it as was found for the Alpha helix. These are called interchain H-bonds since they form between two parts of the polypeptide backbone separated from one another by some distance or length of the amino acid sequence of the polypeptide.
Figure 12. Simple model of H-Bonding in a Beta Sheet.
Two types of backbone chain order is found:
1. PARALLEL where the chains run in the same direction
2. ANTI-PARALLEL where chains run in the opposite direction
Figure 13. Models of (a) Antiparallel and (b) Parallel Beta Sheets (Only two strands of beta-sheet shown).
(From Voet/Biochemistry ©1990 John Wiley)
Figure 14. Simple Model of Antiparallel and Parallel Beta Sheet in a region of a Protein.
In the Beta sheet structure the amino acid side chains project above and below the plane of the sheet. The R groups (amino acid side chains) alternate above and below the sheet along the backbone chain.
Figure 15. Model showing projection of Amino Acid Side Chains above and below plane of Beta Sheet.
©Wilbur H. Campbell, 1995; wcampbel@mtu.edu