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3.2 Sheets
A residue in an antiparallel beta strand has values of -139 and +135 degrees for the backbone dihedral angles phi and psi, respectively. Antiparallel beta sheets are thought to be intrinsically more stable than parallel sheets due to the more optimal orientation of the interstrand hydrogen bonds and that peptide bond dipoles of nearest neighbors within an strand cancel whereas in the parallel sheet, components of the dipoles parallel to the strands align and may interact unfavorably. However, in their exhaustive survey of hydrogen bonds in protein three-dimensional structures, Baker & Hubbard (1984) found no significant difference in the linearity of the hydrogen bonds in parallel and antiparallel sheets. An example of a mixed beta sheet containing an antiparallel component is given using the protein thioredoxin (Figure 10 ).
Figure 10. The three-stranded antiparallel beta sheet in the protein thioredoxin (2TRX.PDB). The three antiparallel strands are shown in both cartoon format (left) and in stick form containing backbone atoms N, CA, C, and O' (right). Hydrogen bonds are identified by arrows connecting the donor nitrogen and acceptor oxygens. Strands are numbered according to their relative position in the polypeptide sequence.
download 2TRX.PDB
download RasMol script for antiparallel sheet
No Title - 31 MAY 96
written by Kurt D. Berndt
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