| Definition: |
A peptide region which hydrogen bonded to another region of peptide running in the oposite direction (both running N-terminal to C-terminal). This orientation is slightly less stable because it introduces nonplanarity in the inter-strand hydrogen bonding pattern. Hydrogen bonding occurs between every other C=O from one strand to every other N-H on the adjacent strand. In this case, if two atoms C-alpha (i)and C-alpha (j) are adjacent in two hydrogen-bonded beta strands, then they do not hydrogen bond to each other; rather, one residue forms hydrogen bonds to the residues that flank the other (but not vice versa). For example, residue i may form hydrogen bonds to residues j - 1 and j + 1; this is known as a wide pair of hydrogen bonds. By contrast, residue j may hydrogen-bond to different residues altogether, or to none at all. The dihedral angles (phi, psi) are about (-120 degrees, 115 degrees) in parallel sheets. |