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Beta strand In a b strand, the torsion angle of N-Ca-C-N in the backbone is about 120 degrees. The following figure shows the conformation of an ideal b strand. Note that the sidechains of two neighboring residues project in the opposite direction from the backbone.
Figure 2-C-6. An ideal b strand.
Beta sheet A b sheet consists of two or more hydrogen bonded b strands. The two neighboring b strands may be parallel if they are aligned in the same direction from one terminus (N or C) to the other, or anti-parallel if they are aligned in the opposite direction.
Figure 2-C-7. The b sheet structure found in RNase A. This figure shows only the backbone atoms, excluding hydrogens. RNase A contains a single peptide chain, which makes a turn at the junction (not shown) between b4 and b6. Therefore, the two strands are anti-parallel.
Beta barrel A b barrel is a closed b sheet. Online pictures: Porin, More pictures.
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