MoBio Beta Strand, Beta Sheet and Beta Barrel Chapter 2

Beta strand

In a β strand, the torsion angle of N-Cα-C-N in the backbone is about 120 degrees. The following figure shows the conformation of an ideal β strand. Note that the sidechains of two neighboring residues project in the opposite direction from the backbone.


Figure 2-C-6. An ideal β strand.

Beta sheet

A β sheet consists of two or more hydrogen bonded β strands. The two neighboring β 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 β 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 β4 and β6. Therefore, the two strands are anti-parallel.

Beta barrel

A β barrel is a closed β sheet.


Figure 2-C-8. The β barrel structure in porins, which are transmembrane proteins that facilitate transfer of small molecules. [Source: Wikipedia]