Beta sheets occur due to hydrogen bonds between the amine (NH) and carboxyl groups (CO) of the polypeptide backbone, thus making it a very strong and rigid structure. Because the hydrogen bonds occur between the groups on the backbone and not the side chains on the amino acids, many different sequences of amino acids (therefore many different proteins) can fold to produce beta sheets.
There are two types of beta sheets, parallel and anti-parallel sheets. Parallel beta sheets are chains of polypeptides which run in the same direction. Anti-parallel beta sheets are chains of polypeptides which run in opposite directions to each other . In the antiparallel structure, hydrogen bonding occurs respectively between the NH group and CO group of one amino acid with the CO group and NH group of the amino acid on the adjacent chain. In the parallel structure, hydrogen bonding is slightly different, rather than the CO group being bonded directly to the adjacent NH group, it is instead bonded to the NH group on the amino acid two residues further along the chain. This means that in the parallel structure, every amino acid is bonded to two different amino acids on the opposite chain rather than one2.
- ↑ Alberts, B, et al, 2008. Molecular Biology of the Cell. 5th ed. United States of America: Garland Science.
2. Berg JM, Tymoczko JL, Gatto, Jr. GJ, Stryer L. Biochemistry. 8th edition, New York: W. H. Freeman and Company. 2015