Beta sheet

From Free net encyclopedia

Image:BetaPleatedSheetProtein.png The β sheet (also β-pleated sheet) is a commonly occurring form of regular secondary structure in proteins, first proposed by Linus Pauling and Robert Corey in 1951. It consists of two or more amino acid sequences within the same protein that are arranged adjacently and in parallel, but with alternating orientation such that hydrogen bonds can form between the two strands. The amino acid chain is almost fully extended throughout a β strand. The N-H groups in the backbone of one strand establish hydrogen bonds with the C=O groups in the backbone of the adjacent, parallel strand(s). The cumulative effect of multiple such hydrogen bonds arranged in this way contributes to the sheet's stability and structural rigidity and integrity. The α-C atoms of adjacent strands stand 350 picometres (0.35 nm) apart.

The side chains from the amino acid residues found in a β sheet structure may also be arranged such that many of the adjacent sidechains on one side of the sheet are hydrophobic, while many of those adjacent to each other on the alternate side of the sheet are polar or charged (hydrophilic).

Some sequences involved in a β sheet, when traced along the backbone, take a hairpin turn in orientation (direction), sometimes through one or more prolines.

Beta sheets actually are not flat as the name might imply. The strands that make up the structure are upon closer observation actually very loosely wound right-hand helices. This is a consequence of the phi and psi rotational angles that are repeated across the backbone of the peptide strands.

Beta sheet aggregation (see amyloid plaque) causes certain diseases including neural diseases like Alzheimer's.

[edit]