Beta Sheet

A beta sheet (β-sheet) is a common secondary structure of proteins in which extended strands of the polypeptide chain lie side by side and are joined by hydrogen bonds. It was proposed by Linus Pauling and Robert Corey in 1951, together with the alpha helix.

Each strand is a nearly fully extended stretch of five to ten residues, with a zigzag or pleated backbone, which gives the structure its alternative name of pleated sheet. In antiparallel sheets neighboring strands run in opposite directions, while in parallel sheets they run in the same direction. Hydrogen bonds link the backbone atoms of adjacent strands, and the side chains point alternately above and below the sheet.

Sheets usually twist and can curl into barrels, as in the porins of the outer membranes of Gram-negative bacteria and in fluorescent proteins. Silk is made of stacked antiparallel sheets, and the folds of antibody domains are built from two sheets packed together.

Proteins that misfold can stack into long fibrils with a cross-beta pattern, held by hydrogen bonds between strands. These amyloid fibers are found in Alzheimer's disease and prion diseases. Chaperone proteins help prevent such misfolding, and the structure's properties were studied through X-ray crystallography.

• Alpha Helix — the other main secondary structure
• Proteins — the molecules that contain it
• Chaperone Proteins — helpers that prevent misfolding