beta sheet(redirected from Psi loop)
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A secondary structure that occurs in many proteins and consists of two or more parallel adjacent polypeptide chains arranged in such a way that hydrogen bonds can form between the chains. Also called beta pleated sheet, pleated sheet.
beta sheetA protein configuration resulting from the alignment of multiple adjacent beta strands and formation of hydrogen bonds between them. The beta sheet is a major secondary protein structure motif elucidated by Pauling and Corey, which consists of polypeptide chains in sheets laid side-by-side and are almost completely extended, with an axial distance of 35 nm vs an axial distance of 15 nm in the helix. The PS is stabilised by hydrogen bonds between NH and CO groups of different polypeptide strands; adjacent molecules may run in the same direction (parallel) or in the opposite (antiparallel) direction—e.g., silk fibroin. The PS is a tertiary structure elucidated by X-ray crystallography and seen by EM; it can be produced experimentally by treating Bence-Jones proteins with enzymes, and is a structure typical of amyloidosis. The PS may be seen by the Congo red stain with polarising light to reveal the characteristic apple-green birefringence.
Extracellular 700–1000 nm in diameter, fine complex non-branching fibrils.
A protein structure in which parallel layers of linked peptides are folded across each other. This structure is characteristic of amyloid proteins.
See also: sheet