Beta sheet
Channel: all the knowledge of the universe PRINCIPIA
Date: 08/12/2021

Beta sheet, by Wikipedia https://en.wikipedia.org/wiki?curid=4906 / CC BY SA 3.0

#Protein_structural_motifs
Three-dimensional structure of parts of a beta sheet in the GFP protein Interactive diagram of hydrogen bonds in protein secondary structure.
Cartoon above, atoms below with nitrogen in blue, oxygen in red （PDB: 1AXC） The beta sheet, （β-sheet） （also β-pleated sheet） is a common motif of the regular protein secondary structure.
Beta sheets consist of beta strands （β-strands） connected laterally by at least two or three backbone hydrogen bonds, forming a generally twisted, pleated sheet.
A β-strand is a stretch of polypeptide chain typically 3 to 10 amino acids long with backbone in an extended conformation.
The supramolecular association of β-sheets has been implicated in the formation of the fibrils and protein aggregates observed in amyloidosis, notably Alzheimer's disease.
An example of a 4-stranded antiparallel β-sheet fragment from a crystal structure of the enzyme catalase （PDB file 1GWE at 0.88 Å resolution）.
a） Front view, showing the antiparallel hydrogen bonds （dotted） between peptide NH and CO groups on adjacent strands.
Arrows indicate chain direction, and electron density contours outline the non-hydrogen atoms.
Oxygen atoms are red balls, nitrogen atoms are blue, and hydrogen atoms are omitted for simplicity; sidechains are shown only out to the first sidechain carbon atom （green）.
b） Edge-on view of the central two β-strands in a, showing the righthanded twist and the pleat of Cαs and sidechains that alternately stick out in opposite directions from the sheet.
The first β-sheet structure was proposed by William Astbury in the 1930s.
He proposed the idea of hydrogen bonding between the peptide bonds of parallel or antiparallel extended β-strands.
However, Astbury did not have the necessary data on the bond geometry of the amino acids in order to build accurate models, especially since he did not then know that the peptide bond was planar.
A refin...