Editing Beta sheet (section)

==History==
[[File:1gwe antipar betaSheet both.png|thumb|right|500px| An example of a 4-stranded [[Antiparallel (biochemistry)|antiparallel]] β-sheet fragment from a crystal structure of the enzyme [[catalase]] ([[Protein Data Bank|PDB]] file 1GWE at 0.88&nbsp;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 C<sup>α</sup>s 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 bond]]s 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 refined version was proposed by [[Linus Pauling]] and [[Robert Corey]] in 1951. Their model incorporated the planarity of the peptide bond which they previously explained as resulting from keto-enol [[tautomerization]].