Back Lámina alfa Spanish Feuillet alpha French Αシート Japanese Alfa ravan Serbo-Croatian Alfa ravan Serbian

Alpha sheet

Diagram of the hydrogen bonding patterns in the alpha sheet structure. Oxygen atoms are shown in red and nitrogen in blue; dotted lines represent hydrogen bonds. R groups represent the amino acid side chains.
A stick representation of a peptide chain in an alpha-sheet configuration.

Alpha sheet (also known as alpha pleated sheet or polar pleated sheet) is an atypical secondary structure in proteins, first proposed by Linus Pauling and Robert Corey in 1951.[1][2][3] The hydrogen bonding pattern in an alpha sheet is similar to that of a beta sheet, but the orientation of the carbonyl and amino groups in the peptide bond units is distinctive; in a single strand, all the carbonyl groups are oriented in the same direction on one side of the pleat, and all the amino groups are oriented in the same direction on the opposite side of the sheet. Thus the alpha sheet accumulates an inherent separation of electrostatic charge, with one edge of the sheet exposing negatively charged carbonyl groups and the opposite edge exposing positively charged amino groups. Unlike the alpha helix and beta sheet, the alpha sheet configuration does not require all component amino acid residues to lie within a single region of dihedral angles; instead, the alpha sheet contains residues of alternating dihedrals in the traditional right-handed (αR) and left-handed (αL) helical regions of Ramachandran space. Although the alpha sheet is only rarely observed in natural protein structures, it has been speculated to play a role in amyloid disease[4] and it was found to be a stable form for amyloidogenic proteins in molecular dynamics simulations.[5][6] Alpha sheets have also been observed in X-ray crystallography structures of designed peptides.[4]

The regular formation of alpha-sheet by unfolded proteins inevitably involves many L amino acid residues readily adopting the alphaL conformation, which appears at first sight to go against textbook chemistry, which is that, of the 20 amino acids, it is glycine that strongly favours this conformation. The conundrum is resolved by realizing that the alphaL region comprises two overlapping areas, here called γL and αL, which should be considered separately. It turns out that, while the γL conformation is adopted, almost exclusively, by glycine, the αL conformation of alpha-sheet is more commonly, or about as commonly, adopted by any of 15 L-amino acids compared to glycine, the exceptions being proline, threonine, valine and isoleucine, which are rare at this conformation.[7] Hence, of the 20 amino acids, 16 readily adopt the αL conformation.

  1. ^ Pauling, L. & Corey, R. B. (1951). The pleated sheet, a new layer configuration of polypeptide chains. Proc. Natl. Acad. Sci. USA 37, 251–6. PMID 14834147
  2. ^ Pauling, L. & Corey, R. B. (1951). The structure of feather rachis keratin. Proc. Natl. Acad. Sci. USA 37, 256–261. doi:10.1073/pnas.37.5.256 PMID 14834148
  3. ^ Pauling, L. & Corey, R. B. (1951). Configurations of Polypeptide Chains With Favored Orientations Around Single Bonds: Two New Pleated Sheets. Proc. Natl. Acad. Sci. USA 37, 729–740. PMID 16578412
  4. ^ a b Daggett V. (2006). Alpha-sheet: The toxic conformer in amyloid diseases? Acc Chem Res 39(9):594-602. doi:10.1021/ar0500719 PMID 16981675
  5. ^ Babin V, Roland C, Sagui C. (2011). The alpha-sheet: A missing in action secondary structure. Proteins 79:937-946. doi:10.1002/prot.22935
  6. ^ Armen RS, DeMarco ML, Alonso DO, Daggett V. (2011). Pauling and Corey's alpha-pleated sheet structure may define the prefibrillar amyloidogenic intermediate in amyloid disease. Proc Natl Acad Sci USA 101(32):11622-7. doi:10.1073/pnas.0401781101 PMID 15280548
  7. ^ Hayward S. (2021). Determination of amino acids that favour the alphaL region using Ramachandran propensity plots. Implications for alpha-sheet as the possible amyloid intermediate. Journal of Structural Biology 213:α107738.

Developed by StudentB