Th1L04 Alpha helices and beta pleated sheets

Th1L04 Alpha helices and beta pleated sheets

1. Types of secondary protein structure

   • The folding/ coiling of a peptide chain

2. Alpha helix

   • Properties
     • Amino acid side chains stick outwards
     • Arrangement due to the strength of the hydrogen bonds b/w peptides
       • Allows for best stabilisation energy between H-bonds
       • between peptide bond cabonyl-O and H of N-H in every 4th peptide
         • 0.54 nm distance between the troughs
   • Regular right-handed helix
     • 3.6 residues/turn stabilised by H-bonds
     • Rigid cylinder shape serves as architectural support for protein
   • Triple alpha helix
     • Three chains
       • H-bonds between alpha chains
     • Found in fibrous proteins
     • 3 residues/ turn
     • Left-handed helix
     • Amino acid chain
       • gly - x - y- gly - x - y
         • x = mainly proline
         • y = mainly hydroxy-proline
   • Unique amino acids
     • Proline
       • Cannot go in the alpha helix because its structure
         • aromatic ring
     • Glycine
       • Does not have an R group, which may explain why it is used in triple alpha helice
         • Results in a more compact structure

3. Beta pleated sheet

   • Linear peptide chains
   • Hydrogen bonds between peptide bonds
   • Side chains in each strand alternately lie above and below the plane of the sheet
   • Types
     • Antiparallel with a beta-hairpin bend
       • Widespread in globular proteins
     • Parallel with upper curve toward C terminus and lower curve toward N terminus
       • Found in fibrillar proteins
         • High tensile strength but not elasticity

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