Dihedral/Dihedral angles in proteins

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<uploadedFileContents>1iy4_34-36.pdb</uploadedFileContents>
<uploadedFileContents>1iy4_34-36.pdb</uploadedFileContents>
<pspeed>8</pspeed>
<pspeed>8</pspeed>
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<script>script /wiki/images/0/0c/Phi-Psi_uni.spt; </script>
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<script>script /wiki/images/0/0c/Phi-Psi_uni.spt; function e_legend() { draw id "d_N" diameter 2 [90 90%] color @{{_N}.color};set echo id "e_N" [91 89%];echo N;color echo @{{_N}.color}; draw id "d_CA" diameter 2 [90 85%] color [x70AB70];set echo id "e_CA" [91 84%];echo "C\u03B1";color echo [x70AB70]; draw id "d_CO" diameter 2 [90 80%] color [xBF9090];set echo id "e_CO" [91 79%];echo "C=O";color echo [xBF9090]; draw id "d_O" diameter 2 [90 75%] color @{{_O}.color};set echo id "e_O" [91 74%];echo "O";color echo @{{_O}.color}; draw id "d_C" diameter 2 [90 70%] color @{{35.CB}.color};set echo id "e_C" [91 69%];echo "C";color echo @{{35.CB}.color}; } e_legend; select all;labels off;</script>
</jmolApplet>
</jmolApplet>
</jmol>
</jmol>

Revision as of 14:20, 15 July 2016

The model displayed on the right is a tripeptide (Trp34–Glu35–Ser36 within the protein lysozyme). This page illustrates the meaning of phi (ϕ) and psi (ψ) angles, both around the alpha carbon of the central residue (Glu35). Both are dihedral angles, meaning an angle formed between two planes (as compared to regular angles, formed between two lines or bonds). They are also called torsion angles, meaning the torsion or rotation around a bond.


phi (ϕ) is defined by these two planes:

  • plane defined by Ci−1, Ni and Cαi
    displayed as (1)
  • plane defined by Ni, Cαi and Ci
    displayed as (2)

Therefore ϕ means rotation around the N-Cα bond.


psi (ψ) is defined by these two planes:

  • plane defined by Ni, Cαi and Ci
    displayed as (3)
  • plane defined by Cαi, Ci and Ni+1
    displayed as (4)

Therefore ψ means rotation around the Cα-C bond.

Note that planes 2 and 3 coincide.
In all these, "C" means the carboxylic carbon, forming the amide or peptide bond

You can run animations that continuously rotate the model changing one of the angles:

animation, and then:

animation, and then:

Bright magenta cylinders are displayed where neighbour atoms collide (hence there is an unfavourable conformation for those particular ϕ, ψ values).

Drag the structure with the mouse to rotate

Proteopedia Page Contributors and Editors (what is this?)

Angel Herraez

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