Asx motif

The Asx motif is a commonly occurring feature in proteins and polypeptides.

Asx motifs occur commonly in proteins and polypeptides.

When one of the hydrogen bonds is between the main chain oxygen of residue i and the side chain NH of residue i+3 the motif incorporates a beta turn.

When one of the hydrogen bonds is between the side chain oxygen of residue i and the main chain NH of residue i+2 the motif incorporates an Asx turn.

Asx motifs have thus often been described as helix capping features.

Asx motif. The image shows a pentapeptide with an N-terminal aspartate that forms two hydrogen bonds to amino acids ahead of it. Except for the aspartate, main chain atoms only are shown. Hydrogen atoms are omitted. Carbons grey, oxygens red and nitrogens blue. The main chain - main chain hydrogen bond is in red and the side chain - main chain hydrogen bond (which also forms an Asx turn ) is dotted grey.