ST motif
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Related on Lably
Through Protein, Peptide and Amino acid
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 ST turn.
As with ST turns, a significant proportion of ST motifs occur at the N-terminus of an alpha helix with the serine or threonine as the N cap residue. They have thus often been described as helix capping features.
A related motif is the asx motif which has aspartate or asparagine as the first residue.
Two well conserved threonines at α-helical N-termini occur as ST motifs and form part of the characteristic nucleotide binding sites of SF1 and SF2 type DNA and RNA helicases.
It has been suggested that the sequences SPXX or STXX are frequently found at DNA-binding sites and also that they are recognized as substrates by some protein kinases. Structural studies of polypeptides indicate that such tetrapeptides can adopt the hydrogen bonding pattern of the ST motif.