The ST staple is a common four- or five-

amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although over 500 amino acids exist in nature, by far the most important are the 22 α-amino acids incorporated into proteins. Only these 22 a ...

residue motif in

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residue (biochemistry), residues. Proteins perform a vast array of functions within organisms, including Enzyme catalysis, catalysing metab ...

s and

polypeptide Peptides are short chains of amino acids linked by peptide bonds. A polypeptide is a longer, continuous, unbranched peptide chain. Polypeptides that have a molecular mass of 10,000 Da or more are called proteins. Chains of fewer than twenty ...

s with

serine Serine (symbol Ser or S) is an α-amino acid that is used in the biosynthesis of proteins. It contains an α- amino group (which is in the protonated − form under biological conditions), a carboxyl group (which is in the deprotonated − ...

threonine Threonine (symbol Thr or T) is an amino acid that is used in the biosynthesis of proteins. It contains an α-amino group (which is in the protonated −NH form when dissolved in water), a carboxyl group (which is in the deprotonated −COO− ...

as the

C-terminal The C-terminus (also known as the carboxyl-terminus, carboxy-terminus, C-terminal tail, carboxy tail, C-terminal end, or COOH-terminus) is the end of an amino acid chain (protein or polypeptide), terminated by a free carboxyl group (-COOH). When t ...

residue. It is characterized by a single hydrogen bond between the hydroxyl group of the

(at residue ''i'' + 3 or ''i'' + 4) and the main chain

carbonyl In organic chemistry, a carbonyl group is a functional group with the formula , composed of a carbon atom double bond, double-bonded to an oxygen atom, and it is divalent at the C atom. It is common to several classes of organic compounds (such a ...

group of residue ''i''. Motifs are of two types, depending whether the motif has 4 or 5 residues. Most ST staples occur in conjunction with an

alpha helix An alpha helix (or α-helix) is a sequence of amino acids in a protein that are twisted into a coil (a helix). The alpha helix is the most common structural arrangement in the Protein secondary structure, secondary structure of proteins. It is al ...

, and are usually associated with a slight bend in the helix. Two websites are available for finding and examining ST staples in proteins:
Motivated Proteins
an
PDBeMotif
{{cite journal, last=Golovin, first=A, author2=Henrick K, title=MSDmotif: exploring protein sites and motifs., journal=BMC Bioinformatics, year=2008, volume=9, pages=312, doi=10.1186/1471-2105-9-312, pmid=18637174, pmc=2491636, issue=1, doi-access=free

References

Protein structural motifs Pentapeptides