Threonine residue ($T$)

A threonine residue is a threonine unit incorporated into a peptide or protein chain, conventionally represented by T. Its hydroxyl-bearing side chain can participate in hydrogen bonding and can be phosphorylated by suitable protein kinases. The side chain is retained during peptide-bond formation, while the amino and carboxyl groups become part of the backbone. Residue identity and modification state are therefore distinct information. ^[ref]