SerineThreonine

Serinethreonine is not a standard amino acid. In most biochemical contexts the two residues, serine (Ser) and threonine (Thr), are treated separately. The term serinethreonine is sometimes used informally to denote a dipeptide consisting of a serine residue linked to a threonine residue (Ser–Thr or Thr–Ser), or more generally to refer to adjacent serine and threonine residues within a protein. It is not a fixed chemical entity recognized as a single amino acid in biology.

Chemical and structural features: As a dipeptide, serinethreonine would present two polar side chains bearing hydroxyl groups, enabling hydrogen bonding and facilitating interactions with solvent and enzymes. The dipeptide can exist in two orders (Ser–Thr and Thr–Ser), which influence its conformational preferences and terminus accessibility. Serine and threonine residues are typical sites of post-translational modification, particularly phosphorylation, which may be studied in the context of serinethreonine-containing dipeptides.

Occurrence and synthesis: In proteins, a Ser–Thr dipeptide occurs whenever serine and threonine residues appear consecutively. Chemically it can be prepared by solid-phase peptide synthesis or enzymatic methods, serving as a model substrate in kinetic and structural studies. It is not, however, a standard building block of the genetic code or a defined biological monomer.

Applications: In research, serinethreonine dipeptides are used as simple models to examine solvation, conformational dynamics, and the effects of proximal hydroxyl groups on peptide behavior. They also serve as calibration or reference compounds in chromatographic separation and mass spectrometry of dipeptides, and as educational examples in peptide chemistry.

See also: serine, threonine, phosphoserine, phosphothreonine, dipeptides.