serthr

SerThr is a shorthand used in biochemistry to refer to the amino acids serine (Ser) and threonine (Thr). Both are polar, uncharged residues with hydroxyl groups in their side chains: serine has -CH2OH, threonine has -CH(OH)CH3. These hydroxyl groups make Ser and Thr good sites for chemical modification and hydrogen bonding, and they are among the most common amino acids in proteins.

Phosphorylation of serine and threonine residues is a major post-translational modification. Serine/threonine kinases catalyze the transfer of a phosphate from ATP to the hydroxyl group, influencing protein activity, interactions, localization, and signaling pathways. Opposing phosphatases remove the phosphate group. This reversible phosphorylation is central to many processes including cell cycle progression, metabolism, and stress responses.

Other modifications include O-linked glycosylation and O-GlcNAc attachment, particularly in cytosolic and nuclear proteins; these modifications can affect stability and interactions. Ser/Thr-rich regions are also common in intrinsically disordered parts of proteins and in mucins and secreted proteins, contributing to solubility and binding properties.

Genetically, serine and threonine are encoded by multiple codons in the genetic code, reflecting their essential roles across organisms. While chemically similar, threonine’s extra methyl group makes it slightly more hydrophobic and sterically demanding than serine, influencing its preferred structural contexts.