Polyserine

Polyserine refers to a polymer consisting entirely of serine amino acids joined by peptide bonds, i.e., a serine homopolymer. In biology, polyserine tracts appear as low–complexity regions within proteins and can vary in length between species and individuals. These repeats are commonly found in intrinsically disordered regions and often contribute to flexible linkers or spacers that connect functional domains.

Physically, polyserine is highly hydrophilic due to the hydroxyl side chain of each serine residue, which promotes extensive interactions with water. A long polyserine chain in aqueous solution is expected to be mostly unstructured, with limited propensity to form well-defined, stable secondary structures. The serine side chains also serve as potential sites for post-translational modification, particularly phosphorylation, which can regulate interactions, localization, or activity of the parent protein when such repeats are present in vivo.

Synthesis and study of polyserine can be achieved through chemical peptide synthesis or recombinant expression of serine-rich sequences. Repetitive sequences can pose technical challenges for cloning and expression due to genetic instability, but polyserine-containing polypeptides are useful as model systems for examining the behavior of intrinsically disordered regions and the effects of serine-rich content on solubility and dynamics.

Functional roles attributed to polyserine in natural proteins include serving as flexible spacers, modulating protein-protein interactions, or influencing the regulation of neighboring domains via phosphorylation states. Polyserine is related to the broader concept of low-complexity regions and intrinsically disordered domains that contribute to protein versatility and regulation.