ST8SIA4

ST8SIA4, also known as ST8 (alpha-2,8-sialyltransferase) or STX, is a protein encoded by the ST8SIA4 gene in humans. This gene is part of the ST8SIA family of enzymes, which are involved in the synthesis of complex carbohydrates, specifically by adding sialic acid residues to other sugar chains. ST8SIA4 is a key player in the formation of polysialic acid (PSA) structures. PSA is a unique post-translational modification that is not found on proteins themselves, but rather on other glycans. This means ST8SIA4 catalyzes the addition of multiple sialic acid units to existing oligosaccharide chains, creating long, unbranched polymers of sialic acid.

The ST8SIA4 enzyme is primarily expressed in the brain and plays a critical role in neuronal development and function. PSA is known to be highly expressed during embryonic development and in the adult brain, particularly in regions associated with learning and memory. Its presence influences cell adhesion, migration, and neuronal plasticity. Dysregulation of PSA synthesis, and consequently ST8SIA4 activity, has been implicated in various neurological disorders, including neurodevelopmental abnormalities and certain types of cancer where PSA expression can be altered. Research into ST8SIA4's function continues to shed light on its multifaceted roles in biological processes.