securin

Securin is a protein that plays a critical role in the control of chromosome segregation during cell division. In many organisms, securin is encoded by the PT TG1 gene in humans and has orthologs including Pds1 in budding yeast and Cut2 in fission yeast. It functions primarily by binding to and inhibiting separase, a protease responsible for cleaving the cohesin complex that holds sister chromatids together.

The inhibition of separase by securin prevents premature separation of sister chromatids during metaphase. Upon activation of the anaphase-promoting complex/cyclosome (APC/C) with its activator Cdc20, securin is ubiquitinated and targeted for proteasomal degradation. This degradation releases separase from inhibition, allowing it to cleave cohesin components such as Scc1/Rad21, which enables sister chromatids to separate and migrate to opposite poles during anaphase.

Beyond its mitotic role, securin is also linked to other cellular processes in some contexts, including potential involvement in DNA repair pathways and centrosome duplication, though the core function remains the regulation of sister chromatid cohesion. Proper timing of securin destruction is essential for accurate chromosome segregation and mitotic progression; failure to degrade securin can lead to mitotic arrest, while premature degradation can cause chromosome mis-segregation.

In humans, overexpression of securin (PTTG1) has been observed in several cancers and is associated with genomic instability and poor prognosis in some tumor types. As a result, securin and its regulation by the APC/C are studied as potential markers and targets in cancer biology.