The Translationally Controlled Tumor Protein (TCTP) associates to and destabilizes the Circadian Factor Period 2 (Per2)

Period 2 (Per2) is a core circadian factor responsible for its own negative regulation. It operates in the circadian clock, which affects multiple biological functions such as metabolic rate, hormone release, and core body temperature. The Per2 protein functions directly with factors in other biological functions such as tumor suppression, immune system, and metabolism. In many cases, the Per2 deficiency caused by disrupted expression is sufficient to create severe abnormalities in many of the mentioned functions. The sequence contains several domains and motifs in Per2 that are traditionally involved in protein interactions which suggests that Per2 serving a regulatory role by effecting downstream biological roles dependent on Per2 stability.

In this work, we perform a two-hybrid screening assay using the C-terminal region of human Per2 and identified an extensive number of interactors. Utilizing a genetic ontology program, we assorted the list of clones into groups of proteins that are biologically relevant or operated in similar function. Through this program, we validated the two-hybrid screening by the clusters of biological function already attributed to hPer2 and identified new putative biological functions. We use the new putative interactors to gain further insight on the regulatory roles that hPer2 performs, in conjunction with operating as a core factor in circadian rhythmicity.

We also show that Translationally Controlled Tumor Protein (TCTP) is capable of binding to hPer2 and is a novel interaction. When a sufficient amount of TCTP (1:1 molar stoichiometric ratio) is present in a system, a cleavage of hPer2 is observed in vitro. This cleavage occurs in reactions independent of ATP, ubiquitin, and the proteasome. The data points towards a method of cleavage similar to that of the archael lon-tk (Thermococcus kodakaraensis) that preferentially cleaved unstructured substrates in ATP-independent reactions.