Phase Separation or Not: The perspective from human circadian clock proteins

講演要旨

Liquid–liquid phase separation (LLPS) was proposed to be involved in diverse biological processes. Intrinsically disorder regions in many proteins have been shown to drive protein LLPS behavior. However, most prior LLPS studies were based on protein overexpression in cells or in vitro biochemical experiments and lacked examination of endogenous proteins. As a result, the physiological relevance of LLPS for endogenous proteins is often unclear.

In this presentation, I will discuss our work on examining the dynamics and interactions of the endogenous human circadian clock proteins. PERIOD, the intrinsically disordered domain-rich proteins, are central mammalian clock components and interact with other clock proteins. We showed that when overexpressed, PER2 protein formed nuclear phosphorylation-dependent slow-moving LLPS condensates that recruited other clock proteins. Examination of endogenous PER2 by super-resolution microscopy, however, revealed that PER2 forms circadian-controlled, rapidly diffusing nuclear microbodies that are distinct from the LLPS condensates caused by protein overexpression. Surprisingly, only a small fraction of PER2 microbodies transiently interact with endogenous BMAL1 and CRY1proteins. Together, these results demonstrate that the dynamic interactions of core clock proteins are a key feature of mammalian circadian clock mechanism and the importance of examining endogenous proteins in LLPS and circadian clock studies.