Driven protein fluxes control the number, size, and position of an essential phase- separated organelle in algae

Linnea Lemma, Princeton University

Title: Driven protein fluxes control the number, size, and position of an essential phase-
separated organelle in algae

Abstract:
Phase separation of biological molecules has emerged as a key mechanism by which cells organize their components. Investigating the physical principles by which these biomolecular condensates facilitate cellular functions, which are generically out-of-equilibrium, remains a grand challenge at the intersection of statistical physics and cell biology. The inherent complexity of biological systems has posed a significant obstacle to conceptual progress in this field. We leverage the algal pyrenoid—an experimentally tractable condensate responsible for 30% of global CO 2 fixation—as a powerful model system. Notably, during cell division, the pyrenoid, consisting of the CO 2 -fixing enzyme Rubisco and the linker protein EPYC1, undergoes rapid dissolution and recondensation. We identify a kinase, KEY1, that regulates pyrenoid dissolution and proves to be essential for maintaining pyrenoid number, size, and function. We develop a minimal mathematical model of kinase activity that recapitulates the dynamic behaviors seen in vivo and suggests how molecular fluxes driven by kinase activity can robustly control condensate formation and localization.