Molecular Crowding Facilitates Bundling of IMPDH Polymers and Cytoophidium Formation

Abstract

The cytoophidium is a unique type of membraneless compartment comprising of filamentous protein polymers. Inosine monophosphate dehydrogenase (IMPDH) catalyzes the rate-limiting step of de novo GTP biosynthesis and plays critical roles in active cell metabolism. However, the molecular regulation of cytoophidium formation is poorly understood. Here we show that human IMPDH2 polymers bundle up to form cytoophidium-like aggregates in vitro when macromolecular crowders are present. The self-association of IMPDH polymers is suggested to rely on electrostatic interactions. In cells, the increase of molecular crowding with hyperosmotic medium induces cytoophidia, while the decrease of that by the inhibition of RNA synthesis perturbs cytoophidium assembly. In addition to IMPDH, CTPS and PRPS cytoophidium could be also induced by hyperosmolality, suggesting a universal phenomenon of cytoophidium-forming proteins. Finally, our results indicate that the cytoophidium can prolong the half-life of IMPDH, which is proposed to be one of conserved functions of this subcellular compartment.

Super-resolution imaging reveals dynamic reticular cytoophidia

“…A large number of hCTPS transforms the morphology of CTPS bundles into complex structures. Cytoophidia are regulated by the level of cell crowding (Chang et al, 2022). The formation and maintenance of the skeletal cytoophidia may be related to cell crowding.…”

“…Cytoophidia in Drosophila female germ cells also exhibit reticular characteristics (Liu, 2010). Cytoophidia are regulated by the level of molecular crowding in the cell (Chang et al, 2022). The formation and maintenance of the reticular cytoophidia may be related to molecular crowding.…”

Asymmetric inheritance of cytoophidia could contribute to determine cell fate and plasticity

“…Indeed, the formation of cytoophidia can protect CTPS as well as IMPDH proteins from degradation in mammalian cells. [56,57] Hence, this contributes to the role of cytoophidia formation in enhancing CTPS or IMPDH catalytic functions in mammalian cells.…”

“…Indeed, the formation of cytoophidia can protect CTPS as well as IMPDH proteins from degradation in mammalian cells. [ 56,57 ] Hence, this contributes to the role of cytoophidia formation in enhancing CTPS or IMPDH catalytic functions in mammalian cells. Serve as a platform that modulates the function of other factors binding to the filament. The APEX technology has been used to map the proteome of CTPS cytoophidia [ 58 ] and antibody‐based immunofluorescence screening has identified 19 proteins that co‐localize with IMPDH filaments.…”

What can asymmetrical cell snakes do?

“…[ 2 ] Cytoophidium assembly is controlled by ligand binding, post‐translational modifications, pH value and molecular crowding. [ 3 ] Therefore, the formation of cytoophidia may reflect the cell status and also influence cell behaviours.…”