The stickers and spacers of Rubiscondensation: assembling the heartpiece of biophysical CO2 concentrating mechanisms.

Aquatic autotrophs that fix carbon using ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) frequently expend metabolic energy to pump inorganic carbon towards the enzyme's active site. A central requirement of this strategy is the formation of highly concentrated Rubisco condensates known as carboxysomes and pyrenoids, which have convergently evolved multiple times in prokaryotes and eukaryotes respectively. Recent data indicates these condensates form by the mechanism of liquid- liquid phase separation (LLPS). LLPS requires networks of weak multivalent interactions typically mediated by intrinsically disordered scaffold proteins. Here we comparatively review recent rapid developments that detail the determinants and precise interactions that underlie diverse Rubisco condensates. The burgeoning field of biomolecular condensates has few examples where LLPS can be linked to clear phenotypic outcomes. When present, Rubisco condensates are essential for photosynthesis and growth, and they are thus emerging as powerful and tractable models to investigate the structure function relationship of phase separation in biology.