The stickers and spacers of Rubiscondensation: assembling the centrepiece of biophysical CO2-concentrating mechanisms

Carbon dioxide is often concentrated near the Rubisco active sites of photosynthetic microorganisms. This necessitates the condensation of the carboxylase, which is mediated by liquid-liquid phase separation. 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 (or Rubiscondensates) known as carboxysomes and pyrenoids, which have convergently evolved multiple times in prokaryotes and eukaryotes, respectively. Recent data indicate that these condensates form by the mechanism of liquid-liquid phase separation. This mechanism 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 liquid-liquid phase separation 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.

Automated summary

Carbon dioxide is often concentrated near the Rubisco active sites through liquid-liquid phase separation. Recent studies have shown that highly concentrated Rubisco condensates are formed by this mechanism. Rubisco condensates are essential for photosynthesis and growth, making them a powerful model for investigating the relationship between phase separation and biological structure-function.