Predicting Rubisco:Linker Condensation from Titration in the Dilute Phase

The condensation of Rubisco holoenzymes and linker proteins into ‘pyrenoids’, a crucial super-charger of photosynthesis in algae, is qualitatively understood in terms of ‘sticker-and-spacer’ theory. We derive semi-analytical partition sums for small Rubisco:linker aggregates, which enable the calculation of both dilute-phase titration curves and dimerisation diagrams. By fitting the titration curves to Surface Plasmon Resonance and Single-Molecule Fluorescence Microscopy data, we extract the molecular properties needed to predict dimerisation diagrams. We use these to estimate typical concentrations for condensation, and successfully compare these to microscopy observations.