Material properties of Rubisco-EPYC1 condensates in an algal pyrenoid model

The photosynthetic alga Chlamydomonas reinhardtii contains a liquid-like membraneless organelle called the pyrenoid which concentrates carbon dioxide for more efficient carbon capture. The matrix of the pyrenoid is packed with the carbon-fixing enzyme Rubisco and a linker protein Essential Pyrenoid Component 1 (EPYC1) which serves as molecular glue. We developed a coarse-grained model for interacting Rubisco and EPYC1, with bonding properties derived from experiments, to understand the dynamics and material properties of Rubisco-EPYC1 condensates. We study how condensate properties such as surface tension and viscosity depend on the microscopic variables such as the number of binding sites on each EPYC1 molecule, bond strengths, and the lengths of the linkers between the sites, as well as on the stoichiometry between EPYC1 and Rubisco. We consider how cells can regulate pyrenoid properties, formation, and dissolution via modifications to EPYC1.