Cellular compartmentalisation is widely used in nature for the separation of biochemical reactions and sequestration of intermediates. These compartments come in a variety of forms such as lipid-bound organelles, biomolecular condensates, or protein cages.
Encapsulins are one such example of protein-based nanocompartments, consisting of either 60, 180, or 240 copies of a single protein monomer self-assembled into icosohedral cages up to 42 nm in diameter. Though the precise function of these cages in vivo is yet to be fully elucidated, they are robust, highly stable, and capable of housing both native and non-native protein cargo. Given their ability to be expressed recombinantly and purified via conventional methods, encapsulins are an attractive option for the design of nanoreactors or synthetic organelles.
Ribulose 1,5-bisphosphate carboxylase/oxygenase (RuBisCO) is the enzyme responsible for carbon fixation in the Calvin cycle. Despite its critical role in nature, RuBisCO has poor selectivity between CO2 and O2, the latter creating undesired products. Carboxysomes, protein-bound organelles found in some autotrophs, help overcome this selectivity issue by housing RuBisCO with carbonic anhydrase and by using its shell to control the flux of O2 and CO2 in and out of the compartment. In this work, I will present the progress we have made toward using encapsulin to engineer synthetic carboxysomes through co-encapsulation of RuBisCO and carbonic anhydrase as well as modulating the passage of O2 by genetically fusing the encapsulin shell to oxygen-scavenging enzymes.