Encapsulation of Heterologous Pathways Within the Pdu Microcompartment of Salmonella Enterica

 

Bacterial microcompartments are subcellular protein structures that encapsulate certain pathways in bacterial cells. They provide some of the same function as the organelles of eukaryotes.  A microcompartment is made up of many hexameric and pentameric shell proteins that fit together to form a polyhedral shape about 100 nm across.  These protein shells may be used to enhance kinetics and product yield of a series of enzymatic reactions by imparting several advantages: increased proximity of enzymes, isolation of toxic intermediates, insulation from inhibitors in the cytosol, and concentration of substrates. These effects have been exhibited by native microcompartments such as the carboxysome in chemoautotrophs and the propanediol utilization (Pdu) microcompartment in Salmonella. It is of interest to learn whether these benefits are also observed for heterologous pathways localized to the microcompartment. To that end, three pathways were expressed in Salmonella and localized to the Pdu microcompartment. Each was chosen to examine a putitative benefit of encapsulation. Here, we discuss the functionality of each encapsulated pathway as compared to the same pathway in the cytosol.  Moreover, we present a strategy for optimizing the Pdu shell proteins for compatibility with non-native metabolites, a potentially critical barrier to successful heterologous pathway encapsulation.