(140f) The Self-Assembling Property of the Major Shell Proteins of the 1,2-Propanediol Bacterial Microcompartment Is Necessary for Compartment Formation (Faculty Candidate)

From small viruses to large eukaryotic cells, biological structures contain proteins that self-assemble into intricate constructs to perform diverse biological functions. The assemblies can be composed of a single protein, as in virus-like-particles, or a more complex mixture of multiple proteins, as in bacterial microcompartments (MCPs). MCPs compartmentalize enzymes and cofactors of a metabolic pathway within a protein shell. This compartmentalization offers solutions to the common bottlenecks of cellular systems used for biomolecule productions, such as reduced flux through the pathway, unwanted side-reactions, and low yield due to cell toxicity from toxic intermediates. The 1,2-propanediol utilization (Pdu) MCP is one of the most studied MCPs. Yet, how the eight shell proteins—PduA, PduB, PduB’, PduJ, PduK, PduN, PduU, and PduT – assemble to form the MCP shell and the critical properties necessary for the assembly is not yet known. This knowledge gap prevents researchers from engineering the native system and harnessing this powerful strategy of subcellular organization. In this work, we fill some of that gap by investigating the role of the self-assembling property of the Pdu shell proteins on the MCP formation. We demonstrate that hexameric shell proteins PduA and PduJ self-assemble into long rods and induce a cell division defect when overexpressed. This property is crucial for MCP formation, and we show that the presence of at least one of the two shell proteins is necessary for the MCPs to properly assemble and cannot be substituted by other shell proteins with no self-assembly property. In the process of our study, we also discovered a new control for the Pdu MCP system, where all enzymes are expressed but no protein shell assemble to encapsulate them. This control will facilitate further characterization of the Pdu MCP shell properties, assembly, and function. The improved understanding will enable engineering and wider application of MCPs, such as in metabolic engineering, that will fully harness the benefits offered by subcellular compartmentalization.