![]() MCPs are among the largest multiprotein complexes known. They consist of sequentially acting metabolic enzymes (an enzymatic core) encapsulated within a protein shell that controls the diffusion of enzyme substrates and products while confining toxic or volatile intermediates ( 10, – 14). The function of MCPs is to optimize metabolic pathways having intermediates that are toxic or poorly retained by the cell envelope ( 5, 7, 9). Hundreds of species of bacteria produce complex proteinaceous organelles known as bacterial microcompartments (MCPs) ( 1, – 8). This finding is of fundamental importance to our understanding of microcompartment assembly and may have application to engineering microcompartments as nanobioreactors for chemical production. We propose that this interaction might be used to define the relative orientation of the shell with respect to the core. The results indicate that it plays a key role in binding the outer shell to the enzymatic core. Here, we show that the N-terminal 37 amino acids of the PduB shell protein are essential for assembly of the 1,2-propanediol utilization microcompartment. IMPORTANCE Bacterial microcompartments consist of metabolic enzymes encapsulated within a protein shell and are widely used to optimize metabolic process. ![]() Considering the findings presented here together with prior work, we propose a new model for MCP assembly. Analyses of 13 site-directed mutants indicated that the key region of the N terminus of PduB required for MCP assembly is a putative helix spanning residues 6 to 18. Electron microscopy substantiated these findings by identifying apparently empty MCP shells but not intact MCPs. Attempts to purify MCPs from these mutants, followed by gel electrophoresis and enzyme assays, indicated that the protein complexes isolated consisted of MCP shells depleted of core enzymes. ![]() Growth tests indicated that three of these deletions were impaired MCP assembly. Several mutations were constructed that deleted short regions of the N terminus of PduB. ![]() In this report, we show that the N-terminal 37 amino acids of the PduB protein have a critical role in binding the shell of the 1,2-propanediol utilization (Pdu) microcompartment to its enzymatic core. A key question in MCP biology is the nature of the interactions that guide the assembly of thousands of protein subunits into a well-ordered metabolic compartment. Bacterial microcompartments (MCPs) are extremely large proteinaceous organelles that consist of an enzymatic core encapsulated within a complex protein shell. ![]()
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