The function of the PduJ microcompartment shell protein is determined by the genomic position of its encoding gene.

Bacterial microcompartments (MCPs) are complex organelles that consist of metabolic enzymes encapsulated within a protein shell. In this study, we investigate the function of the PduJ MCP shell protein. PduJ is 80% identical in amino acid sequence to PduA and both are major shell proteins of the 1,2-propanediol (1,2-PD) utilization (Pdu) MCP of Salmonella. Prior studies showed that PduA mediates the transport of 1,2-PD (the substrate) into the Pdu MCP. Surprisingly, however, results presented here establish that PduJ has no role 1,2-PD transport. The crystal structure revealed that PduJ was nearly identical to that of PduA and, hence, offered no explanation for their differential functions. Interestingly, however, when a pduJ gene was placed at the pduA chromosomal locus, the PduJ protein acquired a new function, the ability to mediate 1,2-PD transport into the Pdu MCP. To our knowledge, these are the first studies to show that that gene location can determine the function of a MCP shell protein. We propose that gene location dictates protein-protein interactions essential to the function of the MCP shell.