Structure of PduT, a trimeric bacterial microcompartment protein with a 4Fe-4S cluster-binding site.

Propanediol metabolism in Citrobacter freundii occurs within a metabolosome, a subcellular proteinaceous bacterial microcompartment. The propanediol-utilization (Pdu) microcompartment shell is constructed from thousands of hexagonal-shaped protein complexes made from seven different types of protein subunit. Here, the structure of the bacterial microcompartment protein PduT, which has a tandem structural repeat within the subunit and forms trimers with pseudo-hexagonal symmetry, is reported. This trimeric assembly forms a flat approximately hexagonally shaped disc with a central pore that is suitable for a 4Fe-4S cluster. The essentially cubic shaped 4Fe-4S cluster conforms to the threefold symmetry of the trimer with one free iron, the role of which could be to supply electrons to an associated microcompartment enzyme, PduS.