The Escherichia coli Cell Division Protein and Model Tat Substrate SufI (FtsP) Localizes to the Septal Ring and Has a Multicopper Oxidase-Like Structure

The Escherichia coli protein SufI (FtsP) has recently been proposed to be a component of the cell division apparatus. The SufI protein is also in widespread experimental use as a model substrate in studies of the Tat (twin arginine translocation) protein transport system. We have used SufI-GFP (green fluorescent protein) fusions to show that SufI localizes to the septal ring in the dividing cell. We have also determined the structure of SufI by X-ray crystallography to a resolution of 1.9 A. SufI is structurally related to the multicopper oxidase superfamily but lacks metal cofactors. The structure of SufI suggests it serves a scaffolding rather than an enzymatic role in the septal ring and reveals regions of the protein likely to be involved in the protein-protein interactions required to assemble SufI at the septal ring.