Summary

Bacterial cytokinesis requires the divisome, a complex of proteins that co-ordinates the invagina-tion of the cytoplasmic membrane, inward growth of the peptidoglycan layer and the outer membrane. Assembly of the cell division proteins is tightly regu-lated and the order of appearance at the future divi-sion site is well organized. FtsQ is a highly conserved component of the divisome among bacteria that have a cell wall, where it plays a central role in the assem-bly of early and late cell division proteins. Here, we describe the crystal structure of the major, periplas-mic domain of FtsQ from Escherichia coli and Yers-inia enterocolitica. The crystal structure reveals two domains; the a-domain has a striking similarity to polypeptide transport-associated (POTRA) domains and the C-terminal b-domain forms an extended b-sheet overlaid by two, slightly curved a-helices. Mutagenesis experiments demonstrate that two func-tions of FtsQ, localization and recruitment, occur in two separate domains. Proteins that localize FtsQ need the second b-strand of the POTRA domain and those that are recruited by FtsQ, like FtsL/FtsB, require the surface formed by the tip of the last a-helix and the two C-terminal b-strands. Both domains act together to accomplish the role of FtsQ in linking upstream and downstream cell division pro-teins within the divisome