Domain architecture and structure of the bacterial cell division protein DivIB

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Abstract
Bacterial cytokinesis requires the coordinated assembly of a complex of proteins, collectively known as the divisome, at the incipient division site. DivIB/FtsQ is a conserved component of the divisome in bacteria with cell walls, suggesting that it plays a role in synthesis and/or remodeling of septal peptidoglycan. We demonstrate that the extracytoplasmic region of DivIB comprises three discrete domains that we designate α, β, and γ from the N to C terminus. The α-domain is proximal to the cytoplasmic membrane and coincident with the polypeptide transport-associated domain that was proposed previously to function as a molecular chaperone. The β-domain has a unique 3D fold, with no eukaryotic counterpart, and we show that it interconverts between two discrete conformations via cis–trans isomerization of a Tyr–Pro peptide bond. We propose that this isomerization might modulate protein–protein interactions of the flanking α- and γ-domains. The C-terminal γ-domain is unstructured in the absence of other divisomal proteins, but we show that it is critical for DivIB function.