The FtsZ protofilament and attachment of ZipA--structural constraints on the FtsZ power stroke.

Bacterial cell division protein FtsZ forms protofilaments in vitro that can shift from a straight to a curved conformation. The inside of the curved protofilaments, which corresponds to the carboxyl terminus, should face the center of the cell as curvature increases during constriction of the Z-ring. ZipA, a membrane-tethered division protein, binds to a highly conserved short peptide on the carboxyl terminus of FtsZ. A model is proposed here for how membrane-bound ZipA can reach around the FtsZ protofilament to bind the carboxy-terminal peptide, which faces away from the membrane.