Reconstitution of contractile FtsZ rings in liposomes
FtsZ, a tubulin homolog, is the major protein involved in cell division in bacteria and archaea. FtsZ assembles along with a number of other proteins into the Z ring, which constricts to divide the cell. This investigation examined the nature of the FtsZ filaments and a Z ring that it forms in bacterial cells, FtsZ attachment to the membrane, and the generation of the constriction force essential for cell division to occur. It had previously been shown that attachment of FtsZ to the membrane is through another protein, FtsA, which has an amphipatic helix that anchors FtsA to the cell membrane. The authors thus constructed a membrane-targeted FtsZ, called FtsZ-mts, in which the segment of FtsZ that binds FtsA was replaced with yellow fluorescent protein (YFP) followed by an amphipathic helix. The authors showed that in Escherichia coli and in a liposome system in vitro, FtsZ attachment is dependent only on the amphipatic anchor to the membrane (i.e., intact FtsA is not required for Z ring formation). Addition of FtsZ-mts and GTP in tubular liposome preparations resulted in the incorporation of FtsZ and the GTP-dependent formation of multiple dim Z rings that moved laterally, coalescing into brighter Z rings. Formation of bright Z rings was succeeded by the appearance of constrictions in the liposome walls (Fig. 1). The force to create constrictions in the liposome was thus generated by FtsZ, either through the alteration of its conformation upon GTP hydrolysis or by creating force in the membrane through the insertion of the anchor of amphipatic helices. The force distorts the membrane, causing the protofilaments to form closed rings that oriented perpendicular to the axis of the tubular liposome. The authors thus concluded that Z ring formation and constriction of the membrane required only FtsZ and attachment to the membrane, which may be mediated by any amphipatic helix. © 2008 Data Trace Publishing Company.
Osawa, M; Anderson, DA; Erickson, HP
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