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PDBsum entry 3zih
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References listed in PDB file
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Key reference
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Title
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Structural and genetic analyses reveal the protein sepf as a new membrane anchor for the z ring.
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Authors
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R.Duman,
S.Ishikawa,
I.Celik,
H.Strahl,
N.Ogasawara,
P.Troc,
J.Löwe,
L.W.Hamoen.
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Ref.
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Proc Natl Acad Sci U S A, 2013,
110,
E4601.
[DOI no: ]
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PubMed id
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Abstract
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A key step in bacterial cell division is the polymerization of the tubulin
homolog FtsZ at midcell. FtsZ polymers are anchored to the cell membrane by FtsA
and are required for the assembly of all other cell division proteins. In
Gram-positive and cyanobacteria, FtsZ filaments are aligned by the protein SepF,
which in vitro polymerizes into large rings that bundle FtsZ filaments. Here we
describe the crystal structure of the only globular domain of SepF, located
within the C-terminal region. Two-hybrid data revealed that this domain
comprises the FtsZ binding site, and EM analyses showed that it is sufficient
for ring formation, which is explained by the filaments in the crystals of SepF.
Site-directed mutagenesis, gel filtration, and analytical ultracentrifugation
indicated that dimers form the basic units of SepF filaments. High-resolution
structured illumination microscopy suggested that SepF is membrane associated,
and it turned out that purified SepF not only binds to lipid membranes, but also
recruits FtsZ. Further genetic and biochemical analyses showed that an
amphipathic helix at the N terminus functions as the membrane-binding domain,
making SepF a unique membrane anchor for the FtsZ ring. This clarifies why
Bacillus subtilis grows without FtsA or the putative membrane anchor EzrA and
why bacteria lacking FtsA contain SepF homologs. Both FtsA and SepF use an
amphipathic helix for membrane binding. These helices prefer positively curved
membranes due to relaxed lipid density; therefore this type of membrane anchor
may assist in keeping the Z ring positioned at the strongly curved leading edge
of the developing septum.
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