FtsZ

FtsZ is a protein encoded by the ftsZ gene that assembles into a ring at the future site of the septum of bacterial cell division. FtsZ, named after filamenting temperature-sensitive mutant Z, is a prokaryotic homologue to the eukaryotic protein tubulin. The gene was discovered in the 1950s by Hirota and his colleagues in a screen for bacterial cell division mutants. The hypothesis was that cell division mutants of E. coli would grow as filaments due to the inability of the daughter cells to separate from one another.

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Discovery of the bacterial cytoskeleton is fairly recent. FtsZ was the first protein of the prokaryotic cytoskeleton to be identified. In 1991 it was shown by Erfei Bi and Joseph Lutkenhaus that FtsZ assembled into the Z-ring. During cell division, FtsZ is the first protein to move to the division site, and is essential for recruiting other proteins that produce a new cell wall between the dividing cells. FtsZ's role in cell division is analogous to that of actin in eukaryotic cell division, but unlike the actin-myosin ring in eukaryotes, FtsZ has no known motor protein associated with it. The origin of the cytokinetic force thus remains unclear, but it is believed that the localized synthesis of new cell wall produces at least part of this force.

How the roles of tubulin-like proteins and actin-like proteins in cell division became reversed is an evolutionary mystery, but the use of the FtsZ ring in dividing chloroplasts and some mitochondria further establishes their prokaryotic ancestry.

Much is known about the dynamic polymerization activities of tubulin and microtubules, but little is known about these activities in FtsZ. While it is known that single-stranded tubulin protofilaments form into 13 stranded microtubules, the multistranded structure of the FtsZ containing Z-ring is not known. Furthermore, there has been a controversy over the apparent cooperativity of single-stranded FtsZ polymer assembly since all established theoretical models for cooperative assembly require multistranded polymers. Recently, Alex Dajkovic and Joe Lutkenhaus have proposed that cooperativity in assembly of FtsZ could be caused by multiple states of FtsZ monomers with differing affinites for each other.

Recently proteins similar to tubulin and FtsZ have been discovered in large plasmids found in Bacillus species. They are believed to function as components of segrosomes, which are multiprotein complexes that partition chromosomes/plasmid in bacteria. The plasmid homologs of tubulin/FtsZ seem to have conserved the ability to polymerize into filaments.

References

1. Chen, J.C., et al., Septal localization of FtsQ, an essential cell division protein in Escherichia coli. J Bacteriol, 1999. 181(2): p. 521-530. PMID 9882666 [1]
2. Löwe, J., and Amos, L.A., Structure of the bacterial tubulin homolog FtsZ Nature, 1998. 391: p. 203-206. Entrez PubMed 9428770
3. Romberg, L., and Levin, P.A., Assembly dynamics of the bacterial cell division protein FTSZ: poised at the edge of stability Annu Rev Microbiol, 2003. 57: p. 125-154. PMID 14527275 [2]
4. Scheffers, D., and Driessen, A.J., The polymerization mechanism of the bacterial cell division protein FtsZ FEBS Letters, 2001. 506(1): p. 6-10. PMID 11591361 [3]
5. van den Ent, F., Amos, L., Lowe, J., Bacterial ancestry of actin and tubulin Curr Opin Microbiol, 2001. 4(6): p. 634-638. PMID 11731313 [4]
6. Bi, E. and Lutkenhaus, J., "FtsZ ring structure associated with division in Escherichia coli." Nature, 1991 354, 161 - 164. Entrez PubMed 1944597
7. Dajkovic, A. and Lutkenhaus, J., "Z ring as executor of bacterial cell division" J Mol Microbiol Biotechnol. 2006;11(3-5):140-51 Entrez PubMed 16983191