Editing Cytoskeleton (section)

==Prokaryotic cytoskeleton==
{{main|Prokaryotic cytoskeleton}}
Prior to the work of Jones et al., 2001, the cell wall was believed to be the deciding factor for many bacterial cell shapes, including rods and spirals. When studied, many misshapen bacteria were found to have mutations linked to development of a [[cell envelope]].<ref>{{Cite journal|last1=Jones|first1=Laura J. F.|last2=Carballido-López|first2=Rut|last3=Errington|first3=Jeffery|date=2001-03-23|title=Control of Cell Shape in Bacteria: Helical, Actin-like Filaments in Bacillus subtilis|journal=Cell|volume=104|issue=6|pages=913–922|doi=10.1016/S0092-8674(01)00287-2|pmid=11290328|s2cid=14207533|doi-access=free}}</ref> The cytoskeleton was once thought to be a feature only of [[eukaryote|eukaryotic]] cells, but [[homology (biology)|homologues]] to all the major proteins of the eukaryotic cytoskeleton have been found in [[prokaryote]]s.<ref name=Shih>{{cite journal | vauthors = Shih YL, Rothfield L | title = The bacterial cytoskeleton | journal = Microbiology and Molecular Biology Reviews | volume = 70 | issue = 3 | pages = 729–54 | date = September 2006 | pmid = 16959967 | pmc = 1594594 | doi = 10.1128/MMBR.00017-06 }}</ref> Harold Erickson notes that before 1992, only eukaryotes were believed to have cytoskeleton components. However, research in the early '90s suggested that bacteria and archaea had homologues of actin and tubulin, and that these were the basis of eukaryotic microtubules and microfilaments.<ref name="Erickson-2017">{{cite journal | vauthors = Erickson HP | title = The discovery of the prokaryotic cytoskeleton: 25th anniversary | journal = Molecular Biology of the Cell | volume = 28 | issue = 3 | pages = 357–358 | date = February 2017 | pmid = 28137947 | pmc = 5341718 | doi = 10.1091/mbc.E16-03-0183 }}</ref> Although the evolutionary relationships are so distant that they are not obvious from protein sequence comparisons alone, the similarity of their three-dimensional [[protein structure|structures]] and similar functions in maintaining cell shape and polarity provides strong evidence that the eukaryotic and prokaryotic cytoskeletons are truly homologous.<ref>{{cite journal | vauthors = Michie KA, Löwe J | title = Dynamic filaments of the bacterial cytoskeleton | journal = Annual Review of Biochemistry | volume = 75 | pages = 467–92 | year = 2006 | pmid = 16756499 | doi = 10.1146/annurev.biochem.75.103004.142452 | url = http://www2.mrc-lmb.cam.ac.uk/groups/JYL/PDF/annrev2006.pdf }}</ref>  Three laboratories independently discovered that FtsZ, a protein already known as a key player in bacterial cytokinesis, had the "tubulin signature sequence" present in all α-, β-, and γ-tubulins.<ref name="Erickson-2017" /> However, some structures in the bacterial cytoskeleton may not have been identified as of yet.<ref name=gunning /><ref>{{cite journal | vauthors = Briegel A, Dias DP, Li Z, Jensen RB, Frangakis AS, Jensen GJ | title = Multiple large filament bundles observed in Caulobacter crescentus by electron cryotomography | journal = Molecular Microbiology | volume = 62 | issue = 1 | pages = 5–14 | date = October 2006 | pmid = 16987173 | doi = 10.1111/j.1365-2958.2006.05355.x | doi-access = free }}</ref>

===FtsZ===
[[FtsZ]] was the first protein of the prokaryotic cytoskeleton to be identified. Like tubulin, FtsZ forms filaments in the presence of [[guanosine triphosphate]] (GTP), but these filaments do not group into tubules. During [[cell division]], FtsZ is the first protein to move to the division site, and is essential for recruiting other proteins that synthesize the new [[cell wall]] between the dividing cells.

===MreB and ParM===
Prokaryotic actin-like proteins, such as [[MreB]], are involved in the maintenance of cell shape. All non-spherical bacteria have [[gene]]s encoding actin-like proteins, and these proteins form a helical network beneath the cell membrane that guides the proteins involved in cell wall [[biosynthesis]].<ref name="mreb_sheets" >{{cite journal | vauthors = Popp D, Narita A, Maeda K, Fujisawa T, Ghoshdastider U, Iwasa M, Maéda Y, Robinson RC | title = Filament structure, organization, and dynamics in MreB sheets | journal = The Journal of Biological Chemistry | volume = 285 | issue = 21 | pages = 15858–65 | date = May 2010 | pmid = 20223832 | pmc = 2871453 | doi = 10.1074/jbc.M109.095901 | doi-access = free }}</ref>

Some [[plasmid]]s encode a separate system that involves an actin-like protein [[ParM]]. Filaments of ParM exhibit [[Microtubule#Dynamic instability|dynamic instability]], and may partition plasmid DNA into the dividing daughter cells by a mechanism [[Analogy (biology)|analogous]] to that used by microtubules during eukaryotic [[mitosis]].<ref name=gunning /><ref name="Alp">{{cite journal | vauthors = Popp D, Narita A, Lee LJ, Ghoshdastider U, Xue B, Srinivasan R, Balasubramanian MK, Tanaka T, Robinson RC | title = Novel actin-like filament structure from Clostridium tetani | journal = The Journal of Biological Chemistry | volume = 287 | issue = 25 | pages = 21121–9 | date = June 2012 | pmid = 22514279 | pmc = 3375535 | doi = 10.1074/jbc.M112.341016 | doi-access = free }}</ref>

===Crescentin===
The bacterium ''[[Caulobacter crescentus]]'' contains a third protein, [[crescentin]], that is related to the intermediate filaments of eukaryotic cells. Crescentin is also involved in maintaining cell shape, such as helical and [[vibrio]]id forms of bacteria, but the mechanism by which it does this is currently unclear.<ref>{{cite journal | vauthors = Ausmees N, Kuhn JR, Jacobs-Wagner C | title = The bacterial cytoskeleton: an intermediate filament-like function in cell shape | journal = Cell | volume = 115 | issue = 6 | pages = 705–13 | date = December 2003 | pmid = 14675535 | doi = 10.1016/S0092-8674(03)00935-8 | s2cid = 14459851 | doi-access = free }}</ref> Additionally, curvature could be described by the displacement of crescentic filaments, after the disruption of peptidoglycan synthesis.<ref>{{Cite journal|title=Dynamics of the Bacterial Intermediate Filament Crescentin In Vitro and In Vivo|last=Esue|first=Osigwe|date=January 2010|journal=PLOS ONE|volume=5|issue=1|pages=e8855|pmid=20140233|doi=10.1371/journal.pone.0008855|pmc=2816638|bibcode=2010PLoSO...5.8855E|doi-access=free}}</ref>