- Prokaryotic cytoskeleton
The prokaryotic cytoskeleton is the collective name for all structural filaments in
prokaryotes. It was once thought that prokaryotic cells did not possess cytoskeletons, but recent advances in visualization technology and structure determination have shown that filaments indeed exist in these cells. In fact, analogues for all major cytoskeletal proteins in eukaryoteshave been found in prokaryotes. Cytoskeletal elements play essential roles in cell division, protection, shape determination, and polarity determination in various prokaryotes. [cite journal |author=Shih YL, Rothfield L |title=The bacterial cytoskeleton |journal=Microbiol. Mol. Biol. Rev. |volume=70 |issue=3 |pages=729–54 |year=2006 |pmid=16959967 |url=http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pubmed&pubmedid=16959967 |doi=10.1128/MMBR.00017-06] [cite journal |author=Michie KA, Löwe J |title=Dynamic filaments of the bacterial cytoskeleton |journal=Annu. Rev. Biochem. |volume=75 |issue= |pages=467–92 |year=2006 |pmid=16756499 |url=http://www2.mrc-lmb.cam.ac.uk/SS/Lowe_J/group/PDF/annrev2006.pdf |doi=10.1146/annurev.biochem.75.103004.142452]
FtsZ, the first identified prokaryotic cytoskeletal element, forms a filamentous ring structure located in the middle of the cell called the Z-ring that constricts during cell division, similar to the actin-myosin contractile ring in eukaryotes.cite journal | author = Bi, E. | coauthors = Lutkenhaus, J. | year = 1991 | title = FtsZ ring structure associated with division in "Escherichia coli" | journal = Nature | volume = 354 | issue = 6349 | pages = 161–164 | doi = 10.1038/354161a0 ] The Z-ring is a highly dynamic structure that consists of numerous bundles of protofilaments that extend and shrink, although the mechanism behind Z-ring contraction and the number of protofilaments involved are unclear.cite journal |author=Gitai Z |title=The new bacterial cell biology: moving parts and subcellular architecture |journal=Cell |volume=120 |issue=5 |pages=577–86 |year=2005 |pmid=15766522 |doi=10.1016/j.cell.2005.02.026] FtsZ acts as an organizer protein and is required for cell division. It is the first component of the septumduring cytokinesis, and it recruits all other known cell division proteins to the division site.cite journal | author = Graumann, P.L. | year = 2004 | title = Cytoskeletal elements in bacteria | journal = Current Opinion in Microbiology | volume = 7 | issue = 6 | pages = 565–571 | pmid = 17506674 | doi = 10.1016/j.mib.2004.10.010]
Despite this functional similarity to
actin, FtsZ is homologous to eukaryal tubulin. Although comparison of the primary structures of FtsZ and tubulin reveal a weak relationship, their 3-dimensional structures are remarkably similar. Furthermore, like tubulin, monomericFtsZ is bound to GTPand polymerizes with other FtsZ monomers with the hydrolysis of GTP in a mechanism similar to tubulin dimerization.cite journal | author = Desai, A. | coauthors = Mitchison, T.J. | year = 1998 | title = Tubulin and FtsZ structures: functional and therapeutic implications | journal = Bioessays | volume = 20 | issue = 7 | pages = 523–527 | pmid = 9722999 | doi = 10.1002/(SICI)1521-1878(199807)20:7<523::AID-BIES1>3.0.CO;2-L | doilabel = 10.1002/(SICI)1521-1878(199807)20:7523::AID-BIES13.0.CO;2-L] Since FtsZ is essential for cell division in bacteria, this protein is a target for the design of new antibiotics. [cite journal |author=Haydon DJ, Stokes NR, Ure R, "et al" |title=An inhibitor of FtsZ with potent and selective anti-staphylococcal activity |journal=Science (journal) |volume=321 |issue=5896 |pages=1673–5 |year=2008 |month=September |pmid=18801997 |doi=10.1126/science.1159961]
MreBis a bacterial protein believed to be analogous to eukaryal actin. MreB and actin have a weak primary structurematch, but are very similar in terms of 3-D structure and filament polymerization.
Almost all non-spherical bacteria rely on MreB to determine their shape. MreB assembles into a helical network of filamentous structures just under the
cytoplasmic membrane, covering the whole length of the cell.cite journal | author = Kurner, J. | coauthors = Medalia, O.; Linaroudis, A.A.; Baumeister, W. | year = 2004 | title = New insights into the structural organization of eukaryotic and prokaryotic cytoskeletons using cryo-electron tomography. | journal = Exp Cell Res | volume = 301 | issue = 1 | pages = 38–42 | url = http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=15501443&dopt=Citation | doi = 10.1016/j.yexcr.2004.08.005] MreB determines cell shape by mediating the position and activity of enzymes that synthesize peptidoglycanand by acting as a rigid filament under the cell membrane that exerts outward pressure to sculpt and bolster the cell. MreB condenses from its normal helical network and forms a tight ring at the septumin " Caulobacter crescentus" right before cell division, a mechanism that is believed to help locate its off-center septum.cite journal | author=Gitai, Z. | coauthors=Dye, N.; Shapiro, L. | title= An actin-like gene can determine cell polarity in bacteria |journal=Proc Natl Acad Sci USA | volume=101 | issue=23 | pages=8643–8648 | year=2004 | doi = 10.1073/pnas.0402638101] MreB is also important for polarity determination in polar bacteria, as it is responsible for the correct positioning of at least four different polar proteins in "C. crescentus".
Crescentin(encoded by "creS" gene) is an analogue of eukaryotic intermediate filaments(IFs). Unlike the other analogous relationships discussed here, crescentin has a rather large primary homology with IF proteins in addition to three-dimensional similarity - the sequence of "creS" has a 25% identity match and 40% similarity to cytokeratin 19 and a 24% identity match and 40% similarity to nuclear lamin A. Furthermore, crescentin filaments are roughly 10 nm in diameter and thus fall within diameter range for eukaryal IFs (8-15 nm).cite journal | author = Ausmees, N. | coauthors = Kuhn, J.R.; Jacobs-Wagner, C. | year = 2003 | title = The Bacterial Cytoskeleton An Intermediate Filament-Like Function in Cell Shape | journal = Cell | volume = 115 | issue = 6 | pages = 705–713 | url = http://linkinghub.elsevier.com/retrieve/pii/S0092867403009358 | doi = 10.1016/S0092-8674(03)00935-8] Crescentin forms a continuous filament from pole to pole alongside the inner, concave side of the crescent-shaped bacterium " Caulobacter crescentus". Both MreB and crescentin are necessary for "C. crescentus" to exist in its characteristic shape; it is believed that MreB molds the cell into a rod shape and crescentin bends this shape into a crescent.
ParM and SopA
ParMis a cytoskeletal element that possesses a similar structure to actin, although it behaves functionally like tubulin. Further, it polymerizes bidirectionally and it exhibits dynamic instability, which are both behaviors characteristic of tubulin polymerization.cite journal | author=Garner, E.C. | coauthors = Campbell, C.S.; Mullins, R. D. | title= Dynamic Instability in a DNA-Segregating Prokaryotic Actin Homolog | journal=Science | volume=306 | pages=1021–1025 | year=2004 | doi = 10.1126/science.1101313] It forms a system with ParR and "parC" that is responsible for R1 plasmid separation. ParM affixes to ParR, a DNA-binding proteinthat specifically binds to 10 direct repeats in the "parC" region on the R1 plasmid. This binding occurs on both ends of the ParM filament. This filament is then extended, separating the plasmids.cite journal | author = Moller-Jensen, J. | coauthors = Jensen, R.B.; Löwe, J.; Gerdes, K. | year = 2002 | title = Prokaryotic DNA segregation by an actin-like filament | journal = The EMBO Journal | volume = 21 | pages = 3119–3127 | doi = 10.1093/emboj/cdf320 ] The system is analogous to eukaryotic chromosome segregation as ParM acts like eukaryotic tubulinin the mitotic spindle, ParR acts like the kinetochorecomplex, and "parC" acts like the centromereof the chromosome.cite journal | author = Gitai, Z. | year = 2006 | title = Plasmid Segregation: A New Class of Cytoskeletal Proteins Emerges | journal = Current Biology | volume = 16 | issue = 4 | pages = 133–136 | url = http://linkinghub.elsevier.com/retrieve/pii/S0960982206011171 | doi = 10.1016/j.cub.2006.02.007] F plasmid segregation occurs in a similar system where SopA acts as the cytoskeletal filament and SopB binds to the "sopC" sequence in the F plasmid, like the kinetochoreand centromererespectively.
The MinCDE system is a filament system that properly positions the
septumin the middle of the cell in " Escherichia coli". According to Shih et al., MinC inhibits the formation of the septum by prohibiting the polymerization of the Z-ring. MinC, MinD, and MinE form a helix structure that winds around the cell and is bound to the membrane by MinD. The MinCDE helix occupies a pole and terminates in a filamentous structure called the E-ring made of MinE at the middle-most edge of the polar zone. From this configuration, the E-ring will contract and move toward that pole, disassembling the MinCDE helix as it moves along. Concomitantly, the disassembled fragments will reassemble at the opposite polar end, reforming the MinCDE coil on the opposite pole while the current MinCDE helix is broken down. This process then repeats, with the MinCDE helix oscillating from pole to pole. This oscillation occurs repeatedly during the cell cycle, thereby keeping MinC (and its septum inhibiting effect) at a lower time-averaged concentration at the middle of the cell than at the ends of the cell.cite journal | author = Shih, Y.L. | coauthors = Le, T.; Rothfield, L. | year = 2003 | title = Division site selection in "Escherichia coli" involves dynamic redistribution of Min proteins within coiled structures that extend between the two cell poles | journal = Proceedings of the National Academy of Sciences | volume = 100 | issue = 13 | pages = 7865–7870 | doi = 10.1073/pnas.1232225100 ]
Wikimedia Foundation. 2010.
Look at other dictionaries:
Cytoskeleton — The eukaryotic cytoskeleton. Actin filaments are shown in red, microtubules in green, and the nuclei are in blue. The cytoskeleton (also CSK) is a cellular scaffolding or skeleton contained within a cell s cytoplasm and is made out of protein.… … Wikipedia
Cell (biology) — Allium cells in different phases of the cell cycle … Wikipedia
Archaea — Archea redirects here. For the geologic eon, see Archean. For the spider family, see Archaeidae. Archaea Temporal range: Paleoarchean – Recent Halobacteria sp. strain NRC 1, each cell about 5 μm long … Wikipedia
Cell membrane — Illustration of a Eukaryotic cell membrane The cell membrane or plasma membrane is a biological mem … Wikipedia
Bacteria — Taxobox color = lightgrey name = Bacteria fossil range = Archean or earlier Recent image width = 210px image caption = Escherichia coli image is 8 micrometres wide. domain = Bacteria subdivision ranks = Phyla [cite web… … Wikipedia
Organelle — A typical animal cell. Within the cytoplasm, the major organelles and cellular structures include: (1) nucleolus (2) nucleus (3) ribosome (4) vesicle (5) rough endoplasmic reticulum (6) Golgi apparatus … Wikipedia
Actin — G Actin (PDB code: 1j6z). ADP and the divalent cation are highlighted … Wikipedia
Flagellum — For the insect anatomical structure, see Antenna (biology). For the flagella of male Solifugae, see Solifugae. Flagella Code TH H1.00.01.1.01032 A flagellum ( … Wikipedia
Myosin — Part of the myosin II structure. Atoms in the heavy chain are colored red on the left hand side, and atoms in the light chains are colored orange and yellow. Myosins comprise a family of ATP dependent motor proteins and are best known for their… … Wikipedia
Crescentin — Space filling model and ribbon diagram of Caulobacter vibrioides crescentin, created from homology model available at Q6IET3 Crescentin is a protein which is a bacterial relative of the intermedi … Wikipedia