MreB explained

Cell shape determining protein MreB/Mbl
Symbol:	MreB
Interpro:	IPR004753
Pfam:	PF06723
Cdd:	cd10225

MreB is a protein found in bacteria that has been identified as a homologue of actin, as indicated by similarities in tertiary structure and conservation of active site peptide sequence. The conservation of protein structure suggests the common ancestry of the cytoskeletal elements formed by actin, found in eukaryotes, and MreB, found in prokaryotes.^[1] Indeed, recent studies have found that MreB proteins polymerize to form filaments that are similar to actin microfilaments. It has been shown to form multilayer sheets comprising diagonally interwoven filaments in the presence of ATP or GTP.^[2]

MreB along with MreC and MreD are named after the mre operon (murein formation gene cluster E) to which they all belong.^[3]

Function

MreB controls the width of rod-shaped bacteria, such as Escherichia coli. A mutant E. coli that creates defective MreB proteins will be spherical instead of rod-like. Also, most bacteria that are naturally spherical do not have the gene encoding MreB. Members of the Chlamydiota are a notable exception, as these bacteria utilize the protein for localized septal peptidoglycan synthesis.^{[4] [5]} Prokaryotes carrying the mreB gene can also be helical in shape. MreB has long been thought to form a helical filament underneath the cytoplasmic membrane, however, this model has been brought into question by three recent publications showing that filaments cannot be seen by electron cryotomography and that GFP-MreB can be seen as patches moving around the cell circumference. It has been shown to interact with several proteins that are proven to be involved in length growth (for instance PBP2). Therefore, it probably directs the synthesis and insertion of new peptidoglycan building units into the existing peptidoglycan layer to allow length growth of the bacteria.

Further reading

• Erickson HP . Cytoskeleton. Evolution in bacteria . Nature . 413 . 6851 . 30 . September 2001 . 11544510 . 10.1038/35092655 . 4430479 . free . 2001Natur.413...30E . - source of information added to this entry as of February 20, 2006
• Swulius MT, Chen S, Jane Ding H, Li Z, Briegel A, Pilhofer M, Tocheva EI, Lybarger SR, Johnson TL, Sandkvist M, Jensen GJ . 6 . Long helical filaments are not seen encircling cells in electron cryotomograms of rod-shaped bacteria . Biochemical and Biophysical Research Communications . 407 . 4 . 650–655 . April 2011 . 21419100 . 3093302 . 10.1016/j.bbrc.2011.03.062 .
• Domínguez-Escobar J, Chastanet A, Crevenna AH, Fromion V, Wedlich-Söldner R, Carballido-López R . Processive movement of MreB-associated cell wall biosynthetic complexes in bacteria . Science . 333 . 6039 . 225–228 . July 2011 . 21636744 . 10.1126/science.1203466 . 45635270 . 2011Sci...333..225D .
• Garner EC, Bernard R, Wang W, Zhuang X, Rudner DZ, Mitchison T . Coupled, circumferential motions of the cell wall synthesis machinery and MreB filaments in B. subtilis . Science . 333 . 6039 . 222–225 . July 2011 . 21636745 . 3235694 . 10.1126/science.1203285 . 2011Sci...333..222G .

Notes and References

1. Gunning PW, Ghoshdastider U, Whitaker S, Popp D, Robinson RC . The evolution of compositionally and functionally distinct actin filaments . Journal of Cell Science . 128 . 11 . 2009–2019 . June 2015 . 25788699 . 10.1242/jcs.165563 . free .
2. Popp D, Narita A, Maeda K, Fujisawa T, Ghoshdastider U, Iwasa M, Maéda Y, Robinson RC . 6 . Filament structure, organization, and dynamics in MreB sheets . The Journal of Biological Chemistry . 285 . 21 . 15858–15865 . May 2010 . 20223832 . 2871453 . 10.1074/jbc.M109.095901 . free .
3. Book: Löwe . Jan . Prokaryotic Cytoskeletons: Filamentous Protein Polymers Active in the Cytoplasm of Bacterial and Archaeal Cells . Amos . Linda A. . 2017-05-11 . Springer . 978-3-319-53047-5 . 255 . en.
4. Ouellette SP, Karimova G, Subtil A, Ladant D . Chlamydia co-opts the rod shape-determining proteins MreB and Pbp2 for cell division . Molecular Microbiology . 85 . 1 . 164–178 . July 2012 . 22624979 . 10.1111/j.1365-2958.2012.08100.x . 5568586 . free .
5. Liechti G, Kuru E, Packiam M, Hsu YP, Tekkam S, Hall E, Rittichier JT, VanNieuwenhze M, Brun YV, Maurelli AT . 6 . Pathogenic Chlamydia Lack a Classical Sacculus but Synthesize a Narrow, Mid-cell Peptidoglycan Ring, Regulated by MreB, for Cell Division . PLOS Pathogens . 12 . 5 . e1005590 . May 2016 . 27144308 . 4856321 . 10.1371/journal.ppat.1005590 . free .