polar organelle

In many bacteria, motility serves as an essential life function for survival, nutrient acquisition, chemotaxis, and more. In many cases, the formation of a polar organelles such as a flagellum and pilli represents the cumulation of charges within an organism's plasma membrane. The precise positioning of these organelles has been influenced by bacteria's rapid turnover rate and genetic variation. This refinement of polar motility organelles allows bacterial movement to be extremely energy efficient. The rapidly-developing field of bacterial localization studies have defined an increasing list of polar protein complexes, which suggests that many prokaryotic functions are confined to the poles. Understanding how these functions are regulated in space and with bacterial motility is important in medical bacteriology, as many virulence factors are linked to cell polarity.{{Cite journal | vauthors = Carlsson F, Joshi SA, Rangell L, Brown EJ | title = Polar Localization of Virulence-Related Esx-1 Secretion in Mycobacteria | journal = PLOS Pathogens | volume = 5 | issue = 1 | pages = e1000285 | date = 2009-01-30 | pmid = 19180234 | pmc = 2628743 | doi = 10.1371/journal.ppat.1000285 | language = en | doi-access = free | issn = 1553-7374 }}{{Cite journal | vauthors = Jain S, Ulsen P, Benz I, Schmidt MA, Fernandez R, Tommassen J, Goldberg MB | title = Polar Localization of the Autotransporter Family of Large Bacterial Virulence Proteins | journal = Journal of Bacteriology | volume = 188 | issue = 13 | pages = 4841–4850 | date = July 2006 | pmid = 16788193 | pmc = 1483012 | doi = 10.1128/jb.00326-06 }}

FlhFG acts as a GTPase, which plays a crucial role in the development of flagellum in many bacterial species. Typical flagellum development originates within the bacterium with regulatory proteins and flagellin accumulating at a pole in the plasma membrane. Next, the basal body of the flagellum is produced which contains the MS-ring. This basal body facilitates the formation of the extracellular hook and flagellar filament.{{Cite journal | vauthors = Macnab RM | title = How bacteria assemble flagella | journal = Annual Review of Microbiology | volume = 57 | pages = 77–100 | date = 2003 | pmid = 12730325 | doi = 10.1146/annurev.micro.57.030502.090832 | url = https://pubmed.ncbi.nlm.nih.gov/12730325/ | issn = 0066-4227 }} An example of the importance of FlhFG is present in Vibrio cholerae, as mutated FlhF reduces the development of viable flagellum. In V. cholerae, FlhF is essential in recruiting the MS-ring protein FliF, and in mutants this process is disrupted. In the absence of FlhF, the flagella are formed at a significantly reduced frequency and in nonpolar locations.{{Cite journal | vauthors = Green JC, Kahramanoglou C, Rahman A, Pender AM, Charbonnel N, Fraser GM | title = Recruitment of the earliest component of the bacterial flagellum to the old cell division pole by a membrane-associated signal recognition particle family GTP-binding protein | journal = Journal of Molecular Biology | volume = 391 | issue = 4 | pages = 679–690 | date = 2009-08-28 | pmid = 19497327 | doi = 10.1016/j.jmb.2009.05.075 | url = https://pubmed.ncbi.nlm.nih.gov/19497327/ | issn = 1089-8638 }} When functional FlhF-GFP is present, the FhF-GFP is localized to the pole in V. Cholerae independently of the flagellar structural proteins.{{Cite journal | vauthors = Ewing CP, Andreishcheva E, Guerry P | title = Functional characterization of flagellin glycosylation in Campylobacter jejuni 81-176 | journal = Journal of Bacteriology | volume = 191 | issue = 22 | pages = 7086–7093 | date = November 2009 | pmid = 19749047 | pmc = 2772469 | doi = 10.1128/JB.00378-09 | issn = 1098-5530 }}

However, FlhF does not have the same effect in each species of bacteria. In Bacillus cereus, a peritrichous flagellated bacteria, FlhF reduction decreased flagellation but resulted in a bias toward polar flagella from the normal peritrichous arrangement.{{Cite journal | vauthors = Salvetti S, Ghelardi E, Celandroni F, Ceragioli M, Giannessi F, Senesi S | title = FlhF, a signal recognition particle-like GTPase, is involved in the regulation of flagellar arrangement, motility behaviour and protein secretion in Bacillus cereus | journal = Microbiology | location = Reading, England | volume = 153 | issue = Pt 8 | pages = 2541–2552 | date = August 2007 | pmid = 17660418 | doi = 10.1099/mic.0.2006/005553-0 | doi-access = free | issn = 1350-0872 }} This identifies that certain bacteria direct FlhF to a specific pole, so FlhF then recruits flagellar components to a polar site.{{Cite journal | vauthors = Kirkpatrick CL, Viollier PH | title = Poles Apart: Prokaryotic Polar Organelles and Their Spatial Regulation | journal = Cold Spring Harbor Perspectives in Biology | volume = 3 | issue = 3 | pages = a006809 | date = Mar 2011 | pmid = 21084387 | pmc = 3039935 | doi = 10.1101/cshperspect.a006809 | language = en }} This allows bacteria to position flagella strategically throughout the bacterial polar membrane. When multiple flagella are present, correct polar localization is especially important when bacteria need to change direction or respond specifically to chemical signals in the external environment.

Different to FlhF, which plays a critical role in MS-ring recruitment, the PfIl protein does not recruit physical equipment of influence flagellum formation. PflI is a positioning protein which is a biotic membrane protein made up of a coiled domain followed by a 102 proline residue stretch. This protein has been identified in Caulobacter crescentus, and this bacteria the Pfli protein was localized to the region of the plasma membrane where the flagella would be created. This localization occurred before the flagellar proteins were expressed, and Pfli was still localized to a pole even when no flagella structure was expressed.{{Cite journal | vauthors = Obuchowski PL, Jacobs-Wagner C | title = PflI, a protein involved in flagellar positioning in Caulobacter crescentus | journal = Journal of Bacteriology | volume = 190 | issue = 5 | pages = 1718–1729 | date = March 2008 | pmid = 18165296 | pmc = 2258662 | doi = 10.1128/JB.01706-07 | issn = 1098-5530 }} Furthermore, when the FliF protein associated with MS-ring formation was absent, the PflI still localized in the membrane.

Additional evidence for the flagella positioning behavior of the PflI protein is evident when inhibiting or promoting the PflI protein. When the production of PflI is varied, a statistically higher proportion of cells contain misplaced flagella within the bacterial plasma membrane. The mechanism in which PflI influences flagella localization and development is unknown. Early research indicates that PflI may be influenced to localize around the future flagellar pole because of TipF, an EAL-domain protein. The EAL domain works with accessory domains to help regulate the bacteria’s modular function.{{Cite journal | vauthors = Sundriyal A, Massa C, Samoray D, Zehender F, Sharpe T, Jenal U, Schirmer T | title = Inherent Regulation of EAL Domain-catalyzed Hydrolysis of Second Messenger Cyclic di-GMP * | journal = The Journal of Biological Chemistry | volume = 289 | issue = 10 | pages = 6978–6990 | date = 2014-03-07 | pmid = 24451384 | pmc = 3945359 | doi = 10.1074/jbc.M113.516195 | language = English | doi-access = free | issn = 0021-9258 }} Altering the location of this polar organelle by influencing PflI function can negatively influence a bacteria’s chances for survival and reproduction.

The MglA GTPase plays a pivotal role in regulating gliding motility in Myxcoccus xanthus.{{Cite journal | vauthors = Patryn J, Allen K, Dziewanowska K, Otto R, Hartzell PL | title = Localization of MglA, an essential gliding motility protein in Myxococcus xanthus | journal = Cytoskeleton | location = Hoboken, N.J. | volume = 67 | issue = 5 | pages = 322–337 | date = 2010 | pmid = 20196075 | pmc = 3225289 | doi = 10.1002/cm.20447 | language = en | issn = 1949-3592 }} Gliding motility primarily takes place on surfaces, and often bacteria contain an extracellular adhesive complex which allows bacteria to smoothly “glide” in contrast to a motor-like flagella. MglA affects the motility of cells by regulating the effectors which control the movement and reversals of movement in bacteria. In M. xanthus, these effectors move from charged pole to pole in the plasma membrane, and this intra-membrane movement relies on the MglA GTPase.{{Cite journal | vauthors = Zhang Y, Franco M, Ducret A, Mignot T | title = A Bacterial Ras-Like Small GTP-Binding Protein and Its Cognate GAP Establish a Dynamic Spatial Polarity Axis to Control Directed Motility | journal = PLOS Biology | volume = 8 | issue = 7 | pages = e1000430 | date = 2010-07-20 | pmid = 20652021 | pmc = 2907295 | doi = 10.1371/journal.pbio.1000430 | language = en | doi-access = free | issn = 1545-7885 }} These poles often are isolated to be regions with the largest negative membrane curvature.{{Cite journal | vauthors = Kholina E, Kovalenko I, Rubin A, Strakhovskaya M | title = Insights into the Formation of Intermolecular Complexes of Fluorescent Probe 10-N-Nonyl Acridine Orange with Cardiolipin and Phosphatidylglycerol in Bacterial Plasma Membrane by Molecular Modeling | journal = Molecules | location = Basel, Switzerland | volume = 28 | issue = 4 | pages = 1929 | date = January 2023 | pmid = 36838917 | pmc = 9961436 | doi = 10.3390/molecules28041929 | language = en | doi-access = free | issn = 1420-3049 }}  In fact, the MglA localizes to a charged pole in the membrane in a very similar mechanism as FihF.

Another protein, MglB,  encoded near MglA, acts in conjunction with MglA and also oscillates to allow gliding motility. MglB and MglA both continuously regulate one another in the localization and movement dynamics for M. xanthus.{{Cite journal | vauthors = Leonardy S, Miertzschke M, Bulyha I, Sperling E, Wittinghofer A, Sogaard-Andersen L | title = Regulation of dynamic polarity switching in bacteria by a Ras-like G-protein and its cognate GAP | journal = The EMBO Journal | volume = 29 | issue = 14 | pages = 2276–2289 | date = 2010-07-21 | pmid = 20543819 | pmc = 2910265 | doi = 10.1038/emboj.2010.114 | issn = 0261-4189 }} Fluorescence microscopy can visualize the coordinated countercyclical localizations of MglA and MglB working in combination with one another within M. xanthus. When either MglB or MglA is inhibited, the conjunctional localization is disrupted. This occurs by blocking the rotating effectors as well as changing the frequency of movement reversals characterized within wild-type M. xanthus. The oscillation of polar localization signals in the plasma membrane mimics a polar organelle that would provide motility in a flagellar bacterium.

Pili are another important form of motility found within prokaryotic bacteria. Pili often surround cell and can have different functional roles to help cells respond to their external environment. An example is Type IV pili which, if present in bacteria, are essential for DNA uptake, motility, biofilm formation, and more. The bacterium P. aeruginosa contains Pili which biochemically act similar in function, structure, and localization to the pili of M. xanthus that provide it gliding motility.{{Cite journal | vauthors = Kaiser D, Robinson M, Kroos L | title = Myxobacteria, polarity, and multicellular morphogenesis | journal = Cold Spring Harbor Perspectives in Biology | volume = 2 | issue = 8 | pages = a000380 | date = August 2010 | pmid = 20610548 | pmc = 2908774 | doi = 10.1101/cshperspect.a000380 | issn = 1943-0264 }} P. aeruginosa specifically utilizes twitching motility, where a pilus extends and contracts to move the cell. Coordination with other pili allows, and minuscule movements of polarity throughout the plasma membrane allow effective movement for the cell. In this way, the polar organelle region of the polar pili and twitching motility cells is much more dynamic compared to that of a cell which utilizes a flagellum.

Cells which exhibit Pili motility are heavily dependent on the MreB cytoskeleton which maintains polar localization in the bacterial polar membrane. This MreB cytoskeleton works as an actin-like filament.{{Cite journal | vauthors = Cowles KN, Gitai Z | title = Surface association and the MreB cytoskeleton regulate pilus production, localization and function in Pseudomonas aeruginosa | journal = Molecular Microbiology | volume = 76 | issue = 6 | pages = 1411–1426 | date = 2010 | pmid = 20398206 | pmc = 3132575 | doi = 10.1111/j.1365-2958.2010.07132.x | language = en | issn = 1365-2958 }} In parallel, MreB plays a specific role in the localization of the specific S effector in the gliding movement dynamics of M. xanthus.{{Cite journal | vauthors = Mauriello EM, Mouhamar F, Nan B, Ducret A, Dai D, Zusman DR, Mignot T | title = Bacterial motility complexes require the actin-like protein, MreB and the Ras homologue, MglA | journal = The EMBO Journal | volume = 29 | issue = 2 | pages = 315–326 | date = 2010-01-20 | pmid = 19959988 | pmc = 2824462 | doi = 10.1038/emboj.2009.356 | issn = 0261-4189 }} When MreB function was inhibited, the bacteria mislocalized their membrane to nonpolar sites and the cells had pili develop at lateral sites rather than the pole. The exact mechanism of how MreB causes membrane localization is unknown. The MreB cytoskeleton has many other functions within a polar pili cell affecting virulence, plasmid distribution cell wall enzymatic behavior, and more.{{Cite journal | vauthors = Shih YL, Kawagishi I, Rothfield L | title = The MreB and Min cytoskeletal-like systems play independent roles in prokaryotic polar differentiation | journal = Molecular Microbiology | volume = 58 | issue = 4 | pages = 917–928 | date = November 2005 | pmid = 16262780 | doi = 10.1111/j.1365-2958.2005.04841.x | issn = 0950-382X }}{{Cite journal | vauthors = Gerdes K, Howard M, Szardenings F | title = Pushing and Pulling in Prokaryotic DNA Segregation | journal = Cell | volume = 141 | issue = 6 | pages = 927–942 | date = 2010-06-11 | pmid = 20550930 | doi = 10.1016/j.cell.2010.05.033 | url = https://www.cell.com/fulltext/S0092-8674(10)00569-6 | language = English | issn = 0092-8674 }}{{Cite journal | vauthors = Dye NA, Pincus Z, Theriot JA, Shapiro L, Gitai Z | title = Two independent spiral structures control cell shape in Caulobacter | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 102 | issue = 51 | pages = 18608–18613 | date = 2005-12-20 | pmid = 16344481 | pmc = 1317941 | doi = 10.1073/pnas.0507708102 | doi-access = free | issn = 0027-8424 | bibcode = 2005PNAS..10218608D }}

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Category:Cell anatomy