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R bodies

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Polymeric protein inclusions
Jessica Polka's electron micrograph of negatively stained purified type 51 R bodies in their extended (low pH) state

R bodies (from refractile bodies, also R-bodies) are polymeric protein inclusions formed inside the cytoplasm of bacteria. Initially discovered in kappa particles, bacterial endosymbionts of the ciliate Paramecium, R bodies (and genes encoding them) have since been discovered in a variety of taxa.

Morphology, assembly, and extension

At neutral pH, type 51 R bodies resemble a coil of ribbon approximately 500 nm in diameter and approximately 400 nm deep. Encoded by a single operon containing four open reading frames, R bodies are formed from two small structural proteins, RebA and RebB. A third protein, RebC, is required for the covalent assembly of these two structural proteins into higher-molecular weight products, visualized as a ladder on an SDS-PAGE gel.

At low pH, Type 51 R bodies undergo a dramatic structural rearrangement. Much like a paper yo-yo, the ribbon extends (from the center) to form hollow tube with pointed ends that can reach up to 20μm in length.

Other types of R bodies from different bacterial species vary in their size, ribbon morphology, and triggers for extension.

Function

When kappa particles shed from a killer paramecium are ingested, R bodies extend within the acidic food vacuole of the predatory paramecium, distending and rupturing the membrane. This liberates the contents of the food vacuole into the cytoplasm of the paramecium. While feeding kappa particles to sensitive paramecium results in the death of paramecium, feeding purified R bodies or R bodies recombinantly expressed in E. coli is not toxic. Thus, R bodies are thought to function as a toxin delivery system.

R bodies are also capable of rupturing E. coli spheroplasts, demonstrating that they can rupture membranes in a foreign context, and they can be engineered to extend at a variety of different pH levels.

References

  1. ^ Pond, F R; Gibson, I; Lalucat, J; Quackenbush, R L (1989-03-01). "R-body-producing bacteria". Microbiological Reviews. 53 (1): 25–67. doi:10.1128/mr.53.1.25-67.1989. ISSN 0146-0749. PMC 372716. PMID 2651865.
  2. Raymann, Kasie; Bobay, Louis-Marie; Doak, Thomas G.; Lynch, Michael; Gribaldo, Simonetta (2013-03-01). "A genomic survey of Reb homologs suggests widespread occurrence of R-bodies in proteobacteria". G3: Genes, Genomes, Genetics. 3 (3): 505–516. doi:10.1534/g3.112.005231. ISSN 2160-1836. PMC 3583457. PMID 23450193.
  3. ^ Kanabrocki, J. A.; Quackenbush, R. L.; Pond, F. R. (1986-10-01). "Organization and expression of genetic determinants for synthesis and assembly of type 51 R bodies". Journal of Bacteriology. 168 (1): 40–48. doi:10.1128/jb.168.1.40-48.1986. ISSN 0021-9193. PMC 213417. PMID 3759909.
  4. Jeblick, Jörn; Kusch, Jürgen (2005-02-01). "Sequence, transcription activity, and evolutionary origin of the R-body coding plasmid pKAP298 from the intracellular parasitic bacterium Caedibacter taeniospiralis". Journal of Molecular Evolution. 60 (2): 164–173. doi:10.1007/s00239-004-0002-2. ISSN 0022-2844. PMID 15785846. S2CID 6301794.
  5. ^ Heruth, D. P.; Pond, F. R.; Dilts, J. A.; Quackenbush, R. L. (1994-06-01). "Characterization of genetic determinants for R body synthesis and assembly in Caedibacter taeniospiralis 47 and 116". Journal of Bacteriology. 176 (12): 3559–3567. doi:10.1128/jb.176.12.3559-3567.1994. ISSN 0021-9193. PMC 205544. PMID 8206833.
  6. Preer, John R.; Hufnagel, Linda A.; Preer, Louise B. (1966-04-01). "Structure and behavior of R bodies from killer paramecia". Journal of Ultrastructure Research. 15 (1): 131–143. doi:10.1016/S0022-5320(66)80100-4. PMID 5936490.
  7. ^ Mueller, Jo Anne (1965-12-01). "Vitally stained kappa in Paramecium aurelia". Journal of Experimental Zoology. 160 (3): 369–372. doi:10.1002/jez.1401600314. ISSN 1097-010X. PMID 4160786.
  8. Schrallhammer, Martina; Galati, Stefano; Altenbuchner, Josef; Schweikert, Michael; Görtz, Hans-Dieter; Petroni, Giulio (2012-11-01). "Tracing the role of R-bodies in the killer trait: absence of toxicity of R-body producing recombinant E. coli on paramecia". European Journal of Protistology. 48 (4): 290–296. doi:10.1016/j.ejop.2012.01.008. ISSN 1618-0429. PMID 22356923.
  9. Polka, Jessica K.; Silver, Pamela A. (2016-04-15). "A Tunable Protein Piston That Breaks Membranes to Release Encapsulated Cargo" (PDF). ACS Synthetic Biology. 5 (4): 303–311. doi:10.1021/acssynbio.5b00237. PMID 26814170.
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