R bodies explained

R bodies (from refractile bodies, also R-bodies) are polymeric protein inclusions formed inside the cytoplasm of bacteria.[1] 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.[2]

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,[3] [4] R bodies are formed from two small structural proteins, RebA and RebB.[5] 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.[6]

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.[7] 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.[8] 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.[9]

Notes and 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. 10.1128/mr.53.1.25-67.1989 . 0146-0749. 372716. 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. 10.1534/g3.112.005231. 2160-1836. 3583457. 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. 0021-9193. 213417. 3759909. 10.1128/jb.168.1.40-48.1986.
  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. 10.1007/s00239-004-0002-2. 0022-2844. 15785846. 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. 0021-9193. 205544. 8206833. 10.1128/jb.176.12.3559-3567.1994.
  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. 10.1016/S0022-5320(66)80100-4. 5936490.
  7. Mueller. Jo Anne. 1965-12-01. Vitally stained kappa in Paramecium aurelia. Journal of Experimental Zoology. en. 160. 3. 369–372. 10.1002/jez.1401600314. 4160786. 1097-010X.
  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. 10.1016/j.ejop.2012.01.008. 1618-0429. 22356923.
  9. Polka. Jessica K.. Silver. Pamela A.. 2016-04-15. A Tunable Protein Piston That Breaks Membranes to Release Encapsulated Cargo. ACS Synthetic Biology. 5. 4. 303–311. 10.1021/acssynbio.5b00237. 26814170. free.

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