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]
At neutral pH, type 51 R bodies resemble a coil of ribbon approximately 500 nm in diameter and approximately 400 nm deep. [1] 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. [5]
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. [1]
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. [7] 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. [3] [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]
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]
At neutral pH, type 51 R bodies resemble a coil of ribbon approximately 500 nm in diameter and approximately 400 nm deep. [1] 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. [5]
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. [1]
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. [7] 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. [3] [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]