Other usual cell inclusions are often temporary inclusions of accumulated proteins, fats, secretory granules, or other insoluble components.[6]
Inclusion bodies are found in bacteria as particles of aggregated protein. They have a higher density than many other cell components but are porous.[7] They typically represent sites of viral multiplication in a bacterium or a eukaryotic cell and usually consist of viral capsid proteins.
Inclusion bodies contain very little host protein, ribosomal components, or DNA/RNA fragments. They often almost exclusively contain the over-expressed protein and aggregation and has been reported to be reversible. It has been suggested that inclusion bodies are dynamic structures formed by an unbalanced equilibrium between aggregated and soluble proteins of Escherichia coli. There is a growing body of information indicating that formation of inclusion bodies occurs as a result of intracellular accumulation of partially folded expressed proteins which aggregate through non-covalent hydrophobic or ionic interactions or a combination of both.[citation needed]
Composition
Inclusion bodies have a non-unit (single) lipid membrane[citation needed]. Protein inclusion bodies are classically thought to contain misfolded protein. However, this has been contested, as green fluorescent protein will sometimes fluoresce in inclusion bodies, which indicates some resemblance of the native structure and researchers have recovered folded protein from inclusion bodies.[8][9][10]
When genes from one organism are expressed in another organism the resulting protein sometimes forms inclusion bodies. This is often true when large evolutionary distances are crossed: a cDNA isolated from Eukarya for example, and expressed as a recombinant gene in a prokaryote risks the formation of the inactive aggregates of protein known as inclusion bodies. While the cDNA may properly code for a translatable mRNA, the protein that results will emerge in a foreign microenvironment. This often has fatal effects, especially if the intent of cloning is to produce a biologically active protein. For example, eukaryotic systems for carbohydrate modification and membrane transport are not found in prokaryotes. The internal microenvironment of a prokaryoticcell (pH, osmolarity) may differ from that of the original source of the gene. Mechanisms for folding a protein may also be absent, and hydrophobic residues that normally would remain buried may be exposed and available for interaction with similar exposed sites on other ectopic proteins. Processing systems for the cleavage and removal of internal peptides would also be absent in bacteria. The initial attempts to clone insulin in a bacterium suffered all of these deficits. In addition, the fine controls that may keep the concentration of a protein low will also be missing in a prokaryotic cell, and overexpression can result in filling a cell with ectopic protein that, even if it were properly folded, would precipitate by saturating its environment.[citation needed]
Basophilic stipplings – these stipplings are either fine or coarse, deep blue to purple staining inclusion that appear on a dried Wright's stain.
Pappenheimer bodies – are siderotic granules which are small, irregular, dark-staining granules that appear near the periphery of a young erythrocyte in a Wright's stain.
Polychromatophilic red cells – young red blood cells that no longer have nucleus but still contain some RNA.
Heinz bodies[11] – round bodies, refractile inclusions not visible on a Wright's stain film. They are best identified by supravital staining with basic dyes.
Hemoglobin H inclusions – alpha thalassemia, greenish-blue inclusion bodies appear in many red blood cells after four drops of blood are incubated with 0.5mL of Brilliant cresyl blue for 20 minutes at 37 °C.
Russell bodies are inclusions of immunoglobulin found in atypical plasma cells. Russell bodies clump together in large numbers displacing the cell nucleus to the edge, and the cell is then called a Mott cell.[12]
Examples of viral inclusion bodies in plants[13] include aggregations of virus particles (like those for Cucumber mosaic virus[14]) and aggregations of viral proteins (like the cylindrical inclusions of potyviruses[15]). Depending on the plant and the plant virus family these inclusions can be found in epidermal cells, mesophyll cells, and stomatal cells when plant tissue is properly stained.[16]
In bacteria
Polyhydroxyalkanoates (PHA) are produced by bacteria as inclusion bodies. The size of PHA granules are limited in E. coli, due to its small size.[17] Bacterial cell's inclusion bodies are not as abundant intracellularly, in comparison to eukaryotic cells.
Polymeric R bodies are found in the bacterial cytoplasm of some taxa, and thought to be involved in toxin delivery.[18]
Isolation of proteins
Between 70% and 80% of recombinant proteins expressed E. coli are contained in inclusion bodies (i.e., protein aggregates).[19] The purification of the expressed proteins from inclusion bodies usually require two main steps: extraction of inclusion bodies from the bacteria followed by the solubilisation of the purified inclusion bodies. Solubilisation of inclusions bodies often involves treatment with denaturing agents, such as urea or guanidine chloride at high concentrations, to de-aggregate the collapsed proteins. Renaturation follows the treatment with denaturing agents and often consists of dialysis and/or use of molecules that promote the refolding of denatured proteins (including chaotopic agents[7] and chaperones).[20]
Pseudo-inclusions
Pseudo-inclusions are invaginations of the cytoplasm into the cell nuclei, which may give the appearance of intranuclear inclusions. They may appear in papillary thyroid carcinoma.[21]
Inclusion body diseases differ from amyloid diseases in that inclusion bodies are necessarily intracellular aggregates of protein, where amyloid can be intracellular or extracellular. Amyloid also necessitates protein polymerization where inclusion bodies do not.[22]
Preventing inclusion bodies in bacteria
Inclusion bodies are often made of denatured aggregates of inactive proteins. Although, the renaturation of inclusion bodies can sometimes lead to the solubilisation and the recovery of active proteins, the process is still very empirical, uncertain and of low efficiency. Several techniques have been developed over the years to prevent the formation of inclusion bodies. These techniques include:
The use of weaker promoters to slowdown the rate of protein expression
^ abCruts M, Gijselinck I, van der Zee J, Engelborghs S, Wils H, Pirici D, Rademakers R, Vandenberghe R, Dermaut B, Martin JJ, van Duijn C, Peeters K, Sciot R, Santens P, De Pooter T, Mattheijssens M, Van den Broeck M, Cuijt I, Vennekens K, De Deyn PP, Kumar-Singh S, Van Broeckhoven C (24 August 2006). "Null mutations in progranulin cause ubiquitin-positive frontotemporal dementia linked to chromosome 17q21". Nature. 442 (7105): 920–4. Bibcode:2006Natur.442..920C. doi:10.1038/nature05017. PMID16862115. S2CID4423699.
^Dorland's illustrated medical dictionary (32 ed.). Philadelphia, PA: Saunders/Elsevier. 2012. p. 928. ISBN9781416062578.
^ abSingh SM, Panda AK (1 April 2005). "Solubilization and refolding of bacterial inclusion body proteins". Journal of Bioscience and Bioengineering. 99 (4): 303–310. doi:10.1263/jbb.99.303. PMID16233795. S2CID24807019. Inclusion bodies are dense electron-refractile particles of aggregated protein found in both the cytoplasmic and periplasmic spaces of E. coli during high-level expression of heterologous protein. It is generally assumed that high level expression of non-native protein (higher than 2% of cellular protein) and highly hydrophobic protein is more prone to lead to accumulation as inclusion bodies in E. coli. In the case of proteins having disulfide bonds, formation of protein aggregates as inclusion bodies is anticipated since the reducing environment of bacterial cytosol inhibits the formation of disulfide bonds. The diameter of spherical bacterial inclusion bodies varies from 0.5–1.3 μm and the protein aggregates have either an amorphous or paracrystalline nature depending on the localization. Inclusion bodies have higher density (~1.3 mg ml−1) than many of the cellular components, and thus can be easily separated by high-speed centrifugation after cell disruption. Inclusion bodies, despite being dense particles, are highly hydrated and have a porous architecture.
^Umetsu M, Tsumoto K, Nitta S, Adschiri T, Ejima D, Arakawa T, Kumagai I (March 2005). "Nondenaturing solubilization of beta2 microglobulin from inclusion bodies by L-arginine". Biochem Biophys Res Commun. 328 (1): 189–97. doi:10.1016/j.bbrc.2004.12.156. PMID15670769.
^Przybycien TM, Dunn JP, Valax P, Georgiou G (January 1994). "Secondary structure characterization of beta-lactamase inclusion bodies". Protein Eng. 7 (1): 131–6. doi:10.1093/protein/7.1.131. PMID8140090.
^Tsumoto K, Umetsu M, Kumagai I, Ejima D, Arakawa T (December 2003). "Solubilization of active green fluorescent protein from insoluble particles by guanidine and arginine". Biochem Biophys Res Commun. 312 (4): 1383–6. doi:10.1016/j.bbrc.2003.11.055. PMID14652027.
^Yang, Zhong, et al. "Highly efficient production of soluble proteins from insoluble inclusion bodies by a two-step-denaturing and refolding method." PloS one 6.7 (2011): e22981.
^Jiang ST, Tzeng SS, Wu WT, Chen GH (19 June 2002). "Enhanced expression of chicken cystatin as a thioredoxin fusion form in Escherichia coli AD494(DE3)pLysS and its effect on the prevention of surimi gel softening". Journal of Agricultural and Food Chemistry. 50 (13): 3731–3737. Bibcode:2002JAFC...50.3731J. doi:10.1021/jf020053v. ISSN0021-8561. PMID12059151.