Bacterial microcompartments are widespread bacterial organelles that are made of a protein shell that is made up of various enzymes.[1] These compartments are typically about 100-200 nanometres across and made of interlocking proteins.[2] They do not contain lipids since they are not surrounded by a membrane. Protein-enclosed compartments are also found in eukaryotes, such as the mysterious vault complex.[3]
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Protein families forming the microcompartment shell
The shells of diverse microcompartments are composed of members of three protein families: the BMC domain protein family, the inconsistently named CsoS4 / CcmL / EutN / OrfAB family, and the encapsulins/linocin-like proteins.
The BMC protein family
In microcompartment shells that have been studied, the major constituents are proteins belonging to the Bacterial Micro-Compartment (BMC) family. The crystal structures of a number of BMC proteins have been determined and invariably reveal assembly into cyclical hexamers with a small pore in the center.
The CsoS4 family
Recent structures have revealed either a pentameric or hexameric structure in this family. In icosahedral or quasi-icosahedral carboxysomes, it is likely that the pentameric form is positioned at the vertices[citation needed].
Encapsulins
Encapsulins are a large and widely-distributed family of proteins and are present in most bacteria and have been identified in Candidatus methanoregula, a species of archaea. They were originally called linocin-like proteins and thought to be a group of bacterial antibiotics, since they showed bacteriostatic activity in culture. However, structural analysis showed these to form a spherical nanocompartment that contains enzymes involved in the defenses against oxidative stress.[3]
Types
A recent survey indicated seven different metabolic systems encapsulated by microcompartment shells.[1] Three are characterized:
Carboxysomes
Carboxysomes encapsulate RuBisCo and carbonic anhydrase in carbon-fixing bacteria as part of a carbon concentrating mechanism.[4]
Pdu microcompartments
Some bacteria can used 1,2-propanediol as a carbon source. They express a microcompartment to encapsulate a number of enzymes used in this pathway.[5] The Pdu compartment is constructed by a set of 21 genes in a single chromosomal locus. These genes are sufficient for assembly of the microcompartment since they can be transferred between bacteria and will produce a functional structure in the recipient.[6]
Eut microcompartments
EUT microcompartments are proposed to form in Salmonella species, and may be involved in the metabolism of ethanolamine.[7]
See also
References
- ^ a b Bobik, T. A. (2007). "Bacterial Microcompartments" (PDF). Microbe (Am Soc Microbiol) 2: 25–31. http://www.asm.org/ASM/files/ccLibraryFiles/Filename/000000002765/znw00107000025.pdf.
- ^ Yeates TO, Kerfeld CA, Heinhorst S, Cannon GC, Shively JM (August 2008). "Protein-based organelles in bacteria: carboxysomes and related microcompartments". Nat. Rev. Microbiol. 6: 681–691. doi:. PMID 18679172.
- ^ a b Sutter M, Boehringer D, Gutmann S, et al. (August 2008). "Structural basis of enzyme encapsulation into a bacterial nanocompartment". Nat. Struct. Mol. Biol. 15: 939–947. doi:. PMID 18758469.
- ^ Badger MR, Price GD (February 2003). "CO2 concentrating mechanisms in cyanobacteria: molecular components, their diversity and evolution". J. Exp. Bot. 54 (383): 609–22. doi:. PMID 12554704. http://jexbot.oxfordjournals.org/cgi/pmidlookup?view=long&pmid=12554704.
- ^ Sampson EM, Bobik TA (April 2008). "Microcompartments for B12-dependent 1,2-propanediol degradation provide protection from DNA and cellular damage by a reactive metabolic intermediate". J. Bacteriol. 190 (8): 2966–71. doi:. PMID 18296526.
- ^ Parsons JB, Dinesh SD, Deery E, et al. (May 2008). "Biochemical and structural insights into bacterial organelle form and biogenesis". J. Biol. Chem. 283 (21): 14366–75. doi:. PMID 18332146.
- ^ Penrod JT, Roth JR (April 2006). "Conserving a volatile metabolite: a role for carboxysome-like organelles in Salmonella enterica". J. Bacteriol. 188 (8): 2865–74. doi:. PMID 16585748. PMC: 1447003. http://jb.asm.org/cgi/pmidlookup?view=long&pmid=16585748.
External links
- Mysterious Bacterial Microcompartments Revealed By Biochemists
- Not so simple after all. A renaissance of research into prokaryotic evolution and cell structure
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