Bacterial microcompartment

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Stylized view of the carboxysome and related bacterial structures such as the propanediol utilization (Pdu) and ethanolamine utilization (Eut) microcompartments. Distinct hexameric BMC shell proteins carrying out different functions in the shell are shown in different shades of blue. Pentameric vertex proteins are shown in magenta. Encapsulated enzymes are shown in green, organized in layers. [Image: T. Yeates
]Bacterial microcompartments are widespread bacterial organelles that are made of a protein shell that surrounds and encloses 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]

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

Main article: BMC domain

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,[4] 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.[5]

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.[6] 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.[7]

Eut microcompartments

EUT microcompartments are proposed to form in Salmonella and other Enterobacteriaceae species, and are involved in the metabolism of ethanolamine.[8]

See also

References

  1. ↑ 1.0 1.1 Bobik, T. A. (2007). "Bacterial Microcompartments" (PDF). Microbe (Am Soc Microbiol) 2: 25–31. 
  2. ↑ Yeates TO, Kerfeld CA, Heinhorst S, Cannon GC, Shively JM (August 2008). "Protein-based organelles in bacteria: carboxysomes and related microcompartments". Nature Reviews Microbiology 6 (9): 681–691. doi:10.1038/nrmicro1913. PMID 18679172. 
  3. ↑ 3.0 3.1 Sutter M, Boehringer D, Gutmann S, et al. (August 2008). "Structural basis of enzyme encapsulation into a bacterial nanocompartment". Nature Structural & Molecular Biology 15 (9): 939–947. doi:10.1038/nsmb.1473. PMID 18758469. 
  4. ↑ Vernizzi G, Sknepnek R, Olvera de la Cruz, M (2011). "Platonic and Archimedan geometries in multi-component elastic membranes". Proceedings of the National Academy of Sciences of the United States of America 108 (11): 4292–4296. doi:10.1073/pnas.1012872108. PMC 3060260. PMID 21368184. 
  5. ↑ 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:10.1093/jxb/erg076. PMID 12554704. 
  6. ↑ 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:10.1128/JB.01925-07. PMC 2293232. PMID 18296526. 
  7. ↑ 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:10.1074/jbc.M709214200. PMID 18332146. 
  8. ↑ 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:10.1128/JB.188.8.2865-2874.2006. PMC 1447003. PMID 16585748. 

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