Bacterial microcompartment

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

• Endomembrane system

References

1. ^ ^{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. 
2. ^ 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 (9): 681–691. doi:10.1038/nrmicro1913. PMID 18679172. 
3. ^ ^{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 (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 National Academy of Sciences, USA 108 (11): 4292–4296. doi:10.1073/pnas.1012872108. PMC 3060260. PMID 21368184. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3060260. 
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. http://jexbot.oxfordjournals.org/cgi/pmidlookup?view=long&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. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2293232. 
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. 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