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]

Contents 1 Protein families forming the microcompartment shell 1.1 The BMC protein family 1.2 The CsoS4 family 1.3 Encapsulins 2 Types 2.1 Carboxysomes 2.2 Pdu microcompartments 2.3 Eut microcompartments 3 See also 4 References 5 External links

[edit] 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.

[edit] 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.

[edit] 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]}.

[edit] 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]

[edit] Types

A recent survey indicated seven different metabolic systems encapsulated by microcompartment shells.^[1] Three are characterized:

[edit] Carboxysomes

Carboxysomes encapsulate RuBisCo and carbonic anhydrase in carbon-fixing bacteria as part of a carbon concentrating mechanism.^[4]

[edit] 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]

[edit] Eut microcompartments

EUT microcompartments are proposed to form in Salmonella species, and may be involved in the metabolism of ethanolamine.^[7]

[edit] See also

• Endomembrane system

[edit] References

[edit] 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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