Encapsulin nanocompartments, or encapsulin protein cages, are spherical bacterial organelle-like compartments roughly 25-30 nm in diameter that are involved in various aspects of metabolism, in particular protecting bacteria from oxidative stress. Encapsulin nanocompartments are structurally similar to the HK97 bacteriophage and their function depends on the proteins loaded into the nanocompartment. The sphere is formed from 60 (for a 25 nm sphere) or 180 (for a 30 nm sphere) copies of a single

protomer In structural biology, a protomer is the structural unit of an oligomeric protein. It is the smallest unit composed of at least two different protein chains that form a larger hetero-oligomer by association of two or more copies of this unit. The ...

, termed

encapsulin The encapsulins are a family of bacterial proteins that serve as the main structural components of encapsulin nanocompartments. There are several different encapsulin proteins, including EncA, which forms the shell, and EncB, EncC, and EncD, whic ...

. Their structure has been studied in great detail using

X-ray crystallography X-ray crystallography is the experimental science determining the atomic and molecular structure of a crystal, in which the crystalline structure causes a beam of incident X-rays to diffract into many specific directions. By measuring the angles ...

and

cryo-electron microscopy Cryogenic electron microscopy (cryo-EM) is a cryomicroscopy technique applied on samples cooled to cryogenic temperatures. For biological specimens, the structure is preserved by embedding in an environment of vitreous ice. An aqueous sample sol ...

. A number of different types of proteins have been identified as being loaded into encapsulin nanocompartments.

Peroxidase Peroxidases or peroxide reductases ( EC numberbr>1.11.1.x are a large group of enzymes which play a role in various biological processes. They are named after the fact that they commonly break up peroxides. Functionality Peroxidases typically ca ...

s or proteins similar to

ferritin Ferritin is a universal intracellular protein that stores iron and releases it in a controlled fashion. The protein is produced by almost all living organisms, including archaea, bacteria, algae, higher plants, and animals. It is the primary ' ...

s are the two most common types of cargo proteins. While most encapsulin nanocompartments contain only one type of cargo protein, in some species two or three types of cargo proteins are loaded. Encapsulins purified from ''Rhodococcus jostii'' can be assembled and disassembled with changes in pH. In the assembled state, the compartment enhances the activity of its cargo, a peroxidase enzyme.

Use as a platform for bioengineering

Recently, encapsulin nanocompartments have begun to receive considerable interest from bioengineers because of their potential to allow the targeted delivery of drugs, proteins, and mRNAs to specific cells of interest.

References

{{reflist Metabolism Cell biology Biological engineering Bacterial proteins