The encapsulins are a family of bacterial proteins that serve as the main structural components of encapsulin nanocompartments.[1] There are several different encapsulin proteins, including EncA, which forms the shell, and EncB, EncC, and EncD, which form the core.[1]
Encapsulins are also used in synthetic biology. They are hard to discover due to their similarity to phage proteins.[2]
Encapsulins were discovered in 1994 as a new class of prokaryotic compartments.[3] Prokaryotic cells usually lack membrane compartments typical for eukaryotes. They instead have numerous protein compartments that are capable of accumulating a large number of molecules.
When protein nanocompartments were discovered in 1994, and later renamed encapsulins, they were found in the supernatant fluid of the Brevibacterium linens culture. This bacterium is present on human skin.
Encapsulin shells compromise icosahedral complexes (12 vertices, 20 faces, 30 edges) formed as a result of self-assembly of protomers.
Encapsulins serve many physiological functions, including catalysis, mineral storage, response to oxidative stress and secondary metabolism. There are ferritin-like encapsulins as well.[2]
Encapsulins can be classified into four different families.
These encaspsulins likely evolved in response to the need for intracellular iron homeostasis. This family of encapsulins typically encapsulate peroxidases of ferritin-like proteins.[4] They are characterized by the encapsulin shell proteins encoded alongside ferritin-like proteins as cargo. The operons usually include genes for ferroxidase enzymes, critical for iron oxidation. They belong to the Pfam family (Encapsulating Protein for Peroxidase) and use short C-terminal targeting (TPs) for cargo loading. This family of encapsulins provide a controlled environment for iron storage and detoxification, as well as preventing oxidative stress.
This family is the largest. They are usually associated with various cargo enzymes like cysteine desulfurase, polyprenyl transferase, terpene cyclase, and xylulose kinase.[5]
Encapsulins have been proven to penetrate cells while carrying functional molecules for targeted delivery.[6]