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1.S.6.  The Bacterial/Archaeal Nanocompartment Encapsulin Shell Protein1 (BANC-SP1) Family

The two main classes of microbial protein compartments are bacterial microcompartments (BMCs) and encapsulin nanocompartments (ENCs). Encapsulins self-assemble into proteinaceous shells with diameters between 24 and 42 nm and are defined by the viral HK97-fold of their shell protein (Giessen 2022). Encapsulins have the ability to encapsulate dedicated cargo proteins, including ferritin-like proteins, peroxidases, and desulfurases. Encapsulation is mediated by targeting sequences present in all cargo proteins. Encapsulins are found in many bacterial and archaeal phyla and have been suggested to play roles in iron storage, stress resistance, sulfur metabolism, and natural product biosynthesis. Phylogenetic analyses indicate that they share a common ancestor with viral capsid proteins. Many pathogens encode encapsulins, and recent evidence suggests that they may contribute toward pathogenicity. The existing information on encapsulin structure, biochemistry, biological function, and biomedical relevance is reviewed by Giessen 2022

Sutter et al. 2008 showed, using X-ray crystallographic, biochemical and EM experiments, that a widespread family of conserved bacterial proteins, the linocin-like proteins, form large assemblies that function as a minimal compartment to package enzymes. We refer to this shell-forming protein as 'encapsulin'. The crystal structure of such a particle from Thermotoga maritima determined at 3.1-angstroms resolution revealed that 60 copies of the monomer assemble into a thin, icosahedral shell with a diameter of 240 angstroms. The interior of this nanocompartment is lined with conserved binding sites for short polypeptide tags present as C-terminal extensions of enzymes involved in oxidative-stress response.

References associated with 1.S.6 family:

Giessen, T.W. (2022). Encapsulins. Annu. Rev. Biochem. 91: 353-380. 35303791
Sutter, M., D. Boehringer, S. Gutmann, S. Günther, D. Prangishvili, M.J. Loessner, K.O. Stetter, E. Weber-Ban, and N. Ban. (2008). Structural basis of enzyme encapsulation into a bacterial nanocompartment. Nat Struct Mol Biol 15: 939-947. 19172747
Williams, E.M., S.M. Jung, J.L. Coffman, and S. Lutz. (2018). Pore Engineering for Enhanced Mass Transport in Encapsulin Nanocompartments. ACS Synth Biol 7: 2514-2517. 30376298
Xiong, X., C. Sun, F.S. Vago, T. Klose, J. Zhu, and W. Jiang. (2020). Cryo-EM Structure of Heterologous Protein Complex Loaded Encapsulin Capsid. Biomolecules 10:. 32961724