title: A virus capsid-like nanocompartment that stores iron and protects bacteria from oxidative stress.
abstract: Living cells compartmentalize materials and enzymatic reactions to increase metabolic efficiency. While eukaryotes use membrane-bound organelles, bacteria and archaea rely primarily on protein-bound nanocompartments. Encapsulins constitute a class of nanocompartments widespread in bacteria and archaea whose functions have hitherto been unclear. Here, we characterize the encapsulin nanocompartment from Myxococcus xanthus, which consists of a shell protein (EncA, 32.5 kDa) and three internal proteins (EncB, 17 kDa; EncC, 13 kDa; EncD, 11 kDa). Using cryo-electron microscopy, we determined that EncA self-assembles into an icosahedral shell 32 nm in diameter (26 nm internal diameter), built from 180 subunits with the fold first observed in bacteriophage HK97 capsid. The internal proteins, of which EncB and EncC have ferritin-like domains, attach to its inner surface. Native nanocompartments have dense iron-rich cores. Functionally, they resemble ferritins, cage-like iron storage proteins, but with a massively greater capacity (~30,000 iron atoms versus ~3,000 in ferritin). Physiological data reveal that few nanocompartments are assembled during vegetative growth, but they increase fivefold upon starvation, protecting cells from oxidative stress through iron sequestration.
authors.affiliation: W. Harry Feinstone Department of Molecular Microbiology and Immunology, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD, USA.
authors.forename: Colleen A
authors.initials: CA
authors.lastname: McHugh
authors.affiliation: Laboratory of Structural Biology Research, National Institute of Arthritis, Musculoskeletal and Skin Diseases, Bethesda, MD, USA.
authors.forename: Juan
authors.initials: J
authors.lastname: Fontana
authors.affiliation: Laboratory of Structural Biology Research, National Institute of Arthritis, Musculoskeletal and Skin Diseases, Bethesda, MD, USA.
authors.forename: Daniel
authors.initials: D
authors.lastname: Nemecek
authors.affiliation: Laboratory of Structural Biology Research, National Institute of Arthritis, Musculoskeletal and Skin Diseases, Bethesda, MD, USA.
authors.forename: Naiqian
authors.initials: N
authors.lastname: Cheng
authors.affiliation: Laboratory of Structural Biology Research, National Institute of Arthritis, Musculoskeletal and Skin Diseases, Bethesda, MD, USA.
authors.forename: Anastasia A
authors.initials: AA
authors.lastname: Aksyuk
authors.affiliation: Laboratory of Structural Biology Research, National Institute of Arthritis, Musculoskeletal and Skin Diseases, Bethesda, MD, USA.
authors.forename: J Bernard
authors.initials: JB
authors.lastname: Heymann
authors.affiliation: Laboratory of Structural Biology Research, National Institute of Arthritis, Musculoskeletal and Skin Diseases, Bethesda, MD, USA.
authors.forename: Dennis C
authors.initials: DC
authors.lastname: Winkler
authors.affiliation: W. Harry Feinstone Department of Molecular Microbiology and Immunology, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD, USA.
authors.forename: Alan S
authors.initials: AS
authors.lastname: Lam
authors.affiliation: Department of Biology, Brookhaven National Laboratory, Upton, NY, USA.
authors.forename: Joseph S
authors.initials: JS
authors.lastname: Wall
authors.affiliation: Laboratory of Structural Biology Research, National Institute of Arthritis, Musculoskeletal and Skin Diseases, Bethesda, MD, USA stevena@mail.nih.gov ehoiczyk@jhsph.edu.
authors.forename: Alasdair C
authors.initials: AC
authors.lastname: Steven
authors.affiliation: W. Harry Feinstone Department of Molecular Microbiology and Immunology, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD, USA stevena@mail.nih.gov ehoiczyk@jhsph.edu.
authors.forename: Egbert
authors.initials: E
authors.lastname: Hoiczyk
mesh_terms: D018407:Bacterial Physiological Phenomena; D001426:Bacterial Proteins / Q000378:metabolism*; D020285:Cryoelectron Microscopy; D007501:Iron / Q000378:metabolism*; D046911:Macromolecular Substances / Q000378:metabolism*; D008958:Models, Molecular; D016941:Myxococcus xanthus / Q000502:physiology* / Q000648:ultrastructure; D053758:Nanoparticles / Q000378:metabolism*; D018384:Oxidative Stress; D055503:Protein Multimerization
chemical_list: D001426:Bacterial Proteins; D046911:Macromolecular Substances; D007501:Iron
keywords: HK97 fold; cryo‐electron microscopy; encapsulin; ferritin; oxidative stress