title: Cryo-EM reveals a novel octameric integrase structure for betaretroviral intasome function.
abstract: Retroviral integrase catalyses the integration of viral DNA into host target DNA, which is an essential step in the life cycle of all retroviruses. Previous structural characterization of integrase-viral DNA complexes, or intasomes, from the spumavirus prototype foamy virus revealed a functional integrase tetramer, and it is generally believed that intasomes derived from other retroviral genera use tetrameric integrase. However, the intasomes of orthoretroviruses, which include all known pathogenic species, have not been characterized structurally. Here, using single-particle cryo-electron microscopy and X-ray crystallography, we determine an unexpected octameric integrase architecture for the intasome of the betaretrovirus mouse mammary tumour virus. The structure is composed of two core integrase dimers, which interact with the viral DNA ends and structurally mimic the integrase tetramer of prototype foamy virus, and two flanking integrase dimers that engage the core structure via their integrase carboxy-terminal domains. Contrary to the belief that tetrameric integrase components are sufficient to catalyse integration, the flanking integrase dimers were necessary for mouse mammary tumour virus integrase activity. The integrase octamer solves a conundrum for betaretroviruses as well as alpharetroviruses by providing critical carboxy-terminal domains to the intasome core that cannot be provided in cis because of evolutionarily restrictive catalytic core domain-carboxy-terminal domain linker regions. The octameric architecture of the intasome of mouse mammary tumour virus provides new insight into the structural basis of retroviral DNA integration.
authors.affiliation: Department of Cancer Immunology and Virology, Dana-Farber Cancer Institute and Department of Medicine, Harvard Medical School, 450 Brookline Avenue, Boston, Massachusetts 02215, USA.
authors.forename: Allison
authors.initials: A
authors.lastname: Ballandras-Colas
authors.affiliation: Laboratory of Genetics and Helmsley Center for Genomic Medicine, The Salk Institute for Biological Studies, 10010 N Torrey Pines Road, La Jolla, California 92037, USA.
authors.forename: Monica
authors.initials: M
authors.lastname: Brown
authors.affiliation: Clare Hall Laboratories, The Francis Crick Institute, Blanche Lane, South Mimms, Potters Bar, Hertfordshire EN6 3LD, UK.
authors.forename: Nicola J
authors.initials: NJ
authors.lastname: Cook
authors.affiliation: Department of Cancer Immunology and Virology, Dana-Farber Cancer Institute and Department of Medicine, Harvard Medical School, 450 Brookline Avenue, Boston, Massachusetts 02215, USA.
authors.forename: Tamaria G
authors.initials: TG
authors.lastname: Dewdney
authors.affiliation: Department of Biochemistry, The University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Drive, San Antonio, Texas 78229, USA.
authors.forename: Borries
authors.initials: B
authors.lastname: Demeler
authors.affiliation: Clare Hall Laboratories, The Francis Crick Institute, Blanche Lane, South Mimms, Potters Bar, Hertfordshire EN6 3LD, UK.|Division of Medicine, Imperial College London, St. Mary's Campus, Norfolk Place, London W2 1PG, UK.
authors.forename: Peter
authors.initials: P
authors.lastname: Cherepanov
authors.affiliation: Laboratory of Genetics and Helmsley Center for Genomic Medicine, The Salk Institute for Biological Studies, 10010 N Torrey Pines Road, La Jolla, California 92037, USA.
authors.forename: Dmitry
authors.initials: D
authors.lastname: Lyumkis
authors.affiliation: Department of Cancer Immunology and Virology, Dana-Farber Cancer Institute and Department of Medicine, Harvard Medical School, 450 Brookline Avenue, Boston, Massachusetts 02215, USA.
authors.forename: Alan N
authors.initials: AN
authors.lastname: Engelman
mesh_terms: D020134:Catalytic Domain; D020285:Cryoelectron Microscopy; D018360:Crystallography, X-Ray; D004279:DNA, Viral / Q000737:chemistry / Q000378:metabolism* / Q000648:ultrastructure*; D019426:Integrases / Q000737:chemistry* / Q000378:metabolism / Q000648:ultrastructure*; D008324:Mammary Tumor Virus, Mouse / Q000737:chemistry / Q000201:enzymology* / Q000235:genetics / Q000648:ultrastructure; D008958:Models, Molecular; D055503:Protein Multimerization; D020836:Protein Structure, Quaternary; D016092:Spumavirus / Q000737:chemistry / Q000201:enzymology; D016662:Virus Integration
chemical_list: D004279:DNA, Viral; D019426:Integrases