title: Structural basis for the enhancement of virulence by viral spindles and their in vivo crystallization.
abstract: The great benefits that chemical pesticides have brought to agriculture are partly offset by widespread environmental damage to nontarget species and threats to human health. Microbial bioinsecticides are considered safe and highly specific alternatives but generally lack potency. Spindles produced by insect poxviruses are crystals of the fusolin protein that considerably boost not only the virulence of these viruses but also, in cofeeding experiments, the insecticidal activity of unrelated pathogens. However, the mechanisms by which spindles assemble into ultra-stable crystals and enhance virulence are unknown. Here we describe the structure of viral spindles determined by X-ray microcrystallography from in vivo crystals purified from infected insects. We found that a C-terminal molecular arm of fusolin mediates the assembly of a globular domain, which has the hallmarks of lytic polysaccharide monooxygenases of chitinovorous bacteria. Explaining their unique stability, a 3D network of disulfide bonds between fusolin dimers covalently crosslinks the entire crystalline matrix of spindles. However, upon ingestion by a new host, removal of the molecular arm abolishes this stabilizing network leading to the dissolution of spindles. The released monooxygenase domain is then free to disrupt the chitin-rich peritrophic matrix that protects insects against oral infections. The mode of action revealed here may guide the design of potent spindles as synergetic additives to bioinsecticides.
authors: School of Biological Sciences, University of Auckland, Auckland, 1010, New Zealand;
authors: Elaine
authors: E
authors: Chiu
authors: Department of Biochemistry and Molecular Biology, School of Biomedical Sciences, Monash University, Clayton, VIC 3800, Australia;
authors: Marcel
authors: M
authors: Hijnen
authors: School of Biological Sciences, University of Auckland, Auckland, 1010, New Zealand;
authors: Richard D
authors: RD
authors: Bunker
authors: Department of Biochemistry and Molecular Biology, School of Biomedical Sciences, Monash University, Clayton, VIC 3800, Australia;
authors: Marion
authors: M
authors: Boudes
authors: Swiss Light Source at Paul Scherrer Institut, 5232 Villigen, Switzerland;
authors: Chitra
authors: C
authors: Rajendran
authors: Department of Biochemistry and Molecular Biology, School of Biomedical Sciences, Monash University, Clayton, VIC 3800, Australia;
authors: Kaheina
authors: K
authors: Aizel
authors: Swiss Light Source at Paul Scherrer Institut, 5232 Villigen, Switzerland;
authors: Vincent
authors: V
authors: Oliéric
authors: Swiss Light Source at Paul Scherrer Institut, 5232 Villigen, Switzerland;
authors: Clemens
authors: C
authors: Schulze-Briese
authors: National Institute of Agrobiological Sciences, Tsukuba, Ibaraki 305-8634, Japan;
authors: Wataru
authors: W
authors: Mitsuhashi
authors: Department of Microbiology and Immunology, School of Medical Sciences, University of Otago, Dunedin, 9054, New Zealand; and.
authors: Vivienne
authors: V
authors: Young
authors: Department of Microbiology and Immunology, School of Medical Sciences, University of Otago, Dunedin, 9054, New Zealand; and.
authors: Vernon K
authors: VK
authors: Ward
authors: Université Montpellier 2, Montpellier 34095, France.
authors: Max
authors: M
authors: Bergoin
authors: School of Biological Sciences, University of Auckland, Auckland, 1010, New Zealand; fasseli.coulibaly@monash.edu peter.metcalf@auckland.ac.nz.
authors: Peter
authors: P
authors: Metcalf
authors: Department of Biochemistry and Molecular Biology, School of Biomedical Sciences, Monash University, Clayton, VIC 3800, Australia; fasseli.coulibaly@monash.edu peter.metcalf@auckland.ac.nz.
authors: Fasséli
authors: F
authors: Coulibaly
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D020134:Catalytic Domain; D002686:Chitin / Q000737:chemistry; D003460:Crystallization; D018360:Crystallography, X-Ray; D004220:Disulfides / Q000737:chemistry; D007313:Insecta; D007306:Insecticides / Q000737:chemistry; D046911:Macromolecular Substances; D006899:Mixed Function Oxygenases / Q000737:chemistry; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010100:Oxygen / Q000737:chemistry; D010105:Oxygenases / Q000737:chemistry; D011134:Polysaccharides; D011212:Poxviridae / Q000378:metabolism; D017434:Protein Structure, Tertiary; D014764:Viral Proteins / Q000737:chemistry; D014774:Virulence; D037521:Virulence Factors / Q000737:chemistry* / Q000502:physiology; D014780:Viruses / Q000737:chemistry*
chemical_list: D004220:Disulfides; D007306:Insecticides; D046911:Macromolecular Substances; D011134:Polysaccharides; D014764:Viral Proteins; D037521:Virulence Factors; C093475:fusolin protein, entomopoxvirus; D002686:Chitin; D006899:Mixed Function Oxygenases; D010105:Oxygenases; D010100:Oxygen
keywords: LPMO; in vivo crystallization; microcrystallography; pesticide; poxvirus