title: The atomic structure of baculovirus polyhedra reveals the independent emergence of infectious crystals in DNA and RNA viruses.
abstract: Baculoviruses are ubiquitous insect viruses well known for their use as bioinsecticides, gene therapy vectors, and protein expression systems. Overexpression of recombinant proteins in insect cell culture utilizes the strong promoter of the polyhedrin gene. In infected larvae, the polyhedrin protein forms robust intracellular crystals called polyhedra, which protect encased virions for prolonged periods in the environment. Polyhedra are produced by two unrelated families of insect viruses, baculoviruses and cypoviruses. The atomic structure of cypovirus polyhedra revealed an intricate packing of trimers, which are interconnected by a projecting N-terminal helical arm of the polyhedrin molecule. Baculovirus and cypovirus polyhedra share nearly identical lattices, and the N-terminal region of the otherwise unrelated baculovirus polyhedrin protein sequence is also predicted to be alpha-helical. These results suggest homology between the proteins and a common structural basis for viral polyhedra. Here, we present the 2.2-A structure of baculovirus polyhedra determined by x-ray crystallography from microcrystals produced in vivo. We show that the underlying molecular organization is, in fact, very different. Although both polyhedra have nearly identical unit cell dimensions and share I23 symmetry, the polyhedrin molecules are structurally unrelated and pack differently in the crystals. In particular, disulfide bonds and domain-swapped N-terminal domains stabilize the building blocks of baculovirus polyhedra and interlocking C-terminal arms join unit cells together. We show that the N-terminal projecting helical arms have different structural roles in baculovirus and cypovirus polyhedra and conclude that there is no structural evidence for a common evolutionary origin for both classes of polyhedra.
authors.affiliation: School of Biological Sciences, University of Auckland, Auckland, New Zealand. fasseli.coulibaly@med.monash.edu.au
authors.forename: Fasséli
authors.initials: F
authors.lastname: Coulibaly
authors.forename: Elaine
authors.initials: E
authors.lastname: Chiu
authors.forename: Sascha
authors.initials: S
authors.lastname: Gutmann
authors.forename: Chitra
authors.initials: C
authors.lastname: Rajendran
authors.forename: Peter W
authors.initials: PW
authors.lastname: Haebel
authors.forename: Keiko
authors.initials: K
authors.lastname: Ikeda
authors.forename: Hajime
authors.initials: H
authors.lastname: Mori
authors.forename: Vernon K
authors.initials: VK
authors.lastname: Ward
authors.forename: Clemens
authors.initials: C
authors.lastname: Schulze-Briese
authors.forename: Peter
authors.initials: P
authors.lastname: Metcalf
mesh_terms: D000818:Animals; D002460:Cell Line; D003460:Crystallization; D008855:Microscopy, Electron, Scanning; D008958:Models, Molecular; D009036:Moths; D046912:Multiprotein Complexes / Q000737:chemistry / Q000648:ultrastructure; D017924:Nucleopolyhedroviruses / Q000737:chemistry* / Q000235:genetics / Q000648:ultrastructure*; D000077183:Occlusion Body Matrix Proteins; D020836:Protein Structure, Quaternary; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000648:ultrastructure; D012087:Reoviridae / Q000737:chemistry* / Q000648:ultrastructure*; D013045:Species Specificity; D018411:Spodoptera; D015678:Viral Structural Proteins / Q000737:chemistry* / Q000235:genetics / Q000648:ultrastructure*
chemical_list: D046912:Multiprotein Complexes; D000077183:Occlusion Body Matrix Proteins; D011994:Recombinant Proteins; D015678:Viral Structural Proteins; C009829:polyhedrin protein, Nucleopolyhedrovirus