title: External scaffold of spherical immature poxvirus particles is made of protein trimers, forming a honeycomb lattice.
abstract: During morphogenesis, poxviruses undergo a remarkable transition from spherical immature forms to brick-shaped infectious particles lacking helical or icosahedral symmetry. In this study, we show that the transitory honeycomb lattice coating the lipoprotein membrane of immature vaccinia virus particles is formed from trimers of a 62-kD protein encoded by the viral D13L gene. Deep-etch electron microscopy demonstrated that anti-D13 antibodies bound to the external protein coat and that lattice fragments were in affinity-purified D13 preparations. Soluble D13 appeared mostly trimeric by gel electrophoresis and ultracentrifugation, which is consistent with structural requirements for a honeycomb. In the presence or absence of other virion proteins, a mutated D13 with one amino acid substitution formed stacks of membrane-unassociated flat sheets that closely resembled the curved honeycombs of immature virions except for the absence of pentagonal facets. A homologous domain that is present in D13 and capsid proteins of certain other lipid-containing viruses support the idea that the developmental stages of poxviruses reflect their evolution from an icosahedral ancestor.
authors.affiliation: Laboratory of Viral Diseases, National Institute of Allergy and Infectious Diseases (NIAID), National Institutes of Health, Bethesda, MD 20892, USA.
authors.forename: Patricia
authors.initials: P
authors.lastname: Szajner
authors.forename: Andrea S
authors.initials: AS
authors.lastname: Weisberg
authors.forename: Jacob
authors.initials: J
authors.lastname: Lebowitz
authors.forename: John
authors.initials: J
authors.lastname: Heuser
authors.forename: Bernard
authors.initials: B
authors.lastname: Moss
mesh_terms: D036022:Capsid Proteins / Q000737:chemistry / Q000648:ultrastructure*; D002846:Chromatography, Affinity; D004587:Electrophoresis, Agar Gel; D004591:Electrophoresis, Polyacrylamide Gel; D005613:Freeze Etching; D005814:Genes, Viral; D006367:HeLa Cells; D006801:Humans; D007150:Immunohistochemistry; D008970:Molecular Weight; D017354:Point Mutation; D017434:Protein Structure, Tertiary; D012995:Solubility; D014461:Ultracentrifugation; D014615:Vaccinia; D014616:Vaccinia virus / Q000737:chemistry* / Q000502:physiology / Q000648:ultrastructure*; D014764:Viral Proteins / Q000737:chemistry* / Q000235:genetics; D014771:Virion / Q000378:metabolism / Q000648:ultrastructure; D019065:Virus Assembly
chemical_list: D036022:Capsid Proteins; D014764:Viral Proteins