The structure of a putative scaffolding protein of immature poxvirus particles as determined by electron microscopy suggests similarity with capsid proteins of large icosahedral DNA viruses.
Orf virus, the prototype parapoxvirus, is responsible for contagious ecthyma in sheep and goats. The central region of the viral genome codes for proteins highly conserved among vertebrate poxviruses and which are frequently essential for viral proliferation. Analysis of the recently published genome sequence of orf virus revealed that among such essential proteins, the protein orfv075 is an orthologue of D13, the rifampin resistance gene product critical for vaccinia virus morphogenesis. Previous studies showed that D13, arranged as "spicules," is necessary for the formation of vaccinia virus immature virions, a mandatory intermediate in viral maturation. We have determined the three-dimensional structure of recombinant orfv075 at approximately 25-A resolution by electron microscopy of two-dimensional crystals. orfv075 organizes as trimers with a tripod-like main body and a propeller-like smaller domain. The molecular envelope of orfv075 shows unexpectedly good agreement to that of a distant homologue, VP54, the major capsid protein of Paramecium bursaria Chlorella virus type 1. Our structural analysis suggests that orfv075 belongs in the double-barreled capsid protein family found in many double-stranded DNA icosahedral viruses and supports the hypothesis that the nonicosahedral poxviruses and the large icosahedral DNA viruses are evolutionarily related.
Hyun
Jae-Kyung
JK
School of Biological Sciences, University of Auckland, Thomas Building, 3A Symonds Street, Auckland, New Zealand.
Coulibaly
Fasséli
F
Turner
Adrian P
AP
Baker
Edward N
EN
Mercer
Andrew A
AA
Mitra
Alok K
AK
D036022:Capsid Proteins / Q000737:chemistry*; D004267:DNA Viruses / Q000737:chemistry*; D008854:Microscopy, Electron; D010802:Phylogeny; D011212:Poxviridae / Q000737:chemistry*; D011487:Protein Conformation; D014764:Viral Proteins / Q000737:chemistry*; D014771:Virion / Q000737:chemistry*
D036022:Capsid Proteins; D014764:Viral Proteins