3-DIMENSIONAL STRUCTURE OF VACCINIA VIRUS-PRODUCED HUMAN PAPILLOMAVIRUS TYPE-1 CAPSIDS

The capsid proteins of papillomavirus self-assemble to form empty capsids or virus-like particles that appear quite similar to naturally occurring virions by conventional electron microscopy. To characterize such virus-like particles more fully, cryoelectron microscopy and image analysis techniques were used to generate three dimensional reconstructions of capsids produced by vaccinia virus recombinants (V capsids) that expressed human papillomavirus type 1 L1 protein only or both L1 and L2 proteins. AH V capsids had 72 pentameric capsomers arranged on a T=7 icosahedral lattice. Each particle (similar to 60 nm in diameter) consisted of an similar to 2-nm-thick shell of protein with a radius of 22 nm with capsomers that extend similar to 6 nm from the shell. At a resolution of 3.5 nm, both V capsid structures appear identical to the capsid structure of native human papillomavirus type 1 (T. S. Baker, W. W. Newcomb, N. H. Olson, L. M. Cowsert, C. Olson, and J. C. Brown, Biophys. J. 60:1445-1456, 1991), thus implying that expressed and native capsids are structurally equivalent.