Structures of hepatitis B virus cores presenting a model epitope and their complexes with antibodies.

The core shell of hepatitis B virus is a potent immune stimulator, giving a strong neutralizing immune response to foreign epitopes inserted at the immunodominant region, located at the tips of spikes on the exterior of the shell. Here, we analyze structures of core shells with a model epitope inserted at two alternative positions in the immunodominant region. Recombinantly expressed core protein assembles into T=3 and T=4 icosahedral shells, and atomic coordinates are available for the T=4 shell. Since the modified protein assembles predominantly into T=3 shells, a quasi-atomic model of the native T=3 shell was made. The spikes in this T=3 structure resemble those in T=4 shells crystallized from expressed protein. However, the spikes in the modified shells exhibit an altered conformation, similar to the DNA containing shells in virions. Both constructs allow full access of antibodies to the foreign epitope, DPAFR from the preS1 region of hepatitis B virus surface antigen. However, one induces a 10-fold weaker immune response when injected into mice. In this construct, the epitope is less constrained by the flanking linker regions and is positioned so that the symmetry of the shell causes pairs of epitopes to come close enough to interfere with one another. In the other construct, the epitope mimics the native epitope conformation and position. The interaction of native core shells with an antibody specific to the immunodominant epitope is compared to the constructs with an antibody against the foreign epitope. Our findings have implications for the design of vaccines based on virus-like particles.

Comparison of the structures of three circoviruses: chicken anemia virus, porcine circovirus type 2, and beak and feather disease virus.

Circoviruses are small, nonenveloped icosahedral animal viruses characterized by circular single-stranded DNA genomes. Their genomes are the smallest possessed by animal viruses. Infections with circoviruses, which can lead to economically important diseases, frequently result in virus-induced damage to lymphoid tissue and immunosuppression. Within the family Circoviridae, different genera are distinguished by differences in genomic organization. Thus, Chicken anemia virus is in the genus Gyrovirus, while porcine circoviruses and Beak and feather disease virus belong to the genus CIRCOVIRUS: Little is known about the structures of circoviruses. Accordingly, we investigated the structures of these three viruses with a view to determining whether they are related. Three-dimensional maps computed from electron micrographs showed that all three viruses have a T=1 organization with capsids formed from 60 subunits. Porcine circovirus type 2 and beak and feather disease virus show similar capsid structures with flat pentameric morphological units, whereas chicken anemia virus has stikingly different protruding pentagonal trumpet-shaped units. It thus appears that the structures of viruses in the same genus are related but that those of viruses in different genera are unrelated.

Low pH induces swiveling of the glycoprotein heterodimers in the Semliki Forest virus spike complex.

Time-resolved cryoelectron microscopy reveals the first step in the conformational changes that enable membrane fusion in Semliki Forest virus. The neutral pH structure reveals a central cavity within the spike complex, plate-like extensions forming a layer above the membrane, and the paths of the paired transmembrane domains connecting the trimeric spikes and pentamer-hexamer clustered capsid subunits. Low pH treatment results in centrifugal movement of E2, the receptor-binding subunit, centripetal movement of E1 to narrow the central cavity initiating the formation of an E1 trimer, and the extension of the E1 fusion sequence toward the target membrane.

Three-dimensional structure of hepatitis B virus core particles determined by electron cryomicroscopy.

Human hepatitis B virus core protein expressed in E. coli assembles into two sizes of particle. We have determined their three-dimensional structures by electron cryomicroscopy and image processing. The large and small particles correspond to triangulation number T = 4 and T = 3 dimer clustered packings, containing 240 and 180 protein subunits, respectively. The local packing of subunits is very similar in the two sizes of particle and shows holes or channels through the shell. The native viral core particle packages RNA and is active in reverse transcription to DNA. The holes we observe may provide access for the necessary small molecules. Shells assembled from the intact core protein contain additional material, probably RNA, which appears as an icosahedrally ordered inner shell in the three-dimensional map.

Three-dimensional structure of the rotavirus haemagglutinin VP4 by cryo-electron microscopy and difference map analysis.

The three-dimensional structure of the rotavirus spike haemagglutinin viral protein 4 (VP4) has been determined to a resolution of 26 A by cryo-electron microscopy and difference analysis of intact virions and smooth (spikeless) particles. Native and spikeless virions were mixed prior to cryo-preservation so that both structures could be determined from the same micrograph, thereby minimizing systematic errors. This mixing strategy was crucial for difference map analysis since VP4 only accounts for approximately 1% of the virion mass. The VP4 spike is multi-domained and has a radial length of approximately 200 A with approximately 110 A projecting from the surface of the virus. Interactions between VP4 and cell surface receptors are facilitated by the bi-lobed head, which allows multi-site interactions, as well as the uniform distribution of the VP4 heads at maximum radius. The bi-lobed head is attached to a square-shaped body formed by two rods that have a slight left-handed helical twist. These rods merge with an angled, rod-like domain connected to a globular base approximately 85 A in diameter. The anchoring base displays pseudo 6-fold symmetry. This surprising finding may represent a novel folding motif in which a single polypeptide of VP4 contributes similar but non-equivalent domains to form the arms of the hexameric base. The VP4 spike penetrates the virion surface approximately 90 A and interacts with both outer (VP7) and inner (VP6) capsid proteins. The extensive VP4-VP7 and VP4-VP6 interactions imply a scaffolding function in which VP4 may participate in maintaining precise geometric register between the inner and outer capsids.(ABSTRACT TRUNCATED AT 250 WORDS)

Rotavirus spike structure and polypeptide composition.

Negatively stained preparations of rotavirus imaged with a low dose of electrons provide sufficient contrast to reveal surface projections or spikes. The number of spikes found projecting from different particles indicates that not all 60 peripentonal sites are occupied. Treatment at pH 11.2 with 250 mM ammonium hydroxide specifically removes the spikes, yielding smooth double-shelled particles of the same diameter as that of the native virus. Protein analysis confirms that the released spikes are composed of polypeptide VP4 (or its two cleavage products VP5* and VP8*) and that the smooth particle retains the other major outer shell protein VP7. Spikeless particles can be decorated by a monoclonal antibody specific for the major immunodominant neutralizing domain of VP7, implying that removal of the spikes does not denature the VP7 that is retained on the surface of the smooth particle.

Intra-articular apatite deposition in mixed connective tissue disease: crystallographic and technetium scanning characteristics.

An acute arthritis in a patient with mixed connective tissue disease (MCTD) was found to be associated with intra-articular deposition of carbonated hydroxyapatite crystals. A technetium hydroxymethylene diphosphonate bone scan showed intense uptake in the delayed phase scan of the affected joints. Synovial fluid analysis demonstrated uptake of the radiopharmaceutical drug directly onto the crystals.

Cytochrome c as a high resolution marker of neurons for light and electron microscopy.

Cytochrome c is taken up by lesioned neurons in the central and peripheral nervous system of the house fly. The enzyme reaction product is evenly distributed in cell bodies, axons, dendrites and axon terminals after 3-6 h uptake. No uptake into undamaged neurons, nor any transneuronal uptake could be demonstrated. Pre- and postsynaptic relations of cytochrome c-labeled neurons can be resolved.