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PubMed1979

Morphogenesis of nuclear inclusions and virus capsids in HEL cells infected with temperature-sensitive mutants of human cytomegalovirus.

The morphogenesis of nuclear inclusions and virus capsids in human embryonic lung cells infected with ts mutants of human cytomegalovirus at permissive (34 degrees C) and non-permissive (39 degrees C) temperatures was studied by indirect immunofluorescence (IF) and electron microscopic analyses and compared with the morphogenesis of these structures in wild-type virus infection with or without phosphonoacetate. Mutants tested belonged to five different complementation groups: two groups were DNA- (those unable to synthesize virus DNA at 39 degrees C) and the others were dna+. Based on the previous finding that the electron-dense, reticular nuclear inclusions (EM-NI) observed by the thin-section analysis correspond with nuclear inclusions (IF-NI) detected by the indirect IF staining (i.e. they occupy the same space in the nucleus), the following conclusions were obtained in ts mutant infection at 39 degrees C: (i) the formation of EM-NI, IF-NI and virus capsids requires replication of virus DNA. (II) The formation of EM-NI is not necessarily accompanied by the formation of IF-NI; EM-NI itself is not IF-positive unless it acquires virus-specific late antigens. (iii) The assembly of virus capsids occurs only in those cells in which EM-NI is formed; however, it can occur without the formation of IF-NI. (iv) Virus capsids assembled are not the major antigens responsible for the fluorescence of nuclear inclusions.

Capsid↗
PubMed1986

The structure of the rotavirus inner capsid studied by electron microscopy of chemically disrupted particles.

The inner capsid structure of the OSU strain of porcine rotavirus was studied by electron microscopy of freeze-dried preparations and of negatively stained chemically disrupted virus particles. The analysis of the particles by the freeze-drying technique revealed a T:13 l (laevo) symmetry for the organization of the inner capsid. Treatment of single-capsid rotavirus particles with 30% formamide or 5 M-urea resulted in their degradation, giving rise to very similar products, corresponding to isolated vertices, edges and faces of the virus icosahedron. An analysis of such structures confirmed the triangulation number and handedness of the rotavirus inner capsid, and provided evidence for the open-mesh model, in which the five- and six-coordinated axes are represented by 'holes' formed by smaller trimeric morphological subunits.

Animals↗
PubMed1988

Nucleotide sequence of the rubella virus capsid protein gene reveals an unusually high G/C content.

The nucleotide sequence of the rubella virus capsid protein (C) gene has been determined from a cDNA clone derived from the 40S genomic RNA. The sequence covers the coding region of the C protein (831 nucleotides), 70 nucleotides of the 5' untranslated region, and the 5' end of the downstream E2 membrane protein gene. The capsid gene is unusually rich in C (41.6%) and G (31.2%) residues (G + C 72.8%), and poor in A (15.4%) and U residues (11.8%). There are regions with long runs of up to 45% C or 35% G residues. The codon usage is non-random, with a strong preference for C and G residues in the third position. Starting from two in-frame AUG codons (seven amino acid residues apart) an open reading frame (ORF) was identified that extended in frame into the ORF coding for the downstream E2 membrane protein gene. Since the amino terminus of the capsid protein is blocked, we could not determine which of the AUGs serve as the initiating codon. To verify that the deduced ORF was correct, we have determined the amino acid sequence of 13 tryptic peptides corresponding to one-third of the C protein. Our data show that the C protein is about 277 residues in length (Mr about 30750). It is very hydrophilic and rich in prolines (14.1%) and arginines (14.4%). Clusters of these amino acids are concentrated in the amino-terminal third of the C protein. No sequence homology to the capsid protein of several alphaviruses was observed. Together with our previous sequence data we have now completed the sequence of the genes coding for the structural proteins C, E2 and E1 of rubella virus.

Amino Acid Sequence↗
PubMed1991

Baculovirus expression of the human papillomavirus type 16 capsid proteins: detection of L1-L2 protein complexes.

The human papillomavirus (HPV) type 16 major capsid proteins L1 and L2 have been produced in a baculovirus expression system. Both proteins are expressed at a high level and can be readily solubilized. The L1 capsid protein migrates close to its expected Mr of 60K. On the other hand L2 exhibits a much higher Mr migrating at 73K, which is considerably greater than its predicted Mr of 50K. The identity of both proteins has been confirmed also by Western blot analysis. Both proteins are produced in drastically reduced amounts in the presence of tunicamycin. In addition both L1 and L2 show interesting patterns of phosphorylation. L1 is phosphorylated only weakly and this appears to be quite labile, whereas L2 is very heavily phosphorylated and this, in contrast, appears to be very stable. We have also made use of a dual expression vector for co-expressing the L1 and L2 proteins within the same baculovirus-infected cell. The results obtained from this system demonstrate the presence of protein complexes forming between the two capsid proteins. These studies indicate that at least the initial events in capsid assembly of HPVs can occur in the absence of viral DNA.

Animals↗
PubMed1992

The cloning, sequencing and expression of a major antigenic region from the feline calicivirus capsid protein.

RNA purified from the feline calicivirus (FCV) F9 vaccine strain was used to prepare a cDNA library in the expression vector lambda gt11. The library was screened for expression of FCV antigen using a rabbit antiserum prepared against purified FCV. A 330 bp cDNA clone was identified and used as a probe to obtain a larger overlapping clone of 1369 bp. Comparative sequence analysis with the CFI and F4 strains showed that the clones were derived from the 3' open reading frame encoding the capsid protein. The region encoded by the 330 bp clone was shown to be variable in the three strains compared, and therefore the probable location of major antigenic variation. This clone was expressed in a bacterial system and antiserum to the recombinant protein was used in immunoblots to confirm that this clone was derived from the gene encoding the capsid protein. From these immunoblots, several other capsid-related polypeptides were identified. Comparison with immunoblots using post-vaccination cat sera showed the antibody response in the cat was directed mainly against the capsid protein. Antiserum to the recombinant protein was shown to be effective in neutralizing the infectivity of FCV, indicating that at least one major neutralizing epitope had been cloned.

Amino Acid Sequence↗
PubMed1993

Analysis of feline calicivirus capsid protein genes: identification of variable antigenic determinant regions of the protein.

Three isolates of feline calicivirus (FCV) designated NADC, KCD and CFI/68 were compared for biochemical, serological and genetic variation within the capsid protein gene. The M(r) of the capsid protein from purified virions was approximately 66,000 for the NADC virus isolate, which differed slightly from the relative mobilities of the purified capsid proteins of the KCD and CFI/68 isolates. Polyclonal antisera from either cats infected or rabbits hyperimmunized with the CFI/68 isolate cross-reacted with all three isolates by Western blot analysis. However, these polyclonal antisera to CFI/68 varied considerably in their virus-neutralization titres to the KCD and NADC isolates. Nucleotide sequence data confirmed the genetic variability among these FCV isolates. Comparison of the predicted amino acid sequence of the capsid protein among isolates revealed two regions of sequence divergence that probably contain the antigenically variable determinants. These hypervariable regions may vary by as much as 55% among isolates of FCV. The amino acid sequence diversity in the hypervariable regions of the KCD and NADC isolates correlated well with the virus-neutralization data and suggests that polyvalent vaccines may be more protective than the commonly used monovalent vaccines.

Amino Acid Sequence↗
PubMed1997

A monoclonal antibody against intact human papillomavirus type 16 capsids blocks the serological reactivity of most human sera.

A type-specific and neutralizing mouse MAb (V5) against human papillomavirus (HPV) type 16 capsids was found to block the serological reactivity of human sera with the corresponding capsids. Out of 352 human serum samples tested for the presence of IgG against HPV-16, more than 75% of reactive sera were completely blocked by the V5 antibody. Type-specific MAbs against HPV-6, -18 and -33 were also found to block serological reactivity with capsids of the corresponding HPV types for the majority of reactive human sera. The results suggest that most antibodies in human sera that are reactive with intact HPV capsids recognize the same or closely related major antigenic determinant(s).

Adolescent↗
PubMed1999

Inhibition of interferon-inducible MxA protein expression by hepatitis B virus capsid protein.

Chronic hepatitis B treatment has been significantly improved by interferon (IFN) treatment. However, some studies have suggested that hepatitis B virus (HBV) might have a direct effect on the resistance to IFN. Defective particles, generated by spliced HBV RNA and associated with chronic hepatitis B, have been previously characterized; expression of these particles leads to cytoplasmic accumulation of the capsid protein. The aim of this study was to investigate the role of these defective genomes in IFN resistance. The global antiviral activity of IFN was studied by virus yield reduction assays, the expression of three IFN-induced antiviral proteins was analysed by Western blotting and confocal microscopy, and the regulation of MxA gene expression was studied by Northern blotting and the luciferase assay, in Huh7 cells transfected with a complete or the defective HBV genome. Results showed that the expression of the defective genome reduces the antiviral activity of IFN and that this modulation involves a selective inhibition of MxA protein induction by the HBV capsid protein. Our results also show the trans-suppressive effect of the HBV capsid on the MxA promoter, which might participate in this phenomenon. In conclusion, this study shows a direct interplay between the IFN-sensitive pathway and the capsid protein and might implicate this defective HBV genome in virus persistence.

Blotting, Northern↗
PubMed2000

Glycosylation of the capsid proteins of cowpea mosaic virus: a reinvestigation shows the absence of sugar residues.

The previously reported (Partridge et al., Nature 247, 391-392, 1974 ) glycosylation of the capsid proteins of cowpea mosaic virus (CPMV) has been reinvestigated. In initial studies, a preparation of purified CPMV particles was hydrolysed with HCl and amino acids and sugars were derivatized with o-phthalaldehyde (OPA). No glucosamine or galactosamine, amino sugars previously reported to occur in significant quantities in CPMV capsids, could be detected by reverse-phase high-performance liquid chromatography (RP-HPLC) of the derivatized hydrolysates. A complete analysis of all sugars potentially present was carried out by hydrolysing a sample of purified CPMV capsid proteins and derivatizing the sugars with 1-phenyl-3-methyl-5-pyrazolone. RP-HPLC analysis demonstrated that the capsids do not contain significant quantities of any sugar. The results show that, contrary to the previous report, the coat proteins of CPMV are not glycosylated.

Capsid↗
PubMed2002

The putative capsid protein of the newly identified avian hepatitis E virus shares antigenic epitopes with that of swine and human hepatitis E viruses and chicken big liver and spleen disease virus.

We recently identified a novel virus, designated avian hepatitis E virus (avian HEV), from chickens with hepatitis-splenomegaly (HS) syndrome in the USA. We showed that avian HEV is genetically related to swine and human HEVs. Here we report the antigenic cross-reactivity of the putative open reading frame 2 (ORF2) capsid protein of avian HEV with those of swine and human HEVs and the Australian chicken big liver and spleen disease virus (BLSV). The region encoding the C-terminal 268 amino acid residues of avian HEV ORF2 was cloned into expression vector pRSET-C. The truncated ORF2 protein was expressed in E. coli as a fusion protein and purified by affinity chromatography. Western blot analysis revealed that the avian HEV ORF2 protein reacted with antisera against the Sar-55 strain of human HEV and with convalescent antisera against swine HEV and the US2 strain of human HEV, as well as with antiserum against BLSV. Convalescent sera from specific-pathogen-free chickens experimentally infected with avian HEV also reacted with the recombinant capsid proteins of swine HEV and Sar-55 human HEV. Antisera against the US2 human HEV also reacted with recombinant ORF2 proteins of both swine HEV and Sar-55 human HEV. The antigenic cross-reactivity of the avian HEV putative capsid protein with those of swine and human HEVs was further confirmed, for the most part, by ELISA assays. The data indicate that avian HEV shares certain antigenic epitopes in its putative capsid protein with swine and human HEVs, as well as with BLSV. The results have implications for HEV diagnosis and taxonomy.

Amino Acid Sequence↗
PubMed2004

Genetic identification of avian hepatitis E virus (HEV) from healthy chicken flocks and characterization of the capsid gene of 14 avian HEV isolates from chickens with hepatitis-splenomegaly syndrome in different geographical regions of the United States.

Avian hepatitis E virus (HEV), a novel virus identified from chickens with hepatitis-splenomegaly (HS) syndrome, is genetically and antigenically related to human HEV. Recently, it was found that avian HEV antibody is also prevalent in healthy chickens. A prospective study was done on a known seropositive but healthy chicken farm to identify avian HEV isolates from healthy chickens. Fourteen chickens were randomly selected, tagged and monitored under natural conditions for 19 weeks. All 14 chickens were seronegative at the beginning of the study at 12 weeks of age. By 21 weeks of age, all 14 chickens had seroconverted to avian HEV antibody. None of the chickens had any sign of HS syndrome. Partial helicase gene and capsid gene sequences of avian HEV isolates recovered from a healthy chicken were determined and found to share 75-97 % nucleotide sequence identity with the corresponding regions of avian HEV isolates from chickens with HS syndrome. Thus far, only one strain of avian HEV from a chicken with HS syndrome has been genetically characterized for its capsid gene, therefore the capsid gene region of an additional 14 isolates from chickens with HS syndrome were also characterized. The capsid genes of avian HEV isolates from chickens with HS syndrome were found to be heterogeneic, sharing 76-100 % nucleotide sequence identity with each other. This study indicates that avian HEV is enzootic in chicken flocks and spreads subclinically among chickens in the United States and that the virus is heterogeneic.

Aging↗
PubMed2005

The cytoplasmic tail of herpes simplex virus envelope glycoprotein D binds to the tegument protein VP22 and to capsids.

Herpes simplex virus (HSV) capsids assemble, mature and package their viral genome in the nucleoplasm. They then exit the nucleus into the cytoplasm, where they acquire their final tegument and envelope. The molecular mechanism of cytoplasmic envelopment is unclear, but evidence suggests that the viral glycoprotein tails play an important role in the recruitment of tegument and capsids at the final envelopment site. However, due to redundancy in protein-protein interactions among the viral glycoproteins, genetic analysis of the role of individual glycoproteins in assembly has been difficult. To overcome this problem, a glutathione S-transferase fusion protein-binding assay was used in this study to test the interaction between the cytoplasmic tail of one specific viral glycoprotein, gD, and tegument proteins. The study demonstrated that the 38 kDa tegument protein VP22 bound specifically to the gD tail. This association was dependent on arginine and lysine residues at positions 5 and 6 in the gD tail. In addition, HSV-1 capsids bound the gD tail and exhibited a similar sequence dependence. It is concluded that VP22 may serve as a linker protein, mediating the interaction of the HSV capsid with gD.

Amino Acid Sequence↗
PubMed1999

Structures of the HIV-1 capsid protein dimerization domain at 2.6 A resolution.

The human immunodeficiency virus type I (HIV-1) capsid protein is initially synthesized as the central domain of the Gag polyprotein, and is subsequently proteolytically processed into a discrete 231-amino-acid protein that forms the distinctive conical core of the mature virus. The crystal structures of two proteins that span the C-terminal domain of the capsid are reported here: one encompassing residues 146-231 (CA146-231) and the other extending to include the 14-residue p2 domain of Gag (CA146-p2). The isomorphous CA146-231 and CA146-p2 structures were determined by molecular replacement and have been refined at 2.6 A resolution to R factors of 22.3 and 20.7% (Rfree = 28.1 and 27.5%), respectively. The ordered domains comprise residues 148-219 for CA146-231 and 148-218 for CA146-p2, and their refined structures are essentially identical. The proteins are composed of a 310 helix followed by an extended strand and four alpha-helices. A crystallographic twofold generates a dimer that is stabilized by parallel packing of an alpha-helix 2 across the dimer interface and by packing of the 310 helix into a groove created by alpha-helices 2 and 3 of the partner molecule. CA146-231 and CA146-p2 dimerize with the full affinity of the intact capsid protein, and their structures therefore reveal the essential dimer interface of the HIV-1 capsid.

Amino Acid Sequence↗
PubMed1984

Infection of neuroblastoma cells by Semliki Forest virus. The interference of viral capsid protein with the binding of host messenger RNAs into initiation complexes is the cause of the shut-off of host protein synthesis.

From ribosomal washes of neuroblastoma cells infected with Semliki Forest virus (SFV) a protein of Mr 33000 was purified, which comigrated with the viral capsid protein on sodium dodecyl sulfate/polyacrylamide gels and was recognized by antibodies against the capsid protein of SFV. This protein selectively inhibits the translation of host and early viral 42S mRNA in vitro, but has no effect on late viral 26S and encephalomyocarditis virus mRNA translation. Eukaryotic initiation factor 4B and cap-binding protein restore the translation of host and 42S mRNA to control levels. The capsid protein specifically prevents the binding of host mRNA into 80S initiation complexes, but has no effect on that of late viral mRNA. We propose that the capsid protein is the component responsible for the shut-off of host protein synthesis in SFV-infected cells and for the decreased translational activity of the crude ribosomal washes from these cells.

Animals↗
PubMed2004

Characterization of virus infectivity and cell-free capsid assembly of SIVMneCL8.

We have previously described a cell-free system that reconstitutes immature capsid assembly of Gag polypeptides from viruses belonging to three major primate lentiviral lineages, including HIV-1, HIV-2 and SIVagm. Studies described here examine a member of the SIVmac/Mne lineage, SIVMneCL8, using assays for virus production and infectivity as well as cellular events in capsid formation. We report that SIVMneCL8, a molecular clone with properties typical of transmitted viral variants, is less infectious per unit p27 Gag than another member of the SIVmac/Mne lineage, SIVmac239. SIVMneCL8 Gag polypeptides are arrested at an early stage of capsid assembly in the cell-free system. Additionally, SIVMneCL8 Gag polypeptides associate minimally with the host factor human HP68. This is the first report of a primate lentivirus that does not complete capsid assembly in the cell-free system.

Animals↗
PubMed2006

Foamy virus capsid assembly occurs at a pericentriolar region through a cytoplasmic targeting/retention signal in Gag.

Foamy viruses (FV) are unusual retroviruses that differ in many aspects of their life cycle from the orthoretroviruses such as human immunodeficiency virus. Similar to Mason-Pfizer monkey virus (MPMV), FV assemble into capsids intracellularly. The capsids are then transported to a cellular membrane for acquisition of envelope (Env) glycoproteins and budding. However, unlike MPMV, budding of FV is dependent upon the presence of Env. Previous work suggested that FV Env proteins are localized to the endoplasmic reticulum (ER) where budding takes place. However, very little was known about the details of FV assembly. We have used immunofluorescence and electron microscopy to visualize the intracellular location of FV assembly and budding. We have found that, as in the case of MPMV, FV capsids assemble at a pericentriolar site in the cytoplasm. Surprisingly, FV Env is mostly absent from this site and, contrary to expectations, FV capsid structural protein (Gag) is absent from the ER. Gag and Env only co-localize at the trans-Golgi network, suggesting that Env-Gag interactions that are required for viral egress from the cell, occurs at this site. Finally, inhibitor studies suggest an important role of microtubule networks for foamy viral assembly and budding.

Capsid↗
PubMed1977

Solid-phase radioimmunoassay of human immunoglobulin M and immunoglobulin G antibodies against herpes simplex virus type 1 capsid, envelope, and excreted antigens.

A solid-phase radioimmunoassay developed in our laboratory for detection of human viral immunoglobulin M (IgM) and IgG antibodies was applied to demonstrate human class-specific antibody response against capsid, envelope, and excreted antigens of herpes simplex virus type 1. In primary infections, a clear IgM and IgG antibody response was found predominantly against the envelope components, whereas the IgM and IgG antibodies to the capsid antigen appeared more slowly. Increasing IgG antibody titers to the excreted antigen were also found in primary infections, though appearing more slowly than antibodies to the other subunit antigens. The antibody response against capsid and envelope antigens was not type specific, whereas in primary infections IgG class antibodies against the excreted antigen showed distinct type specificity. In recurrent infections, no significant level of IgM class antibodies was demonstrated, but in the patients with a severe secondary herpes simplex virus infection a definite IgM class antibody response was found against the envelope antigen. In addition, during severe secondary infections the antibody response against the excreted antigen was enhanced. The host IgG antibody response in recurrent infections was directed against the envelope and excreted antigens, whereas the level of the capsid antibodies was relatively stable.

Antibodies, Viral↗
PubMed1996

Immune response to hepatitis A virus capsid proteins after infection.

This study was undertaken to determine the immune response of humans to viral capsid polypeptides of hepatitis A virus (HAV) after natural infection, which is very important for vaccine development. Antiviral capsids in 73 serum samples from patients with acute and chronic HAV infections were analyzed by immunoblotting against individual HAV capsid polypeptides (VP1, VP2, VP3, and VP4) by using a cell culture-based HAV antigen. For reference, total anti-HAV immunoglobulin G (IgG) and anti-HAV IgM were also determined by radioimmunoassay. As a result, a dominant immune response against VP1 (98% IgG, 94% IgM) was found in the acute phase. However, many other sera also reacted with VP0 (88% IgG; 35% IgM) and VP3 (81% IgG and 29% IgM). In contrast to the acute phase, anti-VP1, anti-VP0, and anti-VP3, IgG antibodies against all three viral proteins (29, 29, and 73% respectively), especially those against VP3, were found years after onset of HAV disease and over long periods in the sera of hepatitis patients. These results suggest that antibodies for capsid polypeptides are present over an extended period in the sera of HAV-infected patients. They are likely of importance in maintaining long-term immunity.

Capsid↗