Effect of recent seasonal influenza vaccination on serum antibody responses to candidate pandemic influenza A/H5N1 vaccines: A meta-analysis.

Recent studies have suggested that among those receiving seasonal influenza vaccine (SIV), reduced immunogenicity is observed in recently vaccinated (RV; within the past season or 2) persons when compared with those not recently vaccinated (NRV). We performed a meta-analysis to assess the effect of recent immunization with SIV on serum H5 hemagglutination inhibition (HAI) antibody responses after influenza A/H5N1 vaccination using data from a series of randomized controlled trials. The primary outcome was seroconversion measured by HAI assays following receipt of 2 doses of H5N1 vaccine. The geometric mean titer (GMT) of serum HAI antibody after vaccination was the secondary outcome. Analyses were performed using propensity score (PS) matching. The PS for each individual in the meta-analysis cohort was calculated using logistic regression and covariates included age, gender, race, antigen dose, adjuvant, statin use and vaccine manufacturer. 2015 subjects enrolled in 7 clinical trials were eligible for inclusion in the meta-analysis cohort; among these, 915 (45%) were RV. 901 RV subjects were matched (1:1) with replacement to a subject who was NRV. Subjects who received SIV within the previous season were significantly less likely to seroconvert following H5N1 vaccination (adjusted odds ratio 0.76; 95%CI 0.60-0.96; p = 0.024), and the GMT was 18% higher among NRV subjects (GM ratio of HAI antibody 1.18; 95%CI 1.04-1.33; p = 0.008). Further work is needed to better define the effects of, and mechanisms contributing to, reduced immune responses to H5N1 vaccine among RV subjects.

Phthalate exposure and semen quality in fertile US men.

Several experimental and observational studies have demonstrated the antiandrogenicity of several phthalates. However, there is limited evidence of an association between phthalate exposure in adult life and semen quality. The aim of this study was to examine phthalate exposure during adulthood in relation to semen quality in fertile US men. This multi-center cross-sectional study included 420 partners of pregnant women who attended a prenatal clinic in one of five US cities during 1999-2001. Nine phthalate metabolites [mono (2-ethylhexyl) phthalate (MEHP), mono (2-ethyl-5-hydroxyhexyl) phthalate (MEHHP), mono (2-ethyl-5-oxohexyl) phthalate (MEOHP), and mono (2-ethyl-5-carboxypentyl) phthalate (MECPP)], as well as mono-n-butyl phthalate (MBP) and mono-isobutyl phthalate (MiBP), mono (three carboxypropyl) phthalate (MCPP), monobenzyl phthalate (MBzP), and monoethyl phthalate (MEP)] were measured in urine collected at the same time as the semen sample. We regressed natural log-transformed (ln) sperm concentration, ln(total sperm count), ln(total motile sperm count), percent motile spermatozoa, and percent spermatozoa with normal morphology on each of the nine natural log-transformed metabolite concentrations and on the molar-weighted sum of DEHP metabolites in separate models. We fit unadjusted models and models that adjusted for confounders determined a priori. In unadjusted models, ln(MiBP) was significantly and positively associated with motility and ln(MBzP) significantly negatively associated with ln(total sperm count). In adjusted linear models, urinary metabolite concentrations of DEHP, DBP, DEP, and DOP were not associated with any semen parameter. We found an inverse association between ln(MBzP) concentrations and sperm motility (ß = -1.47, 95% CI: -2.61, -0.33), adjusted for ln(creatinine concentration), geographic location, age, race, smoking status, stress, recent fever, time from sample collection and time to complete analysis. Several sensitivity analyses confirmed the robustness of these associations. This study and the available literature suggest that impacts of adult exposure to phthalates at environmental levels on classical sperm parameters are likely to be small.

Low-dose aspirin use does not diminish the immune response to monovalent H1N1 influenza vaccine in older adults.

Non-steroidal anti-inflammatory drugs (NSAIDs) may inhibit antibody production by peripheral blood mononuclear cells; one consequence of this could be decreased effectiveness of vaccines in NSAID users. Because many older adults use low-dose aspirin for primary or secondary prevention of coronary events, any inhibitory effect of aspirin on vaccine immune response could reduce the benefits of vaccination programmes in older adults. We tested whether immune response to vaccination differed between users vs. non-users of low-dose aspirin, using data from four randomized trials of monovalent 2009 pandemic influenza A(H1N1) vaccine. Geometric mean haemagglutination inhibition antibody titres were not significantly lower in low-dose aspirin users compared to non-users. Our results provide reassurance that influenza vaccination effectiveness is probably not reduced in older adults taking chronic low-dose aspirin.

Seroprevalence of HSV-1 and HSV-2 antibodies in Canadian women screened for enrolment in a herpes simplex virus vaccine trial.

Herpes simplex virus 1 and 2 (HSV-1 and HSV-2) infections continue to be among the most common and unrecognized sexually transmitted infections in the world. Although treatable, HSV-1 and HSV-2 infections remain incurable. Hence, there is interest in the development of a vaccine to prevent genital herpes. As part of a multicentre, randomized, placebo-controlled trial to test such a vaccine, healthy women 18-30 years were enrolled as volunteers in several Canadian centres between 2005 and 2007. This study reports the seroprevalence of HSV-1 and HSV-2 antibodies in this group. A total of 2694 adult female volunteers in Canada with no known history of herpes simplex were screened for HSV antibodies using Western blot assay (the gold standard for diagnosis of HSV) for potential participation in a randomized, double-blind efficacy field trial of a herpes simplex vaccine. This trial provides a unique opportunity to examine the prevalence of antibodies to HSV-1 and of antibodies to HSV-2 in women with no known history of herpes simplex infection. The prevalence of antibodies to HSV-1 and to HSV-2 is compared with that found in previous Canadian studies that focused on a more general population. The overall seroprevalence of antibody to HSV-1 was 43%; that of HSV-2 was 2.5% and seropositivity to both was 2%. The prevalence of antibody to both HSV-1 and to HSV-2 increased with age. Seronegativity to both HSV-1 and HSV-2 was 56% in participating centres with populations under 250,000 and 46% in participating centres with populations over 250,000. Significant racial differences in seropositivity to HSV-1 and to HSV-2 were noted. The likelihood of participants being seropositive to HSV-1 and to HSV-2 was found to increase with age and to positively correlate with the population of the city in which they resided. Hypotheses are proposed to account for differences in racial seropositivity to HSV-1 and to HSV-2.

X-ray crystal structure of the rotavirus inner capsid particle at 3.8 A resolution.

The rotavirus inner capsid particle, known as the "double-layered particle" (DLP), is the "payload" delivered into a cell in the process of viral infection. Its inner and outer protein layers, composed of viral protein (VP) 2 and VP6, respectively, package the 11 segments of the double-stranded RNA (dsRNA) of the viral genome, as well as about the same number of polymerase molecules (VP1) and capping-enzyme molecules (VP3). We have determined the crystal structure of the bovine rotavirus DLP. There is one full particle (outer diameter approximately 700 A) in the asymmetric unit of the P2(1)2(1)2(1) unit cell of dimensions a=740 A, b=1198 A, and c=1345 A. A three-dimensional reconstruction from electron cryomicroscopy was used as a molecular replacement model for initial phase determination to about 18.5 A resolution, and the 60-fold redundancy of icosahedral particle symmetry allowed phases to be extended stepwise to the limiting resolution of the data (3.8 A). The structure of a VP6 trimer (determined previously by others) fits the outer layer density with very little adjustment. The T=13 triangulation number of that layer implies that there are four and one-third VP6 trimers per icosahedral asymmetric unit. The inner layer has 120 copies of VP2 and thus 2 copies per icosahedral asymmetric unit, designated VP2A and VP2B. Residues 101-880 fold into a relatively thin principal domain, comma-like in outline, shaped such that only rather modest distortions (concentrated at two "subdomain" boundaries) allow VP2A and VP2B to form a uniform layer with essentially no gaps at the subunit boundaries, except for a modest pore along the 5-fold axis. The VP2 principal domain resembles those of the corresponding shells and homologous proteins in other dsRNA viruses: lambda1 in orthoreoviruses and VP3 in orbiviruses. Residues 1-80 of VP2A and VP2B fold together with four other such pairs into a "5-fold hub" that projects into the DLP interior along the 5-fold axis; residues 81-100 link the 10 polypeptide chains emerging from a 5-fold hub to the N-termini of their corresponding principal domains, clustered into a decameric assembly unit. The 5-fold hub appears to have several distinct functions. One function is to recruit a copy of VP1 (or of a VP1-VP3 complex), potentially along with a segment of plus-strand RNA, as a decamer of VP2 assembles. The second function is to serve as a shaft around which can coil a segment of dsRNA. The third function is to guide nascent mRNA, synthesized in the DLP interior by VP1 and 5'-capped by the action of VP3, out through a 5-fold exit channel. We propose a model for rotavirus particle assembly, based on known requirements for virion formation, together with the structure of the DLP and that of VP1, determined earlier.

Molecular interactions in rotavirus assembly and uncoating seen by high-resolution cryo-EM.

Rotaviruses, major causes of childhood gastroenteritis, are nonenveloped, icosahedral particles with double-strand RNA genomes. By the use of electron cryomicroscopy and single-particle reconstruction, we have visualized a rotavirus particle comprising the inner capsid coated with the trimeric outer-layer protein, VP7, at a resolution (4 A) comparable with that of X-ray crystallography. We have traced the VP7 polypeptide chain, including parts not seen in its X-ray crystal structure. The 3 well-ordered, 30-residue, N-terminal "arms" of each VP7 trimer grip the underlying trimer of VP6, an inner-capsid protein. Structural differences between free and particle-bound VP7 and between free and VP7-coated inner capsids may regulate mRNA transcription and release. The Ca(2+)-stabilized VP7 intratrimer contact region, which presents important neutralizing epitopes, is unaltered upon capsid binding.

Structural determinants of rotavirus subgroup specificity mapped by cryo-electron microscopy.

The rotavirus double-layered particle (DLP) is a molecular machine that transcribes 11 genomic segments of double-stranded RNA into full-length mRNA segments during viral replication. DLPs from the human Wa strain of virus, belonging to subgroup II (SG II), possess a significantly reduced level of transcriptase activity compared to bovine UK DLPs that belong to subgroup I (SG I). Cryo-electron microscopy and icosahedral image analysis was used to define the structural basis for this difference in transcriptase activity and to derive three-dimensional density maps of bovine UK and human Wa DLPs at 26 angstroms and 28 angstroms resolution, respectively. The two rotavirus strains had the same diameter, T = 13 l icosahedral lattice symmetry and size of the VP6 trimers on the surface of the DLPs. However, the Wa particles displayed a remarkable absence of VP6 trimers surrounding each 5-fold vertex position. To further explore these structural differences, three-dimensional reconstructions were generated of DLPs decorated with Fab fragments derived from subgroup-specific monoclonal antibodies. The X-ray structures of VP6 and a generic Fab fragment were then docked into the cryo-electron microscopy density maps, which allowed us to propose at "pseudo-atomic" resolution the locations of the amino acid residues defining the subgroup-specific epitopes. Our results demonstrate a correlation between the structure of the VP6 layer and the transcriptase activity of the particles, and suggest that the stability of VP6 trimers, specifically those at the icosahedral 5-fold axes, may be critical for mRNA synthesis. Thus, subgroup specificity of rotavirus may reflect differences in the architecture of the double-layered particle, with resultant consequences for viral mRNA synthesis.

Localization of membrane permeabilization and receptor binding sites on the VP4 hemagglutinin of rotavirus: implications for cell entry.

The surface of rotavirus is decorated with 60 spike-like projections, each composed of a dimer of VP4, the viral hemagglutinin. Trypsin cleavage of VP4 generates two fragments, VP8*, which binds sialic acid (SA), and VP5*, containing an integrin binding motif and a hydrophobic region that permeabilizes membranes and is homologous to fusion domains. Although the mechanism for cell entry by this non-enveloped virus is unclear, it is known that trypsin cleavage enhances viral infectivity and facilitates viral entry. We used electron cryo-microscopy and difference map analysis to localize the binding sites for two neutralizing monoclonal antibodies, 7A12 and 2G4, which are directed against the SA-binding site within VP8* and the membrane permeabilization domain within VP5*, respectively. Fab 7A12 binds at the tips of the dimeric heads of VP4, and 2G4 binds in the cleft between the two heads of the spike. When these binding results are combined with secondary structure analysis, we predict that the VP4 heads are composed primarily of beta-sheets in VP8* and that VP5* forms the body and base primarily in beta-structure and alpha-helical conformations, respectively. Based on these results and those of others, a model is proposed for cell entry in which VP8* and VP5* mediate receptor binding and membrane permeabilization, and uncoating occurs during transfer across the lipid bilayer, thereby generating the transcriptionally active particle.

Immobilization of the early secretory pathway by a virus glycoprotein that binds to microtubules.

Membrane trafficking from the endoplasmic reticulum (ER) to the Golgi complex is mediated by pleiomorphic carrier vesicles that are driven along microtubule tracks by the action of motor proteins. Here we describe how NSP4, a rotavirus membrane glycoprotein, binds to microtubules and blocks ER-to-Golgi trafficking in vivo. NSP4 accumulates in a post-ER, microtubule-associated membrane compartment and prevents targeting of vesicular stomatitis virus glycoprotein (VSV-G) at a pre-Golgi step. NSP4 also redistributes beta-COP and ERGIC53, markers of a vesicular compartment that dynamically cycles between the ER and Golgi, to structures aligned along linear tracks radiating throughout the cytoplasm. This block in membrane trafficking is released when microtubules are depolymerized with nocodazole, indicating that vesicles containing NSP4 are tethered to the microtubule cytoskeleton. Disruption of microtubule-mediated membrane transport by a viral glycoprotein may represent a novel pathogenic mechanism and provides a new experimental tool for the dissection of early steps in exocytic transport.

Membrane-destabilizing activity of rotavirus NSP4 is mediated by a membrane-proximal amphipathic domain.

Expression of the rotavirus non-structural glycoprotein NSP4 in E. coli leads to a decrease in optical density of the culture and release of [(3)H]uridine into the medium, effects attributable to the ability of NSP4 to perturb the bacterial membrane. To identify a domain of NSP4 responsible, different regions of the polypeptide were expressed in E. coli. Membrane destabilization is associated with a region of the protein located within residues 48-91, which includes a potential cationic amphipathic helix. A second region of NSP4 that contains a coiled-coil oligomerization domain and a sequence reported to function as a viral enterotoxin enhances the membrane-destabilizing activity of residues 48-91, but has no direct effect on the membrane stability. These studies suggest that the membrane-destabilizing and enterotoxic properties of NSP4 may be mediated by different regions of the polypeptide and suggest a possible basis for the cytotoxicity of NSP4 in mammalian cells.

Rotavirus VP6 expressed by PVX vectors in Nicotiana benthamiana coats PVX rods and also assembles into viruslike particles.

The rotavirus major inner capsid protein (VP6) has been expressed in Nicotiana benthamiana plants using vectors based on potato virus X (PVX). VP6 was expressed either as a fusion with the PVX coat protein or from an additional subgenomic promoter inserted to enable both VP6 and PVX coat protein to be expressed independently. Both approaches yielded VP6, which retained the ability to form trimers. VP6 expressed from the subgenomic promoter assembled into paracrystalline sheets and tubes. Expression as a fusion protein yielded PVX rods that presented an external "overcoat" of VP6, but unexpectedly, some rotavirus protein also assembled into icosahedral viruslike particles (VLPs). The assembly of viral protein into VLPs suggests that prior display of VP6 on the flexuous PVX rod facilitates the subsequent assembly of VP6 into stable icosahedral particles.

Probing the structure of rotavirus NSP4: a short sequence at the extreme C terminus mediates binding to the inner capsid particle.

The rotavirus nonstructural glycoprotein NSP4 functions as the receptor for the inner capsid particle (ICP) which buds into the lumen of the endoplasmic reticulum during virus maturation. The structure of the cytoplasmic domain of NSP4 from rotavirus strain SA11 has been investigated by using limited proteolysis and mass spectrometry. Digestion with trypsin and V8 protease reveals a C-terminal protease-sensitive region that is 28 amino acids long. The minimal sequence requirements for receptor function have been defined by constructing fusions with glutathione S-transferase and assessing their ability to bind ICPs. These experiments demonstrate that 17 to 20 amino acids from the extreme C terminus are necessary and sufficient for ICP binding and that this binding is cooperative. These observations are consistent with a model for the structure of the NSP4 cytoplasmic region in which four flexible regions of 28 amino acids are presented by a protease-resistant coiled-coil tetramerization domain, with only the last approximately 20 amino acids of each peptide interacting with the surface binding sites on the ICP.

From district general hospital to local general hospital.

Much debate has centred around the future of acute services in the NHS in the UK with particular reference to the role and function of the District General Hospital. This paper explores a new model of hospital development--the 'Local General Hospital' which lies somewhere between the DGH and the cottage or community hospital. The paper uses the case study of Neath General Hospital in South Wales which moved to a LGH model. The paper explores the functional content of the LGH balancing accessibility with cost and clinical effectiveness. The paper makes particular reference to the development of clinical networks which cross organisational boundaries and the support of GPs and consultant medical staff as key success factors in the transition from DGH to LGH.

Serotype classification and characterisation of the rotavirus SA11 VP6 protein using mass spectrometry and two-dimensional gel electrophoresis.

VP6, which makes up the inner capsid of rotavirus, is the major structural protein of this virus. Whilst VP6 has been sequenced at the DNA level in several rotavirus strains, there has been less effort to characterise the protein at the amino acid level. This paper reports the use of peptide mass fingerprinting and post-source decay fragmentation studies using MALDI-TOF and electrospray ionisation mass spectrometry to identify and characterise, in detail, the VP6 protein. We show that mass spectrometric analysis of VP6 peptides successfully distinguished SA11 from other rotavirus serotypes, and identify unique peptides that can be used for serotypic differentiation. For VP6 characterisation, the ExPASy FindMod tool was used to predict post-translational modifications on the protein. Analysis of trypsin and AspN digests predicted that the N-terminal methionine of VP6 was acetylated and this was confirmed using post source decay and electrospray ionisation mass spectrometry-mass spectrometry. An asparagine residue (aa107), which is followed by a glycine residue, was shown to undergo partial deamidation to aspartic acid. VP6 has two additional asparagine-glycine sequences and, in this sequence context, asparagine is known to be particularly susceptible to deamidation. Two-dimensional gel electrophoresis revealed a complex series of VP6 isoforms with an apparent molecular mass of approximately 45,000 Da and a pI ranging from 5.25 to 5.8. This pattern could partly be explained by the potential for deamidation at several sites within the protein.

Expression of translationally controlled tumour protein is regulated by calcium at both the transcriptional and post-transcriptional level.

We have investigated how the programme of protein synthesis is altered in response to a loss of calcium homoeostasis in Cos-7 cells using a differential proteome mapping approach. Exposure of the cells to the calcium ionophore A23187 or thapsigargin, or alternatively, expression of a viral glycoprotein reported to deplete intracellular calcium stores, resulted in the up-regulated expression of a characteristic set of proteins. One of these is the translationally controlled tumour protein (TCTP), a cytoplasmic protein whose expression has not previously been linked to calcium perturbation. Quantitative Northern blot assay demonstrated that steady-state mRNA abundance of TCTP was also increased under these conditions. Clamping the cytosolic calcium concentration by the introduction of bis-(o-aminophenoxy)-ethane-N,N,N',N'-tetra-acetic acid (BAPTA) into cells did not affect the increase in steady-state levels of TCTP mRNA observed in response to ionophore. Therefore depletion of endoplasmic reticulum (ER) calcium, but not elevation of the cytosolic calcium concentration, was responsible for increased transcription of the TCTP gene. However, the presence of BAPTA significantly attenuated the ionophore-mediated increase in levels of the protein. Moreover, the level of TCTP in ionophore-treated cells increased in advance of a detectable increase in the corresponding mRNA abundance. These results indicate that expression of TCTP is regulated at two distinct levels in response to the concentration of calcium in different cellular compartments. Whereas depletion of the ER store causes an increase in TCTP mRNA abundance, increased cytosolic calcium concentrations regulate gene expression at the post-transcriptional level.

BiP (GRP78) and endoplasmin (GRP94) are induced following rotavirus infection and bind transiently to an endoplasmic reticulum-localized virion component.

Rotavirus infection induces profound alterations in the morphology and biochemistry of the host cell. Using two-dimensional (2D) gel electrophoresis combined with metabolic labeling, we have identified four proteins that are specifically upregulated in rotavirus-infected cells. Two of these have been identified as BiP (GRP78) and endoplasmin (GRP94), members of a family of glucose-regulated chaperone proteins that reside in the endoplasmic reticulum (ER) lumen, the site of rotavirus morphogenesis. The level of mRNA and the transcriptional activity of the BiP and endoplasmin genes are increased markedly in rotavirus-infected cells, and these genes are also induced when a single rotavirus protein, the nonstructural glycoprotein NSP4, is expressed in MA104 cells. However, NSP4 does not associate with either BiP or endoplasmin, implying that the mechanism of BiP and endoplasmin gene activation by NSP4 may differ from that triggered by viral membrane glycoproteins of other viruses. The interaction of BiP and endoplasmin with rotavirus structural polypeptides suggests that these chaperones are involved in the process of viral maturation in the ER lumen.

A genomic polymorphism located downstream of the gcvP gene of Escherichia coli that correlates with ecological niche.

Current evolutionary theory proposes that niche-adapted microbial populations might evolve through selection for favoured genotypes followed by clonal expansion (Maynard-Smith, 1991). Possible correlations between genomic variation and ecological niche in Escherichia coli isolates derived from human and animal sources were investigated by randomly amplified polymorphic DNA (RAPD) analysis. A 1.6-kb polymorphic marker was identified which was present in 60% of isolates from human clinical specimens but was present in less than 5% of isolates derived from ovine and bovine faeces. The marker maps to a region of the chromosome located immediately downstream from the gene encoding the glycine decarboxylase P-protein (gcvP). DNA sequences from marker-positive and marker-negative isolates exhibit an abrupt loss of homology immediately downstream from the transcription termination point of the gene which extends for at least 130-base pairs beyond the gcvP transcription terminator. Sequences spanning this region in marker-negative isolates exhibit similarity to the cognate sequence from E. coli K-12, while the corresponding region in marker-positive isolates bears no similarity to any other published sequence. The utility of the marker for investigating the occurrence of human-derived E. coli in the environment was studied in a rural stream. Although the stream carried a high background of animal-derived E. coli, the marker could only be detected in isolates obtained downstream of the human faecal input. The polymorphism therefore shows promise for identification of human-derived E. coli within environments containing isolates from multiple and diverse sources. The methods described here could be used to generate further markers suitable for investigating microbial population ecology.

Rotavirus nonstructural glycoprotein NSP4 alters plasma membrane permeability in mammalian cells.

The endoplasmic reticulum-localized transmembrane glycoprotein NSP4 of rotavirus is a key protein involved in rotavirus cytopathology. We have used a dual-recombinant vaccinia virus system to express NSP4 in monkey kidney epithelial cells at a level comparable to that observed during rotavirus infection. Expression of NSP4 results in loss of plasma membrane integrity, which can be demonstrated by release of both 51Cr and lactate dehydrogenase into the medium. The cytotoxic behavior of NSP4 is dose dependent, and morphological analysis reveals gross changes to cell ultrastructure, indicative of cell death. Thus, intracellular expression of a single rotavirus protein which localizes to the endoplasmic reticulum membrane has profound effects on the stability of the plasma membrane and cell viability. Analysis of NSP4 deletion mutants indicates that a membrane-proximal region located within the cytoplasmic domain may mediate cytotoxicity.

Projection structure of VP6, the rotavirus inner capsid protein, and comparison with bluetongue VP7.

The rotavirus nucleocapsid protein (VP6) is the major structural protein of inner capsid particles (ICP). VP6 is essential for RNA transcription and binds to a virally encoded glycoprotein receptor (NSP4) involved in the rotavirus assembly pathway. To explore the structure of VP6, two-dimensional (2D) crystals of VP6 were generated and examined by electron microscopy and image processing. Fourier transforms computed from low-dose images of negatively stained 2D VP6 crystals displayed complete data to 13 A resolution for p6 plane group symmetry. To correct for the resolution dependent fall-off of the amplitudes derived from electron microscopic images, the rotavirus VP6 amplitudes were scaled to the bluetongue VP7 amplitudes derived from the atomic model by applying a B factor of -360 A-2. The unit cell (a=b=101(+/-2)A, gamma=120(+/-1) degrees) contains two VP6 trimers, each composed of three roughly circular subunits approximately 30 A in diameter. The trimeric organization of VP6 is similar to the oligomeric structure of VP6 when assembled in T=13l icosahedral inner capsid particles at 25 to 40 A resolution. However, a channel at the center of the trimer is better resolved in our map at 15 A resolution. The projection structure of rotavirus VP6 was compared to the homologous protein (VP7) of bluetongue virus, which is also a member of the family of Reoviridae. Notably, both VP6 and bluetongue VP7 assemble as 260 capsomers on the surface of the inner capsid. To compare VP6 and VP7, a projection map of bluetongue VP7 at 15 A resolution was generated using the atomic model derived by X-ray crystallography. VP6 and VP7 both exhibit a trimeric organization with a central channel, even though the alignment identity between the 45 kDa VP6 and the 38 kDa VP7 primary sequences is only 12%. The ability of VP6 to form well-ordered 2D crystals should enable a higher resolution structure analysis by cryo-electron microscopy that will extend our understanding of the icosahedral ICP structure, clarify the mechanism by which VP6 interacts with the NSP4 receptor, and allow a more detailed comparison of VP6 and VP7.