High-resolution molecular and antigen structure of the VP8* core of a sialic acid-independent human rotavirus strain

Epidemiology of viral gastroenteritis in children and genetic diversity of rotavirus strains in Kolkata, West Bengal after introduction of rotavirus vaccine

BACKGROUND

Despite global rotavirus vaccination efforts, rotavirus remains a leading cause of childhood deaths from acute gastroenteritis. Post-vaccination studies in India, particularly in eastern India, have been limited, despite high prevalence of rotavirus in this region prior to vaccine introduction. This study was conducted to assess the impact of rotavirus vaccine on the epidemiology of rotavirus and other enteric viruses, as well as the changes in the diversity of rotavirus strains among children (≤5 years) with acute gastroenteritis.

METHODS

A total of 877 stool samples from children hospitalized with acute diarrhea during 2022-2023, were screened for enteric viruses using multiplex PCR. Rotavirus positive samples were genotyped by sequencing and phylogenetic analysis of VP4 and VP7 genes were done.

RESULTS AND DISCUSSION

Out of 877 diarrheal cases, 47 % tested positive for at least one enteropathogenic virus. Rotavirus was most prevalent (25.9 %), followed by norovirus (11.4 %), adenovirus-F (10.6 %), and astrovirus (5.3 %). Among mixed infections, rotavirus and norovirus co-infections were the most common. Rotavirus infection was highest in children aged 12-24 months, while other enteric viruses were more common in the 6-24 month age group. Clinical severity was higher among rotavirus-infected patients compared to those infected with other enteric viruses. The G3P[8] genotype of rotavirus predominated, with notable increase in G2P[4] and the detection of rare strains like G3P[6] and G11P[25]. G3P[6] was identified for the first time in this region showing Wa-like genome constellation. Unlike pre-vaccine period, G9 genotype was not detected. Mutations in antigenic epitope of circulating strains compared to vaccine strains may affect vaccine efficacy.

CONCLUSION

The study highlights the persistent burden of childhood diarrhea despite rotavirus vaccination. Subtle alterations in the proportion of other enteric viruses and diversity of circulating rotavirus genotypes in the post-vaccination period were observed. Continuous long-term surveillance is required to evaluate the impact of vaccine in this region.

Genomic characterization of the rotavirus G3P[8] strain in vaccinated children, reveals possible reassortment events between human and animal strains in Manhiça District, Mozambique

Mozambique introduced the rotavirus vaccine (Rotarix®; GlaxoSmithKline Biologicals, Rixensart, Belgium) in 2015, and since then, the Centro de Investigação em Saúde de Manhiça has been monitoring its impact on rotavirus-associated diarrhea and the trend of circulating strains, where G3P[8] was reported as the predominant strain after the vaccine introduction. Genotype G3 is among the most commonly detected Rotavirus strains in humans and animals, and herein, we report on the whole genome constellation of G3P[8] detected in two children (aged 18 months old) hospitalized with moderate-to-severe diarrhea at the Manhiça District Hospital. The two strains had a typical Wa-like genome constellation (I1-R1-C1-M1-A1-N1-T1-E1-H1) and shared 100% nucleotide (nt) and amino acid (aa) identities in 10 gene segments, except for VP6. Phylogenetic analysis demonstrated that genome segments encoding VP7, VP6, VP1, NSP3, and NSP4 of the two strains clustered most closely with porcine, bovine, and equine strains with identities ranging from 86.9-99.9% nt and 97.2-100% aa. Moreover, they consistently formed distinct clusters with some G1P[8], G3P[8], G9P[8], G12P[6], and G12P[8] strains circulating from 2012 to 2019 in Africa (Mozambique, Kenya, Rwanda, and Malawi) and Asia (Japan, China, and India) in genome segments encoding six proteins (VP2, VP3, NSP1-NSP2, NSP5/6). The identification of segments exhibiting the closest relationships with animal strains shows significant diversity of rotavirus and suggests the possible occurrence of reassortment events between human and animal strains. This demonstrates the importance of applying next-generation sequencing to monitor and understand the evolutionary changes of strains and evaluate the impact of vaccines on strain diversity.

The Evolution of Post-Vaccine G8P[4] Group a Rotavirus Strains in Rwanda; Notable Variance at the Neutralization Epitope Sites

Africa has a high level of genetic diversity of rotavirus strains, which is suggested to be a possible reason contributing to the suboptimal effectiveness of rotavirus vaccines in this region. One strain that contributes to this rotavirus diversity in Africa is the G8P[4]. This study aimed to elucidate the entire genome and evolution of Rwandan G8P[4] strains. Illumina sequencing was performed for twenty-one Rwandan G8P[4] rotavirus strains. Twenty of the Rwandan G8P[4] strains had a pure DS-1-like genotype constellation, and one strain had a reassortant genotype constellation. Notable radical amino acid differences were observed at the neutralization sites when compared with cognate regions in vaccine strains potentially playing a role in neutralization escape. Phylogenetic analysis revealed that the closest relationship was with East African human group A rotavirus (RVA) strains for five of the genome segments. Two genome sequences of the NSP4 genome segment were closely related to bovine members of the DS-1-like family. Fourteen VP1 and eleven VP3 sequences had the closest relationships with the RotaTeq™ vaccine WC3 bovine genes. These findings suggest that the evolution of VP1 and VP3 might have resulted from reassortment events with RotaTeq™ vaccine WC3 bovine genes. The close phylogenetic relationship with East African G8P[4] strains from Kenya and Uganda suggests co-circulation in these countries. These findings highlight the need for continued whole-genomic surveillance to elucidate the evolution of G8P[4] strains, especially after the introduction of rotavirus vaccination.

Genomic epidemiology of the rotavirus G2P[4] strains in coastal Kenya pre- and post-rotavirus vaccine introduction, 2012-8

The introduction of rotavirus vaccines into the national immunization programme in many countries has led to a decline in childhood diarrhoea disease burden. Coincidentally, the incidence of some rotavirus group A (RVA) genotypes has increased, which may result from non-vaccine-type replacement. Here, we investigate the evolutionary genomics of rotavirus G2P[4] which has shown an increase in countries that introduced the monovalent Rotarix® vaccine. We examined sixty-three RVA G2P[4] strains sampled from children (aged below 13 years) admitted to Kilifi County Hospital, coastal Kenya, pre- (2012 to June 2014) and post-(July 2014 to 2018) rotavirus vaccine introduction. All the sixty-three genome sequences showed a typical DS-1-like genome constellation (G2-P[4]-I2-R2-C2-M2-A2-N2-T2-E2-H2). Pre-vaccine G2 sequences predominantly classified as sub-lineage IVa-3 and co-circulated with low numbers of sub-lineage IVa-1 strains, whereas post-vaccine G2 sequences mainly classified into sub-lineage IVa-3. In addition, in the pre-vaccine period, P[4] sub-lineage IVa strains co-circulated with low numbers of P[4] lineage II strains, but P[4] sub-lineage IVa strains predominated in the post-vaccine period. On the global phylogeny, the Kenyan pre- and post-vaccine G2P[4] strains clustered separately, suggesting that different virus populations circulated in the two periods. However, the strains from both periods exhibited conserved amino acid changes in the known antigenic epitopes, suggesting that replacement of the predominant G2P[4] cluster was unlikely a result of immune escape. Our findings demonstrate that the pre- and post-vaccine G2P[4] strains circulating in Kilifi, coastal Kenya, differed genetically but likely were antigenically similar. This information informs the discussion on the consequences of rotavirus vaccination on rotavirus diversity.

Full genotype constellations analysis of unusual DS-1-like G12P[6] and G6P[8] rotavirus strains detected in Brazil, 2019

Rotavirus A (RVA) is a major cause of acute gastroenteritis (AGE) in children worldwide. We report unusual RVA G12P[6] and G6P[8] strains isolated from fecal samples from Brazilian children hospitalized for AGE. The characterized RVA have genome segments backbone: G12-P[6]/ G6-P[8]-I2-R2-C2-M2-A2-N2-T2-E2-H2 of DS-1-like genogroup. Our study describes the first identification of G6P[8], a DS-1-like genogroup strain. Nucleotide analysis of VP7 and VP4 genes revealed that all G12 Brazilian strains clustered into the sub-lineages IIIB, mostly associated with P[6] lineage I. Additionally, our G6 lineage I strains were closely related to German G6 genotypes, bound with P[8] lineage III, differing from both vaccine strains. The comparative sequence analysis of our strains with vaccine strains revealed amino acid substitutions located in immunodominant regions of VP7 and VP4 proteins. Continuous monitoring of RVA genotypes is essential to evaluate the impact of vaccination on the dynamic nature of RVA evolution.

Molecular epidemiology, genetic diversity, and vaccine availability of viral acute gastroenteritis in the middle East and North Africa (MENA) region

Acute gastroenteritis is the cause of considerable mortality and morbidity worldwide, particularly among children under five years in underdeveloped countries. Most acute gastroenteritis (AGE) cases are attributed to viral etiologies, including rotavirus, norovirus, adenovirus, astrovirus, and sapovirus. This paper aimed to determine the prevalence rate of different viral etiologies of AGE in the Middle East and North Africa (MENA) region. Moreover, this paper explored rotavirus phylogenetic relatedness, compared VP7 and VP4 antigenic regions of rotavirus with vaccine strains, and explored the availability of vaccines in the MENA region. The literature search identified 160 studies from 18 countries from 1980 to 2019. The overall prevalence of rotavirus, norovirus, adenovirus, astrovirus, and sapovirus were 29.8 %, 13.9 %, 6.3 %, 3.5 %, and 3.2 % of tested samples, respectively. The most common rotavirus genotype combinations in the MENA region were G1P[8], G9P[9], and G2P[4], whereas GII.4 was the predominant norovirus genotype all of which were reported in almost all the studies with genotyping data. The comparison of VP7 and VP4 between circulating rotavirus in the MENA region and vaccine strains has revealed discrete divergent regions, including the neutralizing epitopes. Rotavirus vaccine was introduced to most of the countries of the MENA region; however, only a few studies have assessed the effectiveness of vaccine introduction. This paper provides a comprehensive update on the prevalence of the different viral agents of AGE in the MENA region.

Rotavirus vaccine-derived cases in Belgium: Evidence for reversion of attenuating mutations and alternative causes of gastroenteritis

Since the introduction of live-attenuated rotavirus vaccines in Belgium in 2006, surveillance has routinely detected rotavirus vaccine-derived strains. However, their genomic landscape and potential role in gastroenteritis have not been thoroughly investigated. We compared VP7 and VP4 nucleotide sequences obtained from rotavirus surveillance with the Rotarix vaccine sequence. As a result, we identified 80 vaccine-derived strains in 5125 rotavirus-positive infants with gastroenteritis from 2007 to 2018. Using both viral metagenomics and reverse transcription qPCR, we evaluated the vaccine strains and screened for co-infecting enteropathogens. Among the 45 patients with known vaccination status, 39 were vaccinated and 87% received the vaccine less than a month before the gastroenteritis episode. Reconstruction of 30 near complete vaccine-derived genomes revealed 0-11 mutations per genome, with 88% of them being non-synonymous. This, in combination with several shared amino acid changes among strains, pointed at selection of minor variant(s) present in the vaccine. We also found that some of these substitutions were true revertants (e.g., F167L on VP4, and I45T on NSP4). Finally, co-infections with known (e.g., Clostridioides difficile and norovirus) and divergent or emerging (e.g., human parechovirus A1, salivirus A2) pathogens were detected, and we estimated that 35% of the infants likely had gastroenteritis due to a 'non-rotavirus' cause. Conversely, we could not rule out the vaccine-derived gastroenteritis in over half of the cases. Continued studies inspecting reversion to pathogenicity should monitor the long-time safety of live-attenuated rotavirus vaccines. All in all, the complementary approach with NGS and qPCR provided a better understanding of rotavirus vaccine strain evolution in the Belgian population and epidemiology of co-infecting enteropathogens in suspected rotavirus vaccine-derived gastroenteritis cases.

Structural Basis of Glycan Recognition of Rotavirus

Rotavirus (RV) is an important pathogen causing acute gastroenteritis in young humans and animals. Attachment to the host receptor is a crucial step for the virus infection. The recent advances in illustrating the interactions between RV and glycans promoted our understanding of the host range and epidemiology of RVs. VP8*, the distal region of the RV outer capsid spike protein VP4, played a critical role in the glycan recognition. Group A RVs were classified into different P genotypes based on the VP4 sequences and recognized glycans in a P genotype-dependent manner. Glycans including sialic acid, gangliosides, histo-blood group antigens (HBGAs), and mucin cores have been reported to interact with RV VP8*s. The glycan binding specificities of VP8*s of different RV genotypes have been studied. Here, we mainly discussed the structural basis for the interactions between RV VP8*s and glycans, which provided molecular insights into the receptor recognition and host tropism, offering new clues to the design of RV vaccine and anti-viral agents.

Comparative genomic analysis of genogroup 1 and genogroup 2 rotaviruses circulating in seven US cities, 2014-2016

For over a decade, the New Vaccine Surveillance Network (NVSN) has conducted active rotavirus (RVA) strain surveillance in the USA. The evolution of RVA in the post-vaccine introduction era and the possible effects of vaccine pressure on contemporary circulating strains in the USA are still under investigation. Here, we report the whole-gene characterization (eleven ORFs) for 157 RVA strains collected at seven NVSN sites during the 2014 through 2016 seasons. The sequenced strains included 52 G1P[8], 47 G12P[8], 18 G9P[8], 24 G2P[4], 5 G3P[6], as well as 7 vaccine strains, a single mixed strain (G9G12P[8]), and 3 less common strains. The majority of the single and mixed strains possessed a Wa-like backbone with consensus genotype constellation of G1/G3/G9/G12-P[8]-I1-R1-C1-M1-A1-N1-T1-E1-H1, while the G2P[4], G3P[6], and G2P[8] strains displayed a DS-1-like genetic backbone with consensus constellation of G2/G3-P[4]/P[6]/P[8]-I2-R2-C2-M2-A2-N2-T2-E2-H2. Two intergenogroup reassortant G1P[8] strains were detected that appear to be progenies of reassortment events between Wa-like G1P[8] and DS-1-like G2P[4] strains. Two Rotarix^® vaccine (RV1) and two RV5 derived (vd) reassortant strains were detected. Phylogenetic and similarity matrices analysis revealed 2-11 sub-genotypic allelic clusters among the genes of Wa- and DS-1-like strains. Most study strains clustered into previously defined alleles. Amino acid (AA) substitutions occurring in the neutralization epitopes of the VP7 and VP4 proteins characterized in this study were mostly neutral in nature, suggesting that these RVA proteins were possibly under strong negative or purifying selection in order to maintain competent and actual functionality, but fourteen radical (AA changes that occur between groups) AA substitutions were noted that may allow RVA strains to gain a selective advantage through immune escape. The tracking of RVA strains at the sub-genotypic allele constellation level will enhance our understanding of RVA evolution under vaccine pressure, help identify possible mechanisms of immune escape, and provide valuable information for formulation of future RVA vaccines.

Whole genome and in-silico analyses of G1P[8] rotavirus strains from pre- and post-vaccination periods in Rwanda

Rwanda was the first low-income African country to introduce RotaTeq vaccine into its Expanded Programme on Immunization in May 2012. To gain insights into the overall genetic make-up and evolution of Rwandan G1P[8] strains pre- and post-vaccine introduction, rotavirus positive fecal samples collected between 2011 and 2016 from children under the age of 5 years as part of ongoing surveillance were genotyped with conventional RT-PCR based methods and whole genome sequenced using the Illumina MiSeq platform. From a pool of samples sequenced (n = 158), 36 were identified as G1P[8] strains (10 pre-vaccine and 26 post-vaccine), of which 35 exhibited a typical Wa-like genome constellation. However, one post vaccine strain, RVA/Human-wt/RWA/UFS-NGS:MRC-DPRU442/2012/G1P[8], exhibited a RotaTeq vaccine strain constellation of G1-P[8]-I2-R2-C2-M2-A3-N2-T6-E2-H3, with most of the gene segments having a close relationship with a vaccine derived reassortant strain, previously reported in USA in 2010 and Australia in 2012. The study strains segregated into two lineages, each containing a paraphyletic pre- and post-vaccine introduction sub-lineages. In addition, the study strains demonstrated close relationship amongst each other when compared with globally selected group A rotavirus (RVA) G1P[8] reference strains. For VP7 neutralization epitopes, amino acid substitutions observed at positions T91A/V, S195D and M217T in relation to the RotaTeq vaccine were radical in nature and resulted in a change in polarity from a polar to non-polar molecule, while for the VP4, amino acid differences at position D195G was radical in nature and resulted in a change in polarity from a polar to non-polar molecule. The polarity change at position T91A/V of the neutralizing antigens might play a role in generating vaccine-escape mutants, while substitutions at positions S195D and M217T may be due to natural fluctuation of the RVA. Surveillance of RVA at whole genome level will enhance further assessment of vaccine impact on circulating strains, the frequency of reassortment events under natural conditions and epidemiological fitness generated by such events.

Human Neonatal Rotavirus Vaccine (RV3-BB) Produces Vaccine Take Irrespective of Histo-Blood Group Antigen Status

BACKGROUND

VP4 [P] genotype binding specificities of rotaviruses and differential expression of histo-blood group antigens (HBGAs) between populations may contribute to reduced efficacy against severe rotavirus disease. P[6]-based rotavirus vaccines could broaden protection in such settings, particularly in Africa, where the Lewis-negative phenotype and P[6] rotavirus strains are common.

METHODS

The association between HBGA status and G3P[6] rotavirus vaccine (RV3-BB) take was investigated in a phase 2A study of RV3-BB vaccine involving 46 individuals in Dunedin, New Zealand, during 2012-2014. FUT2 and FUT3 genotypes were determined from DNA extracted from stool specimens, and frequencies of positive cumulative vaccine take, defined as an RV3-BB serum immune response (either immunoglobulin A or serum neutralizing antibody) and/or stool excretion of the vaccine strain, stratified by HBGA status were determined.

RESULTS

RV3-BB produced positive cumulative vaccine take in 29 of 32 individuals (91%) who expressed a functional FUT2 enzyme (the secretor group), 13 of 13 (100%) who were FUT2 null (the nonsecretor group), and 1 of 1 with reduced FUT2 activity (i.e., a weak secretor); in 37 of 40 individuals (93%) who expressed a functional FUT3 enzyme (the Lewis-positive group) and 3 of 3 who were FUT3 null (the Lewis-negative group); and in 25 of 28 Lewis-positive secretors (89%), 12 of 12 Lewis-positive nonsecretors (100%), 2 of 2 Lewis-negative secretors, and 1 of 1 Lewis-negative weak secretor.

CONCLUSIONS

RV3-BB produced positive cumulative vaccine take irrespective of HBGA status. RV3-BB has the potential to provide an improved level of protection in settings where P[6] rotavirus disease is endemic, irrespective of the HBGA profile of the population.

Recombinant Subunit Rotavirus Trivalent Vaccine Candidate: Physicochemical Comparisons and Stability Evaluations of Three Protein Antigens

Although live attenuated Rotavirus (RV) vaccines are available globally to provide protection against enteric RV disease, efficacy is substantially lower in low- to middle-income settings leading to interest in alternative vaccines. One promising candidate is a trivalent nonreplicating RV vaccine, comprising 3 truncated RV VP8 subunit proteins fused to the P2 CD4⁺ epitope from tetanus toxin (P2-VP8-P[4/6/8]). A wide variety of analytical techniques were used to compare the physicochemical properties of these 3 recombinant fusion proteins. Various environmental stresses were used to evaluate antigen stability and elucidate degradation pathways. P2-VP8-P[4] and P2-VP8-P[6] displayed similar physical stability profiles as function of pH and temperature while P2-VP8-P[8] was relatively more stable. Forced degradation studies revealed similar chemical stability profiles with Met¹ most susceptible to oxidation, the single Cys residue (at position 173/172) forming intermolecular disulfide bonds (P2-VP8-P[6] was most susceptible), and Asn⁷ undergoing the highest levels of deamidation. These results are visualized in a structural model of the nonreplicating RV antigens. The establishment of key structural attributes of each antigen, along with corresponding stability-indicating methods, have been applied to vaccine formulation development efforts (see companion paper), and will be utilized in future analytical comparability assessments.

Pregnancy Galectinology: Insights Into a Complex Network of Glycan Binding Proteins

Galectins are a phylogenetically conserved family of soluble β-galactoside binding proteins, consisting of 15 different types, each with a specific function. Galectins contribute to placentation by regulating trophoblast development, migration, and invasion during early pregnancy. In addition, galectins are critical players regulating maternal immune tolerance to the embedded embryo. Recently, the role of galectins in angiogenesis during decidualization and in placenta formation has gained attention. Altered expression of galectins is associated with abnormal pregnancies and infertility. This review focuses on the role of galectins in pregnancy-associated processes and discusses the relevance of galectin-glycan interactions as potential therapeutic targets in pregnancy disorders.

The C Terminus of Rotavirus VP4 Protein Contains an Actin Binding Domain Which Requires Cooperation with the Coiled-Coil Domain for Actin Remodeling

The interactions between viruses and actin cytoskeleton have been widely studied. We showed that rotaviruses remodel microfilaments in intestinal cells and demonstrated that this was due to the VP4 spike protein. Microfilaments mainly occur in the apical domain of infected polarized enterocytes and favor the polarized apical exit of viral progeny. The present work aims at the identification of molecular determinants of actin-VP4 interactions. We used various deletion mutants of VP4 that were transfected into Cos-7 cells and analyzed interactions by immunofluorescence confocal microscopy. It has been established that the C-terminal part of VP4 is embedded within viral particles when rotavirus assembles. The use of specific monoclonal antibodies demonstrated that VP4 is expressed in different forms in infected cells: classically as spike on the outer layer of virus particles, but also as free soluble protein in the cytosol. The C terminus of free VP4 was identified as interacting with actin microfilaments. The VP4 actin binding domain is unable to promote microfilament remodeling by itself; the coiled-coil domain is also required in this process. This actin-binding domain was shown to dominate a previously identified peroxisomal targeting signal, located in the three last amino acids of VP4. The newly identified actin-binding domain is highly conserved in rotavirus strains from species A, B, and C, suggesting that actin binding and remodeling is a general strategy for rotavirus exit. This provides a novel mechanism of protein-protein interactions, not involving cell signaling pathways, to facilitate rotavirus exit.IMPORTANCE Rotaviruses are causal agents of acute infantile viral diarrhea. In intestinal cells, in vitro as well as in vivo, virus assembly and exit do not imply cell lysis but rely on an active process in which the cytoskeleton plays a major role. We describe here a novel molecular mechanism by which the rotavirus spike protein VP4 drives actin remodeling. This relies on the fact that VP4 occurs in different forms. Besides its structural function within the virion, a large proportion of VP4 is expressed as free protein. Here, we show that free VP4 possesses a functional actin-binding domain. This domain, in coordination with a coiled-coil domain, promotes actin cytoskeleton remodeling, thereby providing the capacity to destabilize the cell membrane and allow efficient rotavirus exit.

Both ganglioside GM2 and cholesterol in the cell membrane are essential for Bombyx mori cypovirus cell entry

Bombyx mori cypovirus (BmCPV) enters permissive cells via clathrin-mediated endocytosis pathway. However, the distinct entry mechanism for BmCPV is still ambiguous. The aim of this study is to investigate the role of gangliosides and cholesterol in BmCPV cell entry. The number of BmCPV virions attached to the cell surface and the expression level of BmCPV vp1 gene was significantly decreased by digestion of terminal sialic acids in gangliosides with neuraminidase (NA). Preincubation of different concentration of ganglioside GM1, GM2 or GM3 with BmCPV prior to infection, the reduction of BmCPV infectivity was found by GM2-treated in a dose-depend manner. BmCPV virions were found to colocalize with GM2 in the cell surface. The infectivity of BmCPV was reduced by anti-GM2 antibody treatment cells. Moreover, BmCPV infection was impaired by depletion of membrane cholesterol with MβCD, but the inhibitory effect of MβCD was restored by supplementing with cholesterol. The number of viral particles attached on the BmN cells was significantly decreased by pretreated with MβCD, and BmCPV infection was inhibited by silencing the expression of 3-hydroxy-3-methylglutaryl-CoA reductase gene (Hmg-r) in cholesterol biosynthesis pathway. These results indicate that ganglioside GM2 and cholesterol in membrane lipid rafts are essential for BmCPV attachment to cell surface for its cell entry.

Full-genome characterization by deep sequencing of rotavirus A isolates from outbreaks of neonatal diarrhoea in pigs in Spain

Since early 2017, in Spain there was an apparent increase in reports on rotavirus involvement in neonatal diarrhoea outbreaks, affecting also adult sows. In this study, 16 unrelated outbreaks of diarrhoea in suckling pigs and sows, where rotavirus A was the only pathogen detected, were investigated. Deep-sequencing was performed on total RNA from twenty-four positive faecal samples. Genotyping, phylogenetic and bayesian analyses showed that all isolates had a common ancestor of porcine, or human porcine-like, origin. The new strain was introduced in the population shortly before the onset of the outbreaks. Besides, a high diversification of the VP7 and VP4 genes occurred in a short time. Isolates presented a high number of amino acid changes in the neutralizing epitopes compared to vaccine sequences. The present report illustrates how a new rotavirus A strain may disseminate rapidly and the extremely high diversification that this pathogen may undergo in a short period.

Glycan recognition in globally dominant human rotaviruses

Rotaviruses (RVs) cause life-threatening diarrhea in infants and children worldwide. Recent biochemical and epidemiological studies underscore the importance of histo-blood group antigens (HBGA) as both cell attachment and susceptibility factors for the globally dominant P[4], P[6], and P[8] genotypes of human RVs. How these genotypes interact with HBGA is not known. Here, our crystal structures of P[4] and a neonate-specific P[6] VP8*s alone and in complex with H-type I HBGA reveal a unique glycan binding site that is conserved in the globally dominant genotypes and allows for the binding of ABH HBGAs, consistent with their prevalence. Remarkably, the VP8* of P[6] RVs isolated from neonates displays subtle structural changes in this binding site that may restrict its ability to bind branched glycans. This provides a structural basis for the age-restricted tropism of some P[6] RVs as developmentally regulated unbranched glycans are more abundant in the neonatal gut.

Human rotaviruses (RV) bind to histo-blood group antigens (HBGA) for attachment, but how different viral genotypes interact with HBGA isn’t known. Here, Hu et al. report crystal structures of a prevalent and a neonate-specific RV in complex with HBGA and provide insights into glycan recognition and age-restricted tropism of RVs.

Glycan Binding Specificity and Mechanism of Human and Porcine P[6]/P[19] Rotavirus VP8*s

Rotaviruses (RVs), which cause severe gastroenteritis in infants and children, recognize glycan ligands in a genotype-dependent manner via the distal VP8* head of the spike protein VP4. However, the glycan binding mechanisms remain elusive for the P[II] genogroup RVs, including the widely prevalent human RVs (P[8], P[4], and P[6]) and a rare P[19] RV. In this study, we characterized the glycan binding specificities of human and porcine P[6]/P[19] RV VP8*s and found that the P[II] genogroup RV VP8*s could commonly interact with mucin core 2, which may play an important role in RV evolution and cross-species transmission. We determined the first P[6] VP8* structure, as well as the complex structures of human P[19] VP8*, with core 2 and lacto-N-tetraose (LNT). A glycan binding site was identified in human P[19] VP8*. Structural superimposition and sequence alignment revealed the conservation of the glycan binding site in the P[II] genogroup RV VP8*s. Our data provide significant insight into the glycan binding specificity and glycan binding mechanism of the P[II] genogroup RV VP8*s, which could help in understanding RV evolution, transmission, and epidemiology and in vaccine development.IMPORTANCE Rotaviruses (RVs), belonging to the family Reoviridae, are double-stranded RNA viruses that cause acute gastroenteritis in children and animals worldwide. Depending on the phylogeny of the VP8* sequences, P[6] and P[19] RVs are grouped into genogroup II, together with P[4] and P[8], which are widely prevalent in humans. In this study, we characterized the glycan binding specificities of human and porcine P[6]/P[19] RV VP8*s, determined the crystal structure of P[6] VP8*, and uncovered the glycan binding pattern in P[19] VP8*, revealing a conserved glycan binding site in the VP8*s of P[II] genogroup RVs by structural superimposition and sequence alignment. Our data suggested that mucin core 2 may play an important role in P[II] RV evolution and cross-species transmission. These data provide insight into the cell attachment, infection, epidemiology, and evolution of P[II] genogroup RVs, which could help in developing control and prevention strategies against RVs.

Structural basis of glycan specificity of P[19] VP8*: Implications for rotavirus zoonosis and evolution

Recognition of specific cell surface glycans, mediated by the VP8* domain of the spike protein VP4, is the essential first step in rotavirus (RV) infection. Due to lack of direct structural information of virus-ligand interactions, the molecular basis of ligand-controlled host ranges of the major human RVs (P[8] and P[4]) in P[II] genogroup remains unknown. Here, through characterization of a minor P[II] RV (P[19]) that can infect both animals (pigs) and humans, we made an important advance to fill this knowledge gap by solving the crystal structures of the P[19] VP8* in complex with its ligands. Our data showed that P[19] RVs use a novel binding site that differs from the known ones of other genotypes/genogroups. This binding site is capable of interacting with two types of glycans, the mucin core and type 1 histo-blood group antigens (HBGAs) with a common GlcNAc as the central binding saccharide. The binding site is apparently shared by other P[II] RVs and possibly two genotypes (P[10] and P[12]) in P[I] as shown by their highly conserved GlcNAc-interacting residues. These data provide strong evidence of evolutionary connections among these human and animal RVs, pointing to a common ancestor in P[I] with a possible animal host origin. While the binding properties to GlcNAc-containing saccharides are maintained, changes in binding to additional residues, such as those in the polymorphic type 1 HBGAs may occur in the course of RV evolution, explaining the complex P[II] genogroup that mainly causes diseases in humans but also in some animals.

Resurgence of Rotavirus Genotype G12 in St. Louis During the 2014-2015 Rotavirus Season

BACKGROUND

Rotaviruses are a leading cause of gastroenteritis. Rotavirus vaccination has dramatically reduced rotavirus occurrence; however, we have noticed mild to moderate recurrences in the St. Louis area in alternate years. In 2013, we found rotavirus genotype G12 to be the dominant strain in the St. Louis region. In this study, we again determined the distribution of genotypes and ascertained vaccine history in patients infected with rotavirus G12 during the 2014-15 season.

METHODS

Samples submitted to the St. Louis Children's Hospital Microbiology Laboratory were tested for rotavirus using an antigen assay. We determined the VP7 genotype using amplicon sequence analysis. We determined genome sequences using high-throughput sequencing. We evaluated rotavirus immunization records when available.

RESULTS

Of 30 typed viruses from 2014-15, 29 were G12 (97%). Whole-genome sequencing revealed few changes from G12 viruses analyzed in 2012-13. VP4 and VP7 sequences were >99% identical to previously sequenced G12 strains from St. Louis, and immune epitopes were conserved. Vaccination histories were available from 17 patients. Of these, 4 had been vaccinated, 3 had received incomplete vaccination or had a vaccine history that could not be confirmed, and 10 had not been vaccinated.

CONCLUSIONS

G12 re-emerged as the predominant rotavirus genotype in 2014-15, comprising a higher percentage of cases than in 2012-13. The majority of patients with G12 and available vaccination histories were unvaccinated. There was no genomic evidence to indicate that the G12 strains in St. Louis had evolved to escape vaccine protection. Our work emphasizes the need for continued surveillance.

VP4- and VP7-specific antibodies mediate heterotypic immunity to rotavirus in humans

Human rotaviruses (RVs) are the leading cause of severe diarrhea in young children worldwide. The molecular mechanisms underlying the rapid induction of heterotypic protective immunity to RV, which provides the basis for the efficacy of licensed monovalent RV vaccines, have remained unknown for more than 30 years. We used RV-specific single cell-sorted intestinal B cells from human adults, barcode-based deep sequencing of antibody repertoires, monoclonal antibody expression, and serologic and functional characterization to demonstrate that infection-induced heterotypic immunoglobulins (Igs) primarily directed to VP5*, the stalk region of the RV attachment protein, VP4, are able to mediate heterotypic protective immunity. Heterotypic protective Igs against VP7, the capsid glycoprotein, and VP8*, the cell-binding region of VP4, are also generated after infection; however, our data suggest that homotypic anti-VP7 and non-neutralizing VP8* responses occur more commonly in people. These results indicate that humans can circumvent the extensive serotypic diversity of circulating RV strains by generating frequent heterotypic neutralizing antibody responses to VP7, VP8*, and most often, to VP5* after natural infection. These findings further suggest that recombinant VP5* may represent a useful target for the development of an improved, third-generation, broadly effective RV vaccine and warrants more direct examination.

Genotypic and epitope characteristics of group A porcine rotavirus strains circulating in Canada

Surveillance of Rotavirus A (RVA) infections in North America swine populations are limited and not performed over a significant time period to properly assess the diversity of RVA strains in swine. The VP7 (G) and VP4 (P) genes of 32 Canadian RVA strains, circulating between 2009 and 2015 were sequenced, identifying the G3P[13], G5P[7], G9P[7], G9[13], and G9[19] genotype combinations. The Canadian RVA strains were compared to the RVA strains present in the swine ProSystems RCE rotavirus vaccine. The comparison revealed multiple amino acid differences in the G and P antigenic epitopes, regardless of the G and P genotypes but specifically in the Canadian G3, P[13] and P[19] genotypes. Our study further contributes to the characterization of RVA's evolution and disease mitigation among swine, which may optimize target vaccine design, thereby minimizing RVA disease in this economically important animal population.

Functional and Structural Characterization of P[19] Rotavirus VP8* Interaction with Histo-blood Group Antigens

Rotaviruses (RVs) of species A (RVA) are a major causative agent of acute gastroenteritis. Recently, histo-blood group antigens (HBGAs) have been reported to interact with human RVA VP8* proteins. Human P[19] is a rare P genotype of porcine origin that infects humans sporadically. The functional and structural characteristics of P[19] VP8* interaction with HBGAs are unknown. In this study, we expressed and purified the VP8* proteins of human and porcine P[19] RVs. In oligosaccharide and saliva binding assays, P[19] VP8* proteins showed obvious binding to A-, B-, and O-type saliva samples irrespective of the secretor status, implying broad binding patterns. However, they did not display specific binding to any of the oligosaccharides tested. In addition, we solved the structure of human P[19] VP8* at 2.4 Å, which revealed a typical galectin-like fold. The structural alignment demonstrated that P[19] VP8* was most similar to that of P[8], which was consistent with the phylogenetic analysis. Structure superimposition revealed the basis for the lack of binding to the oligosaccharides. Our study indicates that P[19] RVs may bind to other oligosaccharides or ligands and may have the potential to spread widely among humans. Thus, it is necessary to place the prevalence and evolution of P[19] RVs under surveillance.

IMPORTANCE

Human P[19] is a rare P genotype of porcine origin. Based on phylogenetic analysis of VP8* sequences, P[19] was classified in the P[II] genogroup, together with P[4], P[6], and P[8], which have been reported to interact with HBGAs in a genotype-dependent manner. In this study, we explored the functional and structural characteristics of P[19] VP8* interaction with HBGAs. P[19] VP8* showed binding to A-, B-, and O-type saliva samples, as well as saliva of nonsecretors. This implies that P[19] has the potential to spread among humans with a broad binding range. Careful attention should be paid to the evolution and prevalence of P[19] RVs. Furthermore, we solved the structure of P[19] VP8*. Structure superimposition indicated that P[19] may bind to other oligosaccharides or ligands using potential binding sites, suggesting that further investigation of the specific cell attachment factors is warranted.

Integrated molecular and bioprocess engineering for bacterially produced immunogenic modular virus-like particle vaccine displaying 18 kDa rotavirus antigen

A high global burden of rotavirus disease and the unresolved challenges with the marketed rotavirus vaccines, particularly in the developing world, have ignited efforts to develop virus-like particle (VLP) vaccines for rotavirus. While rotavirus-like particles comprising multiple viral proteins can be difficult to process, modular VLPs presenting rotavirus antigenic modules are promising alternatives in reducing process complexity and cost. In this study, integrated molecular and bioprocess engineering approaches were used to simplify the production of modular murine polyomavirus capsomeres and VLPs presenting a rotavirus 18 kDa VP8* antigen. A single construct was generated for dual expression of non-tagged murine polyomavirus capsid protein VP1 and modular VP1 inserted with VP8*, for co-expression in Escherichia coli. Co-expressed proteins assembled into pentameric capsomeres in E. coli. A selective salting-out precipitation and a polishing size exclusion chromatography step allowed the recovery of stable modular capsomeres from cell lysates at high purity, and modular capsomeres were successfully translated into modular VLPs when assembled in vitro. Immunogenicity study in mice showed that modular capsomeres and VLPs induced high levels of VP8*-specific antibodies. Our results demonstrate that a multipronged synthetic biology approach combining molecular and bioprocess engineering enabled simple and low-cost production of highly immunogenic modular capsomeres and VLPs presenting conformational VP8* antigenic modules. This strategy potentially provides a cost-effective production route for modular capsomere and VLP vaccines against rotavirus, highly suitable to manufacturing economics for the developing world. Biotechnol. Bioeng. 2017;114: 397-406. © 2016 Wiley Periodicals, Inc.

Diversity in Rotavirus-Host Glycan Interactions: A "Sweet" Spectrum

Interaction with cellular glycans is a critical initial step in the pathogenesis of many infectious agents. Technological advances in glycobiology have expanded the repertoire of studies delineating host glycan-pathogen interactions. For rotavirus, the VP8* domain of the outer capsid spike protein VP4 is known to interact with cellular glycans. Sialic acid was considered the key cellular attachment factor for rotaviruses for decades. Although this is true for many rotavirus strains causing infections in animals, glycan array screens show that many human rotavirus strains bind nonsialylated glycoconjugates, called histo-blood group antigens, in a strain-specific manner. The expression of histo-blood group antigens is determined genetically and is regulated developmentally. Variations in glycan binding between different rotavirus strains are biologically relevant and provide new insights into multiple aspects of virus pathogenesis such as interspecies transmission, host range restriction, and tissue tropism. The genetics of glycan expression may affect susceptibility to different rotavirus strains and vaccine viruses, and impact the efficacy of rotavirus vaccination in different populations. A multidisciplinary approach to understanding rotavirus-host glycan interactions provides molecular insights into the interaction between microbial pathogens and glycans, and opens up new avenues to translate findings from the bench to the human population.

Emergence of Rotavirus G12P[8] in St. Louis During the 2012-2013 Rotavirus Season

BACKGROUND

We observed an increase in the number of rotavirus cases in the St. Louis area during the 2012-2013 rotavirus season compared with recent seasons. We aimed to determine whether the rotavirus cases during the 2012-2013 rotavirus season were of types not included in licensed vaccines.

METHODS

Microbiology laboratories of 3 children's hospitals in St. Louis provided samples that were positive using rapid antigen tests from 2010 to 2013. The majority of samples were from St. Louis Children's Hospital. We determined rotavirus genotypes by polymerase chain reaction tests and further characterized a subset of viruses by genome sequencing and comparative sequence analysis.

RESULTS

Eighty-six percent (24 of 28) of typed viruses analyzed from the 2012-2013 rotavirus season were G12. We performed whole genome sequencing on 8 G12 viruses, all of which were VP4 type P[8]. The sequenced viruses showed differences from vaccine strains in major antigenic epitopes on the VP7 protein, but most epitopes on VP4 were conserved. Rotavirus vaccine histories were available for 11 G12 cases, of whom 10 had not been vaccinated.

CONCLUSIONS

G12 was a dominant community-wide genotype in 2013. Most of the G12 cases for whom vaccine histories were available had not received rotavirus vaccine. The experience demonstrates the potential for rapid shifts in rotavirus genotype distribution and underscores the need for vigilant surveillance to detect unusual genotypes that might escape from vaccine protection.

Structural basis of glycan specificity in neonate-specific bovine-human reassortant rotavirus

Strain-dependent variation of glycan recognition during initial cell attachment of viruses is a critical determinant of host specificity, tissue-tropism and zoonosis. Rotaviruses (RVs), which cause life-threatening gastroenteritis in infants and children, display significant genotype-dependent variations in glycan recognition resulting from sequence alterations in the VP8* domain of the spike protein VP4. The structural basis of this genotype-dependent glycan specificity, particularly in human RVs, remains poorly understood. Here, from crystallographic studies, we show how genotypic variations configure a novel binding site in the VP8* of a neonate-specific bovine-human reassortant to uniquely recognize either type I or type II precursor glycans, and to restrict type II glycan binding in the bovine counterpart. Such a distinct glycan-binding site that allows differential recognition of the precursor glycans, which are developmentally regulated in the neonate gut and abundant in bovine and human milk provides a basis for age-restricted tropism and zoonotic transmission of G10P[11] rotaviruses.

Synthetic biology design to display an 18 kDa rotavirus large antigen on a modular virus-like particle

Virus-like particles are an established class of commercial vaccine possessing excellent function and proven stability. Exciting developments made possible by modern tools of synthetic biology has stimulated emergence of modular VLPs, whereby parts of one pathogen are by design integrated into a less harmful VLP which has preferential physical and manufacturing character. This strategy allows the immunologically protective parts of a pathogen to be displayed on the most-suitable VLP. However, the field of modular VLP design is immature, and robust design principles are yet to emerge, particularly for larger antigenic structures. Here we use a combination of molecular dynamic simulation and experiment to reveal two key design principles for VLPs. First, the linkers connecting the integrated antigenic module with the VLP-forming protein must be well designed to ensure structural separation and independence. Second, the number of antigenic domains on the VLP surface must be sufficiently below the maximum such that a "steric barrier" to VLP formation cannot exist. This second principle leads to designs whereby co-expression of modular protein with unmodified VLP-forming protein can titrate down the amount of antigen on the surface of the VLP, to the point where assembly can proceed. In this work we elucidate these principles by displaying the 18.1 kDa VP8* domain from rotavirus on the murine polyomavirus VLP, and show functional presentation of the antigenic structure.

Substantial Receptor-induced Structural Rearrangement of Rotavirus VP8*: Potential Implications for Cross-Species Infection

Rotavirus-cell binding is the essential first step in rotavirus infection. This binding is a major determinant of rotavirus tropism, as host cell invasion is necessary to initiate infection. Initial rotavirus-cell interactions are mediated by carbohydrate-recognizing domain VP8* of the rotavirus capsid spike protein VP4. Here, we report the first observation of significant structural rearrangement of VP8* from human and animal rotavirus strains upon glycan receptor binding. The structural adaptability of rotavirus VP8* delivers important insights into how human and animal rotaviruses utilize the wider range of cellular glycans identified as VP8* binding partners. Furthermore, our studies on rotaviruses with atypical genetic makeup provide information expected to be critical for understanding the mechanisms of animal rotavirus gene emergence in humans and support implementation of epidemiologic surveillance of animal reservoirs as well as future vaccination schemes.

Binding Patterns of Rotavirus Genotypes P[4], P[6], and P[8] in China with Histo-Blood Group Antigens

Rotaviruses (RVs) are an important cause of severe gastroenteritis in children. It has been found that RV may recognize the histo-blood group antigens (HBGAs) as ligands or receptors and bind HBGAs in a type-dependent manner. In this study, we investigated the binding specificity of VP8* proteins from human rotaviruses (RV) that are prevalent in China including genotypes P[4], P[6], and P[8]. Through the saliva- and oligosaccharide-based binding assays, we found that the VP8* proteins of P[4] and P[8] RV showed similar reactivity with the Le^b and H type 1 antigens, while P[6] RV weakly bound the Le^b antigen. These findings may facilitate further research into RV host specificity and vaccine development.

Comparative genomic analysis of genogroup 1 (Wa-like) rotaviruses circulating in the USA, 2006-2009

Group A rotaviruses (RVA) are double stranded RNA viruses that are a significant cause of acute pediatric gastroenteritis. Beginning in 2006 and 2008, respectively, two vaccines, Rotarix™ and RotaTeq®, have been approved for use in the USA for prevention of RVA disease. The effects of possible vaccine pressure on currently circulating strains in the USA and their genome constellations are still under investigation. In this study we report 33 complete RVA genomes (ORF regions) collected in multiple cities across USA during 2006-2009, including 8 collected from children with verified receipt of 3 doses of rotavirus vaccine. The strains included 16 G1P[8], 10 G3P[8], and 7 G9P[8]. All 33 strains had a Wa like backbone with the consensus genotype constellation of G(1/3/9)-P[8]-I1-R1-C1-M1-A1-N1-T1-E1-H1. From maximum likelihood based phylogenetic analyses, we identified 3-7 allelic constellations grouped mostly by respective G types, suggesting a possible allelic segregation based on the VP7 gene of RVA, primarily for the G3 and G9 strains. The vaccine failure strains showed similar grouping for all genes in G9 strains and most genes of G3 strains suggesting that these constellations were necessary to evade vaccine-derived immune protection. Substitutions in the antigenic region of VP7 and VP4 genes were also observed for the vaccine failure strains which could possibly explain how these strains escape vaccine induced immune response. This study helps elucidate how RVA strains are currently evolving in the population post vaccine introduction and supports the need for continued RVA surveillance.

The sweet spot: defining virus-sialic acid interactions

Viral infections are initiated by attachment of the virus to host cell surface receptors, including sialic acid-containing glycans. It is now possible to rapidly identify specific glycan receptors using glycan array screening, to define atomic-level structures of virus-glycan complexes and to alter the glycan-binding site to determine the function of glycan engagement in viral disease. This Review highlights general principles of virus-glycan interactions and provides specific examples of sialic acid binding by viruses with stalk-like attachment proteins, including influenza virus, reovirus, adenovirus and rotavirus. Understanding virus-glycan interactions is essential to combating viral infections and designing improved viral vectors for therapeutic applications.

Glycan Engagement by Viruses: Receptor Switches and Specificity

A large number of viruses, including many human pathogens, bind cell-surface glycans during the initial steps of infection. Viral glycan receptors such as glycosaminoglycans and sialic acid-containing carbohydrates are often negatively charged, but neutral glycans such as histo-blood group antigens can also function as receptors. The engagement of glycans facilitates attachment and entry and, consequently, is often a key determinant of the host range, tissue tropism, pathogenicity, and transmissibility of viruses. Here, we review current knowledge about virus-glycan interactions using representative crystal structures of viral attachment proteins in complex with glycans. We illuminate the determinants of specificity utilized by different glycan-binding viruses and explore the potential of these interactions for switching receptor specificities within or even between glycan classes. A detailed understanding of these parameters is important for the prediction of binding sites where structural information is not available, and is invaluable for the development of antiviral therapeutics.

Histo-blood group antigens: a common niche for norovirus and rotavirus

Noroviruses (NoVs) and rotaviruses (RVs), the two most important causes of viral acute gastroenteritis, are found to recognise histo-blood group antigens (HBGAs) as receptors or ligands for attachment. Human HBGAs are highly polymorphic containing ABO, secretor and Lewis antigens. In addition, both NoVs and RVs are highly diverse in how they recognise these HBGAs. Structural analysis of the HBGA-binding interfaces of NoVs revealed a conserved central binding pocket (CBP) interacting with a common major binding saccharide (MaBS) of HBGAs and a variable surrounding region interacting with additional minor binding saccharides. The conserved CBP indicates a strong selection of NoVs by the host HBGAs, whereas the variable surrounding region explains the diverse recognition patterns of different HBGAs by NoVs and RVs as functional adaptations of the viruses to human HBGAs. Diverse recognition of HBGAs has also been found in bacterial pathogen Helicobacter pylori. Thus, exploratory research into whether such diverse recognitions also occur for other viral and bacterial pathogens that recognise HBGAs is warranted.

Epidemiological and genetic analysis of human group C rotaviruses isolated from outbreaks of acute gastroenteritis in Yokohama, Japan, between 2006 and 2012

Group C rotavirus (GCRV) infection has been described in several parts of the world, predominantly as sporadic cases of acute gastroenteritis. Little is known about the yearly changes in the GCRV strains from diarrheal outbreaks. Stool samples collected from outbreaks of acute gastroenteritis in Yokohama, Japan, between 2006 and 2012 that were negative for norovirus, sapovirus, and group A rotavirus, were screened for GCRV using a reverse passive hemagglutination method. The GCRV strains were characterized by nucleotide sequence and phylogenetic analysis of their VP6, VP7, VP4, and NSP4 genes. Samples from nine of 735 outbreaks in Yokohama (1 %) contained GCRV, and eight of these outbreaks occurred in primary schools. The nucleotide sequences of the strains detected in this study were more closely related to Asian strains than to those from other regions of the world. The nucleotide sequences of the VP7 gene in these nine strains differed, and yearly changes were observed in the amino acid sequences of the VP4 genes. Phylogenetic trees constructed using the nucleotide sequences of the VP6, VP7, VP4, and NSP4 genes showed that sublineage S1 has divided into S1-1 and S1-2 in the VP4 gene only. Our results confirm that the prevalent strains of GCRV change yearly in Yokohama. This is the first study to demonstrate GCRV-associated gastroenteritis outbreaks in Yokohama, Japan.

Sialic Acid Receptors of Viruses

Sialic acid linked to glycoproteins and gangliosides is used by many viruses as a receptor for cell entry. These viruses include important human and animal pathogens, such as influenza, parainfluenza, mumps, corona, noro, rota, and DNA tumor viruses. Attachment to sialic acid is mediated by receptor binding proteins that are constituents of viral envelopes or exposed at the surface of non-enveloped viruses. Some of these viruses are also equipped with a neuraminidase or a sialyl-O-acetyl-esterase. These receptor-destroying enzymes promote virus release from infected cells and neutralize sialic acid-containing soluble proteins interfering with cell surface binding of the virus. Variations in the receptor specificity are important determinants for host range, tissue tropism, pathogenicity, and transmissibility of these viruses.

Expression of human rotavirus chimeric fusion proteins from replicating but non disseminating adenovectors and elicitation of rotavirus-specific immune responses in mice

The aim of this study was to evaluate the usefulness of replicating but non disseminating adenovirus vectors (AdVs) as vaccine vector using human rotavirus (HRV) as a model pathogen. HRV VP7, VP4, or VP4Δ (N-terminal 336 amino acids of VP4) structural proteins as well as the VP4Δ::VP7 chimeric fusion protein were expressed in mammalian cells when delivered with the AdVs. A preliminary experiment demonstrated that VP4Δ was able to induce a HRV-specific IgG response in BALB/c mice inoculated intramuscularly with AdVs expressing the rotaviral protein. Moreover, an AdV-prime/plasmid DNA-boost regimen of vectors resulted in VP4Δ-specific antibody (Ab) titers ~4 times higher than those obtained from mice immunized with AdVs alone. Subsequently, the various HRV protein-encoding AdVs were compared using the AdV-prime/plasmid DNA-boost regimen. Higher IgG and IgA responses to HRV were obtained when VP4Δ::VP7 fusion protein was used as an immunogen as compared to VP7 or VP4 alone or to a mix of both proteins delivered independently by AdVs. A synergetic effect in terms of Ab was obtained with VP4Δ::VP7. In conclusion, this study demonstrated for the first time the suitability of using replicating but non disseminating AdVs as vaccine vector and the VP4Δ::VP7 fusion protein as an immunogen for vaccination against HRV.

Epidemiology and genetic diversity of rotavirus strains in children with acute gastroenteritis in Lahore, Pakistan

Pakistan harbors high disease burden of gastro-enteric infections with majority of these caused by rotavirus. Unfortunately, lack of proper surveillance programs and laboratory facilities have resulted in scarcity of available data on rotavirus associated disease burden and epidemiological information in the country. We investigated 1306 stool samples collected over two years (2008–2009) from hospitalized children under 5 years of age for the presence of rotavirus strains and its genotypic diversity in Lahore. The prevalence rate during 2008 and 2009 was found to be 34% (n = 447 out of 1306). No significant difference was found between different age groups positive for rotavirus (p>0.05). A subset of EIA positive samples was further screened for rotavirus RNA through RT-PCR and 44 (49.43%) samples, out of total 89 EIA positive samples, were found positive. G and P type prevalence was found as follows: G1P [4] = 3(6.81%); G1P [6] = 9(20.45%); G1P [8] = 1(2.27%); G2P [4] = 21(47.72%); G2P [8] = 1(2.27%); G9P [4] = 1(2.27%); G9P [6] = 1(2.27%) and G9P [8] = 7(15.90%). Phylogenetic analysis revealed that the VP7 and VP4 sequences clustered closely with the previously detected strains in the country as well as Belgian rotaviruses. Antigenic characterization was performed by analyzing major epitopes in the immunodominant VP7 and VP4 gene segments. Although the neutralization conferring motifs were found variable between the Pakistani strains and the two recommended vaccines strains (Rotarix™ and RotaTeq™), we validate the use of rotavirus vaccine in Pakistan based on the proven and recognized vaccine efficacy across the globe. Our findings constitute the first report on rotavirus’ genotype diversity, their phylogenetic relatedness and epidemiology during the pre-vaccination era in Lahore, Pakistan and support the immediate introduction of rotavirus vaccine in the routine immunization program of the country.

The VP8* domain of neonatal rotavirus strain G10P[11] binds to type II precursor glycans

Naturally occurring bovine-human reassortant rotaviruses with a P[11] VP4 genotype exhibit a tropism for neonates. Interaction of the VP8* domain of the spike protein VP4 with sialic acid was thought to be the key mediator for rotavirus infectivity. However, recent studies have indicated a role for nonsialylated glycoconjugates, including histo-blood group antigens (HBGAs), in the infectivity of human rotaviruses. We sought to determine if the bovine rotavirus-derived VP8* of a reassortant neonatal G10P[11] virus interacts with hitherto uncharacterized glycans. In an array screen of >600 glycans, VP8* P[11] showed specific binding to glycans with the Galβ1-4GlcNAc motif, which forms the core structure of type II glycans and is the precursor of H type II HBGA. The specificity of glycan binding was confirmed through hemagglutination assays; GST-VP8* P[11] hemagglutinates type O, A, and B red blood cells as well as pooled umbilical cord blood erythrocytes. Further, G10P[11] infectivity was significantly enhanced by the expression of H type II HBGA in CHO cells. The bovine-origin VP4 was confirmed to be essential for this increased infectivity, using laboratory-derived reassortant viruses generated from sialic acid binding rotavirus SA11-4F and a bovine G10P[11] rotavirus, B223. The binding to a core glycan unit has not been reported for any rotavirus VP4. Core glycan synthesis is constitutive in most cell types, and modification of these glycans is thought to be developmentally regulated. These studies provide the first molecular basis for understanding neonatal rotavirus infections, indicating that glycan modification during neonatal development may mediate the age-restricted infectivity of neonatal viruses.

Gangliosides have a functional role during rotavirus cell entry

Cell entry of rotaviruses is a complex process, which involves sequential interactions with several cell surface molecules. Among the molecules implicated are gangliosides, glycosphingolipids with one or more sialic acid (SA) residues. The role of gangliosides in rotavirus cell entry was studied by silencing the expression of two key enzymes involved in their biosynthesis--the UDP-glucose:ceramide glucosyltransferase (UGCG), which transfers a glucose molecule to ceramide to produce glucosylceramide GlcCer, and the lactosyl ceramide-α-2,3-sialyl transferase 5 (GM3-s), which adds the first SA to lactoceramide-producing ganglioside GM3. Silencing the expression of both enzymes resulted in decreased ganglioside levels (as judged by GM1a detection). Four rotavirus strains tested (human Wa, simian RRV, porcine TFR-41, and bovine UK) showed a decreased infectivity in cells with impaired ganglioside synthesis; however, their replication after bypassing the entry step was not affected, confirming the importance of gangliosides for cell entry of the viruses. Interestingly, viral binding to the cell surface was not affected in cells with inhibited ganglioside synthesis, but the infectivity of all strains tested was inhibited by preincubation of gangliosides with virus prior to infection. These data suggest that rotaviruses can attach to cell surface in the absence of gangliosides but require them for productive cell entry, confirming their functional role during rotavirus cell entry.

Interactions among capsid proteins orchestrate rotavirus particle functions

Rotaviruses are members of the Reoviridae family of non-enveloped viruses and important etiologic agents of acute gastroenteritis in infants and young children. In recent years, high-resolution structures of triple-layered rotavirus virions and the constituent proteins have provided valuable insights into functions. Of note, structural studies have revealed the position of the viral RNA-dependent RNA polymerase, VP1, within the inner capsid, which in turn provides clues about the location of the viral capping machinery and the route of viral transcript egress. Mechanisms by which the viral spike protein, VP4, mediates receptor binding and membrane penetration have also been aided by high-resolution structural studies. Future work may serve to fill the remaining gaps in understanding of rotavirus particle structure and function.

Spike protein VP8* of human rotavirus recognizes histo-blood group antigens in a type-specific manner

Rotaviruses (RVs), an important cause of severe diarrhea in children, have been found to recognize sialic acid as receptors for host cell attachment. While a few animal RVs (of P[1], P[2], P[3], and P[7]) are sialidase sensitive, human RVs and the majority of animal RVs are sialidase insensitive. In this study, we demonstrated that the surface spike protein VP8* of the major P genotypes of human RVs interacts with the secretor histo-blood group antigens (HBGAs). Strains of the P[4] and P[8] genotypes shared reactivity with the common antigens of Lewis b (Le(b)) and H type 1, while strains of the P[6] genotype bound the H type 1 antigen only. The bindings between recombinant VP8* and human saliva, milk, or synthetic HBGA oligosaccharides were demonstrated, which was confirmed by blockade of the bindings by monoclonal antibodies (MAbs) specific to Le(b) and/or H type 1. In addition, specific binding activities were observed when triple-layered particles of a P[8] (Wa) RV were tested. Our results suggest that the spike protein VP8* of RVs is involved in the recognition of human HBGAs that may function as ligands or receptors for RV attachment to host cells.

Cell attachment protein VP8* of a human rotavirus specifically interacts with A-type histo-blood group antigen

As with many other viruses, the initial cell attachment of rotaviruses, major causative agent of infantile gastroenteritis, is mediated by interactions with specific cellular glycans^1–4. The distally located VP8* domain of the rotavirus spike protein VP4⁵ mediates such interactions. The existing paradigm is that ‘sialidase-sensitive’ animal rotavirus strains bind to glycans with terminal sialic acid (Sia), whereas ‘sialidase-insensitive’ human rotavirus (HR) strains bind to glycans with internal Sia such as GM1³. Although the involvement of Sia in the animal strains is firmly supported by crystallographic studies^1,3,6,7, it is not yet known how VP8* of HRs interacts with Sia and whether their cell attachment necessarily involves sialoglycans. We found that VP8* of a HR strain specifically recognizes A-type histo-blood group antigen (HBGA) using a glycan array screen comprised of 511 glycans, and that virus infectivity in HT-29 cells is abrogated by anti-Atype antibodies as well as significantly enhanced in CHO cells genetically modified to express the A-type HBGA, providing a novel paradigm for initial cell attachment of HR. HBGAs are genetically determined glycoconjugates present in mucosal secretions, epithelial and on red blood cells⁸, and are recognized as susceptibility and cell attachment factors for gastric pathogens like H. pylori⁹ and noroviruses¹⁰. Our crystallographic studies show that the A-type HBGA binds to the HR VP8* at the same location as the Sia in the VP8* of animal rotavirus, and suggest how subtle changes within the same structural framework allow for such receptor switching. These results raise the possibility that host susceptibility to specific HR strains and pathogenesis are influenced by genetically controlled expression of different HBGAs among the world’s population.

Structural insights into the coupling of virion assembly and rotavirus replication

Viral replication is rapid and robust, but it is far from a chaotic process. Instead, successful production of infectious progeny requires that events occur in the correct place and at the correct time. Rotaviruses (segmented double-stranded RNA viruses of the Reoviridae family) seem to govern their replication through ordered disassembly and assembly of a triple-layered icosahedral capsid. In recent years, high-resolution structural data have provided unprecedented insight into these events. In this Review, we explore the current understanding of rotavirus replication and how it compares to replication of other Reoviridae family members.