Ionic strength- and temperature-induced K(Ca) shifts in the uncoating reaction of rotavirus strains RF and SA11: correlation with membrane permeabilization

Molecular basis for the different PCV2 susceptibility of T-lymphoblasts in Landrace and Piétrain pigs

Clinically, Landrace pigs are more susceptible to porcine circovirus-associated diseases (PCVADs) than Piétrain pigs. We previously found that porcine circovirus type 2 (PCV2) can infect T-lymphoblasts. The present study examined the replication kinetics of six PCV2 strains in the lymphoblasts of Landrace and Piétrain pigs. The results showed that T-lymphoblasts from Landrace pigs are much more susceptible to PCV2 infection than those from Piétrain pigs. In addition, PCV2 replication was strain-dependent. PCV2 binding to T-lymphoblasts was partially mediated by chondroitin sulfate (CS) and dermatan sulfate (DS). Phosphacan, an effective internalization mediator in monocytes that contains several CS chains, was also demonstrated to be involved in PCV2 internalization. Viral binding and internalization were not different between the two breeds, however, the subsequent step, the disassembly was. Although inhibition of serine proteases blocked PCV2 replication in both Landrace and Piétrain pigs, this only occurred at a neutral pH in Piétrain pigs, whereas this occurred also at a low pH in Landrace. This suggested that more proteases can cleave PCV2 in Landrace lymphoblasts than in Piétrain lymphoblasts, explaining the better replication. Through co-localization studies of viral particles with endo-lysosomal markers, and quantitative analysis of organelle sizes during viral internalization, it was observed that PCV2 may exhibit a higher propensity for viral escape from late endosomes in Landrace pigs (smaller) compared to Piétrain pigs. These results provide new understandings of the different PCV2 susceptibility in Landrace and Piétrain pigs.

Solar and temperature treatments affect the ability of human rotavirus wa to bind to host cells and synthesize viral RNA

Rotavirus, the leading cause of diarrheal diseases in children under the age of five, is often resistant to conventional wastewater treatment and thus can remain infectious once released into the aquatic environment. Solar and heat treatments can inactivate rotavirus, but it is unknown how these treatments inactivate the virus on a molecular level. To answer this question, our approach was to correlate rotavirus inactivation with the inhibition of portions of the virus life cycle as a means to identify the mechanisms of solar or heat inactivation. Specifically, the integrity of the rotavirus NSP3 gene, virus-host cell interaction, and viral RNA synthesis were examined after heat (57°C) or solar treatment of rotavirus. Only the inhibition of viral RNA synthesis positively correlated with a loss of rotavirus infectivity; 57°C treatment of rotavirus resulted in a decrease of rotavirus RNA synthesis at the same rate as rotavirus infectivity. These data suggest that heat treatment neutralized rotaviruses primarily by targeting viral transcription functions. In contrast, when using solar disinfection, the decrease in RNA synthesis was responsible for approximately one-half of the decrease in infectivity, suggesting that other mechanisms, including posttranslational, contribute to inactivation. Nevertheless, both solar and heat inactivation of rotaviruses disrupted viral RNA synthesis as a mechanism for inactivation.

Cross-linking of rotavirus outer capsid protein VP7 by antibodies or disulfides inhibits viral entry

Antibodies that neutralize rotavirus infection target outer coat proteins VP4 and VP7 and inhibit viral entry. The structure of a VP7-Fab complex (S. T. Aoki, et al., Science 324:1444-1447, 2009) led us to reclassify epitopes into two binding regions at inter- and intrasubunit boundaries of the calcium-dependent trimer. It further led us to show that antibodies binding at the intersubunit boundary inhibit uncoating of the virion outer layer. We have now tested representative antibodies for each of the defined structural epitope regions and find that antibodies recognizing epitopes in either binding region neutralize by cross-linking VP7 trimers. Antibodies that bind at the intersubunit junction neutralize as monovalent Fabs, while those that bind at the intrasubunit region require divalency. The VP7 structure has also allowed us to design a disulfide cross-linked VP7 mutant which recoats double-layered particles (DLPs) as efficiently as does wild-type VP7 but which yields particles defective in cell entry as determined both by lack of infectivity and by loss of α-sarcin toxicity in the presence of recoated particles. We conclude that dissociation of the VP7 trimer is an essential step in viral penetration into cells.

Impact of physicochemical parameters on in vitro assembly and disassembly kinetics of recombinant triple-layered rotavirus-like particles

Virus-like particles constitute potentially relevant vaccine candidates. Nevertheless, their behavior in vitro and assembly process needs to be understood in order to improve their yield and quality. In this study we aimed at addressing these issues and for that purpose triple- and double-layered rotavirus-like particles (TLP 2/6/7 and DLP 2/6, respectively) size and zeta potential were measured using dynamic light scattering at different physicochemical conditions, namely pH, ionic strength, and temperature. Both TLP and DLP were stable within a pH range of 3-7 and at 5-25 degrees C. Aggregation occurred at 35-45 degrees C and their disassembly became evident at 65 degrees C. The isoelectric points of TLP and DLP were 3.0 and 3.8, respectively. In vitro kinetics of TLP disassembly was monitored. Ionic strength, temperature, and the chelating agent employed determined disassembly kinetics. Glycerol (10%) stabilized TLP by preventing its disassembly. Disassembled TLP was able to reassemble by dialysis at high calcium conditions. VP7 monomers were added to DLP in the presence of calcium to follow in vitro TLP assembly kinetics; its assembly rate being mostly affected by pH. Finally, DLP and TLP were found to coexist under certain conditions as determined from all reaction products analyzed by capillary electrophoresis. Overall, these results contribute to the design of new strategies for the improvement of TLP yield and quality by reducing the VP7 detachment from TLP.

VP5* rearranges when rotavirus uncoats

Trypsin primes rotavirus for efficient infectivity by cleaving the spike protein, VP4, into VP8* and VP5*. A recombinant VP5* fragment has a trimeric, folded-back structure. Comparison of this structure with virion spikes suggests that a rearrangement, analogous to those of enveloped virus fusion proteins, may mediate membrane penetration by rotavirus during entry. To detect this inferred rearrangement of virion-associated authentic VP5*, we raised conformation-specific monoclonal antibodies against the recombinant VP5* fragment in its putative post-membrane penetration conformation. Using one of these antibodies, we demonstrate that rotavirus uncoating triggers a conformational change in the cleaved VP4 spike to yield rearranged VP5*.

[Physiopathology of Rotavirus diarrhea]

The rotavirus is the major cause of infantile gastroenteritis. The virus infects the mature enterocytes of the villus tip of the small intestine and induces a watery diarrhea. Diarrhea can occur in the absence of histological changes in the intestine, and, conversely, the histological changes can be asymptomatic. Rotavirus decreases the activities of digestive enzymes at the apical brush border membrane and inhibits Na+ -solute cotransport systems. Accumulation of carbohydrates in the intestinal lumen as well as malabsorption of nutrients and a concomitant inhibition of water absorption can lead to a malabsorptive component of diarrhea. Since the discovery of the NSP4 enterotoxin, several hypotheses have been proposed in favour of an additional secretion component in the pathogenesis of diarrhea. Rotavirus induces a moderate net chloride secretion at the onset of the diarrhea. The mechanisms appear to different from those used by bacterial enterotoxin that cause pure secretory diarrhea. Rotavirus stimulated C1- reabsorption in villi, and failed to stimulate C1- secretion in crypt. Intestinal villi could secrete chloride as a result of rotavirus infection. The chloride secretory response is regulated by a dependant calcium signalling pathway induced by NSP4. The overall response is weak, suggesting that NSP4 may exert both secretory and subsequent antisecretory actions, hence limiting C1- secretion.

Prevention and treatment of enteric viral infections: possible benefits of probiotic bacteria

The structure and function of the intestinal epithelium is briefly described, with the principal mechanisms involved in diarrhea. Human enteric viruses and probiotics are presented. We then review how probiotic bacteria could interfere with virus-induced pathology, we present our own view and describe specific interactions that would be valuable targets for future studies.

Downstream processing of viral vectors and vaccines

Viral vectors and viral vaccines more and more play an important role in current medical approaches. Gene vectors like adenoviruses, adeno-associated viruses or retroviruses are the vehicles being developed for delivering genetic material to the target cell in gene therapy. Viral vaccines, like attenuated or inactivated rabies virus, influenza virus or hepatitis virus vaccines, are powerful tools to limit the number of serious viral infections and pandemics. Higher safety demands, that is, reduction of side effects, by regulatory authorities like Food and Drug Administration (FDA) and European Agency for the Evaluation of Medicinal Products (EMEA), nowadays force developers as well as manufacturers to improve their production and purification processes for viral vectors and vaccines. Like for influenza viral vaccines, manufacturers begin to switch from egg cultivation to mammalian cell culture systems. Also within the purification procedure, a clear trend from classical purification methods like sucrose gradient centrifugation towards more sophisticated techniques like tangential flow filtration and liquid chromatography can be observed.

Adenovirus protein VI mediates membrane disruption following capsid disassembly

In contrast to enveloped viruses, the mechanisms involved in membrane penetration by nonenveloped viruses are not as well understood. In these studies, we determined the relationship between adenovirus (Ad) capsid disassembly and the development of membrane lytic activity. Exposure to low pH or heating induced conformational changes in wild-type Ad but not in temperature-sensitive Ad (ts1) particles that fail to escape the early endosome. Wild-type Ad but not ts1 particles permeabilized model membranes (liposomes) and facilitated the cytosolic delivery of a ribotoxin. Alterations in wild-type Ad capsids were associated with the exposure of a pH-independent membrane lytic factor. Unexpectedly, this factor was identified as protein VI, a 22-kDa cement protein located beneath the peripentonal hexons in the viral capsid. Recombinant protein VI and preprotein VI, but not a deletion mutant lacking an N-terminal amphipathic alpha-helix, possessed membrane lytic activity similar to partially disassembled virions. A new model of Ad entry is proposed based on our present observations of capsid disassembly and membrane penetration.