Inhibition of Cellular Autophagy Deranges Dengue Virion Maturation
JOURNAL OF VIROLOGY
2013; 87 (3): 1312-1321
Autophagy is an important component of the innate immune response, directly destroying many intracellular pathogens. However, some pathogens, including several RNA viruses, subvert the autophagy pathway, or components of the pathway, to facilitate their replication. In the present study, the effect of inhibiting autophagy on the growth of dengue virus was tested using a novel inhibitor, spautin-1 (specific and potent autophagy inhibitor 1). Inhibition of autophagy by spautin-1 generated heat-sensitive, noninfectious dengue virus particles, revealing a large effect of components of the autophagy pathway on viral maturation. A smaller effect on viral RNA accumulation was also observed. Conversely, stimulation of autophagy resulted in increased viral titers and pathogenicity in the mouse. We conclude that the presence of functional autophagy components facilitates viral RNA replication and, more importantly, is required for infectious dengue virus production. Pharmacological inhibition of host processes is an attractive antiviral strategy to avoid selection of treatment-resistant variants, and inhibitors of autophagy may prove to be valuable therapeutics against dengue virus infection and pathogenesis.
View details for DOI 10.1128/JVI.02177-12
View details for Web of Science ID 000313558100003
Systematic Study of the Genetic Response of a Variable Virus to the Introduction of Deleterious Mutations in a Functional Capsid Region
JOURNAL OF VIROLOGY
2009; 83 (19): 10140-10151
We have targeted the intersubunit interfaces in the capsid of foot-and-mouth disease virus to investigate the genetic response of a variable virus when individual deleterious mutations are systematically introduced along a functionally defined region of its genome. We had previously found that the individual truncation (by mutation to alanine) of 28 of the 42 amino acid side chains per protomer involved in interactions between capsid pentameric subunits severely impaired infectivity. We have now used viral RNAs individually containing each of those 28 deleterious mutations (or a few others) to carry out a total of 96 transfections of susceptible cells, generally followed by passage(s) of the viral progeny in cell culture. The results revealed a very high frequency of fixation in the capsid of second-site, stereochemically diverse substitutions that compensated for the detrimental effect of primary substitutions at many different positions. Most second-site substitutions occurred at or near the capsid interpentamer interfaces and involved residues that are spatially very close to the originally substituted residue. However, others occurred far from the primary substitution, and even from the interpentamer interfaces. Remarkably, most second-site substitutions involved only a few capsid residues, which acted as "second-site hot spots." Substitutions at these hot spots compensated for the deleterious effects of many different replacements at diverse positions. The remarkable capacity of the virus to respond to the introduction of deleterious mutations in the capsid with the frequent fixation of diverse second-site mutations, and the existence of second-site hot spots, may have important implications for virus evolution.
View details for DOI 10.1128/JVI.00903-09
View details for Web of Science ID 000269614300046
View details for PubMedID 19625409
Engineering Viable Foot-and-Mouth Disease Viruses with Increased Thermostability as a Step in the Development of Improved Vaccines
JOURNAL OF VIROLOGY
2008; 82 (24): 12232-12240
We have rationally engineered foot-and-mouth disease virus to increase its stability against thermal dissociation into subunits without disrupting the many biological functions needed for its infectivity. Amino acid side chains located near the capsid intersubunit interfaces and either predicted or found to be dispensable for infectivity were replaced by others that could establish new disulfide bonds or electrostatic interactions between subunits. Two engineered viruses were normally infectious, genetically stable, and antigenically indistinguishable from the natural virus but showed substantially increased stability against irreversible dissociation. Electrostatic interactions mediated this stabilizing effect. For foot-and-mouth disease virus and other viruses, some evidence had suggested that an increase in virion stability could be linked to an impairment of infectivity. The results of the present study show, in fact, that virion thermostability against dissociation into subunits may not be selectively constrained by functional requirements for infectivity. The thermostable viruses obtained, and others similarly engineered, could be used for the production, using current procedures, of foot-and-mouth disease vaccines that are less dependent on a faultless cold chain. In addition, introduction of those stabilizing mutations in empty (nucleic acid-free) capsids could facilitate the production of infection-risk-free vaccines against the disease, one of the economically most important animal diseases worldwide.
View details for DOI 10.1128/JVI.01553-08
View details for Web of Science ID 000261164000024
View details for PubMedID 18829763
Insights into RNA virus mutant spectrum and lethal mutagenesis events: Replicative interference and complementation by multiple point mutants
JOURNAL OF MOLECULAR BIOLOGY
2007; 369 (4): 985-1000
RNA virus behavior can be influenced by interactions among viral genomes and their expression products within the mutant spectra of replicating viral quasispecies. Here, we report the extent of interference of specific capsid and polymerase mutants of foot-and-mouth disease virus (FMDV) on replication of wild-type (wt) RNA. The capsid and polymerase mutants chosen for this analysis had been characterized biochemically and structurally. Upon co-electroporation of BHK-21 cells with wt RNA and a tenfold excess of mutant RNA, some mutants displayed strong interference (<10% of progeny production by wt RNA alone), while other mutants did not show detectable interference. The capacity to interfere required an excess of mutant RNA and was associated with intracellular replication, irrespective of the formation of infectious particles by the mutant virus. The extent of interference did not correlate with the known types and number of interactions involving the amino acid residue affected in each mutant. Synergistic interference was observed upon co-electroporation of wt RNA and mixtures of capsid and polymerase mutants. Interference was specific, in that the mutants did not affect expression of encephalomyocarditis virus RNA, and that a two nucleotide insertion mutant of FMDV expressing a truncated polymerase did not exert any detectable interference. The results support the lethal defection model for viral extinction by enhanced mutagenesis, and provide further evidence that the population behavior of highly variable viruses can be influenced strongly by the composition of the quasispecies mutant spectrum as a whole.
View details for DOI 10.1016/j.jmb.2007.03.074
View details for Web of Science ID 000247096000009
View details for PubMedID 17481660
Thermostable variants are not generally represented in foot-and-mouth disease virus quasispecies
JOURNAL OF GENERAL VIROLOGY
2007; 88: 859-864
A severe limitation to fully realize the dramatic potential for adaptation of RNA virus quasispecies may occur if mutations in vast regions of the sequence space of virus genomes lead to significant decreases in biological fitness. In this study the detection and selection by heat of thermostable variants from different foot-and-mouth disease virus (FMDV) populations were attempted, in order to explore whether FMDV may generally accept a substantial increase in thermostability without compromising its infectivity. The results obtained with both uncloned and cloned populations of different serotypes, recovered from cytolytic or persistent infections and subjected to either very few passages or extensive passaging in cells, indicate that the presence of thermostable virus variants, even in small proportions, is not a general feature of FMDV quasispecies. This suggests that no substantial increase in the thermostability of FMDV may readily occur without a negative effect on viral function.
View details for Web of Science ID 000245045500015
View details for PubMedID 17325358
Thermodynamic stability of a cold-adapted protein, type III antifreeze protein, and energetic contribution of salt bridges
2007; 16 (2): 227-238
A thermodynamic analysis of a cold-adapted protein, type III anti-freeze protein (AFP), was carried out. The results indicate that the folding equilibrium of type III AFP is a reversible, unimolecular, two-state process with no populated intermediates. Compared to most mesophilic proteins whose folding is two-state, the psychrophilic type III AFP has a much lower thermodynamic stability at 25 degrees C, approximately 3 kcal/mol, and presents a remarkably downshifted stability-temperature curve, reaching a maximum of 5 kcal/mol around 0 degrees C. Type III AFPs contain few and non-optimally distributed surface charges relative to their mesophilic homologs, the C-terminal domains of sialic acid synthases. We used thermodynamic double mutant cycles to evaluate the energetic role of every surface salt bridge in type III AFP. Two isolated salt bridges provided no contribution to stability, while the Asp36-Arg39 salt bridge, involved in a salt bridge network with the C-terminal carboxylate, had a substantial contribution (approximately 1 kcal/mol). However, this contribution was more than counteracted by the destabilizing effect of the Asp36 carboxylate itself, whose removal led to a net 30% increase in stability at 25 degrees C. This study suggests that type III AFPs may have evolved for a minimally acceptable stability at the restricted, low temperature range (around 0 degrees C) at which AFPs must function. In addition, it indicates that salt bridge networks are used in nature also for the stability of psychrophilic proteins, and has led to a type III AFP variant of increased stability that could be used for biotechnological purposes.
View details for DOI 10.1110/ps.062448907
View details for Web of Science ID 000243640600007
View details for PubMedID 17189482
Deterministic, compensatory mutational events in the capsid of foot-and-mouth disease virus in response to the introduction of mutations found in viruses from persistent infections
JOURNAL OF VIROLOGY
2007; 81 (4): 1879-1887
The evolution of foot-and-mouth disease virus (FMDV) (biological clone C-S8c1) in persistently infected cells led to the emergence of a variant (R100) that displayed increased virulence, reduced stability, and other modified phenotypic traits. Some mutations fixed in the R100 genome involved a cluster of highly conserved residues around the capsid pores that participate in interactions with each other and/or between capsid protomers. We have investigated phenotypic and genotypic changes that occurred when these replacements were introduced into the C-S8c1 capsid. The C3007V and M3014L mutations exerted no effect on plaque size or viral yield during lytic infections, or on virion stability, but led to a reduction in biological fitness; the D3009A mutation caused drastic reductions in plaque size and viability. Remarkably, competition of the C3007V mutant with the nonmutated virus invariably resulted in the fixation of the D3009A mutation in the C3007V capsid. In turn, the presence of the D3009A mutation invariably led to the fixation of the M3014L mutation. In both cases, two individually disadvantageous mutations led, together, to an increase in fitness, as the double mutants outcompeted the nonmutated genotype. The higher fitness of C3007V/D3009A was related to a faster multiplication rate. These observations provide evidence for a chain of linked, compensatory mutational events in a defined region of the FMDV capsid. Furthermore, they indicate that the clustering of unique amino acid replacements in viruses from persistent infections may also occur in cytolytic infections in response to changes caused by previous mutations without an involvement of the new mutations in the adaptation to a different environment.
View details for DOI 10.1128/JVI.01899-06
View details for Web of Science ID 000244241400032
View details for PubMedID 17151123
Complete alanine scanning of intersubunit interfaces in a foot-and-mouth disease virus capsid reveals critical contributions of many side chains to particle stability and viral function
JOURNAL OF BIOLOGICAL CHEMISTRY
2003; 278 (42): 41019-41027
Spherical virus capsids are large, multimeric protein shells whose assembly and stability depend on the establishment of multiple non-covalent interactions between many polypeptide subunits. In a foot-and-mouth disease virus capsid, 42 amino acid side chains per protomer are involved in noncovalent interactions between pentameric subunits that function as assembly/disassembly intermediates. We have individually truncated to alanine these 42 side chains and assessed their relevance for completion of the virus life cycle and capsid stability. Most mutations provoked a drastic reduction in virus yields. Nearly all of these critical mutations led to virions whose thermal inactivation rates differed from that of the parent virus, and many affected also early steps in the viral cycle. Rapid selection of genotypic revertants or variants with forward or compensatory mutations that restored viability was occasionally detected. The results with this model virus indicate the following. (i). Most of the residues at the interfaces between capsid subunits are critically important for viral function, in part but not exclusively because of their involvement in intersubunit recognition. Each hydrogen bond and salt bridge buried at the subunit interfaces may be important for capsid stability. (ii). New mutations able to restore viability may arise frequently at the subunit interfaces during virus evolution. (iii). A few interfacial side chains are functionally tolerant to truncation and may provide adequate mutation sites for the engineering of a thermostable capsid, potentially useful as an improved vaccine.
View details for DOI 10.1074/jbc.M304990200
View details for Web of Science ID 000185847200076
View details for PubMedID 12857761