Foot-and-mouth disease virus 2C is a hexameric AAA+ protein with a coordinated ATP hydrolysis mechanism

A critical role of N-myc and STAT interactor (Nmi) in foot-and-mouth disease virus (FMDV) 2C-induced apoptosis

Foot-and-mouth disease virus (FMDV) 2C, is one of the most highly-conserved viral proteins among the serotypes of FMDV. However, its effect on host cells is not very clear. Using yeast two-hybrid system and immunoprecipitation approaches, we found that FMDV 2C interacted with the N-myc and STAT interactor (Nmi) protein. When expressed in cells, FMDV 2C is mainly associated with endoplasmic reticulum in the forms of speckles. In the absence of FMDV 2C, Nmi was distributed diffusely in the cytoplasm. However, upon FMDV 2C overexpression Nmi was recruited into FMDV 2C containing speckles where both proteins are co-localized. In addition, FMDV 2C induced apoptosis in BHK-21 cells, which was markedly inhibited by Nmi knockdown, suggesting that Nmi may play a critical role in FMDV 2C-induced apoptosis. These findings may help to further understand the molecular mechanism of pathogenesis of FMDV infection.

Foot-and-mouth disease virus nonstructural protein 2C interacts with Beclin1, modulating virus replication

Foot-and-mouth disease virus (FMDV), the causative agent of foot-and-mouth disease, is an Apthovirus within the Picornaviridae family. Replication of the virus occurs in association with replication complexes that are formed by host cell membrane rearrangements. The largest viral protein in the replication complex, 2C, is thought to have multiple roles during virus replication. However, studies examining the function of FMDV 2C have been rather limited. To better understand the role of 2C in the process of virus replication, we used a yeast two-hybrid approach to identify host proteins that interact with 2C. We report here that cellular Beclin1 is a specific host binding partner for 2C. Beclin1 is a regulator of the autophagy pathway, a metabolic pathway required for efficient FMDV replication. The 2C-Beclin1 interaction was further confirmed by coimmunoprecipitation and confocal microscopy to actually occur in FMDV-infected cells. Overexpression of either Beclin1 or Bcl-2, another important autophagy factor, strongly affects virus yield in cell culture. The fusion of lysosomes to autophagosomes containing viral proteins is not seen during FMDV infection, a process that is stimulated by Beclin1; however, in FMDV-infected cells overexpressing Beclin1 this fusion occurs, suggesting that 2C would bind to Beclin1 to prevent the fusion of lysosomes to autophagosomes, allowing for virus survival. Using reverse genetics, we demonstrate here that modifications to the amino acids in 2C that are critical for interaction with Beclin1 are also critical for virus growth. These results suggest that interaction between FMDV 2C and host protein Beclin1 could be essential for virus replication.

Selection and characterisation of guanidine-resistant mutants of human enterovirus 71

The replication of human enterovirus 71 (HEV71) in cell culture is inhibited by concentrations of guanidine that do not have an observable adverse effect on host cell metabolism. Although the HEV71 non-structural protein 2C is known to play an important role in viral RNA replication, its precise biochemical activities and structure have not been fully determined. Here we describe amino acid substitutions in HEV71 protein 2C that confer resistance to guanidine. Three guanidine-resistant virus populations were independently isolated and found to contain five mutations in protein 2C, one of which, A4657T (2C-M193L), was present in two of the independently selected populations. This mutation was introduced into a HEV71 infectious cDNA clone and was sufficient to confer complete resistance to growth inhibition in the presence of 4mM guanidine. In the first guanidine-resistant population selected, the 2C-M193L mutation occurred in association with an additional mutation, A4459G (2C-I127V), located in the putative cis-acting replication element (cre) of coding region 2C. This mutation conferred only partial guanidine resistance when introduced into the HEV71-26M infectious clone. When the 2C-I127V and 2C-M193L mutations were introduced into HEV71-26M together, the 2C-I127V mutation did not increase the level of guanidine resistance due to the 2C-M193L mutation alone. This study confirms that guanidine resistance can be readily selected in HEV71 and is attributable to mutations within protein 2C.

Mutations that hamper dimerization of foot-and-mouth disease virus 3A protein are detrimental for infectivity

Foot-and-mouth disease virus (FMDV) nonstructural protein 3A plays important roles in virus replication, virulence, and host range. In other picornaviruses, homodimerization of 3A has been shown to be relevant for its biological activity. In this work, FMDV 3A homodimerization was evidenced by an in situ protein fluorescent ligation assay. A molecular model of the FMDV 3A protein, derived from the nuclear magnetic resonance (NMR) structure of the poliovirus 3A protein, predicted a hydrophobic interface spanning residues 25 to 44 as the main determinant for 3A dimerization. Replacements L38E and L41E, involving charge acquisition at residues predicted to contribute to the hydrophobic interface, reduced the dimerization signal in the protein ligation assay and prevented the detection of dimer/multimer species in both transiently expressed 3A proteins and in synthetic peptides reproducing the N terminus of 3A. These replacements also led to production of infective viruses that replaced the acidic residues introduced (E) by nonpolar amino acids, indicating that preservation of the hydrophobic interface is essential for virus replication. Replacements that favored (Q44R) or impaired (Q44D) the polar interactions predicted between residues Q44 and D32 did not abolish dimer formation of transiently expressed 3A, indicating that these interactions are not critical for 3A dimerization. Nevertheless, while Q44R led to recovery of viruses that maintained the mutation, Q44D resulted in selection of infective viruses with substitution D44E with acidic charge but with structural features similar to those of the parental virus, suggesting that Q44 is involved in functions other than 3A dimerization.

The 2C putative helicase of echovirus 30 adopts a hexameric ring-shaped structure

The 2C protein, which is an essential ATPase and one of the most conserved proteins across the Picornaviridae family, is an emerging antiviral target for which structural and functional characterization remain elusive. Based on a distant relationship to helicases of small DNA viruses, piconavirus 2C proteins have been predicted to unwind double-stranded RNAs. Here, a terminally extended variant of the 2C protein from echovirus 30 has been studied by means of enzymatic activity assays, transmission electron microscopy, atomic force microscopy and dynamic light scattering. The transmission electron-microscopy technique showed the existence of ring-shaped particles with ∼12 nm external diameter. Image analysis revealed that these particles were hexameric and resembled those formed by superfamily 3 DNA virus helicases.