Viral RNA modulates the acid sensitivity of foot-and-mouth disease virus capsids

Abstract

Foot-and-mouth disease virus (FMDV) manifests an extreme sensitivity to acid, which is thought to be important for entry of the RNA genome into the cell. We have compared the low-pH-induced disassembly in vitro of virions and natural empty capsids of three subtypes of serotype A FMDV by enzyme-linked immunosorbent assay and sucrose gradient sedimentation analysis. For all three subtypes (A22 Iraq 24/64, A10 61 , and A24 Cruzeiro), the empty capsid was more stable by 0.5 pH unit on average than the corresponding virion. Unexpectedly, in the natural empty capsids used in this study, the precursor capsid protein VP0 was found largely to be cleaved into VP2 and VP4. For picornaviruses the processing of VP0 is closely associated with encapsidation of viral RNA, which is considered likely to play a catalytic role in the cleavage. Investigation of the cleavage of VP0 in natural empty capsids failed to implicate the viral RNA. However, it remains possible that these particles arise from abortive attempts to encapsidate RNA. Empty capsids expressed from a vaccinia virus recombinant showed essentially the same acid lability as natural empty capsids, despite differing considerably in the extent of VP0 processing, with the synthetic particles containing almost exclusively uncleaved VP0. These results indicate that it is the viral RNA that modulates acid lability in FMDV. In all cases the capsids dissociate at low pH directly into pentameric subunits. Comparison of the three viruses indicates that FMDV A22 Iraq is about 0.5 pH unit more sensitive to low pH than types A10 61 and A24 Cruzeiro. Sequence analysis of the three subtypes identified several differences at the interface between pentamers and highlighted a His-␣-helix dipole interaction which spans the pentamer interface and appears likely to influence the acid lability of the virus.

Synthesis of empty capsid-like particles of Asia I foot-and-mouth disease virus in insect cells and their immunogenicity in guinea pigs

“…It is also possible that empty capsids of the Asia I virus strain that we used were more resistant to acid conditions than those of the O type virus. Curry et al (1995) found that acid-resistance varied among different strains of FMDV within the same serotype.…”

The structure and function of a foot-and-mouth disease virus-oligosaccharide receptor complex

“…It exists in seven serotypes (O, A, C, Asia, SAT1, SAT2 and SAT3), and has the basic picornavirus structure depicted in Figure 1 (terms defined there will be used throughout this paper). FMDV enters cells through receptor-mediated endocytosis followed by acid pH-dependent release and translocation of RNA across the endosomal membrane (Carrillo et al, 1984;Mason et al, 1994;Curry et al, 1995). FMDV can attach to cells via argine-glycine-aspartic acid (RGD)-binding integrin molecules (Surovoi et al, 1988;Fox et al, 1989;Baxt and Becker, 1990;Mason et al, 1994;Berinstein et al, 1995), such as α v β 3 (Berinstein et al, 1995;Jackson et al, 1997;Neff et al, 1998).…”

Negatively charged amino acids at the foot-and-mouth disease virus capsid reduce the virion-destabilizing effect of viral RNA at acidic pH

“…Thus, recombinant empty capsids (WT and mutants VP1 N17D and VP1 N17D + VP2 H145Y) were produced in the absence of FMDV RNA by co-expression in BHK-21 cells of the P1-2A capsid precursor and the viral protease 3 C from plasmids pL1-1 and pSKRH-3C, respectively 34 . Previous evidence has unambiguously shown that in recombinant FMDV empty capsids VP0 is fully processed due to an RNA-independent, autocatalytic cleavage of VP0 to render VP4 and VP2 28,30 . In particular, the crystal structure of the empty capsid shows that cleavage and reveals that the empty capsid is virtually identical to the RNA-filled virion, even at atomic resolution, except for the absence of the RNA itself.…”

“…In addition to any putative effect of the VP1 N17D substitution on intracapsid interactions, its acid-stabilizing effect could be related also (or instead) to some change in capsid-RNA interactions. Some evidence obtained with FMDV 30,31 and Coxsackie B3 virus 32 indicates that not only capsid proteins determine the stability of these picornaviruses, but also the viral RNA could contribute to determine virion stability or instability at both acidic pH and increased temperature. However, the potential role in virion stability of RNA-capsid interactions had not been explored for these viruses.…”