A Novel Interaction Network Used by Potyviruses in Virus–Host Interactions at the Protein Level

Abstract

Host proteins that are central to infection of potyviruses (genus Potyvirus; family Potyviridae) include the eukaryotic translation initiation factors eIF4E and eIF(iso)4E. The potyviral genome-linked protein (VPg) and the helper component proteinase (HCpro) interact with each other and with eIF4E and eIF(iso)4E and proteins are involved in the same functions during viral infection. VPg interacts with eIF4E/eIF(iso)4E via the 7-methylguanosine cap-binding region, whereas HCpro interacts with eIF4E/eIF(iso)4E via the 4E-binding motif YXXXXLΦ, similar to the motif in eIF4G. In this study, HCpro and VPg were found to interact in the nucleus, nucleolus, and cytoplasm in cells infected with the potyvirus potato virus A (PVA). In the cytoplasm, interactions between HCpro and VPg occurred in punctate bodies not associated with viral replication vesicles. In addition to HCpro, the 4E-binding motif was recognized in VPg of PVA. Mutations in the 4E-binding motif of VPg from PVA weakened interactions with eIF4E and heavily reduced PVA virulence. Furthermore, mutations in the 4G-binding domain of eIF4E reduced interactions with VPg and abolished interactions with HCpro. Thus, HCpro and VPg can both interact with eIF4E using the 4E-binding motif. Our results suggest a novel interaction network used by potyviruses to interact with host plants via translation initiation factors.

Insights into the Functions of eIF4E-Binding Motif of VPg in Potato Virus A Infection

“…However, the exact nature of the molecular functions of the VPg-eIF4E interaction in potyvirus infection has remained elusive. In this study, we approached the functions of the VPg-eIF(iso)4E interaction in PVA infection by dissecting the infection process with the mutated PVA VPgmut that carried similar mutations in the conserved eIF4E binding site YXXXXLΦ in PVA VPg as in [43,45]. In [45], the authors demonstrated that this binding site contributes to the capacity of PVA VPg to bind eIF(iso)4E and reported that it is crucial for the infectivity of PVA.…”

“…This study showed that the PG-like aggregates contained, in addition to the P0 protein, a substantial amount of eIF(iso)4E in VPg mut -expressing cells. An interesting network of binding sites was demonstrated in [45], in which PVA VPg binds to HCPro and to two binding sites in eIF4E/(iso)4E, one of which is shared with HCPro (the binding domain for proteins that carry the YXXXXLΦ motif). The abundant presence of eIF(iso)4E in PGs in spite of VPg mut may arise from the interaction of eIF(iso)4E with HCPro [43,45].…”

“…It is based on an infectious cDNA (icDNA) clone of PVA (PVA WT ) that expresses 3'RLUC as part of the viral polyprotein from a cistron between nuclear inclusion protein b (NIb; RNA-dependent RNA polymerase) and CP cistrons in PVA RNA [36]. To enable the quantitation of PVA gene expression in the absence of the consensus eIF(iso)4E-binding motif YXXXLΦ, we replaced the tyrosine and leucine codons of the YTDIRLI encoding sequence in PVA icDNA with those encoding for alanine, similarly to that shown in [45]. This construct was named PVA VPgmut ( Figure 1B).…”

“…These 3'RLUC activity levels suggested that PVA VPgmut RNA, or at least the capped PVA VPgmut transcripts derived from the nucleus, may replicate. enable the quantitation of PVA gene expression in the absence of the consensus eIF(iso)4E-binding motif YXXXLΦ, we replaced the tyrosine and leucine codons of the YTDIRLI encoding sequence in PVA icDNA with those encoding for alanine, similarly to that shown in [45]. This construct was named PVA VPgmut ( Figure 1B).…”

“…The substitution of the tyrosine and leucine residues with alanine in the eIFiso4E binding motif of HCPro has been shown to abolish binding and compromis PVA infection. A similar mutation in the PVA VPg motif reduced eIF(iso)4E binding and compromised infection [45].…”