Identification of conserved motifs in the Westnile virus envelope essential for particle secretion

Himanshu Garg,Raphael Tc Lee,Ng Oon Tek,Sebastian Maurer-Stroh,Anjali Joshi

doi:10.1186/1471-2180-13-197

Abstract

BackgroundEnveloped viruses utilize cellular membranes to bud from infected cells. The process of virion assembly and budding is often facilitated by the presence of certain conserved motifs within viral proteins in conjunction with cellular factors. We hence examined the West Nile Virus (WNV) Envelope protein for the presence of any such motifs and their functional characterization.ResultsWe identified conserved 461PXAP464 and 349YCYL352 motifs in the WNV envelope glycoprotein bearing resemblance to retroviral late domains. Disruptive mutations of PXAP to LAAL and of the highly conserved Cys350 in the YCYL motif, led to a severe reduction in WNV particle production. Similar motifs in case of retroviruses are known to interact with components of host sorting machinery like PXAP with Tsg101 and YXXL with Alix. However, in the case of WNV, siRNA mediated depletion of Alix or Tsg101 did not have an effect on WNV release. Molecular modeling suggested that while the 461PXAP464 motif is surface accessible and could potentially interact with cellular proteins required for WNV assembly, the 349YCYL352 motif was found to be internal with Cys350 important for protein folding via disulphide bonding.ConclusionsThe conserved 461PXAP464 and 349YCYL352 motifs in the WNV envelope are indispensable for WNV particle production. Although these motifs bear sequence similarity to retroviral late domains and are essential for WNV assembly, they are functionally distinct suggesting that they are not the typical late domain like motifs of retroviruses and may play a role other than Alix/Tsg101 utilization/dependence.

Highlights

Enveloped viruses utilize cellular membranes to bud from infected cells
Three types of consensus late domain motifs have been identified far: (i) the PT/SAP motif recruits the Endosomal sorting complex required for transport (ESCRT)-1 component Tumor susceptibility growth factor 101 (Tsg101) (Tumor Susceptibility growth factor 101) [9,10], (ii) the YXXL late domain motif interacts with the ESCRT associated protein Alix [11,12] and the (iii) PPXY late domain motif binds to the Nedd4 family of E3 ubiquitin ligases that are involved in cargo recruitment during Multivesicular Body (MVB) formation [13,14]
Using sequence analysis and information based on work with other viruses we undertook this study to identify the presence of conserved motifs in the Flavivirus structural E proteins and determine whether they play a role in virus assembly and release

Summary

Introduction

The process of virion assembly and budding is often facilitated by the presence of certain conserved motifs within viral proteins in conjunction with cellular factors. Conclusions: The conserved 461PXAP464 and 349YCYL352 motifs in the WNV envelope are indispensable for WNV particle production These motifs bear sequence similarity to retroviral late domains and are essential for WNV assembly, they are functionally distinct suggesting that they are not the typical late domain like motifs of retroviruses and may play a role other than Alix/Tsg101 utilization/dependence. Following the synthesis of viral genome and proteins, enveloped viruses utilize cellular membranes to bud from infected cells This is often facilitated by the presence of certain conserved motifs within viral proteins and their ability to interact with the cellular processes/ machinery. Currently there is no information on the presence of late domains in WNV proteins

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Conclusion