During virus infection, uncoating is a key step to release the viral genome into host cells, and this step is an attractive antiviral target. However, virus uncoating, especially influenza A virus (IAV), which contains an unusual genome of eight segmented RNAs, has been a poorly understood process due to limitation in applicable methodology for detecting this transient and dynamic event.

In a study, Prof. CUI Zongqiang from Wuhan Institute of Virology of the Chinese Academy of Sciences has reported a novel approach to allow the studying of the dynamic uncoating of individual IAV in live cells.

In this approach, quantum dots (QDs) with the single-particle sensitivity were site-specifically conjugated to the viral ribonucleoprotein complexes (vRNPs) and encapsulated in IAV particles during virus assembly.

By incorporating differently colored QD-vRNP segments or by combining internal QD encapsulation with QD surface decoration into single virions, the researchers also constructed multi-color IAV particles.

Using single-particle tracking, the researchers monitored viral uncoating of individual influenza viruses in real time.

Around 30% of IAV particles fused with late endosomes, a cellular sorting compartment, and shed their coats in the region surrounding the host nucleus within 30-90 minutes of infection.

VRNPs from each virion separated into distinct units and entered the nucleus in a three-step process and displayed two diffusion patterns when inside the nucleus.

The scientists have developed a new method for studying of IAV uncoating, and believe that the findings unveil a critical step in IAV infection and may aid the development of therapeutic strategies.

The results have been published in PNAS entitled "Real-time dissection of dynamic uncoating of individual influenza viruses".   

This work was supported by the Strategic Priority Research Program of the Chinese Academy of Sciences, the National Key Research and Development Program of China, the National Natural Science Foundation of China, and the Youth Innovation Promotion Association of the Chinese Academy of Sciences.

Model for IAV uncoating and vRNP dynamics. (Image by CUI Zongqiang)