Intra-Virion Structural Resolution. Is it possible? Sure it is.

The case for influenza A virus genome packaging

I was watching the latest live broadcast from Gigaohmbiological with JJ. Couey, which you can watch on his stream (here) or in Rumble (here), and I was very curious about the following statement:

Having work with Atomic Force Microscopy (AFM) for a brief period of time and being aware of the current structural resolution techniques used in related fields, I am pretty sure that we can know if the viral ribunucloprotein complexes (vRNPs) are indeed present inside a virion. For those who are unaware, this is the basic structure of an influenza virus:

(Ref. 1) Influenza A Virus Cell Entry, Replication, Virion Assembly and Movement

It has 8 vRNPs inside of it in a ‘1+7’ configuration, and of course, each vRNP contains the enzyme required for replication, the RNA-dependent RNA polymerase with subunits PB1, PB2 and PA. How do we know?

First of all, the Virus Polymerase Complex (described below in more detail, Ref. 2) is absolutely required for replication, there would be no influenza virus without this complex; even though defective interfering particles are also produced during viral replication. Therefore, we must be able to purify it by lysing Influenza virions and observe the replication machinery.

(Ref. 2) The Influenza Virus Polymerase Complex: An Update on Its Structure, Functions, and Significance for Antiviral Drug Design

This can be done in several ways and this study is a good example of it:

(Ref. 3) Ultrastructure of influenza virus ribonucleoprotein complexes during viral RNA synthesis

*First Step, purification of vRNPs:

*Second step, in vitro RNA synthesis for cryo-EM and AFM:

**cryo-EM:

** AFM:

This demonstrates the presence of virus polymerase complexes and its active replication machinery via in vitro RNA synthesis after purification, once the virions have been lysed.

The next question would be, ‘how do the vRNPs get packaged inside a virion in a 7+1 configuration? Can we observe it?’. A simple way to observed that is via ultrathin section EM of virions and budding virions.

(Ref. 4) Importance of the 1+7 configuration of ribonucleoprotein complexes for influenza A virus genome packaging

The packaging process can be seen with more detail here:

(Ref. 5) Structure and assembly of the influenza A virus ribonucleoprotein complex

In conclusion, Intra-Virion Structural Resolution is indeed possible. I hope it helps 🙏