Interview: Professor William Gelbart talks about viral capsids for gene delivery

Reconstituted plant viral capsids can release genes to mammalian cells

Read the full article for free on ScienceDirect.

In Virology’s highlighted article for the 20 June 2013 issue, researchers explore the use of plant viral capsids as vectors for gene delivery. They demonstrate that hybrid virus-like particles, assembled in vitro from Cowpea Chlorotic Mottle Virus (CCMV) capsid protein (CP) and a heterologous RNA derived from a mammalian virus (Sindbis), are capable of releasing their RNA in the cytoplasm of mammalian cells.

Here Professor William Gelbart, Corresponding Author of the article from UCLA, tells us more about his research, and the future of the work.

Professor William Gelbart
Professor William Gelbart

What is your area of research?

We are physical chemists who have been concentrating over the past 10 years on identifying and elucidating physical aspects of viral infectivity. We try to understand the qualitatively different life cycles of DNA and RNA viruses in terms of the fact that their genomes (double-stranded DNA and single-stranded RNA) are fundamentally different physical objects. More explicitly, the former (DNA) is a stiff, linear, polymer, while the latter (RNA) is a flexible, branched polymer. As a consequence, for example, DNA viruses are strongly pressurized while RNA viruses can self-assemble spontaneously, resulting in their infectivities being associated with very different mechanisms of genome packaging and delivery.

What is your interest in CCMV?

We are in interested in CCMV because it was the first spherical virus to be reconstituted ‘from scratch’, i.e., to be synthesized in vitro from its purified components, namely the viral RNA genome and capsid protein. Furthermore, its capsid protein will package, via spontaneous self-assembly, not only its viral genome, but also all kinds of other RNA molecules, and the resulting virus-like particles are stable against aggregation and their protein shells protect their RNA cargo against nuclease (RNase) enzymes.

What was the main outcome of the research published in Virology?

We demonstrated that in vitro reconstituted virus-like particles — whose protein shells are made of plant viral (CCMV) capsid protein — are capable of releasing their RNA cargo in mammalian cells, and that reporter genes included in that RNA are expressed, resulting in a high level of protein synthesis.

Why is this significant?

Instead of trying to deliver desired proteins (e.g., vaccines or enzymes or toxins) to specific cells, it is more powerful to deliver the RNA genes for these proteins to the cells. Work by many others has shown that the outside of the protein shells of plant viruses like CCMV can be chemically modified so that they target and are taken up by specific mammalian cells. Accordingly, the results of our Virology paper take us one step closer to our goal of using well-characterized, stable, long-shelf-life, in vitro synthesized, virus-like particles to deliver RNA genes to targeted cells.

What will be your next steps in this area?

Our recent paper involved packaging an RNA gene of interest in virus-like particles, getting the particle into mammalian cells, and providing in trans an RNA replicon molecule that replicates the RNA gene a million-fold before the gene is translated into protein. Our next challenge is to package the RNA gene and the replicon as a single RNA molecule, so that the resulting virus-like particle is capable — all by itself — of protecting, delivering, amplifying, and expressing the target gene in specific mammalian cells.

About the research

The article ‘Reconstituted plant viral capsids can release genes to mammalian cells’ was published in the 20 June 2013 issue of Virology. You can read it for free on Science Direct:

Reconstituted plant viral capsids can release genes to mammalian cellsfree access
Odisse Azizgolshani, Rees F. Garmann, Ruben Cadena-Nava, Charles M. Knobler, William M. Gelbart

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