RNA Genes are Released to Mammalian Cells by Self-Assembled Plant-Virus-Like Particles

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Work on viral capsids for gene delivery, from the research group of Professors William Gelbart and Charles Knobler, was the highlighted article of the June 20, 2013 issue of the journal Virology. 

The Gelbart/Knobler research group has recently demonstrated that RNA genes can be packaged in vitro in virus-like particles made from the capsid protein of a plant virus [cowpea chlorotic mottle virus (CCMV)] and then released, replicated, and expressed in mammalian cells.

Gelbart Photo Api
Professor William Gelbart (left) & Professor Charles Knobler (right)

Earlier, the Gelbart/Knobler research group had shown [Journal of Virology 86, 3318-26 (2012)] that the CCMV capsid protein is capable of packaging RNAs of a wide range of lengths and sequences into monodisperse (26nm-diameter) nucleocapsids that are stable against aggregation and against digestion by RNases. Now, in a paper highlighted in the June 20 2013 issue of the journal Virology, they report that an RNA gene – coding in this instance for a fluorescent protein – can be released by CCMV capsids in mammalian cells and replicated to a high level before being translated.

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Graphical abstract from the Virology paper

The work was performed by graduate student Rees Garmann and postdoctoral associates Odisse Azizgolshani and Ruben Cadena.

An interview with Prof. Gelbart about this work is posted on the Virology journal website. It is envisioned that by conjugating the capsid proteins to ligands that facilitate targeting of and uptake of the particles by specific cells, many important applications of this novel system will be developed for in vivo delivery of self-replicating genes.

Personal bio of Prof. Gelbart: Starting in the late 1970s, I began working in the then-emerging field of “complex fluids,” concentrating over the following two decades on developing molecular theories of liquid crystals, polymer solutions, colloidal and nanoparticle suspensions, self-assembling systems, and biological membranes. About 10 years ago I became intrigued by the physical basis of viral infectivity and, with my colleague Charles M. Knobler, established a laboratory to investigate a wide range of viruses outside their hosts and isolated in test tubes. We work on both DNA and RNA viruses, attempting to identify and explain the generic differences in their “live cycles” in terms of the differences between stiff linear genomes (double-stranded DNA) and flexible branched ones (single-stranded RNA). In particular, we have focused on the role of pressure in DNA packaging and delivery, and on the role of spontaneous self-assembly in the case of RNA viruses. A large part of our effort is devoted to understanding the physical forces driving the syntheses of viruses and virus-like particles (i.e., single-molecule-thick protein shells [capsids] containing nucleic acid), and their wrapping by phospholipid bilayer. Experimental methods include fluorescence microscopy and correlation spectroscopy, small-angle synchrotron X-ray scattering, and cryo-electron microscopy; theoretical approaches involve both analytical and computational treatments of RNA structure and of the statistical thermodynamics and kinetics of nucleocapsid self-assembly.

After completing my formal education (Harvard B.S. [1967], University of Chicago Ph.D. [1970], and NSF and Miller Institute postdoctoral fellowships at the University of Paris [1971] and UC Berkeley [1972]), I joined the faculty at UC Berkeley in 1972 as an Assistant Professor of Chemistry, moving as Associate Professor in 1975 to UCLA, where I have served as Professor since 1979, Chair (2001-4), and Distinguished Professor since 1999. I am also a Member of the California NanoSystems Institute and of the Molecular Biology Institute.

Personal bio of Prof. Knobler: My research, almost exclusively experimental, has been in soft condensed matter physics, a field that lies at the fuzzy border between physics, physical chemistry and chemical engineering. Much of the work concerned phase transitions and included studies of critical phenomena, nucleation and growth and two-dimensional systems, largely monolayers at the air/water interface. About 10 years ago, however, I and my colleague Bill Gelbart made an abrupt change and began to focus on viruses. We have played a major role in the development of the new science of physical virology in which the properties of viruses – their structures, their assembly, their replication and their mode of infection – are examined both experimentally and theoretically in terms of general physical principles. Our research is broad based and involves studies of bacterial, plant and mammalian viruses.

Background: After receiving my BA in chemistry from NYU, I spent 3 years as a graduate student in Physical Chemistry at Penn State. As a recipient of a Fulbright Award I began research in Low-Temperature Molecular Physics in the Kamerlingh Onnes Laboratory in the Netherlands. After completing my doctorate there I was a postdoc in chemistry at Ohio State and then in chemical engineering at CalTech. I then joined the faculty in chemistry at UCLA.

Honors.: Fulbright Scholar. UCLA Herbert Newby McCoy Award, Fellow, American Physical Society, UCLA Alumni Association Distinguished Teaching Award, Alexander von Humboldt Senior Award, University of Mainz, UCLA College of Letters and Science Faculty Award, Alexander von Humboldt Senior Award, Max Planck Institute, Potsdam, Kolthoff Lecturer, University of Minnesota, American Chemical Society Award in Colloid Chemistry, Fellow, Royal Society of Chemistry, Dickson Award