Journal
JOURNAL OF MOLECULAR RECOGNITION
Volume 27, Issue 4, Pages 230-237Publisher
WILEY-BLACKWELL
DOI: 10.1002/jmr.2354
Keywords
autocatalysis; cryoEM; virus maturation; virus capsid quasi-equivalence; maximum likelihood estimation; variance map; NV; virus particle dynamics
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Funding
- National Institutes of Health [RO1 GM54076, RO1 GM033050]
- National Science Foundation [NSF 0836656, NSF 1217867]
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Quasi-equivalent viruses that infect animals and bacteria require a maturation process in which particles transition from initially assembled procapsids to infectious virions. Nudaurelia capensis virus (NV) is a T=4, eukaryotic, single-stranded ribonucleic acid virus that has proved to be an excellent model system for studying the mechanisms of viral maturation. Structures of NV procapsids (diameter=480 angstrom), a maturation intermediate (410 angstrom), and the mature virion (410 angstrom) were determined by electron cryo-microscopy and three-dimensional image reconstruction (cryoEM). The cryoEM density for each particle type was analyzed with a recently developed maximum likelihood variance (MLV) method for characterizing microstates occupied in the ensemble of particles used for the reconstructions. The procapsid and the mature capsid had overall low variance (i.e., uniform particle populations) while the maturation intermediate (that had not undergone post-assembly autocatalytic cleavage) had roughly two to four times the variance of the first two particles. Without maturation cleavage, the particles assume a variety of microstates, as the frustrated subunits cannot reach a minimum energy configuration. Geometric analyses of subunit coordinates provided a quantitative description of the particle reorganization during maturation. Superposition of the four quasi-equivalent subunits in the procapsid had an average root mean square deviation (RMSD) of 3 angstrom while the mature particle had an RMSD of 11 angstrom, showing that the subunits differentiate from near equivalent environments in the procapsid to strikingly non-equivalent environments during maturation. Autocatalytic cleavage is clearly required for the reorganized mature particle to reach the minimum energy state required for stability and infectivity. Copyright (c) 2014 John Wiley & Sons, Ltd.
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