  Cowpea chlorotic mottle virus (CCMV) is a widely used model for virus
replication studies. A major challenge lies in distinguishing between the roles
of the interaction between coat proteins and that between the coat proteins and
the viral RNA in assembly and disassembly processes. Here, we report on the
spontaneous and reversible size conversion of the empty capsids of a CCMV
capsid protein functionalized with a hydrophobic elastin-like polypeptide which
occurs following a pH jump. We monitor the concentration of T = 3 and T = 1
capsids as a function of time and show that the time evolution of the
conversion from one T number to another is not symmetric: the conversion from T
= 1 to T = 3 is a factor of 10 slower than that of T = 3 to T = 1. We explain
our experimental findings using a simple model based on classical nucleation
theory applied to virus capsids, in which we account for the change in the free
protein concentration, as the different types of shells assemble and
disassemble by shedding or absorbing single protein subunits. As far as we are
aware, this is the first study confirming that both the assembly and
disassembly of viruslike shells can be explained through classical nucleation
theory, reproducing quantitatively results from time-resolved experiments.
