The unfolding of protein ions in gas phase (or a vacuum) proceeds rapidly once the total charge reaches a critical value q". The actual q* value depends on temperature, protein composition, and force field parameters. Here, using molecular dynamics simulations, we explore the onset of the unfolding transition at q > q* and its dependence on the nonbonded interaction between monomers. Using lysozyme, we show that, although a loss of attractive cohesion reduces the critical charge for unfolding, the mechanism for the transition may remain essentially unchanged over a range of Coulombic and van der Waals interactions.