  ZSPA-1 is an engineered protein that binds to its parent, the
three-helix-bundle Z domain of staphylococcal protein A. Uncomplexed ZSPA-1
shows a reduced helix content and a melting behavior that is less cooperative,
compared with the wild-type Z domain. Here we show that the difference in
folding behavior between these two sequences can be partly understood in terms
of an off-lattice model with 5-6 atoms per amino acid and a minimalistic
potential, in which folding is driven by backbone hydrogen bonding and
effective hydrophobic attraction.
