  We apply the Wako-Saito-Munoz-Eaton model to the study of Myotrophin, a small
ankyrin repeat protein, whose folding equilibrium and kinetics have been
recently characterized experimentally. The model, which is a native-centric
with binary variables, provides a finer microscopic detail than the Ising
model, that has been recently applied to some different repeat proteins, while
being still amenable for an exact solution. In partial agreement with the
experiments, our results reveal a weakly three-state equilibrium and a
two-state-like kinetics of the wild type protein despite the presence of a
non-trivial free-energy profile. These features appear to be related to a
careful "design" of the free-energy landscape, so that mutations can alter this
picture, stabilizing some intermediates and changing the position of the
rate-limiting step. Also the experimental findings of two alternative pathways,
an N-terminal and a C-terminal one, are qualitatively confirmed, even if the
variations in the rates upon the experimental mutations cannot be
quantitatively reproduced. Interestingly, folding and unfolding pathway appear
to be different, even if closely related: a property that is not generally
considered in the phenomenological interpretation of the experimental data.
