  A phenomenological model hamiltonian to describe the folding of a protein
with any given sequence is proposed. The protein is thought of as a collection
of pieces of helices; as a consequence its configuration space increases with
the number of secondary structure elements rather than with the number of
residues. The hamiltonian presents both local (i.e. single helix, accounting
for the stiffness of the chain) and non local (interactions between
hydrophobically-charged helices) terms, and is expected to provide a first tool
for studying the folding of real proteins. The partition function for a
simplified, but by no means trivial, version of the model is calculated almost
completely in an analytical way. The latter simplified model is also applied to
the study of a synthetic protein, and some preliminary results are shown.
