  We show that the interplay between excluded volume effects, hydrophobicity,
and hydrogen bonding of a tube-like representation of a polypeptide chain gives
rise to free energy landscapes that exhibit a small number of metastable minima
corresponding to common structural motifs observed in proteins. The complexity
of the landscape increases only moderately with the length of the chain.
Analysis of the temperature dependence of these landscapes reveals that the
stability of specific metastable states is maximal at a temperature close to
the mid-point of folding. These mestastable states are therefore likely to be
of particular significance in determining the generic tendency of proteins to
aggregate into potentially pathogenic agents.
