Abstract:
In the absence of intramolecular long range interactions, the extended local conformation
of a peptide chain is entropically favoured over compact ones, since the
area of the Ramachandran basin of attraction is larger for the extended local conformation
than for any other. In consequence, a random coil is predominantly in
the extended conformation. Under refolding conditions, the high entropic content
of the random coil is countered by the enthalpy loss associated with intramolecular
contact formation (“hydrophobic collapse”) and compactification of the chain.
At an appropriate protein-binding surface, however, the enthalpy loss can be
achieved at minimal cost of conformational entropy, since contacts can be formed
between the protein and the surface and hence do not require compactification of
the protein chain. This saving in entropic cost is a central concept for understanding
the surface-induced denaturation of folded proteins.