The thermodynamic basis of the fuzzy interaction of an intrinsically disordered protein
 

The thermodynamic basis of the fuzzy interaction of an intrinsically disordered protein


Many intrinsically disordered proteins (IDP) that fold upon binding retain conformational heterogeneity in IDP-target complexes. The thermodynamics of such fuzzy interactions is poorly understood. Here we introduce a thermodynamic framework, based on analysis of ITC and CD spectroscopy data, that provides experimental description of IDP association in terms of folding and binding contributions which can be predicted using sequence folding propensities and molecular modeling. We show how IDP can modulate the entropy and enthalpy by adapting their bound-state structural ensemble to achieve optimal binding. This is explained in terms of a free energy landscape that provides the relationship between free energy, sequence folding propensity and disorder. The observed "fuzzy" behavior is possible not only because of IDP flexibility but also because backbone and side chain interactions are, to some extent, energetically decoupled allowing IDP to minimize energetically unfavorable folding.

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