Before revision: Many intrinsically disordered proteins (IDPs) , proteinsthat do not fold into a unique tertiary structure in isolation because of their depletion in hydrophobicity whereas enrichment in charge and aromaticity, retain their structural disorderness when participating in IDP-IDP binding andIDP phase separation via a sequence-specific "fuzzy  " molecular recognition mechanism.
After revision: Many intrinsically disordered proteins (IDPs) , proteinsthat do not fold into a unique tertiary structure in isolation because of their depletion in hydrophobicity whereas enrichment in charge and aromaticity, retain their structural disorderness when participating in IDP-IDP binding andIDP phase separation via a sequence-specific "fuzzy " in that their binding and/or phase separation are stochastically governed by the interacting IDPs' amino acid sequences while their assembled conformations remain largely disordered. To help elucidate a basic aspect of this fascinating yet poorly understood phenomenon, the binding of a homo- or hetero-dimeric pair of polyampholytic IDPs is modeled statistical mechanically using cluster expansion. We find that the binding affinities of binary fuzzy complexes in the model correlate strongly with a newly derived simple "jSCD " molecular recognition mechanism.