Freezing Transition of Compact Polyampholytes

Polyampholytes (PAs) are heteropolymers with long range Coulomb interactions. Unlike polymers with short range forces, PA energy levels have nonvanishing correlations and are thus very different from the random energy model (REM). Nevertheless, if charges in the PA globule are screened as in a regular plasma, PAs freeze in REM fashion. Our results shed light on the potential role of Coulomb interactions in folding and evolution of proteins, which are weakly charged PAs, in particular, making connection with the finding that sequences of charged amino acids in proteins are not random.