Molecular Dynamics Simulations of Intrinsically Disordered Proteins: On the Accuracy of the TIP4P-D Water Model and the Representativeness of Protein Disorder Models.

Here, we first present a follow-up to a previous work by our group on the problematic of molecular dynamics simulations of intrinsically disordered proteins (IDPs) [ Henriques et al. J. Chem. Theory Comput. 2015 , 11 , 3420 - 3431 ], using the recently developed TIP4P-D water model. When used in conjunction with the standard AMBER ff99SB-ILDN force field and applied to the simulation of Histatin 5, our IDP model, we obtain results which are in excellent agreement with the best performing IDP-suitable force field from the earlier study and with experiment. We then assess the representativeness of the IDP models used in these and similar studies, finding that most are too short in comparison to the average IDP and contain a bias toward hydrophilic amino acid residues. Moreover, several key order- and disorder-promoting residues are also found to be misrepresented. It seems appropriate for future studies to address these issues.