(623br) Computational and Thermodynamic Characterization of a Mostly Disordered Protein and An Aging Related Mutant

Hutchinson-Gilford progeria syndrome (HGPS) is a premature aging syndrome caused by the expression and accumulation of a mutant lamin A protein, progerin. We report experimental and computational results that characterize the thermodynamic stability of the lamin A and progerin tail domains, which are mostly disordered. We study protein unfolding using tryptophan fluorescence and circular dichroism of purified, recombinant wild type (wt) and progerin tail domains. Both methods indicate that the progerin tail has a higher transition melting temperature than its wt counterpart. Replica Exchange Molecular Dynamics (REMD) simulations predict the progerin tail to be a more compact structure. Simulated protein unfolding confirms our experimental results; the predicted energy to unfold the progerin tail is higher than the wt lamin A tail. Structural simulations of the wt lamin tail show that the main site for proteolysis during normal posttranslational modification of lamin A is an unfolded region located at the periphery of all the predicted protein configurations, suggesting ample accessibility to proteolysis. Progerin lacks this region for posttranslational proteolysis, but its further compactness suggests a general resistance to turnover and more stable filament structures, potentially leading to the toxic accumulation observed in disease and during normal aging. We believe that this combination of thermodynamic characterization and REMD simulations is a useful method of studying structure of disordered proteins.