Abstract

Folding thermodynamics of the disordered protein "paratox" and how it can be used to probe the mechanism of osmolyte action

Mazdak Khajehpour
University of Manitoba
Winnipeg, Manitoba R3T 2N2

Contrary to globular proteins, intrinsically disordered proteins do not have a well-defined folded structure in solution. In this work, we discuss the folding of an interesting intrinsically disordered protein paratox, a phage protein that prevents the Staphylococcus aureus bacterium from acquiring environmental DNA (natural competence). We show that this protein folds reversibly via a two-state mechanism in the presence of denaturant or heat. This special property can be used to investigate an important question: namely, do osmolytes effect the protein folding free energy through modulating entropy or enthalpy. In this case we have specifically investigated the effect of the well-known osmolyte TMAO (Trimethylamine N-oxide) upon the folding free energy of paratox. Our work demonstrates that TMAO addition effects both the entropy and enthalpy of folding: the entropic effect stabilizes, while the enthalpic effect destabilizes the folded form of paratox. These results are contextualized in terms of our current understanding of the TMAO action mechanism.