| The intracellular milieu is filled with small molecules, nucleic acids, lipids and proteins. Theories have attempted to explain how macromolecules react to this environment for over 30 years. Recent experiment-based studies have shown that protein stability and dynamics are altered in this environment. I used the loop of chymotrypsin inhibitor 2 and two unfolded proteins (alpha-synuclein and FlgM) to show that the crowded cellular matrix does not necessarily cause structuring of these dynamic regions. Most importantly, I have shown the thermodynamic and mechanistic basis for how protein stability is changed in the cellular environment. To do this I use a marginally stable globular protein (an isolated SH3 domain) to measure stability, dynamics, and folding rates in cells and cell-like environments. Proteins are enthalpically destabilized in cells. The destabilization arises from charge-charge interactions of the cellular environment with the unfolded ensemble of the protein. These interactions also slow folding of the protein. This work will allow creation of a more complete picture of protein thermodynamics inside the cell. Furthermore, the SH3 domain is amenable to studying in vitro protein stability over a broad range of pH values, and allows acquisition of folding and unfolding rates with a variety of crowders. Future efforts will facilitate a better understanding of surface charge interactions and will allow elucidation of a crowder's interaction with the transition state. |
