Macromolecular Crowding Affects the Mechanical Unfolding Forces in Titin: The Size Effect

Abstract

Macromolecules can occupy a large fraction of the volume of the cell and this affects many properties of the proteins inside the cell, such as thermal stability and rates of folding. We present a study comparing the effects of the size of molecular crowders on the unfolding forces of titin. We used an atomic force microscope based single molecule method to measure the effects of the crowding on the mechanical stability of this protein. We used dextran as the crowding agent with three different molecular weights, with concentrations varying from zero to 300 grams per liter in the buffer solution. The results show that the forces that are required to unfold molecules are enhanced when high concentration of dextran molecules is added to the buffer solution and also that there is a maximun force when the crowder size is comparable to the protein.