Entropic and Electrostatic Effects on the Folding Free Energy of a Surface-Attached Biomolecule: An Experimental and Theoretical Study

Citations Over TimeTop 15% of 2012 papers

Abstract

Surface-tethered biomolecules play key roles in many biological processes and biotechnologies. However, while the physical consequences of such surface attachment have seen significant theoretical study, to date this issue has seen relatively little experimental investigation. In response we present here a quantitative experimental and theoretical study of the extent to which attachment to a charged-but otherwise apparently inert-surface alters the folding free energy of a simple biomolecule. Specifically, we have measured the folding free energy of a DNA stem loop both in solution and when site-specifically attached to a negatively charged, hydroxylalkane-coated gold surface. We find that whereas surface attachment is destabilizing at low ionic strength, it becomes stabilizing at ionic strengths above ~130 mM. This behavior presumably reflects two competing mechanisms: excluded volume effects, which stabilize the folded conformation by reducing the entropy of the unfolded state, and electrostatics, which, at lower ionic strengths, destabilizes the more compact folded state via repulsion from the negatively charged surface. To test this hypothesis, we have employed existing theories of the electrostatics of surface-bound polyelectrolytes and the entropy of surface-bound polymers to model both effects. Despite lacking any fitted parameters, these theoretical models quantitatively fit our experimental results, suggesting that, for this system, current knowledge of both surface electrostatics and excluded volume effects is reasonably complete and accurate.

Related Papers

• → On the role of electrostatics in protein–protein interactions(2011)174 cited
• → Electrostatics in Protein Binding and Function(2002)150 cited
• → Electrostatics, structure prediction, and the energy landscapes for protein folding and binding(2015)100 cited
• → Electrostatics in Computational Biophysics and Its Implications for Disease Effects(2022)20 cited
• → Forces mediating protein–protein interactions: a computational study of p53 “approaching” MDM2(2009)17 cited