Protein Shape and Electrical Dipole Moment Characterization with Nanopore and DLS/ELS Measurement, and MD Simulation

The shape and electrical dipole moment are important parameters of protein molecules that govern it's conformational stability, molecular interactions, and biological function. We measure the variation in the shape and electrical dipole moment of bovine serum albumin (BSA) protein molecules under different electrical field strengths, temperatures, and pH values at the single-molecule level using a solid-state nanopore device. We analyzed BSA protein across a range of conditions, including temperatures from 18-60 °C, electric field strength ≈5-10 mV/nm, and pH from 3-11. Our analysis fits the measured histograms of ionic current blockade amplitude (△I) to a convolution model of an ellipsoidal protein's orientational distribution. The fit directly yields a protein molecule's aspect ratio, volume, and effective dipole moment, allowing us to map the variation of these parameters of the BSA protein. Across conditions,(△I) histograms are often bimodal, consistent with two favored orientations or coexisting conformers. We cross-validate nanopore-derived size and charge trends with ensemble dynamic and electrophoretic light scattering (DLS/ELS) technique and interpret condition-dependent shape changes using molecular dynamics simulations. Together, these results establish a practical route to extract protein shape, volume, and dipole strength directly from nanopore data and to chart how solution chemistry and electric field change protein stability.

Keywords

Single-molecule spectroscopy; protein shape; electrical dipole moment; nanopore sensing