(228dq) Using Plasmon Waveguide Resonance Spectroscopy to Study the Conformational Change of Membrane Proteins

Membrane proteins are unique and essential for carrying out cellular operation. Studying conformation change of membrane proteins upon stimulation is important for investigating their functions. However, measuring the real-time dynamic change at nanometer scale is still challenging. Here, we developed a method to estimate how the structures of membrane proteins change in supported lipid bilayers by plasmon waveguide resonance (PWR) spectroscopy, which is a birefringent optical label-free sensing technique. The method uses both p- and s-polarized lights to detect the membrane protein mass density change and structure change in the directions perpendicular to and parallel to the lipid membrane plane. We built a PWR sensor platform with a silicon dioxide layer on a thin gold layer, and used 2D COMSOL Multiphysics material model and Maxwell equation to simulate the influence of protein configuration alternation on the PWR sensor chip. We reported the correlations between the PWR resonance angle shifts and the protein mass density and conformational changes. The overall mass density change is found to be majorly correlated to the resonance angle shift of s-polarized light, and the conformational change can be derived from the resonance angle shift of p-polarized light. We used bacteria rhodopsins with known structural responses to light to verify that the sensor chip and the methodology we developed can be used to estimate the conformational change of membrane proteins in supported lipid bilayers.