In-Cell DEER Spectroscopy of Nanodisc-Delivered Membrane Proteins in Living Cell Membranes

Membrane proteins are integral to numerous cellular processes, yet their conformational dynamics in native environments remains difficult to study. This study introduces a nanodelivery method using nanodiscs to transport spin-labeled membrane proteins into the membranes of living cells, enabling direct in-cell double electron–electron resonance (DEER) spectroscopy measurements. We investigated the membrane protein BsYetJ, incorporating spin labels at key positions to monitor conformational changes. Our findings demonstrate successful delivery and high-quality DEER data for BsYetJ in both Gram-negative E. coli and Gram-positive B. subtilis membranes. The delivered BsYetJ retains its ability to transport calcium ions. DEER analysis reveals distinct conformational states of BsYetJ in different membrane environments, highlighting the influence of lipid composition on the protein structure. This nanodelivery method overcomes traditional limitations, enabling the study of membrane proteins in more physiologically relevant conditions.