Despite the growing number of atomic-resolution membrane protein structures, direct structural information about proteins in their native membrane environment is scarce. This problem is particularly relevant in the case of the highly-charged S1–S4 voltage-sensing domains responsible for nerve impulses, where interactions with the lipid bilayer are critical for the function of voltage-activated potassium channels. Here we use neutron diffraction, solid-state nuclear magnetic resonance spectroscopy, and molecular dynamics simulations to investigate the structure and hydration of bilayer membranes containing S1–S4 voltage-sensing domains. Our results show that voltage sensors adopt transmembrane orientations, cause a modest reshaping of the surrounding lipid bilayer, and that water molecules intimately interact with the protein within the membrane. These structural findings reveal that voltage sensors have evolved to interact with the lipid membrane while keeping the energetic and structural perturbations to a minimum, and that water penetrates into the membrane to hydrate charged residues and shape the transmembrane electric field.

Mixed self-assembled monolayers (SAMs) of β-mercaptoethanol and the new synthetic lipid 1,2-di-O-palmityl-3-[ω-mercapto-nona(ethylene oxide) glycerol], FC16, were investigated for their ability to form sparsely-tethered bilayer lipid membranes (stBLMs) completed with various phospholipids. We investigated the structural and functional properties of FC16-based stBLMs and compared these to stBLMs prepared using a previously characterized synthetic lipid, 1,2-di-O-myristyl-3-[ω-mercaptohexa(ethylene oxide) glycerol] (WC14). FC16-based stBLMs show increased resistivity to ion transfer and an increase in the submembrane space of ≈ 0.5 nm. Importantly, FC16-based stBLMs formed well-defined, complete bilayers with charged phospholipids such as POPG. In these, POPG, incorporates into the outer monolayer leaflet in the same ratio as in the immersion solution, but is excluded from the inner leaflet. In all cases we investigated thus far, the area densities of the lipids within the bilayers were on average close to those in free bilayer membranes. For charged phospholipids, FC16 appears to provide a distinct advantage over WC14 for the formation of well-defined stBLMs.-2 -