Abstract
Available experimental techniques cannot determine high-resolution three-dimensional structures of membrane proteins under a transmembrane voltage. Hence, the mechanism by which voltage-gated cation channels couple conformational changes within the four voltage sensor domains, in response to either depolarizing or polarizing transmembrane voltages, to opening or closing of the pore domain's ion channel remains unresolved. Single-membrane specimens, composed of a phospholipid bilayer containing a vectorially oriented voltage-gated K+ channel protein at high in-plane density tethered to the surface of an inorganic multilayer substrate, were developed to allow the application of transmembrane voltages in an electrochemical cell. Time-resolved neutron reflectivity experiments, enhanced by interferometry enabled by the multilayer substrate, were employed to provide directly the low-resolution profile structures of the membrane containing the vectorially oriented voltage-gated K+ channel for the activated, open and deactivated, closed states of the channel under depolarizing and hyperpolarizing transmembrane voltages applied cyclically. The profile structures of these single membranes were dominated by the voltage-gated K+ channel protein because of the high in-plane density. Importantly, the use of neutrons allowed the determination of the voltage-dependent changes in both the profile structure of the membrane and the distribution of water within the profile structure. These two key experimental results were then compared to those predicted by three computational modeling approaches for the activated, open and deactivated, closed states of three different voltage-gated K+ channels in hydrated phospholipid bilayer membrane environments. Of the three modeling approaches investigated, only one state-of-the-art molecular dynamics simulation that directly predicted the response of a voltage-gated K+ channel within a phospholipid bilayer membrane to applied transmembrane voltages by utilizing very long trajectories was found to be in agreement with the two key experimental results provided by the time-resolved neutron interferometry experiments.
| Original language | English |
|---|---|
| Pages (from-to) | 751-766 |
| Number of pages | 16 |
| Journal | Biophysical Journal |
| Volume | 117 |
| Issue number | 4 |
| DOIs | |
| State | Published - Aug 20 2019 |
Funding
Funding was provided by the National Institutes of Health grant P01-GM55876 . The Spallation Neutron Source, Oak Ridge National Laboratory, is a user facility sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy . X-ray interferometry measurements were performed at the Multi-Angle X-ray Scattering Facility in the Laboratory for Research on the Structure of Matter, a Materials Research Science and Engineering Center at the University of Pennsylvania funded by the National Science Foundation . MD simulations were performed on the Stampede2 supercomputer at the Texas Advanced Computing Center, University of Texas Austin, funded under the Extreme Science and Engineering Discovery Environment program by the National Science Foundation (grant number ACI-1548562 ).