(Color online) The Fresnel-normalized reflectivity data (a) for bare Si-Ni-Si substrate itself [green (light gray)], with a KvAP-DM monolayer tethered to its surface via the SA approach [red (gray)], and subsequently for the KvAP-POPC reconstituted membrane [blue (dark gray)]. Corresponding absolute electron density profiles (b) (same color scheme) and the corresponding difference electron density profiles (c) for the KvAP-DM monolayer [red (gray)] and the KvAP-POPC membrane [blue (dark gray)], referenced to the profile of the Si-Ni-Si substrate itself, all in a moist helium environment. The electron density profile for Kv1.2 channel (d), calculated from the x-ray crystal structure in a mixed detergent-phospholipid environment. The oriented Kv1.2 cartoon is shown to guide the eye for the “profile structure” which is a projection of the 3D structure parallel to the plane of the membrane onto the normal to that plane.