Electrochemistry of Biomimetic Membranes - Applications of Electrochemistry and Nanotechnology in Biology and Medicine - page 237

A micropatterned layer, consisting of regions of thiolipid mol-
ecules with a lipid monolayer on top alternated with regions of
mercaptoundecanoic acid with a lipid bilayer on top, was used to
incorporate rhodopsin. 204,206 This integral protein contributes to the
closing of the Na + channels of the plasma membrane of the outer
segment of the vertebrate rod cell. When rhodopsin is photoacti-
vated, it starts an enzyme cascade that amplifies the absorption of
light by a factor of one million. The first step of this cascade is the
interaction of the photoactivated rhodopsin with transducin, a pe-
ripheral protein that binds to guanosine-5'-diphosphate (GDP) in
its inactive state, and to guanosine-5'-triphosphate (GTP) in its
active state, as schematically depicted in Fig. 2 0 . Transducin is
Figure 20. Schematic picture of rhodopsin-transducin coupling on patterned gold-
supported bilayers, as described in the text. Rhodopsin is preferentially incorpo-
rated in the freely suspended bilayer domains, while transducin is adsorbed indif-
ferently on anchored and freely suspended bilayer regions of the tBLM. When
rhodopsin is photoactivated, transducin is depleted only in the freely suspended
bilayer regions, and therefore diffuses from anchored to freely suspended bilayer
domains. This lateral displacement of transducin and its release from defined do-
mains are observed by one-dimensional imaging SPR. (Reprinted from Ref. 204 with
kind permission from the American Chemical Society.)