Determination of structure of integral membrane proteins, especially in their native environment, is a formidable challenge in structural biology. Here we demonstrate that magic angle spinning solid-state NMR spectroscopy can be used to determine structures of membrane proteins reconstituted in synthetic lipids, an environment similar to the natural membrane. We combined a large number of experimentally determined interatomic distances and local torsional restraints to solve the structure of an oligomeric membrane protein of common seven-helical fold, Anabaena sensory rhodopsin (ASR). We determined the atomic resolution detail of the oligomerization interface of the ASR trimer, and the arrangement of helices, side chains and the retinal cofactor in the monomer.

Bacteriorhodopsin-like proteins provide archaea and eubacteria with a unique bioenergetic pathway comprising light-driven transmembrane proton translocation by a single retinal-binding protein.Recently, homologous proteins were found to perform photosensory functions in lower eukaryotes, but no active ion transport by eukaryotic rhodopsins was detected. By demonstrating lightdriven proton pumping in a fungal rhodopsin from Leptosphaeria maculans, we present a case of a retinal-based proton transporter from a eukaryote. This result implies that in addition to oxidative phosphorylation and chlorophyll photosynthesis, some lower eukaryotes may have retained the archaeal route of building an electrochemical transmembrane gradient of protons.proton transport ͉ sensory rhodopsins