Surface dynamics of the integral membrane protein bacteriorhodopsin

Recently, there has been great interest in determining the three-dimensional structures of membrane proteins, particularly bacteriorhodopsin, for which a variety of possible folding arrangements have been suggested^1-4. In this paper we present nuclear magnetic resonance (NMR) spectra^5-8 of deuterated bacteriorhodopsin, and use the data to help interpret the various suggested bacteriorhodopsin folding patterns. The results strongly indicate that (1) a membrane surface (±1 residue) may be defined by NMR in bacteriorhodopsin; (2) all amino acids inside the surface are essentially crystalline; (3) all amino acids outside the surface (surface residues) in bacteriorhodopsin are highly mobile on the time scale of the ²H NMR experiments; (4) NMR data may be used to help evaluate the various structural models that have been proposed; (5) aggregation of purple membrane sheets may lead to an immobilization of the surface residues.