Dynamic pictures of membrane proteins in two-dimensional crystal, lipid bilayer and detergent as revealed by site-directed solid-state 13C NMR

Abstract

We have compared site-directed 13C solid-state NMR spectra of [3- 13C]Ala- and/or [1- 13C]Val-labeled membrane proteins, including bacteriorhodopsin (bR), pharaonis phoborhodopin ( ppR), its cognate transducer ( pHtrII) and Escherichia coli diacylglycerol kinase (DGK) , in two-dimensional (2D) crystal, lipid bilayers, and detergent. Restricted fluctuation motions of these membrane proteins due to oligomerization of bR by specific protein–protein interactions in the 2D crystalline lattice or protein complex between ppR and pHtrII provide the most favorable environment to yield well-resolved, fully visible 13C NMR signals for [3- 13C]Ala-labeled proteins. In contrast, several signals from such membrane proteins were broadened or lost owing to interference of inherent fluctuation frequencies (10 4–10 5 Hz) with frequency of either proton decoupling or magic angle spinning, if their 13C NMR spectra were recorded as a monomer in lipid bilayers at ambient temperature. The presence of such protein dynamics is essential for the respective proteins to achieve their own biological functions. Finally, spectral broadening found for bR and DGK in detergents were discussed.