DIPOLAR CORRELATION NMR-SPECTROSCOPY OF A MEMBRANE-PROTEIN

We demonstrate the application of a new NMR experiment-RF-driven recou pling (RFDR)-for establishing spatial connectivities and measuring int ernuclear distances in spinning solids. RFDR employs rotor-synchronize d pi-pulses in a longitudinal mixing scheme to reintroduce dipolar cou plings into magic angle spinning (MAS) NMR experiments. We have utiliz ed this technique to measure a 0.25 nm distance in polycrystalline D,L -alanine and to determine relative distances in the integral membrane protein bacteriorhodopsin (bR). In the latter case, we have focused on an internuclear distance that defines the configuration about the ret inal-protein Schiff base linkage in the two conformers comprising dark -adapted bR. Our results demonstrate that RFDR is a valid and practica l technique for structural investigations of solids including biologic al molecules with molecular weights as great as 85 kDa.