NH-NH vector correlation in peptides by solid-state NMR

Chromophore distortions in the bacteriorhodopsin photocycle: evolution of the H-C14-C15-H dihedral angle measured by solid-state NMR

In recent years, structural information about bacteriorhodopsin has grown substantially with the publication of several crystal structures. However, precise measurements of the chromophore conformation in the various photocycle states are still lacking. This information is critical because twists about the chromophore backbone chain can influence the Schiff base nitrogen position, orientation, and proton affinity. Here, we focus on the C14-C15 bond, using solid-state nuclear magnetic resonance spectroscopy to measure the H-C14-C15-H dihedral angle. In the resting state (bR(568)), we obtain an angle of 164 +/- 4 degrees, indicating a 16 degrees distortion from a planar all-trans chromophore. The dihedral angle is found to decrease to 147 +/- 10 degrees in the early M intermediate (M(o)) and to 150 +/- 4 degrees in the late M intermediate (M(n)). These results demonstrate changes in the chromophore conformation undetected by recent X-ray diffraction studies.

1H-1H MAS correlation spectroscopy and distance measurements in a deuterated peptide

In this Communication, we demonstrate the use of deuteration together with back substitution of exchangeable protons as a means of attenuating the strong 1H-1H couplings that broaden 1H magic angle spinning (MAS) spectra of solids. The approach facilitates 15N-1H correlation experiments as well as experiments for the measurement of 1H-1H distances. The distance measurement relies on the excellent resolution in the 1H MAS spectrum and homonuclear double quantum recoupling techniques. The 1H-1H dipolar recoupling can be analyzed in an analytical fashion by fitting the data to a 2- or 3-spin system. The experiments are performed on a sample of the dipeptide N-Ac-Val-Leu-OH, which was synthesized from uniformly [2H, 15N] labeled materials and back-exchanged in H2O.

Biomolecular solid state NMR: advances in structural methodology and applications to peptide and protein fibrils

Solid state nuclear magnetic resonance (NMR) methods can provide atomic-level structural constraints on peptides and proteins in forms that are not amenable to characterization by other high-resolution structural techniques, owing to insolubility, high molecular weight, noncrystallinity, or other characteristics. Important examples include peptide and protein fibrils and membrane-bound peptides and proteins. Recent advances in solid state NMR methodology aimed at structural problems in biological systems are reviewed. The power of these methods is illustrated by experimental results on amyloid fibrils and other protein fibrils.

Frequency selective heteronuclear dipolar recoupling in rotating solids: accurate (13)C-(15)N distance measurements in uniformly (13)C,(15)N-labeled peptides

We describe a magic-angle spinning NMR experiment for selective (13)C-(15)N distance measurements in uniformly (13)C,(15)N-labeled solids, where multiple (13)C-(15)N and (13)C-(13)C interactions complicate the accurate measurement of structurally interesting, weak (13)C-(15)N dipolar couplings. The new experiment, termed FSR (frequency selective REDOR), combines the REDOR pulse sequence with a frequency selective spin-echo to recouple a single (13)C-(15)N dipolar interaction in a multiple spin system. Concurrently the remaining (13)C-(15)N dipolar couplings and all (13)C-(13)C scalar couplings to the selected (13)C are suppressed. The (13)C-(15)N coupling of interest is extracted by a least-squares fit of the experimentally observed modulation of the (13)C spin-echo intensity to the analytical expression describing the dipolar dephasing in an isolated heteronuclear spin pair under conventional REDOR. The experiment is demonstrated in three uniformly (13)C,(15)N-labeled model systems: asparagine, N-acetyl-L-Val-L-Leu and N-formyl-L-Met-L-Leu-L-Phe; in N-formyl-[U-(13)C,(15)N]L-Met-L-Leu-L-Phe we have determined a total of 16 internuclear distances in the 2.5-6 A range.