Morten Hohwy

De novo determination of peptide structure with solid-state magic-angle spinning NMR spectroscopy

The three-dimensional structure of the chemotactic peptide N-formyl-l-Met-l-Leu-l-Phe-OH was determined by using solid-state NMR (SSNMR). The set of SSNMR data consisted of 16 13C–15N distances and 18 torsion angle constraints (on 10 angles), recorded from uniformly 13C,15N- and 15N-labeled samples. The peptides structure was calculated by means of simulated annealing and a newly developed protocol that ensures that all of conformational space, consistent with the structural constraints, is searched completely. The result is a high-quality structure of a molecule that has thus far not been amenable to single-crystal diffraction studies. The extensions of the SSNMR techniques and computational methods to larger systems appear promising.

Band-selective homonuclear dipolar recoupling in rotating solids

In this paper, we introduce approaches to band-selective homonuclear dipolar recoupling with the SPC-5 sequence described previously [Hohwy et al., J. Chem. Phys. 110, 7983 (1999)]. The technique, denoted SPC-53, restores the homonuclear dipolar coupling during magic angle spinning (MAS) and introduces a fifth-order residual offset term of controllable magnitude. The fifth order term truncates the dipolar coupling to spins that fall outside the operational bandwidth of the experiment. It is shown with high-order average Hamiltonian theory, multiple-spin simulations, and experiments, that polarization within a spin cluster can be propagated to destination spins with improved efficiency using this approach. Further, we show that a spin system subjected to band-selective recoupling obeys the equation of motion of the reduced spin cluster and that modeling of the polarization transfer process is simplified. Thus, in the important case of peptides and proteins, all of the backbone and side-chain carbonyl spins...

Determination of Torsion Angles in Membrane Proteins

Bacteriorhodopsin (bR) harnesses light energy to transport protons across the cell membrane of H. salinarium. Absorption of a photon by the protonated retinal chromophore initiates a cycle in which the chromophore releases a proton to an aspartate on the extracellular side and reprotonates from an aspartic acid on the cytoplasmic side. Vectorial proton transport depends on a switch in accessibility of the chromophore Schiff base nitrogen from the extracellular to cytoplasmic side. Changes in the retinal conformation are expected to be particularly important for understanding the pumping mechanism.