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Mapping the Orientation of Helices in Micelle-Bound Peptides by Paramagnetic Relaxation Waves
journal contribution
posted on 2007-04-25, 00:00 authored by Michal Respondek, Tobias Madl, Christoph Göbl, Regina Golser, Klaus ZanggerMany antimicrobial peptides form α-helices when bound to a membrane. In addition, around
80% of residues in membrane-bound proteins are found in α-helical regions. The orientation and location
of such helical peptides and proteins in the membrane are key factors determining their function and activity.
Here we present a new solution state NMR method for obtaining the orientation of helical peptides in a
membrane-mimetic environment (micelle-bound) without any chemical perturbation of the peptide−micelle
system. By monitoring proton longitudinal relaxation rates upon addition of the freely water-soluble and
inert paramagnetic probe Gd(DTPA-BMA) to an α-helical peptide, a wavelike pattern with a periodicity of
3.6 residues per turn is observed. The tilt and azimuth (rotation) angle of the helix determine the shape of
this paramagnetic relaxation wave and can be obtained by least-square fitting of measured relaxation
enhancements. Results are presented for the 15-residue antimicrobial peptide CM15 which forms an
amphipathic helix almost parallel to the surface of the micelle. Thus, a few fast experiments enable the
identification of helical regions and determination of the helix orientation within the micelle without the
need for covalent modification, isotopic labeling, or sophisticated equipment. This approach opens a path
toward the topology determination of α-helical membrane−proteins without the need for a complete NOE-based structure determination.