Solid state nuclear magnetic resonance (SSNMR) can be used to study the structures of molecules such as small peptides and large proteins. Different structures correspond to different chemical environments and thus yield different chemical shifts in NMR spectra. In addition, SSNMR can also be used to probe membrane locations of peptides and proteins and provide insights into their biological functions. This dissertation mainly focuses on the structural and membrane location studies of peptides by rotational-echo double-resonance (REDOR) SSNMR, which is a technique for measuring distances between two coupled hetero nuclei such as 13C and 15N.Influenza fusion peptide (IFP) is the N-terminal peptide of the HA2 subunit of the influenza hemagglutinin (HA) protein and this peptide plays an important role in the membrane fusion between the virus and the endosome of the host cell. There are 15 different HA subtypes. I studied the structure of membrane-associated H3 subtype IFP (H3_IFP) by 13C-15N REDOR SSNMR. SIMPSON simulations of the data indicate that H3_IFP adopts predominantly closed and semi-closed structures in membranes. Similar to IFP, human immunodeficiency virus (HIV) fusion peptide (HFP) is the N-terminal peptide of the viral gp41 fusion protein and this peptide plays a key role in the HIV-host cell membrane fusion. HFP adopts major antiparallel and minor parallel fÒ sheet structures in membranes. Earlier fluorescence spectroscopy and SSNMR studies support a strong positive correlation between the membrane insertion depth and fusogenicity of HFP. However, the 19F labeling in earlier membrane location studies of HFP may perturb the membrane bilayer integrity. Due to this concern, 13C-2H REDOR was developed to detect the residue-specific membrane location of HFP, where one residue of HFP is backbone 13CO labeled and the lipid is either perdeuterated or selectively deuterated in its acyl chains. Since 1H and 2H are chemically equivalent, there is no perturbation on membrane bilayer integrity as well as peptide-lipid interaction regardless of what fraction of deuterated lipid is used. The 13C-2H REDOR pulse sequence was optimized using the setup peptide I4. The membrane locations of two peptides, HFP and KALP, were studied by 13C-2H REDOR, where KALP is a designed transmembrane fÑ helical peptide. Fitting of the REDOR data revealed that both peptides have multiple locations within the membrane hydrocarbon core. The multiple locations are attributed to the snorkeling of lysine sidechains on both termini for KALP and to the distribution of antiparallel fÒ sheet registries for HFP. HFP has a ~0.7 fraction of deep insertion and a ~0.3 fraction of shallow insertion in the membrane. The predominant deep insertion of HFP may significantly perturb the membrane bilayer structure and lower the activation energy of membrane fusion, which is consistent with the observed positive correlation between the membrane insertion depth and fusion rate for different HFP constructs.
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