| Popis: |
We present results from experiments that focused in the following two areas: characterization and evaluation of lyotropic liquid crystal matrices as potential model membrane systems and using O2 as a paramagnetic probe of membrane immersion depth by NMR. Lyotropic liquid crystal structural studies focused on characterization of the structure of the isotropic bicelle as either a spheroidal mixed micelle or disc structure. Measurement of the extent of intermixing of the two principle phospholipids components of the system, DMPC and DHPC supported the disc structure of the isotropic bicelle. We also evaluated five materials known to form lyotropic liquid crystals, three dyes cromolyn, blue 20, and violet 27, a metal polymer V2O5, and a biopolymer, 2-isopropyl cellulose for their ability to align in the static field of the spectrometer. Of these materials, the cromolyn LC proved the best candidate as a host liquid crystal matrix for weak alignment studies. O2 was used as a paramagnetic agent to determine membrane immersion depth. The paramagnetic effects of the O2 molecule on nuclear spins are increases in relaxation rates and chemical shift perturbations, both of which are short range in nature. Additionally, O2 molecules assume exhibit an approximately Gaussian distribution across a lipid bilayer, with the highest concentration at the center of the membrane. By measuring changes in chemical shift perturbations and nuclear relaxation rates, we were able to determine the immersion depth of individual atoms of lipids, small peptides (indolicidin), and the large membrane protein diacylglycerol kinase (DAGK). We also determined that a dipolar interaction was responsible paramagnetic relaxation rate enhancement, while chemical shift perturbations were due to a contact interaction. In addition, O2 proved useful for determining which amino acids involved in the binding interaction of two water soluble proteins, the Fc fragment of an immunoglobin protein and its binding ligand, a fragment of protein A from S. aureus. |
