Membrane models and proteins
Small fast-tumbling bicelles are ideal models of studying membrane interactions at molecular level by solution NMR approaches. Using 31P-NMR relaxation measurements we obtain detailed information on lipid head-group dynamics.
We explored the effect of two topologically different membrane-interacting peptides on DMPC/DMPG neutral and DMPC/DMPG/DHPC negatively charged bicelles. KALP21 is a model transmembrane peptide, designed to span a DMPC bilayer and dynorphin B is a membrane surface active neuropeptide. Results indicate that the positively charged dynorphin B decreases the mobility of the lipid molecules -in particular for the negatively charged DMPG- while KALP21 has a more modest influence, which demonstrates that while a transmembrane peptide has severe effects on overall bilayer properties, the surface bound peptide has a more dramatic effect in reducing lipid head-group mobility.
We focused on changes in lipid dynamics upon interaction with the putative "paddle" domains from different K+-channels:KvAP (from Aeropyrum pernix) and HsapBK (human). 13C longitudinal relaxation time values and 13C-1H NOE data for DMPC in DMPC/DHPC bicelles and for DHPC in micelles showed that the lipid acyl chains in the bicelles become less flexible in the presence of either of the fragments. An even more pronounced effect is seen on the glycerol carbons. 2H NMR spectra of magnetically aligned bicelles showed that the peptide derived from KvAP had no or little effect on bilayer order, while the peptide derived from HsapBK had the effect of lowering the order of the bilayer.
Dr. Lena Mäler, Department of Biochemistry and Biophysics, Stockholm University, Stockholm, Sweden
Dr. Katalin Kövér, Department of Inorganic and Analytical Chemistry, University of Debrecen