Glycolipid conformation and dynamics in model and biological membranes.

The focus of this dissertation has been the biophysical analysis of two related research subjects: a model membrane glycolipid system and glycolipid-rich biomembranes. The objective of the model system study was to provide a biological understanding of the molecular conformation and dynamics at the membrane surface. The biomembrane project is in the first stages of development where the immediate goal is to observe the structure and phase behaviour of cyanobacterial thylakoid membranes. It has been possible to apply a motional model deduced for the glycerol C3$\sp\prime$ position of 1,2-di-O-tetradecyl-3-O-$(\beta$-D-glucopyranosyl)-sn-glycerol $(\beta$-DTGL) in the gel state not only to the more fluid liquid crystalline state, but also to the analysis of the glucose head group ($\{$1-$\rm \sp2H\sb1\})$ motions. The above model, however, did not completely simulate the relaxation data of the $\beta$-DTGL glucose head group. Therefore, conformational energy calculations have been used to assess the flexibility of the head group about its glycosidic bond, in a liquid-crystalline membrane matrix. Algal thylakoid membranes are known for their ability to undergo conformational changes during periods of photosynthetic activity. The ultimate goal of the biomembrane project was to use $\sp2$H NMR to study such conformational changes in thylakoid membranes. However, this project is in the first stages of development; the more modest but attainable short term goal was to observe directly the structure and phase behaviour of two strains of cyanobacterial thylakoid membranes, Anacystis nidulans and A. nidulans R2. In both the previous studies and this study, it was found that the heterogeneous systems undergo broad phase transitions and that acyl chain unsaturation lowers the phase transition temperature of the membranes. Although pure digalactosyldiacyglycerol is known to stabilize lamellar membrane phases, it appears as though phosphatidylglycerol (PG) is more influential in stabilizing the lamellar membrane structure of the cyanobacterial thylakoid membranes. This effect was more noticeable for the spectra of extracted lipids; in the absence of protein and with low PG levels, the lipids formed non-lamellar phases at lower temperatures. (Abstract shortened by UMI.