Membrane dynamics studied by FTIR spectroscopy in thylakoid and cytoplasmic membranes of Synechocystis PCC6803. Lipids and the effect of protein to lipid ratios

Abstract

In Cyanobacteria the growth temperature determines the fatty acid composition of the cell membranes, having more unsaturated fatty acyl chains at lower growth temperatures. For proper functioning, membrane constituents require the liquid-crystalline state of the membrane lipids in which rotational transmembrane movements of lipid and protein molecules are possible. In photosynthetic membranes phase behaviour of glyc-erolipids is also regulated by the level of their unsaturation, a process mediated by the activity of fatty acid desaturases that introduce double bonds directly into the fatty acids of glycerolipids. The cyanobacterium strain Synechocystis PCC6803 is transformable and thus, desaturase deficient transformant strains can be obtained from it up to the point where oleic acids are the only unsaturated fatty acid species in the membranes of the mutant cells. We were interested what kind of membranes are constructed from the altered lipid choice, and by this to learn more about the role of lipids in membrane dynamics. For structural studies FTIR spectroscopy has been applied making use of our recent interpretation of the origin of the frequency upshift of v_symCH₂ frequencies upon increasing lipid disorder as a consequence of increasing gauche and decreasing trans segment populations in the fatty acyl chains [1].