Biophysical studies of membrane proteins/peptides. Interaction with ...

INTRODUCTION: BIOMEMBRANES
Figure I.2 – a) Schematic representation of the phosphoglycerolipid structure. b) Most common alcohols
found in the headgroups of phosphoglycerolipids. From Berg et al., 2002). c) Structure of a
phosphatidylcholine - 1,2-dimyristoyl-sn-glycero-3-phosphatidylcholine (DMPC).
The acyl-chains found in each class of phosphoglycerolipids is also different.
PC’s are mainly composed of short saturated chains (16 to 18 carbons) or 18:1 and 18:2
unsaturated chains. PE’s have a large fraction of polyunsaturated chains, in particular
20:4 (arachidonoyl). Charged phosphoglycerolipids also present a significant content of
unsaturated acyl-chains (Sackmann, 1995).
Other types of glycerolipids are found in biomembranes, namely the
plasmalogens, in which one of the acyl-chains is bound to glycerol by a vinyl ether
linkage. Plasmalogens constitute about 20 % of the total content of phosphoglycerides
in humans, although their abundance varies dramatically among tissues and species.
Human brain and heart tissues are particularly enriched in this class of lipids (Lodish et
al., 2000). Cardiolipin is a dimer lipid since it contains four acyl chains. It constitutes
about 20 % of the inner mitochondrial membrane and is also found in the membrane of
plant chloroplasts and of certain bacterias.
1.2.1.2. Sphingolipids
Sphingolipids are based on sphingosine instead of glycerol. Sphingosine is an
aminoalcohol with a long unsaturated hydrocarbon chain. A long fatty-acid is attached
to sphingosine by an amide bound. This basic structure is a ceramide, which is involved
in cell death and is an essential component of skin (Mouritsen, 2005). The linkage of a
choline to the terminal hydroxyl group of sphingosine in ceramide leads to
5