Synthesis And Characterization Of Photoactivatable Phospholipidic Probes

Biomembranes are composed of lipid bilayers and membrane proteins. The phospholipids are the major components of the lipids. Phospholipids are involved in many important biological processes of biomembranes and themselves have many biological and physiological functions such as signal transduction, virus infection and nutrition.Membrane proteins associate with biomembrane lipid bilayers and mediate important biological functions, such as signal transduction, energy conversion, transport of ions and molecules across the membrane. They are important targets for drug developmen. Understanding the structures and functions of these membrane proteins is therefore important for searching novel therapeutic targets as well as pursuing drug development programs. It is therefore necessary to be able to obtain direct, reliable evidence about the topology of membrane proteins and protein-lipid interactions. Since it's difficult to get the X-ray crystallography data and high-resolution NMR data of membrane proteins, we propose photo-affinity labeling of biomembranes with photoactivatable phospholipidic probes.We have therefore synthesized and characterized a series of photoactivatable phospholipidic probes. They have either the coumarin azide group or fluorinated aryl azide group at the lipid polar head or on the fatty acid chain of phospholipids.Aryl azides are by far the most frequently used photoaffinity probes because they can be easily synthesized, as well as being chemically stable in the dark and highly reactive upon photoirradiation. Among the arylazides, fluorinated aryl azides are exceptionally promising because upon photoactivation, they lead to much more efficient photolabeling than non-fluorinated arylazides. Furthermore, the coumarine derivatives with azide group is of special interest because they can be used as both photoaffinity probes and fluorescent probes. Several phospholipidic probes have been previously synthesized with various photoactiovatable groups on the fatty acid chainor at the polar head. However, so far to our knowledge, no phospholipidic probes have been developed based on fluorinated aryl azide or coumarine azide.The photochemistry of the probes was studied in organic solvents and in phosphate buffer. All probes underwent rapid and clean photodecomposition upon irradiation at > 300 nm, at which most biological macromolecules will not be damaged by UV irradiation. Further, the probes with a coumarine azide group can be used as both photoaffinity probes and fluorescent probes, allow us to follow the photolabeling process by fluorescent detection. Therefore, our photochemical results showed that these probes hold promises for the photolabeling studies of biomembranes.