Thermodynamics of apolipoprotein-phospholipid association

Apolipoproteins are multifunctional in that they contain some protein sequences that associate with a phospholipid surface and others that mediate a biological activity. This chapter describes the helical amphipathic moment, measurement of thermodynamic parameters, methods, and compares the results. The association of apolipoproteins and phospholipids is due to several spectroscopic changes. The results show that there is no correlation between free energy and size of the apolipoprotein. The free energies have been determined for peptide association with single bilayer vesicles and dissociation from small micellar lipid–protein complexes, such that the trend of increasing hydrophobicity appears to correspond with increasing free energy of association. Additionally, the intrinsic surface activities of proteins and peptides, as determined by surface pressure at the air–water interface, correlate with the product. Thus the use of amphipathic helical moment analysis has proved promising in correlating structure with function and in the design of model lipid-binding peptides.