Thermodynamics of lipid protein associations. Thermodynamics of helix formation in the association of high density apolipoprotein A-I (apoA-I) to dimyristoyl phosphatidylcholine.
The structure and phospholipid-binding properties of human plasma high density apolipoprotein A-I (apoA-I) has been studied at pH 7.4 and 3.1 by microcalorimetry, circular dichroism and density gradient ultracentrifugation. At pH values of 7.4 and 3.1, apoA-I binds to dimyristoyl phosphatidylcholine (DMPC) to form complexes of similar composition (molar ratio of DMPC/apoA-I of 100) and helical content (67%). At pH 7.4, the lipid-protein association is accompanied by an increase in helical content from 58 to 67% and an exothermic enthalpy of binding (deltaHB) of -90 kcal/mol apoA-I. At pH 3.1, the helical content of apoA-I is increased from 48 to 67% on binding to DMPC and the enthalpy of binding was -170 kcal/mol. We suggest that the difference in the enthalpies of binding (-80 kcal/mol) at pH 3.1 compared to 7.4 is due to the greater coil leads to helix transition at the lower pH.
D001053:Apolipoproteins / Q000097:blood; D002151:Calorimetry; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008075:Lipoproteins, HDL / Q000097:blood; D009227:Myristic Acids; D010713:Phosphatidylcholines / Q000097:blood; D011485:Protein Binding; D011487:Protein Conformation; D013816:Thermodynamics
D001053:Apolipoproteins; D008075:Lipoproteins, HDL; D009227:Myristic Acids; D010713:Phosphatidylcholines