Effects of phospholipid on the structure of human apolipoprotein A-IV.

摘要: We have used fluorescence and circular dichroism spectroscopy to investigate the effect of phospholipid on structure molecular stability human apolipoprotein A-IV (apo-A-IV). Binding apo-A-IV egg phosphatidylcholine vesicles was rapid did not cause release encapsulated 6-carboxyfluorescein. Fluorometric titration established that bound with an association constant 1.36 x 10(6) liters/mol a binding maximum 2 molecules per vesicle. vesicle surface caused progressive increase in alpha helicity from 43% at baseline 83% saturation; denaturation studies showed free energy stabilization 6.31 kcal/mol. Fluorescence quenching revealed associated dramatic decrease fractional exposure tyrosine iodide, efficiency intramolecular tyrosine-tryptophan transfer. These findings suggest may involve relaxation globular protein conformation which containing alpha-helical domains surrounding tryptophan "unfold" reorient their hydrophobic faces toward monolayer, consequent induction additional structure. However, our data also does penetrate deeply into region fatty acyl chains, but rather sits higher intercalated between charged head groups. This characteristic determine labile interaction high density lipoproteins.