Abstract
Apolipoprotein A-I (apoA-I) has a great conformational flexibility to exist in lipid-free, lipid-poor, and lipid-bound states during lipid metabolism. To address the lipid binding and the dynamic desorption behavior of apoA-I at lipoprotein surfaces, apoA-I, Δ(185-243)apoA-I, and Δ(1-59)(185-243)apoA-I were studied at triolein/water and phosphatidylcholine/triolein/water interfaces with special attention to surface pressure. All three proteins are surface active to both interfaces lowering the interfacial tension and thus increasing the surface pressure to modify the interfaces. Δ(185-243)apoA-I adsorbs much more slowly and lowers the interfacial tension less than full-length apoA-I, confirming that the C-terminal domain (residues 185-243) initiates the lipid binding. Δ(1-59)(185-243)apoA-I binds more rapidly and lowers the interfacial tension more than Δ(185-243)apoA-I, suggesting that destabilizing the N-terminal α-helical bundle (residues 1-185) restores lipid binding. The three proteins desorb from both interfaces at different surface pressures revealing that different domains of apoA-I possess different lipid affinity. Δ(1-59)(185-243)apoA-I desorbs at lower pressures compared with apoA-I and Δ(185-243)apoA-I indicating that it is missing a strong lipid association motif. We propose that during lipoprotein remodeling, surface pressure mediates the adsorption and partial or full desorption of apoA-I allowing it to exchange among different lipoproteins and adopt various conformations to facilitate its multiple functions.
Highlights
Apolipoprotein A-I has a great conformational flexibility to exist in lipid-free, lipid-poor, and lipid-bound states during lipid metabolism
The (1-44)Apolipoprotein A-I (apoA-I) peptide binds less strongly than the (198-243)apoA-I peptide at both the TO/W and the POPC/ TO/W interfaces (53, 58). These results suggest that the surface pressure-mediated desorption and readsorption, apoA-I deletion mutants at model lipoprotein interfaces 479 and the conformational flexibility of apoA-I probably provide lipoprotein stability during metabolic remodeling reactions in plasma
At a protein concentration of ف4 × 10Ϫ7 M, the ␥ of the TO/W interface was lowered to 15.4 mN/m with apoA-I and 15.1 mN/m with ⌬(1-59)(185-243)apoA-I, while ⌬(185243)apoA-I ␥ was lowered to 19.6 mN/m
Summary
Apolipoprotein A-I (apoA-I) has a great conformational flexibility to exist in lipid-free, lipid-poor, and lipid-bound states during lipid metabolism. ␥ rose to a new equilibrium level while the compressed area was held constant, indicating that the interfacial concentration decreased due to desorption of bound proteins from the interface.
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