Thermodynamic and Kinetic Stability of Discoidal High-Density Lipoprotein Formation from Phosphatidylcholine/Apolipoprotein A-I Mixture

Abstract

Nascent high-density lipoproteins (HDLs), which are also known as discoidal HDLs, are formed by the interaction of apolipoprotein A-I (apoA-I) with transmembrane ATP-binding cassette transporter A1 (ABCA1). However, the molecular mechanism governing disc formation is not fully understood. Here, we evaluated the thermodynamic and kinetic stability of disc formation from mixtures of 1-palmitoyl-2-oleoylphosphatidylcholine and apoA-I by quantifying the discs and vesicles produced. Sodium cholate dialysis experiments revealed that the discs are thermodynamically more stable than the vesicle/apoA-I mixture (Delta*G = -52 kJ/disc mol at 37.0 degrees C) because the decrease in enthalpy (Delta*H = -620 kJ/disc mol) exceeds the decrease in entropy (TDelta*S = -570 kJ/disc mol). Circular dichroism spectral measurements ascribed 68% of the decrease in enthalpy during disc formation to the formation of helices in apoA-I. Fluorescence measurements suggested that phospholipids enclosed in the discs are more closely packed than those in the vesicles so that they are entropically destabilized. To determine if the disc could be spontaneously produced from vesicles, we measured the decrease in the turbidity of vesicles in response to the addition of apoA-I. However, the rate of disc formation was very slow, suggesting that the large kinetic barrier against disc formation makes the vesicle/apoA-I mixtures metastable. These results raise the possibility that ABCA1 may act to lower the activation energy, thereby facilitating disc formation.

Conformational Changes in High-Density Lipoprotein Nanoparticles Induced by High Payloads of Paramagnetic Lipids

“…These values are of the same order of magnitude as the published values of those parameters for HDL particles doped with Gd-DTPA–DSA. 16 , 17 , 25 …”

Preferential incorporation of shorter and less unsaturated acyl phospholipids into high density lipoprotein-like particles in the ABCA1- and ABCA7-mediated biogenesis with apoA-I

“…However, cholesterol by itself does not form lipid-protein complex particles with apolipoprotein, though it may directly bind to some proteins such as serum albumin (Ha et al, 2003;Peng et al, 2008). To the contrary, physicochemical assembly of the HDL-like particles, similarly to those produced by the ABCA1-mediated cell-apolipoprotein interaction may not essentially require cholesterol (Fukuda et al, 2010;Jayaraman et al, 2010). Also, HDL-like particles can be generated even without cholesterol upon the ABCA1-mediated cell-apolipoprotein interaction (Yamauchi et al, 2002).…”

“…Disk-like particles can be generated as a physicochemical reaction between helical apolipoprotein and phospholipid with the help of sonication, presence of detergent or even spontaneously (Guo et al, 1980;Hoff et al, 1973;Jonas, 1986). Cholesterol is not essential for constructing such particles (Fukuda et al, 2010). The initial biogenesis/assembly of the discoidal HDL thus includes two components: formation of the disk-like particles of apolipoprotein/phospholipid, and incorporation of cholesterol into the particles.…”

(r)HDL in theranostics: how do we apply HDL's biology for precision medicine in atherosclerosis management?

“…Studies on rHDL formation thermodynamics demonstrated that although rHDL formation is favoured by an enthalpic component (mainly by α-helices folding after protein-lipid complexation), rHDL cannot be formed spontaneously since the activation barrier is markedly high. 45 Various strategies to overcome this energetic barrier have led to the development of different methodologies for rHDL synthesis. Sonication: Sonication was the first documented method used for rHDL formation, 46 but current use of this methodology has made some adaptations to the original protocol.…”