An Apo A-I Protein A Hybrid Used for the Study of HDL Receptor Binding and Endocytosis
HDL (high-density lipoprotein) interacts with cells in reverse cholesterol transport and gains cholesterol. The molecular mechanism and the subcellular localization of this acquisition are not understood. A major problem has been the difficulty in determining whether HDL follows a receptor-mediated pathway, and whether receptor-mediated endocytosis is a prerequisite for reverse cholesterol transport [1–4]. Common steps have been defined for receptor mediated endocytosis of most ligands. They bind to cell surface receptors at 4 °C and at 37 °C, they are rapidly internalized into an early endosomal compartment. In most cases the acidic pH of the endosomal lumen allows the receptor-ligand complex to dissociate. Receptors and ligands may either be degraded in the lysosomes after 15–30 min or recycled, reappearing on the cell surface with a half-time of 5–8 min. In some systems it is possible experimentally to manipulate the proportion of molecules degraded or recycled [5, 6]. With the fundamental properties of receptor-mediated endocytosis in mind, we examined the HDL pathway using as the ligands HDL and an apo A-I containing hybrid protein constructed using recombinant DNA techniques. The apo A-I hybrid permits the analysis of the specific role of this apolipoprotein in HDL function.
KeywordsCholesterol Urea Europium Oligomer Trypsin
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