Key result
Apolipoproteins require at least 4 amphiphilic helical segments to generate HDL-like particles and induce cholesterol efflux.
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The structural requirement has been studied for apolipoproteins in their free form to interact with cells, to generate high density lipoprotein (HDL), and to cause cellular lipid efflux (J. Biol. Chem. 266, 3080-3086, 1991). It is shown that human apolipoprotein (apo) A-IV and apolipophorin III of Manduca sexta cause cholesterol efflux from cholesterol-loaded mouse peritoneal macrophages and reduce intracellularly accumulated cholesteryl ester as a result of forming HDL-like particles with cellular lipids, as do apoA-I, A-II and E. On the other hand, similar to apoC-III, reduced-and-carboxymethylated human apoA-II had no such effect. Thus, apolipoproteins seem to require at least four amphiphilic helical segments per molecule to express this function.
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Hara et al. (1992) studied Cellular lipid efflux and HDL generation. Human apolipoprotein A-IV and Manduca sexta apolipophorin III vs. Reduced-and-carboxymethylated human apoA-II and apoC-III was evaluated on Cholesterol efflux, intracellular cholesteryl ester reduction, and formation of HDL-like particles. Free apolipoproteins require at least 4 amphiphilic helical segments per molecule (like apoA-IV and apolipophorin III) to generate HDL-like particles and induce cellular cholesterol efflux.
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