Immunoreactivity of Apolipoprotein B-100 and Binding to LDL-Receptor of Phospholipase A₂-Treated Low Density Lipoproteins

A. A. Korotaeva, N. K. Golovanova, T. N. Vlasik, E. V. Yanushevskaya, V. P. Tsibulsky, V. V. Yakushkin, M. G. Tvorogova, A. D. Morozkin, and N. V. Prokazova^*

Institute of Experimental Cardiology, Cardiology Research Center, Russian Academy of Medical Sciences, 3-ya Cherepkovskaya ul. 15a, Moscow, 121552 Russia; fax: (095) 415-2962; E-mail: korot@cardio.med.msu.su

^* To whom correspondence should be addressed.

Received March 24, 1998; Revision received June 2, 1998

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Lipid--protein particles were obtained by treatment of low density lipoproteins (LDL) with phospholipase A₂ from bee venom. Under these conditions, half of the phosphatidylcholine (PC) of LDL was changed to lysophosphatidylcholine (LPC). At the same time, the composition of other lipids and the apoprotein structure were unaffected. Three monoclonal antibodies (MAbs) against various apo B epitopes were used to test immunoreactivity of phospholipase A₂-treated LDL (pl-LDL). The apo B epitope interacting with MAb 4C11 (amino acid residues 2377-2658) showed significantly decreased immunoreactivity. Increase in MAb 4C11 binding was demonstrated to depend on oxidation degree of LDL. Thus, changing of half of PC to LPC modified apo B translocation in the lipoprotein globule in an opposite manner as compared with changes induced by oxidative modification. A minor increase in immunoreactivity of pl-LDL with 1D1 MAb against a large middle part of apo B (residues 1297-3249) may be due to the effect of the change of surface lipid composition on the extent of immersion of apo B into the hydrophobic phase. No changes in the interaction of pl-LDL with MAb 2G8 (residues 3748-4306) were observed in comparison with native LDL. This fact demonstrates that 50% phospholipolysis of LDL does not affect the expression of apo B C-terminal residues in pl-LDL. Twofold increase in pl-LDL affinity to immobilized LDL-receptor was shown in contrast to LDL. The data indicate that LPC accumulation in LDL results in better elimination of LDL from the blood stream than in case of accumulation of oxidative products.

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KEY WORDS: low density lipoproteins modified with phospholipase A₂, lysophosphatidylcholine, monoclonal antibodies against low density lipoproteins, receptor of low density lipoproteins

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