LDL phospholipid hydrolysis produces modified electronegative particles with an unfolded apoB-100 protein

Electronegative low density lipoprotein (LDL-) formation that structurally resembles LDL- isolated from plasma was evaluated after LDL treatment with snake venom phospholipase A(2) (PLA(2)). PLA(2) treatment of LDL increased its electrophoretic mobility in proportion to the amount of LDL- formed without evidence of lipid peroxidation. These changes dose-dependently correlated with the degree of phospholipid hydrolysis. Strong immunoreactivity of LDL- subfraction from plasma and PLA(2)-treated LDL (PLA(2)-LDL) to amyloid oligomer-specific antibody was observed. Higher P-strand structural content and unfolding proportionate to the loss of alpha-helical structure of apolipoprotein B-100 (apoB-100) of LDL- isolated from both native and PLA(2)-LDLs was demonstrated by circular dichroism (CD) spectropolarimetry. These structural changes resembled the characteristics of some oxidatively modified LDLs and soluble oligomeric aggregates of amyloidogenic proteins. PLA(2)-LDL was also more susceptible to nitration by peroxynitrite, likely because of exposure of otherwise inaccessible hydrophilic and hydrophobic domains arising from apoB-100 unfolding. This was also demonstrated for plasma LDL-. In contrast, PLA(2)-LDL was more resistant to copper-mediated oxidation that was reversed upon the addition of small amounts of unsaturated fatty acids. The observed similarities between PLA(2)-LDL--derived LDL- and plasma LDL- implicate a role for secretory PLA(2) in producing modified LDL- that is facilitated by unfolding of apoB-100.