Proteomic analysis of human low density lipoprotein reveals the presence of prenylcysteine lyase, a hydrogen peroxide-generating enzyme

Objectives Detailed information on the protein composition of low density lipoprotein (LDL) may help to reveal its role in atherogenesis and coronary artery disease in humans. Methods Liquid-phase IEF followed by mass spectrometry analysis has been used to separate LDL proteins, into well-defined pools with individual pI values. Results Besides known LDL-associated proteins this approach revealed the presence of several proteins not previously described to reside in LDL, including prenylcysteine lyase (PCL), orosomucoid, retinol-binding protein, and paroxonase. PCL, an enzyme crucial to the lysosomal degradation of prenylated proteins, is a flavin adenine dinucleotide (FAD)-dependent thioether oxidase which generates free cysteine, isoprenoid aldehyde and hydrogen peroxide. Addition of the substrate farnesylcysteine to lipoprotein resulted in a time-dependent generation of hydrogen peroxide measured with a nonfluorogenic substrate in the presence of horseradish peroxidase. This reaction was stronger in VLDL than in LDL or HDL, reflecting the greater content of PCL in VLDL. PCL is generated along with nascent lipoprotein, as shown by its presence in the lipoprotein secreted by HepG2 cells in culture. Conclusions The finding that an enzyme associated with atherogenic lipoproteins can itself generate an oxidant suggests that PCL may play a significant role in atherogenesis.