Structure and stability of apolipoprotein J-containing high-density lipoproteins

Apolipoprotein J (apoJ) defines a heterogeneous subclass of human plasma high-density lipoproteins (HDL) having a bimodal distribution of molecular mass of 70-90 kDa (approximately 50%) and 200 kDa or larger (approximately 50%). ApoJ-HDL are unstable in stored plasma, and must be evaluated within 24 h. All apoJ-HDL in freshly obtained plasma have alpha 2 electrophoretic mobility and are distinct from a minor subpopulation of apoAI-HDL which electrophorese in the pre beta region. Although apoAI is not associated with the majority of plasma apoJ-HDL, a small fraction of these particles also containing apoAI. There is little variation in the apoJ/apoAI mole ratio of apoJ-HDL immunoaffinity purified from the same individual on different days. In addition, there is a constant ratio among individuals, assessed for five volunteers, of 4.9 +/- 0.6. Purified apoJ added directly to apoJ-depleted plasma can interact with apoAI or with apoAI-containing lipoproteins, as evidenced by the association of apoAI with apoJ that is reisolated by immunoaffinity chromatography. The amount of apoAI associated with apoJ increases linearly with increasing amount of apoJ added, over the range of apoJ concentrations tested. No other known apolipoprotein is associated with apoJ. By two-dimensional electrophoretic analysis, the lipoproteins containing both apoJ and apoAI have approximate molecular masses of 350-400 kDa. Taken together, the results suggest that the interaction between apoJ and apoAI is physiologically important and that lipoproteins which contain both apoJ and apoAI can be produced in the plasma. ApoJ-HDL and apoJ/apoAI-HDL may have different functions and metabolic fates or may represent different stages of apoJ catabolism.