APOLIPOPROTEIN-L, A NEW HUMAN HIGH-DENSITY-LIPOPROTEIN APOLIPOPROTEINEXPRESSED BY THE PANCREAS - IDENTIFICATION, CLONING, CHARACTERIZATION, AND PLASMA DISTRIBUTION OF APOLIPOPROTEIN-L

In this study, we have identified and characterized a new protein pres ent in human high density lipoprotein that we have designated apolipop rotein L. Using a combination of liquid-phase isoelectrophoresis and h igh resolution two-dimensional gel electrophoresis, apolipoprotein L w as identified and partially sequenced from immunoisolated high density lipoprotein (Lp(A-I)). Expression was only detected in the pancreas, The cDNA sequence encoding the full-length protein was cloned using re verse transcription-polymerase chain reaction, The deduced amino acid sequence contains 383 residues, including a typical signal peptide of 12 amino acids, No significant homology was found with known sequences , The plasma protein is a single chain polypeptide with an apparent mo lecular mass of 42 kDa, Antibodies raised against this protein detecte d a truncated form with a molecular mass of 39 kDa, Both forms were pr edominantly associated with immunoaffinity-isolated apoA-I-containing lipoproteins and detected mainly in the density range 1.123 < d < 1.21 g/ml. Free apoL was not detected in plasma. Anti-apoL immunoaffinity chromatography was used to purify apoL-containing lipoproteins (Lp(L)) directly from plasma. Nondenaturing gel electrophoresis of Lp(L) show ed two major molecular species with apparent diameters of 12.2-17 and 10.4-12.2 nm. Moreover, Lp(L) exhibited both pre-beta and alpha electr omobility. Apolipoproteins A-I, A-II, A-IV, and C-III were also detect ed in the apoL-containing lipoprotein particles.