Identification of a distinct human high-density lipoprotein subspecies defined by a lipoprotein-associated protein, K-45. Identity of K-45 with paraoxonase.
In an attempt to provide immunological tools for subfractionation of high-density lipoproteins (HDL), monoclonal antibodies were raised against HDL complexes. Two clones identified a peptide, provisionally named K-45 (pI 4.5-4.9; molecular mass 45 kDa, range 42-48 kDa), whose plasma distribution and lipoprotein association were fully characterised. Gel filtration localised the peptide to the HDL region of human plasma where it co-eluted with apolipoprotein (apo) A-I, the structural protein of HDL. Complementary studies employing immunoabsorption with anti-(apo A-I) antibodies removed 90% of K-45 from plasma: conversely, anti-(apo A-II) antibodies eliminated only 10% of K-45. Immunoaffinity chromatography on an anti-(K-45) column revealed that the peptide was present in a distinct HDL subsepecies containing three major proteins: K-45, apo A-I and clusterin or apo J. The lipoprotein nature of the bound fraction was indicated by electron microscopy (diameter 9.6 +/- 3.3 nm) and quantification of lipids, the latter showing an unusually high triacyglycerol concentration. Plasma concentrations of K-45 were positively correlated with apo A-I and HDL-cholesterol and negatively correlated with apo B and total cholesterol. Thus, the peptide appears to be linked, directly or indirectly, to processes which give rise to an anti-atherogenic lipid profile. After completion of the present studies, an N-terminal sequence identical to that of K-45 was reported in recently isolated cDNA clones. These clones encode paraoxonase.
Department of Medicine, University Hospital, Geneva, Switzerland.
M C
MC
Blatter
R W
RW
James
S
S
Messmer
F
F
Barja
D
D
Pometta
D000595:Amino Acid Sequence; D016632:Apolipoprotein A-I / Q000032:analysis; D043303:Aryldialkylphosphatase; D005591:Chemical Fractionation; D008076:Cholesterol, HDL / Q000097:blood; D002846:Chromatography, Affinity; D002850:Chromatography, Gel; D006801:Humans; D007163:Immunosorbent Techniques; D007526:Isoelectric Point; D008075:Lipoproteins, HDL / Q000097:blood* / Q000737:chemistry; D008969:Molecular Sequence Data; D008970:Molecular Weight; D010744:Phosphoric Monoester Hydrolases / Q000097:blood* / Q000737:chemistry; D012044:Regression Analysis; D014461:Ultracentrifugation
D016632:Apolipoprotein A-I; D008076:Cholesterol, HDL; D008075:Lipoproteins, HDL; D010744:Phosphoric Monoester Hydrolases; D043303:Aryldialkylphosphatase