Apolipoprotein A4 of primates

Monkey apoA-I was isolated by ultracentrifugation or immunoprecipitation and analyzed by isoelectric focusing and two-dimensional polyacrylamide gel electrophoresis. The plasma apoA-I of 26 Old World monkeys (1 2 cynomolgus and 14 rhesus), 40 New World monkeys (8 cebus, 8 squirrel, 8 spider, 8 owl, and 8 marmosets), 6 prosimians (lemurs) and 10 apes (5 gibbons and 5 chimpanzees) were compared with each other as well as with human apoA-I. These analyses showed that monkey apoA-I contained one major and one to three minor (two basic and one acidic) isoproteins. The basic and acidic minor isoproteins differed by +2, +1, and -1 charges from the major apoA-I isoprotein designated apoA-I*. We have observed profound differences among the apoA-I electrophoretic patterns of the various primate species studied. The apparent isoelectric points of the major isoproteins of apoA-I of prosimians, Old World monkeys, New World monkeys, chimpanzees, gibbons, and humans were 5.70, 5.80, 5.35, 5.64, 5.42, and 5.64, respectively. The entire apoA-I isoprotein pattern of prosimians, Old World monkeys, chimpanzees, gibbons, and New World monkeys with respect to humans was shifted by approximately +1.5, +0.5, 0, -2.0, and -2.5 charges, respectively. The apoA-I synthesized by organ cultures of cynomolgus monkey intestine and liver overlaps on the twodimensional system with the corresponding most basic minor plasma apoA-I isoprotein designated apoA-12. !lB These findings suggest: a) that monkey apoA-I is secreted as a proform and is subsequently modified in plasma, and b) the charge differences among apoA-I of the different nonhuman primate species and of humans are consistent with structural apoA-I gene mutations that occurred during the evolution of primates.-Nicolosi, R. J., and V. 1. Zannis. Apolipoprotein A-I of primates. J. Lipid Res. 1984. 2 5 879-887. Supplementary key words nonhuman primates apoA-I isoproteins hepatic and intestinal apoA-I Apolipoprotein A-I (apoA-I), the major apolipoprotein of high density lipoproteins (HDL) with a plasma concentration of 1.0 to 1.5 mg/ml (1) consists of a single polypeptide chain composed of 243 amino acid residues of known primary amino acid sequence (2). ApoA-I serves as a cofactor for plasma enzyme 1ecithin:cholesterol acyltransferase (LCAT), the enzyme that is responsible for the formation of most cholesteryl esters in plasma (3). ApoA-I in lipoprotein particles of d > 1.1 g/ml promotes cholesterol efflux from cells and through this mechanism might be important in maintaining cellular cholesterol homeostasis (4). In mammalian systems, apoA-I synthesis is thought to occur in liver and small intestine (1, 5-9) as a preproapoA-I (10-12) and undergoes intracellular (10, 12, 13) and extracellular (1 1, 12) proteolysis to attain the major apoA-I isoprotein form observed in plasma (7, 8, 14). Recent studies in humans indicate that various conditions leading to either severe or moderate plasma HDL and apoA-I deficiencies are genetically heterogeneous and are associated to varying degrees with the development of premature atherosclerosis (1 5-20). These findings suggest that mutations in apoA-I could affect lipoprotein metabolism and may predispose individuals to the development of atherosclerosis. In this report, we characterize the apoAI isoproteins of nonhuman primates and compare them with human apoA-I. We show that genetic differences in apoA-I isoproteins exist between the various monkey species and that, similar to human apoA-I, monkey apoA-I is synthesized as a precursor form which is more basic than the plasma apoA-I. Therefore, this precursor plasma apoA-I is apparently modified to attain the isoprotein form observed in plasma. MATERIALS AND METHODS