Kushwaha R S, Hasan S Q, McGill H C, Getz G S, Dunham R G, Kanda P
Department of Physiology, Southwest Foundation for Biomedical Research, San Antonio, TX 78228-0147.
J Lipid Res. 1993 Aug;34(8):1285-97.
Selective breeding has produced families of baboons that accumulate large high density lipoproteins (HDL1) when challenged with a high cholesterol and high fat (HCHF) diet. In the plasma isolated from these high HDL1 baboons there is a factor that decreases the transfer of cholesteryl ester from HDL to lower density lipoproteins. The purpose of these studies was to identify and characterize this inhibitor of cholesteryl ester transfer. A protein with molecular mass of approximately 4 kDa was detected in greater amounts in the plasma lipoproteins of high HDL1 baboons fed the HCHF diet than in plasma lipoproteins of low HDL1 baboons. This 4 kDa protein appeared to associate with apolipoprotein (apo) A-I, resulting in modified apoA-I with an apparent molecular mass of 31 kDa. A small amount of modified apoE was also identified with a molecular mass of 41 kDa. N-terminal amino acid sequencing of the 4 kDa peptide identified it as an N-terminal fragment of apoC-I. Like apoC-I, the fragment is also a slightly basic protein (pI 7.1). The apoC-I fragment and modified apoA-I presented at equimolar concentrations exhibited similar inhibition of cholesteryl ester transfer protein (CETP) activity in HDL of low HDL1 baboons. On the basis of baboon apoC-I amino acid sequence and the molecular mass of the inhibitor peptide, a peptide corresponding to the N-terminal 38 amino acids of apoC-I was synthesized chemically. This synthetic peptide also inhibited CETP activity in vitro. Rabbit polyclonal antisera prepared against the 38 amino acid synthetic peptide recognized the 4 kDa molecular mass inhibitor protein, apoC-I (6.6 kDa), and the modified apoA-I protein (31 kDa molecular mass) in the plasma lipoproteins of high HDL1 baboons. On the other hand, the antibody detected only apoC-I in the plasma lipoproteins of low HDL1 baboons. The IgG fraction isolated from antiserum raised against the synthetic inhibitor peptide increased cholesteryl ester transfer from HDL of high HDL1 baboons, whereas the IgG antibody against CETP decreased cholesteryl ester transfer from HDL of both high and low HDL1 baboons. These studies suggest that the CETP inhibitor is an N-terminal fragment of apoC-I, and this fragment also modifies apoA-I and apoE in the plasma.
选择性育种培育出了一些狒狒家族，这些狒狒在接受高胆固醇和高脂肪（HCHF）饮食挑战时会积累大量高密度脂蛋白（HDL1）。在从这些高HDL1狒狒分离出的血浆中，有一种因子可减少胆固醇酯从HDL向低密度脂蛋白的转移。这些研究的目的是鉴定和表征这种胆固醇酯转移抑制剂。在喂食HCHF饮食的高HDL1狒狒的血浆脂蛋白中检测到的一种分子量约为4 kDa的蛋白质，比低HDL1狒狒的血浆脂蛋白中的含量更多。这种4 kDa的蛋白质似乎与载脂蛋白（apo）A-I结合，产生表观分子量为31 kDa的修饰apoA-I。还鉴定出少量分子量为41 kDa的修饰apoE。对4 kDa肽段进行N端氨基酸测序，确定其为apoC-I的N端片段。与apoC-I一样，该片段也是一种略带碱性的蛋白质（pI 7.1）。等摩尔浓度的apoC-I片段和修饰apoA-I对低HDL1狒狒HDL中的胆固醇酯转移蛋白（CETP）活性表现出相似的抑制作用。根据狒狒apoC-I的氨基酸序列和抑制剂肽段的分子量，化学合成了一段对应于apoC-I N端38个氨基酸的肽段。这种合成肽在体外也抑制CETP活性。针对38个氨基酸合成肽制备的兔多克隆抗血清识别高HDL1狒狒血浆脂蛋白中的4 kDa分子量抑制剂蛋白、apoC-I（6.6 kDa）和修饰apoA-I蛋白（31 kDa分子量）。另一方面，该抗体在低HDL1狒狒的血浆脂蛋白中仅检测到apoC-I。从针对合成抑制剂肽产生的抗血清中分离出的IgG组分增加了高HDL1狒狒HDL中的胆固醇酯转移，而针对CETP的IgG抗体则降低了高HDL1和低HDL1狒狒HDL中的胆固醇酯转移。这些研究表明，CETP抑制剂是apoC-I的N端片段，并且该片段还修饰血浆中的apoA-I和apoE。
