Thuahnai Stephen T, Lund-Katz Sissel, Anantharamaiah G M, Williams David L, Phillips Michael C
Division of GI/Nutrition, Lipid Research Group, The Children's Hospital of Philadelphia, University of Pennsylvania School of Medicine, 19104-4318, USA.
J Lipid Res. 2003 Jun;44(6):1132-42. doi: 10.1194/jlr.M200429-JLR200. Epub 2003 Apr 1.
Competitive binding experiments were performed using Y1-BS1 adrenal cells to provide information about the interaction of HDL apolipoproteins with scavenger receptor class B, type I (SR-BI). Exchangeable apolipoproteins apolipoprotein A-I (apoA-I), apoA-II, apoE-2, apoE-3, and apoE-4 as phospholipid complexes bind like HDL3 to SR-BI via their multiple amphipathic alpha-helices; the concentrations required to reduce the binding of HDL3 to SR-BI by 50% (IC50) were similar and in the range of 35-50 microgram protein/ml. In the case of apoA-I, peptides corresponding to segments 1-85, 44-65, 44-87, 149-243, and 209-241 all had the same IC50 as each other (P = 0.86), showing that a specific amino acid sequence in apoA-I is not responsible for the interaction with SR-BI. The distribution of charged residues in the amphipathic alpha-helix affects the interaction, with class A and Y helices binding better than class G* helices. Synthetic alpha-helical peptides composed of either l or d amino acids can bind equally to the receptor. Association with phospholipid increases the amount of apolipoprotein binding to SR-BI without altering the affinity of binding. Lipid-free apolipoproteins compete only partially with the binding of HDL to SR-BI, whereas lipidated apolipoproteins compete fully. These results are consistent with the existence of more than one type of apolipoprotein binding site on SR-BI.
利用Y1-BS1肾上腺细胞进行了竞争性结合实验，以提供有关高密度脂蛋白（HDL）载脂蛋白与B类I型清道夫受体（SR-BI）相互作用的信息。可交换载脂蛋白载脂蛋白A-I（apoA-I）、apoA-II、apoE-2、apoE-3和apoE-4作为磷脂复合物，通过其多个两亲性α螺旋像HDL3一样与SR-BI结合；将HDL3与SR-BI的结合减少50%（IC50）所需的浓度相似，范围为35 - 50微克蛋白质/毫升。就apoA-I而言，对应于1 - 85、44 - 65、44 - 87、149 - 243和209 - 241片段的肽彼此具有相同的IC50（P = 0.86），表明apoA-I中的特定氨基酸序列与与SR-BI的相互作用无关。两亲性α螺旋中带电残基的分布影响相互作用，A类和Y类螺旋比G*类螺旋结合更好。由l或d氨基酸组成的合成α螺旋肽可同等程度地与受体结合。与磷脂结合增加了载脂蛋白与SR-BI的结合量，而不改变结合亲和力。无脂载脂蛋白仅部分竞争HDL与SR-BI的结合，而脂化载脂蛋白则完全竞争。这些结果与SR-BI上存在不止一种类型的载脂蛋白结合位点一致。
