Identification of the proteoglycan binding site in apolipoprotein B48
Identification of the proteoglycan binding site in apolipoprotein B48
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DOI：
10.1074/jbc.m204053200
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发表时间：
2002-08-30
影响因子：
4.8
通讯作者：
Borén, J
中科院分区：
文献类型：
--
作者：
Flood, C;Gustafsson, M;Borén, J
动脉粥样硬化的初始事件是脂蛋白在血管壁内膜内的滞留。以前我们鉴定了载脂蛋白（apo）B100中的位点B（残基3359-3369）作为低密度脂蛋白（LDL）中的蛋白聚糖结合序列，并表明含apoB的脂蛋白的致动脉粥样硬化性与其对动脉壁蛋白聚糖的亲和力有关。然而，含有apoB 100和apoB 48的脂蛋白具有相同的致动脉粥样硬化性，即使位点B位于apoB 100的羧基末端的一半，而在apoB 48中不存在。如果与蛋白聚糖结合是动脉粥样硬化形成的关键步骤，那么含有apoB 48的脂蛋白必须通过apoB氨基末端48%的其他蛋白聚糖结合位点与蛋白聚糖结合。体外研究已经鉴定了脱脂apoB 48中结合带负电荷的糖-氨基聚糖的五个碱性氨基酸簇。为了确定这些位点中的哪一个在LDL颗粒上起作用，我们分析了来自转基因小鼠或大鼠肝癌细胞的重组人LDL的蛋白聚糖结合活性。用中性氨基酸取代位点B-Ib（残基84-94）中的碱性氨基酸，消除了重组apoB 53的蛋白聚糖结合活性。羧基截短的apoB 80以比apoB 100和apoB 48更高的亲和力结合双糖链。其中位点B突变的ApoB 80与apoB 48具有相同的蛋白聚糖亲和力。这些数据支持这样的假设：apoB 100的羧基末端“掩盖”了位点B-Ib（氨基末端蛋白聚糖结合位点），并且该位点在羧基截短形式的apoB中暴露。在apoB的氨基末端区域存在蛋白聚糖结合位点可以解释为什么含apoB 48和apoB 100的脂蛋白具有相同的致动脉粥样硬化性。
An initial event in atherosclerosis is the retention of lipoproteins within the intima of the vessel wall. Previously we identified Site B (residues 3359-3369) in apolipoprotein (apo) B100 as the proteoglycan binding sequence in low density lipoproteins (LDLs) and showed that the atherogenicity of apoB-containing lipoproteins is linked to their affinity for artery wall proteoglycans. However, both apoB100- and apoB48-containing lipoproteins are equally atherogenic even though Site B lies in the carboxyl-terminal half of apoB100 and is absent in apoB48. If binding to proteoglycans is a key step in atherogenesis, apoB48-containing lipoproteins must bind to proteoglycans via other proteoglycan binding sites in the amino-terminal 48% of apoB. In vitro studies have identified five clusters of basic amino acids in delipidated apoB48 that bind negatively charged glycos-aminoglycans. To determine which of these sites is functional on LDL particles, we analyzed the proteoglycan binding activity of recombinant human LDLs from transgenic mice or rat hepatoma cells. Substitution of neutral amino acids for the basic amino acids in Site B-Ib (residues 84-94) abolished the proteoglycan binding activity of recombinant apoB53. Carboxyl-truncated apoB80 bound biglycan with higher affinity than apoB100 and apoB48. ApoB80 in which Site B was mutated had the same affinity for proteoglycans as apoB48. These data support the hypothesis that the carboxyl terminus of apoB100 "masks" Site B-Ib, the amino-terminal proteoglycan binding site, and that this site is exposed in carboxyl-truncated forms of apoB. The presence of a proteoglycan binding site in the amino-terminal region of apoB may explain why apoB48- and apoB100-containing lipoproteins are equally atherogenic.