Williams D L, de La Llera-Moya M, Thuahnai S T, Lund-Katz S, Connelly M A, Azhar S, Anantharamaiah G M, Phillips M C
Department of Pharmacological Sciences, University Medical Center, State University of New York, Stony Brook, New York 11794, USA.
J Biol Chem. 2000 Jun 23;275(25):18897-904. doi: 10.1074/jbc.M002411200.
Scavenger receptor, class B, type I (SR-BI) mediates the selective uptake of high density lipoprotein (HDL) cholesteryl ester without the uptake and degradation of the particle. In transfected cells SR-BI recognizes HDL, low density lipoprotein (LDL) and modified LDL, protein-free lipid vesicles containing anionic phospholipids, and recombinant lipoproteins containing apolipoprotein (apo) A-I, apoA-II, apoE, or apoCIII. The molecular basis for the recognition of such diverse ligands by SR-BI is unknown. We have used direct binding analysis and chemical cross-linking to examine the interaction of murine (m) SR-BI with apoA-I, the major protein of HDL. The results show that apoA-I in apoA-I/palmitoyl-oleoylphosphatidylcholine discs, HDL(3), or in a lipid-free state binds to mSR-BI with high affinity (K(d) congruent with 5-8 microgram/ml). ApoA-I in each of these forms was efficiently cross-linked to cell surface mSR-BI, indicating that direct protein-protein contacts are the predominant feature that drives the interaction between HDL and mSR-BI. When complexed with dimyristoylphosphatidylcholine, the N-terminal and C-terminal CNBr fragments of apoA-I each bound to SR-BI in a saturable, high affinity manner, and each cross-linked efficiently to mSR-BI. Thus, mSR-BI recognizes multiple sites in apoA-I. A model class A amphipathic alpha-helix, 37pA, also showed high affinity binding and cross-linking to mSR-BI. These studies identify the amphipathic alpha-helix as a recognition motif for SR-BI and lead to the hypothesis that mSR-BI interacts with HDL via the amphipathic alpha-helical repeat units of apoA-I. This hypothesis explains the interaction of SR-BI with a wide variety of apolipoproteins via a specific secondary structure, the class A amphipathic alpha-helix, that is a common structural motif in the apolipoproteins of HDL, as well as LDL.
I 型清道夫受体 B 类（SR-BI）介导高密度脂蛋白（HDL）胆固醇酯的选择性摄取，而不摄取和降解颗粒。在转染细胞中，SR-BI 识别 HDL、低密度脂蛋白（LDL）和修饰的 LDL、含有阴离子磷脂的无蛋白脂质囊泡以及含有载脂蛋白（apo）A-I、apoA-II、apoE 或 apoCIII 的重组脂蛋白。SR-BI 识别如此多样配体的分子基础尚不清楚。我们使用直接结合分析和化学交联来研究小鼠（m）SR-BI 与 HDL 的主要蛋白质 apoA-I 的相互作用。结果表明，apoA-I/palmitoyl-oleoylphosphatidylcholine 圆盘、HDL(3) 或无脂质状态下的 apoA-I 以高亲和力（K(d) 约为 5-8 微克/毫升）与 mSR-BI 结合。这些形式的每种中的 apoA-I 都有效地与细胞表面 mSR-BI 交联，表明直接的蛋白质-蛋白质接触是驱动 HDL 与 mSR-BI 相互作用的主要特征。当与二肉豆蔻酰磷脂酰胆碱复合时，apoA-I 的 N 端和 C 端 CNBr 片段均以可饱和的高亲和力方式与 SR-BI 结合，并且均有效地与 mSR-BI 交联。因此，mSR-BI 识别 apoA-I 中的多个位点。一个 A 类两亲性α-螺旋，37pA，也显示出与 mSR-BI 的高亲和力结合和交联。这些研究将两亲性α-螺旋鉴定为 SR-BI 的识别基序，并提出了 mSR-BI 通过 apoA-I 的两亲性α-螺旋重复单元与 HDL 相互作用的假设。该假设解释了 SR-BI 通过特定的二级结构 A 类两亲性α-螺旋与多种载脂蛋白的相互作用，A 类两亲性α-螺旋是 HDL 以及 LDL 的载脂蛋白中的常见结构基序。
