Pearson A M, Rich A, Krieger M
Department of Biology, Massachusetts Institute of Technology, Cambridge 02139.
J Biol Chem. 1993 Feb 15;268(5):3546-54.
Macrophage scavenger receptors exhibit unusually broad, but circumscribed, polyanionic ligand-binding specificity. For example, the polyribonucleotides poly(I) and poly(G) are ligands but poly(A) and poly(C) are not. To further investigate the molecular basis of this polynucleotide-binding specificity, we tested the capacity of various oligodeoxyribonucleic acids to inhibit the scavenger receptor-mediated degradation of 125I-labeled acetylated low density lipoprotein by Chinese hamster ovary cells expressing the type I bovine scavenger receptor. A series of short oligodeoxyriboguanines (dGn, where 5 < or = n < or = 37) were effective inhibitors. The dG6, dG12, and dA5G37 members of this series were shown by circular dichroism and UV spectroscopy to be assembled into four-stranded helices stabilized by G-quartets. [32P]dA5G37 bound directly to scavenger receptors. Partial or complete denaturation of the quadruplex structures of these oligonucleotides by boiling destroyed their inhibitory activity. Receptor activity was also inhibited by d(T4G4)4, a telomere-like oligonucleotide which forms an intramolecular quadruplex. In addition, conversion of the four-stranded potassium salt of poly(I) to the single-stranded lithium salt dramatically reduced its inhibitory activity. Addition of KCl to the Li+ salt resulted in the reformation of poly(I)'s quadruplex structure and restoration of its inhibitory activity. A variety of single-stranded and double-stranded oligo- and polydeoxyribonucleotides (e.g. dA37, HaeIII restriction fragments of phi X174) exhibited very little or no inhibitory activity. Thus, a base-quartet-stabilized four-stranded helix appears to be a necessary structural determinant for polynucleotide binding to and inhibition of scavenger receptors. This conformational requirement accounts for the previously unexplained polyribonucleotide-binding specificity of scavenger receptors. The spatial distribution of the negatively charged phosphates in polynucleotide quadruplexes may form a charged surface which is complementary to the positively charged surface of the collagenous ligand-binding domain of the scavenger receptor.
巨噬细胞清道夫受体表现出异常广泛但有限的多阴离子配体结合特异性。例如，多聚核糖核苷酸聚（I）和聚（G）是配体，而聚（A）和聚（C）则不是。为了进一步研究这种多核苷酸结合特异性的分子基础，我们测试了各种寡脱氧核糖核酸抑制表达I型牛清道夫受体的中国仓鼠卵巢细胞对125I标记的乙酰化低密度脂蛋白的清道夫受体介导降解的能力。一系列短的寡脱氧鸟嘌呤（dGn，其中5≤n≤37）是有效的抑制剂。通过圆二色性和紫外光谱显示，该系列中的dG6、dG12和dA5G37成员组装成由G-四联体稳定的四链螺旋。[32P]dA5G37直接与清道夫受体结合。通过煮沸使这些寡核苷酸的四重结构部分或完全变性会破坏它们的抑制活性。受体活性也受到d（T4G4）4的抑制，d（T4G4）4是一种形成分子内四重结构的端粒样寡核苷酸。此外，将聚（I）的四链钾盐转化为单链锂盐会显著降低其抑制活性。向Li+盐中添加KCl会导致聚（I）的四重结构重新形成并恢复其抑制活性。各种单链和双链寡脱氧核糖核苷酸和聚脱氧核糖核苷酸（例如dA37、φX174的HaeIII限制性片段）表现出很少或没有抑制活性。因此，碱基四联体稳定的四链螺旋似乎是多核苷酸与清道夫受体结合并抑制其活性的必要结构决定因素。这种构象要求解释了清道夫受体以前无法解释的多聚核糖核苷酸结合特异性。多核苷酸四重体中带负电荷的磷酸根的空间分布可能形成一个带电荷的表面，该表面与清道夫受体胶原质配体结合域的带正电荷表面互补。
