Department of Chemistry, University of Iowa, Iowa City, Iowa 52241, USA.
J Am Chem Soc. 2010 Jul 7;132(26):9087-95. doi: 10.1021/ja1021766.
In this study, we present a general-purpose methodology for deriving the three-dimensional (3D) arrangement of multivalent transmembrane complexes in the presence of their ligands. Specifically, we predict the most likely families of structures of the experimentally intractable trimeric asialoglycoprotein receptor (ASGP-R), which consists of human hepatic subunits (two subunits of H1 and one subunit of H2), bound to a triantennary oligosaccharide (TA). Because of the complex nature of this multivalent type-II transmembrane hetero-oligomeric receptor, structural studies have to date been unable to provide the 3D arrangement of these subunits. Our approach is based on using the three-pronged ligand of ASGP-R as a computational probe to derive the 3D conformation of the complex and then using this information to predict the relative arrangement of the protein subunits on the cell surface. Because of interprotein subunit clashes, only a few families of TA conformers are compatible with the trimeric structure of ASGP-R. We find that TA displays significant flexibility, matching that detected previously in FRET experiments, and that the predicted complexes derived from the viable TA structures are asymmetric. Significant variation exists with respect to TA presentation to the receptor complex. In summary, this study provides detailed information about TA-ASGP-R interactions and the symmetry of the complex.
在这项研究中，我们提出了一种通用的方法，用于推导出配体存在下多价跨膜复合物的三维（3D）排列。具体来说，我们预测了实验上难以处理的三聚体唾液酸糖蛋白受体（ASGP-R）的最可能的结构家族，该受体由人肝亚基（H1 的两个亚基和 H2 的一个亚基）组成，与三触角寡糖（TA）结合。由于这种多价 II 型跨膜异源寡聚受体的复杂性质，结构研究迄今为止无法提供这些亚基的 3D 排列。我们的方法基于使用 ASGP-R 的三臂配体作为计算探针来推导出复合物的 3D 构象，然后使用该信息来预测蛋白亚基在细胞表面上的相对排列。由于蛋白亚基之间的冲突，只有少数 TA 构象家族与 ASGP-R 的三聚体结构兼容。我们发现 TA 显示出显著的灵活性，与之前在 FRET 实验中检测到的灵活性相匹配，并且从可行的 TA 结构得出的预测复合物是不对称的。TA 向受体复合物的呈现存在显著差异。总之，这项研究提供了关于 TA-ASGP-R 相互作用和复合物对称性的详细信息。
