Institute of Molecular BioSciences, Massey University, Palmerston North, New Zealand.
PLoS One. 2012;7(7):e40066. doi: 10.1371/journal.pone.0040066. Epub 2012 Jul 20.
Dystrophin and utrophin link the F-actin cytoskeleton to the cell membrane via an associated glycoprotein complex. This functionality results from their domain organization having an N-terminal actin-binding domain followed by multiple spectrin-repeat domains and then C-terminal protein-binding motifs. Therapeutic strategies to replace defective dystrophin with utrophin in patients with Duchenne muscular dystrophy require full-characterization of both these proteins to assess their degree of structural and functional equivalence. Here the high resolution structures of the first spectrin repeats (N-terminal repeat 1) from both dystrophin and utrophin have been determined by x-ray crystallography. The repeat structures both display a three-helix bundle fold very similar to one another and to homologous domains from spectrin, α-actinin and plectin. The utrophin and dystrophin repeat structures reveal the relationship between the structural domain and the canonical spectrin repeat domain sequence motif, showing the compact structural domain of spectrin repeat one to be extended at the C-terminus relative to its previously defined sequence repeat. These structures explain previous in vitro biochemical studies in which extending dystrophin spectrin repeat domain length leads to increased protein stability. Furthermore we show that the first dystrophin and utrophin spectrin repeats have no affinity for F-actin in the absence of other domains.
肌营养不良蛋白和 utrophin 通过相关糖蛋白复合物将 F-肌动蛋白细胞骨架连接到细胞膜上。这种功能源自它们的结构域组织，具有 N 端肌动蛋白结合结构域，随后是多个 spectrin 重复结构域，然后是 C 端蛋白结合基序。在杜氏肌营养不良症患者中用 utrophin 替代有缺陷的肌营养不良蛋白的治疗策略需要对这两种蛋白进行充分表征，以评估其结构和功能等效程度。在这里，通过 X 射线晶体学确定了来自肌营养不良蛋白和 utrophin 的第一个 spectrin 重复（N 端重复 1）的高分辨率结构。重复结构均显示出三螺旋束折叠，彼此非常相似，与 spectrin、α-actinin 和 plectin 的同源结构域也非常相似。utrophin 和 dystrophin 重复结构揭示了结构域与规范 spectrin 重复结构域序列基序之间的关系，显示 spectrin 重复 1 的紧凑结构域在 C 末端相对于其先前定义的序列重复得到扩展。这些结构解释了先前的体外生化研究，其中延长肌营养不良蛋白 spectrin 重复结构域的长度会导致蛋白质稳定性增加。此外，我们还表明，在没有其他结构域的情况下，第一个肌营养不良蛋白和 utrophin spectrin 重复结构域与 F-肌动蛋白没有亲和力。
