Graduate School of Medical Life Science, Yokohama City University, Yokohama 230-0045, Japan.
Structural Biology Research Center, Institute of Materials Structure Science, KEK/High Energy Accelerator Research Organization, Tsukuba 305-0801, Japan.
Structure. 2023 Nov 2;31(11):1452-1462.e4. doi: 10.1016/j.str.2023.08.016. Epub 2023 Sep 11.
Myelin protein zero (MPZ or P0) is a transmembrane protein which functions to glue membranes in peripheral myelin. Inter-membrane adhesion is mediated by homophilic interactions between the extracellular domains (ECDs) of MPZ. Single amino acid substitutions in an ECD cause demyelinating neuropathy, Charcot-Marie-Tooth disease (CMT), with unknown mechanisms. In this study, by using a novel assay system "nanomyelin," we revealed that a stacked-rings-like ECD-8-mer is responsible for membrane adhesion. Two inter-ECD interactions, cis and head-to-head, are essential to constituting the 8-mer and to gluing the membranes. This result was reinforced by the observation that the CMT-related N87H substitution at the cis interface abolished membrane-adhesion activity. In contrast, the CMT-related D32G and E68V variants retained membrane-stacking activity, whereas their thermal stability was lower than that of the WT. Reduced thermal stability may lead to impairment of the long-term stability of ECD and the layered membranes of myelin.
髓鞘蛋白零 (MPZ 或 P0) 是一种跨膜蛋白，其功能是将外周髓鞘中的膜粘在一起。膜间黏附是通过 MPZ 细胞外结构域 (ECDs) 之间的同种型相互作用介导的。ECDs 中的单个氨基酸取代会导致脱髓鞘神经病，即 Charcot-Marie-Tooth 病 (CMT)，但其机制尚不清楚。在这项研究中，我们使用一种新型的“纳米髓鞘”检测系统揭示了堆叠环样 ECD-8 -mer 负责膜黏附。两个 ECD 内相互作用，顺式和头对头，对于构成 8-mer 和粘合并将膜是必不可少的。这一结果得到了加强，因为在顺式界面处的 CMT 相关 N87H 取代会破坏膜黏附活性。相比之下，CMT 相关的 D32G 和 E68V 变体保留了膜堆积活性，但其热稳定性低于 WT。热稳定性降低可能导致 ECD 和髓鞘层状膜的长期稳定性受损。
