背景:编码跨膜通道样蛋白1的TMC1在听觉毛细胞中形成机械电传导(MET)通道,必要的听觉功能。已知TMC1变异会导致常染色体显性遗传(DFNA36)和常染色体隐性遗传(DFNB7/11)非综合征性听力损失,但只有少数的TMC1变体与DFNA36相关,妨碍基因型-表型相关性分析。
方法:在本研究中,我们回顾性审查了内部数据库中的338先证者遗传性听力损失,评估与DFNA36相关的新型TMC1变体的临床表型和基因型。为了分析这些变体的结构影响,我们利用秀丽隐杆线虫TMC1的Cryo-EM结构作为模板和AlphaFold蛋白结构数据库,生成了人类TMC1的两个结构模型。具体来说,脂质双层嵌入蛋白数据库用于构建TMC1的膜嵌入模型.然后,我们检查了TMC1变体对分子内相互作用的影响,并预测了它们的潜在致病性。
结果:我们鉴定了与DFNA36相关的两种新型TMC1变体(c.1256T>C:p。Phe419Ser和c.1444T>C:p。Trp482Arg)。受影响的受试者有双边,中度,迟发性,进行性感觉神经性听力损失与向下倾斜的配置。位于TMC1的跨膜结构域4中的Phe419残基面向外朝向通道孔,并且紧邻脂质双层的疏水尾部。非极性到极性变体(p。Phe419Ser)改变了膜中的疏水性,损害蛋白质-脂质相互作用。另一方面,位于跨膜结构域5和6之间的细胞外接头区域中的Trp482残基通过其芳环锚定到膜界面,介导几种稳定TMC1结构的分子相互作用。在同源跨膜蛋白如OSCA1.2中也观察到这种基于芳香环的锚定。相反,Trp被Arg(Trp482Arg)取代破坏了阳离子-π与磷脂的相互作用,磷脂位于磷脂双层的外部小叶中,不稳定的蛋白质-脂质相互作用。此外,Trp482Arg破坏了Trp482和Pro511之间的CH-π相互作用,可能降低了蛋白质的整体稳定性。与分子建模并行,与野生型蛋白相比,这两种突变体的降解速度明显更快,损害蛋白质的稳定性。
结论:该结果扩展了与DFNA36相关的致病TMC1变异的遗传谱,并提供了对TMC1跨膜蛋白-脂质相互作用的见解。
TMC1, which encodes transmembrane channel-like protein 1, forms the mechanoelectrical transduction (MET) channel in auditory hair cells, necessary for auditory function.
TMC1 variants are known to cause autosomal dominant (DFNA36) and autosomal recessive (DFNB7/11) non-syndromic hearing loss, but only a handful of TMC1 variants underlying DFNA36 have been reported, hampering analysis of genotype-phenotype correlations.
In this study, we retrospectively reviewed 338 probands in an in-house database of genetic hearing loss, evaluating the clinical phenotypes and genotypes of novel TMC1 variants associated with DFNA36. To analyze the structural impact of these variants, we generated two structural models of human
TMC1, utilizing the Cryo-EM structure of C. elegans TMC1 as a template and AlphaFold protein structure database. Specifically, the lipid bilayer-embedded protein database was used to construct membrane-embedded models of TMC1. We then examined the effect of TMC1 variants on intramolecular interactions and predicted their potential pathogenicity.
We identified two novel
TMC1 variants related to DFNA36 (c.1256T > C:p.Phe419Ser and c.1444T > C:p.Trp482Arg). The affected subjects had bilateral, moderate, late-onset, progressive sensorineural hearing loss with a down-sloping configuration. The Phe419 residue located in the transmembrane domain 4 of TMC1 faces outward towards the channel pore and is in close proximity to the hydrophobic tail of the lipid bilayer. The non-polar-to-polar variant (p.Phe419Ser) alters the hydrophobicity in the membrane, compromising protein-lipid interactions. On the other hand, the Trp482 residue located in the extracellular linker region between transmembrane domains 5 and 6 is anchored to the membrane interfaces via its aromatic rings, mediating several molecular interactions that stabilize the structure of TMC1. This type of aromatic ring-based anchoring is also observed in homologous transmembrane proteins such as OSCA1.2. Conversely, the substitution of Trp with Arg (Trp482Arg) disrupts the cation-π interaction with phospholipids located in the outer leaflet of the phospholipid bilayer, destabilizing protein-lipid interactions. Additionally, Trp482Arg collapses the CH-π interaction between Trp482 and Pro511, possibly reducing the overall stability of the protein. In parallel with the molecular modeling, the two mutants degraded significantly faster compared to the wild-type protein, compromising protein stability.
This results expand the genetic spectrum of disease-causing TMC1 variants related to DFNA36 and provide insight into
TMC1 transmembrane protein-lipid interactions.