Microtubules, composed of conserved α/β-tubulin dimers, undergo complex post-translational modifications (PTMs) that fine-tune their properties and interactions with other proteins. Cilia exhibit several tubulin PTMs, such as polyglutamylation, polyglycylation, detyrosination, and acetylation, with functions that are not fully understood. Mutations in AGBL5, which encodes the deglutamylating enzyme CCP5, have been linked to retinitis pigmentosa, suggesting that altered polyglutamylation may cause photoreceptor cell degeneration, though the underlying mechanisms are unclear. Using super-resolution ultrastructure expansion microscopy (U-ExM) in mouse and human photoreceptor cells, we observed that most tubulin PTMs accumulate at the connecting cilium that links outer and inner photoreceptor segments. Mouse models with increased glutamylation (Ccp5-/- and Ccp1-/-) or loss of tubulin acetylation (Atat1-/-) showed that aberrant glutamylation, but not acetylation loss, disrupts outer segment architecture. This disruption includes exacerbation of the connecting cilium, loss of the bulge region, and destabilization of the distal axoneme. Additionally, we found significant impairment in tubulin glycylation, as well as reduced levels of intraflagellar transport proteins and of retinitis pigmentosa-associated protein RPGR. Our findings indicate that proper glutamylation levels are crucial for maintaining the molecular architecture of the photoreceptor cilium.

中文翻译：

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谷氨酰化失衡会损害感光器纤毛的分子结构。


微管由保守的 α/β-微管蛋白二聚体组成，经历复杂的翻译后修饰 （PTM），以微调其特性和与其他蛋白质的相互作用。纤毛表现出几种微管蛋白 PTM，例如多谷氨酰化、多甘氨酸化、脱酪氨酸和乙酰化，其功能尚不完全清楚。编码脱谷氨酰化酶 CCP5 的 AGBL5 突变与视网膜色素变性有关，表明改变的聚谷氨酰化可能导致感光细胞变性，但潜在机制尚不清楚。在小鼠和人感光细胞中使用超分辨率超微结构扩增显微镜 （U-ExM），我们观察到大多数微管蛋白 PTM 积聚在连接外部和内部感光器段的连接纤毛处。谷氨酰化增加（Ccp5-/- 和 Ccp1-/-）或微管蛋白乙酰化缺失 （Atat1-/-） 的小鼠模型显示，异常的谷氨酰化，而不是乙酰化丢失，破坏了外段结构。这种破坏包括连接纤毛的恶化、隆起区域的丧失和远端轴丝的不稳定。此外，我们发现微管蛋白甘氨酸化显着受损，鞭毛内转运蛋白和视网膜色素变性相关蛋白 RPGR 水平降低。我们的研究结果表明，适当的谷氨酰化水平对于维持感光器纤毛的分子结构至关重要。