Yang Jeong Bin, Kim Kwang Sub, Heo Jiwon, Chung Jeong Min, Jung Hyun Suk
Division of Chemistry and Biochemistry, College of Natural Sciences, Kangwon National University, Chuncheon, Gangwon, South Korea.
Department of Biotechnology, The Catholic University of Korea, Bucheon, Gyeonggi, South Korea.
Front Cell Dev Biol. 2022 Nov 4;10:1022096. doi: 10.3389/fcell.2022.1022096. eCollection 2022.
Actin is a multifunctional biomolecule that forms not only basic structural bodies such as filopodia and lamellipodia, but also large microvilli-like organelles like stereocilia. Actin consists of four sub-domains (S1, S2, S3, and S4), and the "target-binding groove" formed between S1 and S3 is the major binding site for various actin binding proteins. Actin filament dynamics are regulated by numerous actin binding proteins with different mechanisms of actin binding, assembly, and disassembly such as actin severing, branching, and bundling. Ectoplasmic specialization protein 1 (espin 1) is an actin binding and bundling protein that is specifically implicated in the elongation and stabilization of stereocilia as a binding partner with myosin III. However, little is known about the molecular structure, actin bundling, and stabilizing mechanism of espin 1; hence, we investigated the interaction between actin and espin 1 through structural data. In this study, we first purified human espin 1 in an system following a new detergent-free approach and then demonstrated the 2D structure of full-length espin 1 using transmission electron microscopy along with Nickel nitrilotriacetic acid nanogold labeling and 2D averaging using SPIDER. Furthermore, we also determined the espin 1 binding domain of actin using a co-sedimentation assay along with gelsolin and myosin S1. These findings are not only beneficial for understanding the actin binding and bundling mechanism of espin 1, but also shed light on its elongation, stabilization, and tip-localization mechanisms with myosin III. This study thus provides a basis for understanding the molecular structure of espin 1 and can contribute to various hearing-related diseases, such as hearing loss and vestibular dysfunction.
肌动蛋白是一种多功能生物分子，它不仅形成诸如丝状伪足和片状伪足等基本结构体，还形成像静纤毛这样的大型微绒毛样细胞器。肌动蛋白由四个亚结构域（S1、S2、S3和S4）组成，S1和S3之间形成的“靶标结合凹槽”是各种肌动蛋白结合蛋白的主要结合位点。肌动蛋白丝动力学受众多具有不同肌动蛋白结合、组装和拆卸机制的肌动蛋白结合蛋白调控，如肌动蛋白切断、分支和捆绑。胞质特化蛋白1（espin 1）是一种肌动蛋白结合和捆绑蛋白，作为与肌球蛋白III的结合伙伴，它特别参与静纤毛的伸长和稳定。然而，关于espin 1的分子结构、肌动蛋白捆绑和稳定机制知之甚少；因此，我们通过结构数据研究了肌动蛋白与espin 1之间的相互作用。在本研究中，我们首先采用一种新的无去污剂方法在一个系统中纯化了人espin 1，然后使用透射电子显微镜以及镍三乙酸纳米金标记和SPIDER二维平均法展示了全长espin 1的二维结构。此外，我们还使用共沉降测定法以及凝溶胶蛋白和肌球蛋白S1确定了肌动蛋白的espin 1结合结构域。这些发现不仅有助于理解espin 1的肌动蛋白结合和捆绑机制，还揭示了其与肌球蛋白III的伸长、稳定和尖端定位机制。因此，本研究为理解espin 1的分子结构提供了基础，并有助于研究各种与听力相关的疾病，如听力损失和前庭功能障碍。
