Division of Biomedical Sciences, University of California, Riverside, Riverside, CA 92521, USA.
Division of Biomedical Sciences, University of California, Riverside, Riverside, CA 92521, USA.
J Mol Biol. 2020 Jun 26;432(14):4154-4166. doi: 10.1016/j.jmb.2020.04.025. Epub 2020 May 1.
The actin cytoskeleton plays a pivotal role in cell development, morphogenesis, and other cellular functions. Precise control of actin dynamics requires actin-binding proteins. Here, we characterize multifarious regulation of SHTN1 (shootin1) and show that, unlike known actin-binding proteins, SHTN1's actin binding activity is intrinsically inhibited by a putative coiled-coil domain (CCD) and the autoinhibition is overcome by alternative splicing regulation. We found SHTN1 contains a noncanonical WH2 domain and an upstream proline-rich region (PRR) that by themselves are sufficient for actin interaction. Alternative splicing of Shtn1 at the C terminus and downstream of the WH2-PRR domain produces a long (SHTN1L or shootin1b) and a short (SHTN1S or shootin1a) isoform, which both contain the described PRR and WH2 domains. However, SHTN1S does not interact with actin due to inhibition mediated by an N-terminal CCD. A SHTN1L-specific C-terminal motif counters the intramolecular inhibition and allows SHNT1L to bind actin. A nuclear localization signal is embedded between PRR and WH2 and is subject to similar autoinhibition. SHTN1 would be the first WH2-containing molecule that adopts CCD-dependent autoinhibition and alternative splicing-dependent actin interaction.
肌动蛋白细胞骨架在细胞发育、形态发生和其他细胞功能中起着关键作用。肌动蛋白动力学的精确控制需要肌动蛋白结合蛋白。在这里，我们描述了 SHTN1（shootin1）的多种调节方式，并表明与已知的肌动蛋白结合蛋白不同，SHTN1 的肌动蛋白结合活性被假定的卷曲螺旋结构域（CCD）内在抑制，而自动抑制是通过选择性剪接调节来克服的。我们发现 SHTN1 包含一个非典型的 WH2 结构域和一个上游富含脯氨酸的区域（PRR），它们本身足以与肌动蛋白相互作用。Shtn1 在 WH2-PRR 结构域的 C 末端和下游的选择性剪接产生一个长（SHTN1L 或 shootin1b）和一个短（SHTN1S 或 shootin1a）异构体，它们都包含所述的 PRR 和 WH2 结构域。然而，由于 N 端 CCD 介导的抑制，SHTN1S 不能与肌动蛋白相互作用。SHTN1L 特异性的 C 末端基序抵消了分子内抑制，使 SHNT1L 能够与肌动蛋白结合。一个核定位信号位于 PRR 和 WH2 之间，也受到类似的自动抑制。SHTN1 将是第一个采用 CCD 依赖性自动抑制和选择性剪接依赖性肌动蛋白相互作用的含有 WH2 的分子。
