Miyanoiri Youhei, Kobayashi Hisanori, Imai Takao, Watanabe Michinao, Nagata Takashi, Uesugi Seiichi, Okano Hideyuki, Katahira Masato
Department of Environment and Natural Sciences, Graduate School of Environment and Information Sciences, Yokohama National University, 79-7 Tokiwadai, Hodogaya-ku, Yokohama 240-8501, Japan.
J Biol Chem. 2003 Oct 17;278(42):41309-15. doi: 10.1074/jbc.M306210200. Epub 2003 Aug 7.
Musashi1 is an RNA-binding protein abundantly expressed in the developing mouse central nervous system. Its restricted expression in neural precursor cells suggests that it is involved in maintenance of the character of progenitor cells. Musashi1 contains two ribonucleoprotein-type RNA-binding domains (RBDs), RBD1 and RBD2, the affinity to RNA of RBD1 being much higher than that of RBD2. We previously reported the structure and mode of interaction with RNA of RBD2. Here, we have determined the structure and mode of interaction with RNA of RBD1. We have also analyzed the surface electrostatic potential and backbone dynamics of both RBDs. The two RBDs exhibit the same ribo-nucleoprotein-type fold and commonly make contact with RNA on the beta-sheet side. On the other hand, there is a remarkable difference in surface electrostatic potential, the beta-sheet of RBD1 being positively charged, which is favorable for binding negatively charged RNA, but that of RBD2 being almost neutral. There is also a difference in backbone dynamics, the central portion of the beta-sheet of RBD1 being flexible, but that of RBD2 not being flexible. The flexibility of RBD1 may be utilized in the recognition process to facilitate an induced fit. Thus, comparative studies have revealed the origin of the higher affinity of RBD1 than that of RBD2 and indicated that the affinity of an RBD to RNA is not governed by its fold alone but is also determined by its surface electrostatic potential and/or backbone dynamics. The biological role of RBD2 with lower affinity is also discussed.
Musashi1是一种在发育中的小鼠中枢神经系统中大量表达的RNA结合蛋白。它在神经前体细胞中的限制性表达表明它参与祖细胞特性的维持。Musashi1包含两个核糖核蛋白型RNA结合结构域（RBDs），即RBD1和RBD2，RBD1对RNA的亲和力远高于RBD2。我们之前报道了RBD2的结构及其与RNA的相互作用模式。在此，我们确定了RBD1的结构及其与RNA的相互作用模式。我们还分析了两个RBD的表面静电势和主链动力学。这两个RBD呈现相同的核糖核蛋白型折叠，并且通常在β-折叠面与RNA接触。另一方面，表面静电势存在显著差异，RBD1的β-折叠带正电，有利于结合带负电的RNA，而RBD2的β-折叠几乎呈中性。主链动力学也存在差异，RBD1的β-折叠中部灵活，而RBD2的β-折叠中部不灵活。RBD1的灵活性可能在识别过程中被利用以促进诱导契合。因此，比较研究揭示了RBD1比RBD2具有更高亲和力的原因，并表明RBD对RNA的亲和力不仅由其折叠决定，还由其表面静电势和/或主链动力学决定。我们还讨论了亲和力较低的RBD2的生物学作用。
