Schmidt Tobias, Knick Paul, Lilie Hauke, Friedrich Susann, Golbik Ralph Peter, Behrens Sven-Erik
Institute of Biochemistry and Biotechnology (NFI), Section Microbial Biotechnology, Martin Luther University Halle-Wittenberg, Kurt-Mothes-Str. 3, D-06120 Halle/Saale, Germany.
Section Protein Biochemistry, Martin Luther University Halle-Wittenberg, Kurt-Mothes-Str. 3, D-06120 Halle/Saale, Germany.
Biochem J. 2017 Jan 15;474(2):259-280. doi: 10.1042/BCJ20160790. Epub 2016 Nov 14.
Nuclear factor 90 (NF90) is an RNA-binding protein (RBP) that regulates post-transcriptionally the expression of various mRNAs. NF90 was recently shown to be capable of discriminating between different RNA substrates. This is mediated by an adaptive and co-operative interplay between three RNA-binding motifs (RBMs) in the protein's C-terminus. In many cell types, NF90 exists predominantly in a complex with NF45. Here, we compared the RNA-binding properties of the purified NF90 monomer and the NF90-NF45 heterodimer by biophysical and biochemical means, and demonstrate that the interaction with NF45 considerably affects the characteristics of NF90. Along with a thermodynamic stabilization, complex formation substantially improves the RNA-binding capacity of NF90 by modulating its binding mode and by enhancing its affinity for single- and double-stranded RNA substrates. Our data suggest that features of both the N- and C-termini of NF90 participate in the heterodimerization with NF45 and that the formation of NF90-NF45 changes the conformation of NF90's RBMs to a status in which the co-operative interplay of the RBMs is optimal. NF45 is considered to act as a conformational scaffold for NF90's RBMs, which alters the RNA-binding specificity of NF90. Accordingly, the monomeric NF90 and the NF90-NF45 heterodimer may exert different functions in the cell.
核因子90（NF90）是一种RNA结合蛋白（RBP），可在转录后调节各种mRNA的表达。最近研究表明，NF90能够区分不同的RNA底物。这是由该蛋白C末端的三个RNA结合基序（RBM）之间的适应性协同相互作用介导的。在许多细胞类型中，NF90主要与NF45形成复合物存在。在这里，我们通过生物物理和生化方法比较了纯化的NF90单体和NF90-NF45异二聚体的RNA结合特性，并证明与NF45的相互作用会显著影响NF90的特性。除了热力学稳定作用外，复合物的形成还通过调节其结合模式并增强其对单链和双链RNA底物的亲和力，大大提高了NF90的RNA结合能力。我们的数据表明，NF90的N末端和C末端的特征都参与了与NF45的异二聚化，并且NF90-NF45的形成将NF90的RBM构象改变为RBM协同相互作用最佳的状态。NF45被认为是NF90的RBM的构象支架，它改变了NF90的RNA结合特异性。因此，单体NF90和NF90-NF45异二聚体可能在细胞中发挥不同的功能。
