Molecular Biophysics Unit, Indian Institute of Science, Bengaluru 560012, India.
NMR Research Centre, Indian Institute of Science, Bengaluru 560012, India.
Nucleic Acids Res. 2018 Nov 2;46(19):10246-10261. doi: 10.1093/nar/gky854.
hnRNPA1 is a member of heteronuclear ribonucleoproteins that has been shown to promote telomere elongation apart from its roles in RNA transport and alternative splicing. It is a modular protein with an N-terminal domain called UP1 that consists of two RNA Recognition Motifs (RRM1 and RRM2 domains) and a C-terminal region that harbors functional motifs such as RGG-box, a prion-like domain, and a nuclear shuttling sequence. UP1 has been reported to bind and destabilize telomeric DNA G-quadruplexes and thereby participate in DNA telomere remodeling. An RGG-box motif that consists of four RGG repeats (containing arginine and glycine residues) is located C-terminal to the UP1 domain and constitutes an additional nucleic acid and protein-binding domain. However, the precise role of the RGG-box of hnRNPA1 in telomere DNA recognition and G-quadruplex DNA unfolding remains unexplored. Here, we show that the isolated RGG-box interacts specifically with the structured telomere G-quadruplex DNA but not with the single-stranded DNA. Further the interaction of the RGG-box with the G-quadruplex DNA is dependent on the loop nucleotides of the G-quadruplex. Finally, we show that the RGG-box enhances the G-quadruplex unfolding activity of the adjacent UP1 domain. We propose that UP1 and RGG-box act synergistically to achieve complete telomere G-quadruplex DNA unfolding.
hnRNPA1 是核不均一核糖核蛋白的成员,它除了在 RNA 转运和选择性剪接中的作用外,还被证明可以促进端粒的延长。它是一种具有模块化结构的蛋白质,其 N 端结构域称为 UP1,由两个 RNA 识别基序(RRM1 和 RRM2 结构域)和一个 C 端区域组成,该区域包含功能基序,如 RGG 盒、类朊病毒结构域和核穿梭序列。已有报道称 UP1 可以结合并破坏端粒 DNA G-四链体,从而参与 DNA 端粒重塑。位于 UP1 结构域 C 端的 RGG 盒基序由四个 RGG 重复(包含精氨酸和甘氨酸残基)组成,构成了另一个核酸和蛋白质结合结构域。然而,hnRNPA1 的 RGG 盒在端粒 DNA 识别和 G-四链体 DNA 展开中的精确作用仍未被探索。在这里,我们表明分离的 RGG 盒与结构域化的端粒 G-四链体 DNA 特异性相互作用,但不与单链 DNA 相互作用。此外,RGG 盒与 G-四链体 DNA 的相互作用依赖于 G-四链体的环核苷酸。最后,我们表明 RGG 盒增强了相邻 UP1 结构域的 G-四链体展开活性。我们提出 UP1 和 RGG 盒协同作用以实现完整的端粒 G-四链体 DNA 展开。