Destabilization of tetraplex structures of the fragile X repeat sequence (CGG)n is mediated by homolog-conserved domains in three members of the hnRNP family

Abstract

Hairpin or tetrahelical structures formed by a d(CGG)n sequence in the FMR1 gene are thought to promote expansion of the repeat tract. Subsequent to this expansion FMR1 is silenced and fragile X syndrome ensues. The injurious effects of d(CGG)n secondary structures may potentially be countered by agents that act to decrease their stability. We showed previously that the hnRNP-related protein CBF-A destabilized G'2 bimolecular tetraplex structures of d(CGG)n. Analysis of mutant proteins revealed that the CBF-A-conserved domains RNP11 and ATP/GTP binding box were sufficient and necessary for G'2 d(CGG)n disruption while the RNP21 motif inhibited the destabilization activity. Here, we report that a C-terminal fragment of CBF-A whose only remaining conserved domain was the ATP/GTP binding motif, disrupted G'2 d(CGG)n more selectively than wild-type CBF-A. Further, two additional members of the hnRNP family, hnRNP A2 and mutant hnRNP A1 effectively destabilized G'2 d(CGG)n. Examination of mutant hnRNP A2 proteins revealed that, similar to CBF-A, their RNP11 element and ATP/GTP binding motif mediated G'2 d(CGG)n disruption, while the RNP21 element blocked their action. Similarly, the RNP11 and RNP21 domains of hnRNP A1 were, respectively, positive and negative mediators of G'2 d(CGG)n destabilization. Last, employing the same conserved motifs that mediated disruption of the DNA tetraplex G'2 d(CGG)n, hnRNP A2 destabilized r(CGG)n RNA tetraplex.

Structural Diversity of Triplet Repeat RNAs

“…In a more recent NMR study, G/G mismatches were shown to exist in a dynamic equilibrium between the anti-and syn-conformations required to form two symmetric hydrogen bonds between the N1 and carbonyl oxygen atoms of two guanines (31). The CGG repeats were also reported to form G-quadruplexes in both RNA (11)(12)(13) and DNA (14,15). In the current study, we analyzed the structural features of CGG and other types of CNG repeats under identical conditions using biochemical and biophysical methods.…”

Translational Repression of the Disintegrin and Metalloprotease ADAM10 by a Stable G-quadruplex Secondary Structure in Its 5′-Untranslated Region

“…Therefore, methylation of RGG motifs in FMRP by PMRT1 might regulate the interaction of FMRP with polyribosomes and G-quadruplex-containing mRNAs (81). In addition, members of the hnRNP A family were reported to destabilize G-quadruplex structures by a so-far unknown mechanism (44,82). Apart from FMRP and hnRNP A, there are several proteins described that are able to interact and modify G-quadruplex structures in DNA and RNA substrates.…”

Hnrpab regulates neural development and neuron cell survival after glutamate stimulation

“…Neither bona fide Hnrpab RNA-binding sites nor consensus sites have been identified; however, its preference for G-and/or U-rich RNA or DNA has been reported (Kumar et al 1987;Sarig et al 1997;Khateb et al 2004;Raju et al 2008). Hnrpab1 specifically associates with AU-rich stability elements (AREs) of some mRNAs, suggesting a role in cell-type and differentiation-regulated mRNA stability for at least some mRNAs.…”