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Structural Insights Reveal the Dynamics of the Repeating r(CAG) Transcript Found in Huntington's Disease (HD) and Spinocerebellar Ataxias (SCAs).

Tawani A, Kumar A - PLoS ONE (2015)

Bottom Line: Moreover, mutant huntingtin protein translated from expanded r(CAG) also yields toxic effects.The overall RNA structure has helical parameters intermediate to the A- and B-forms of nucleic acids due to the global widening of major grooves and base-pair preferences near internal AA loops.The comprehension of structural behaviour by studying the spectral features and the dynamics also supports the flexible nature of the r(CAG) motif.

View Article: PubMed Central - PubMed

Affiliation: Centre for Biosciences and Biomedical Engineering, Indian Institute of Technology Indore, Indore, Madhya Pradesh, India.

ABSTRACT
In humans, neurodegenerative disorders such as Huntington's disease (HD) and many spinocerebellar ataxias (SCAs) have been found to be associated with CAG trinucleotide repeat expansion. An important RNA-mediated mechanism that causes these diseases involves the binding of the splicing regulator protein MBNL1 (Muscleblind-like 1 protein) to expanded r(CAG) repeats. Moreover, mutant huntingtin protein translated from expanded r(CAG) also yields toxic effects. To discern the role of mutant RNA in these diseases, it is essential to gather information about its structure. Detailed insight into the different structures and conformations adopted by these mutant transcripts is vital for developing therapeutics targeting them. Here, we report the crystal structure of an RNA model with a r(CAG) motif, which is complemented by an NMR-based solution structure obtained from restrained Molecular Dynamics (rMD) simulation studies. Crystal structure data of the RNA model resolved at 2.3 Å reveals non-canonical pairing of adenine in 5´-CAG/3´-GAC motif samples in different syn and anti conformations. The overall RNA structure has helical parameters intermediate to the A- and B-forms of nucleic acids due to the global widening of major grooves and base-pair preferences near internal AA loops. The comprehension of structural behaviour by studying the spectral features and the dynamics also supports the flexible nature of the r(CAG) motif.

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Portion of 300ms NOESY spectrum showing base to 1´ region for the sequence for 5´ r(CCGCAGCGG)2 at different temperatures A. 288 K and B. 308 K.The distances marked in the spectra shows the perturbation owing to change in temperature.
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pone.0131788.g006: Portion of 300ms NOESY spectrum showing base to 1´ region for the sequence for 5´ r(CCGCAGCGG)2 at different temperatures A. 288 K and B. 308 K.The distances marked in the spectra shows the perturbation owing to change in temperature.

Mentions: NOESY walk examines the sequential connectivity to sugars and succeeding base protons [60]. The sequential assignment for the 5´ r(CCGCAGCGG)2 duplex in NOESY spectra collected at 300 ms mixing time at two different temperatures, 288 and 308 K, show that the interproton distance between A5H8 and G6H8 increases with increasing temperature. This result indicates the existence of adenine conformational dynamics. In addition, the A5H1´- A5H2 cross peak intensity also varied with a change in temperature (Fig 6A and 6B). This change in intranucleotide (A5) resonance peak intensity also indicates the probability of adenine dynamics. Similarly, disappearance of the cross peak between C4H5 and A5H8 at 308 K further supports the above results (Fig 6B).


Structural Insights Reveal the Dynamics of the Repeating r(CAG) Transcript Found in Huntington's Disease (HD) and Spinocerebellar Ataxias (SCAs).

Tawani A, Kumar A - PLoS ONE (2015)

Portion of 300ms NOESY spectrum showing base to 1´ region for the sequence for 5´ r(CCGCAGCGG)2 at different temperatures A. 288 K and B. 308 K.The distances marked in the spectra shows the perturbation owing to change in temperature.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4493008&req=5

pone.0131788.g006: Portion of 300ms NOESY spectrum showing base to 1´ region for the sequence for 5´ r(CCGCAGCGG)2 at different temperatures A. 288 K and B. 308 K.The distances marked in the spectra shows the perturbation owing to change in temperature.
Mentions: NOESY walk examines the sequential connectivity to sugars and succeeding base protons [60]. The sequential assignment for the 5´ r(CCGCAGCGG)2 duplex in NOESY spectra collected at 300 ms mixing time at two different temperatures, 288 and 308 K, show that the interproton distance between A5H8 and G6H8 increases with increasing temperature. This result indicates the existence of adenine conformational dynamics. In addition, the A5H1´- A5H2 cross peak intensity also varied with a change in temperature (Fig 6A and 6B). This change in intranucleotide (A5) resonance peak intensity also indicates the probability of adenine dynamics. Similarly, disappearance of the cross peak between C4H5 and A5H8 at 308 K further supports the above results (Fig 6B).

Bottom Line: Moreover, mutant huntingtin protein translated from expanded r(CAG) also yields toxic effects.The overall RNA structure has helical parameters intermediate to the A- and B-forms of nucleic acids due to the global widening of major grooves and base-pair preferences near internal AA loops.The comprehension of structural behaviour by studying the spectral features and the dynamics also supports the flexible nature of the r(CAG) motif.

View Article: PubMed Central - PubMed

Affiliation: Centre for Biosciences and Biomedical Engineering, Indian Institute of Technology Indore, Indore, Madhya Pradesh, India.

ABSTRACT
In humans, neurodegenerative disorders such as Huntington's disease (HD) and many spinocerebellar ataxias (SCAs) have been found to be associated with CAG trinucleotide repeat expansion. An important RNA-mediated mechanism that causes these diseases involves the binding of the splicing regulator protein MBNL1 (Muscleblind-like 1 protein) to expanded r(CAG) repeats. Moreover, mutant huntingtin protein translated from expanded r(CAG) also yields toxic effects. To discern the role of mutant RNA in these diseases, it is essential to gather information about its structure. Detailed insight into the different structures and conformations adopted by these mutant transcripts is vital for developing therapeutics targeting them. Here, we report the crystal structure of an RNA model with a r(CAG) motif, which is complemented by an NMR-based solution structure obtained from restrained Molecular Dynamics (rMD) simulation studies. Crystal structure data of the RNA model resolved at 2.3 Å reveals non-canonical pairing of adenine in 5´-CAG/3´-GAC motif samples in different syn and anti conformations. The overall RNA structure has helical parameters intermediate to the A- and B-forms of nucleic acids due to the global widening of major grooves and base-pair preferences near internal AA loops. The comprehension of structural behaviour by studying the spectral features and the dynamics also supports the flexible nature of the r(CAG) motif.

No MeSH data available.


Related in: MedlinePlus