Limits...
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.

No MeSH data available.


Related in: MedlinePlus

The secondary structure and refined structure of the RNA construct 5´ r(UUGGGCCAGCAGCAGGUCC)2.A. The secondary structure of oligonucleotide r(CAG) repeat duplex model that allowed crystal growth. B. The global structure of the RNA including the electron density map at 1.0 σ C. The electron density map of non-canonical A-A pairs at 1.0σ. D. The backbone structure of the RNA construct.
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4493008&req=5

pone.0131788.g001: The secondary structure and refined structure of the RNA construct 5´ r(UUGGGCCAGCAGCAGGUCC)2.A. The secondary structure of oligonucleotide r(CAG) repeat duplex model that allowed crystal growth. B. The global structure of the RNA including the electron density map at 1.0 σ C. The electron density map of non-canonical A-A pairs at 1.0σ. D. The backbone structure of the RNA construct.

Mentions: The RNA duplex was constructed to contain 5´ UU dangling ends and a duplex region flanking the three CAG motifs. The duplex region adjacent to the 5´-CAG/3´-GAC motifs imparts stability to the duplex and may be used for phasing (Fig 1A). These regions non-covalently bind to heavy atoms and heavy atom derivatives, which were used to infer the phases lost during data collection [50]. Electron density maps contoured at 1.0 σ for the AA internal loops were in accordance with different conformations of the internal AA loops (Fig 1B). The central AA internal loop and one of the terminal 1x1 nucleotide AA internal loops have both adenines in an anti conformation. Despite being in the anti conformation, one of the A's in the central AA internal loop was slightly tilted and did not have well-defined electron density (Fig 1C). This observation stipulates a dynamic nature for the AA internal loop. In addition, the third AA internal loop had one of the A’s in the syn conformation with the other in the anti conformation.


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)

The secondary structure and refined structure of the RNA construct 5´ r(UUGGGCCAGCAGCAGGUCC)2.A. The secondary structure of oligonucleotide r(CAG) repeat duplex model that allowed crystal growth. B. The global structure of the RNA including the electron density map at 1.0 σ C. The electron density map of non-canonical A-A pairs at 1.0σ. D. The backbone structure of the RNA construct.
© Copyright Policy
Related In: Results  -  Collection

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

pone.0131788.g001: The secondary structure and refined structure of the RNA construct 5´ r(UUGGGCCAGCAGCAGGUCC)2.A. The secondary structure of oligonucleotide r(CAG) repeat duplex model that allowed crystal growth. B. The global structure of the RNA including the electron density map at 1.0 σ C. The electron density map of non-canonical A-A pairs at 1.0σ. D. The backbone structure of the RNA construct.
Mentions: The RNA duplex was constructed to contain 5´ UU dangling ends and a duplex region flanking the three CAG motifs. The duplex region adjacent to the 5´-CAG/3´-GAC motifs imparts stability to the duplex and may be used for phasing (Fig 1A). These regions non-covalently bind to heavy atoms and heavy atom derivatives, which were used to infer the phases lost during data collection [50]. Electron density maps contoured at 1.0 σ for the AA internal loops were in accordance with different conformations of the internal AA loops (Fig 1B). The central AA internal loop and one of the terminal 1x1 nucleotide AA internal loops have both adenines in an anti conformation. Despite being in the anti conformation, one of the A's in the central AA internal loop was slightly tilted and did not have well-defined electron density (Fig 1C). This observation stipulates a dynamic nature for the AA internal loop. In addition, the third AA internal loop had one of the A’s in the syn conformation with the other in the anti conformation.

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