Frontiers of Chemical Science and Engineering
>> 2016,
Volume 10,
Issue 2
doi:
10.1007/s11705-016-1556-4
RESEARCH ARTICLE
G-quadruplex formation of oligonucleotides containing ALS and FTD related GGGGCC repeat
. Slovenian NMR Center, National Institute of Chemistry, Hajdrihova 19, SI-1000, Ljubljana, Slovenia.. Faculty of Chemistry and Chemical Technology, University of Ljubljana, SI-1000, Ljubljana, Slovenia.. EN-FIST Center of Excellence, SI-1000, Ljubljana, Slovenia
Accepted: 2016-02-01
Available online: 2016-05-19
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Abstract
A largely increased number of GGGGCC repeats located in the non-coding region of gene have been identified as the leading cause of two related neurological disorders, familial amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). We examined G-quadruplex forming ability of GGGGCC-repeat containing oligonucleotides with four guanine tracts chosen as the smallest possible model to form a unimolecular G-quadruplex. These oligonucleotides are readily to folded into G-quadruplexes in the presence of K ions. However, the formation of multiple structures makes structural analysis challenging and time consuming. We observed that flanking sequences on 5'- and 3'-ends as well as mutations of loop residues have a profound effect on folding. Sequence d[(G C ) G ] was chosen for further scrutiny and optimization of nuclear magnetic resonance (NMR) spectroscopic properties with dG to 8Br-dG substitutions at specific positions in the sequence under different folding conditions. Expectedly, folding into desired predominant topology is facilitated when substituted residue adopted a conformation in the naturally-occurring structure. Single dG to 8Br-dG substitution at position 21 and fine tuning of folding conditions facilitate folding of d[(G C ) GG GG] into (mostly) a single G-quadruplex, and thus enable determination of its high-resolution structure by high-field NMR.