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==Solution NMR structure of a 14-mer dsDNA complexed with a novel NIR fluorescent probe QCy-DT==
<StructureSection load='6ijv' size='340' side='right'caption='[[6ijv]]' scene=''>
== Structural highlights ==
<table><tr><td colspan='2'>[[6ijv]] is a 2 chain structure with sequence from [https://en.wikipedia.org/wiki/Homo_sapiens Homo sapiens]. Full experimental information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=6IJV OCA]. For a <b>guided tour on the structure components</b> use [https://proteopedia.org/fgij/fg.htm?mol=6IJV FirstGlance]. <br>
</td></tr><tr id='ligand'><td class="sblockLbl"><b>[[Ligand|Ligands:]]</b></td><td class="sblockDat" id="ligandDat"><scene name='pdbligand=QCY:2,2-{(4-hydroxy-1,3-phenylene)di[(E)ethene-2,1-diyl]}bis(3-methyl-1,3-benzothiazol-3-ium)'>QCY</scene></td></tr>
<tr id='resources'><td class="sblockLbl"><b>Resources:</b></td><td class="sblockDat"><span class='plainlinks'>[https://proteopedia.org/fgij/fg.htm?mol=6ijv FirstGlance], [http://oca.weizmann.ac.il/oca-bin/ocaids?id=6ijv OCA], [https://pdbe.org/6ijv PDBe], [https://www.rcsb.org/pdb/explore.do?structureId=6ijv RCSB], [https://www.ebi.ac.uk/pdbsum/6ijv PDBsum], [https://prosat.h-its.org/prosat/prosatexe?pdbcode=6ijv ProSAT]</span></td></tr>
</table>
<div style="background-color:#fffaf0;">
== Publication Abstract from PubMed ==
The discovery of small molecules that exhibit turn-on far-red or near-infrared (NIR) fluorescence upon DNA binding and understanding how they bind DNA are important for imaging and bioanalytical applications. Here we report the DNA-bound structure and the DNA binding mechanism of quinone cyanine dithiazole (QCy-DT), a recently reported AT-specific turn-on NIR fluorescent probe for double-stranded DNA. The nuclear magnetic resonance (NMR)-derived structure showed minor groove binding but no specific ligand-DNA interactions, consistent with an endothermic and entropy-driven binding mechanism deduced from isothermal titration calorimetry. Minor groove binding is typically fast because it minimally perturbs the DNA structure. However, QCy-DT exhibited unusually slow DNA binding. The cyanine-based probe is capable of cis-trans isomerization due to overlapping methine bridges, with 16 possible slowly interconverting cis/trans isomers. Using NMR, density functional theory, and free energy calculations, we show that the DNA-free and DNA-bound environments of QCy-DT prefer distinctly different isomers, indicating that the origin of the slow kinetics is a cis-trans isomerization and that the minor groove preferentially selects an otherwise unstable cis/trans isomer of QCy-DT. Flux analysis showed the conformational selection pathway to be the dominating DNA binding mechanism at low DNA concentrations, which switches to the induced fit pathway at high DNA concentrations. This report of cis/trans isomerization of a ligand, upon binding the DNA minor groove, expands the prevailing understanding of unique discriminatory powers of the minor groove and has an important bearing on using polymethine cyanine dyes to probe the kinetics of molecular interactions.

DNA Minor Groove-Induced cis-trans Isomerization of a Near-Infrared Fluorescent Probe.,Ganguly S, Murugan NA, Ghosh D, Narayanaswamy N, Govindaraju T, Basu G Biochemistry. 2021 Jun 18. doi: 10.1021/acs.biochem.1c00281. PMID:34142803<ref>PMID:34142803</ref>

From MEDLINE&reg;/PubMed&reg;, a database of the U.S. National Library of Medicine.<br>
</div>
<div class="pdbe-citations 6ijv" style="background-color:#fffaf0;"></div>
== References ==
<references/>
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</StructureSection>
[[Category: Homo sapiens]]
[[Category: Large Structures]]
[[Category: Basu G]]
[[Category: Ganguly S]]