AUTHOR=Sato Shinobu , Ohzawa Shinsuke , Sota Kojiro , Sakamoto Naoto , Udo Ayano , Sueda Shinji , Matsuda Tomoki , Nagai Takeharu , Takenaka Shigeori TITLE=Fluorescence Imaging of Extracellular Potassium Ion Using Potassium Sensing Oligonucleotide JOURNAL=Frontiers in Chemistry VOLUME=10 YEAR=2022 URL=https://www.frontiersin.org/journals/chemistry/articles/10.3389/fchem.2022.922094 DOI=10.3389/fchem.2022.922094 ISSN=2296-2646 ABSTRACT=

Potassium-sensing oligonucleotide, PSO, a conjugate of a quadruplex structure-forming oligonucleotide with a peptide incorporating a Förster Resonance Energy Transfer (FRET) chromophore pair, has been developed for fluorescent detection of potassium ion (K⁺) in aqueous medium. PSO 1 could be introduced into cells for real-time imaging of cytoplasmic K⁺ concentrations. To perform fluorescent imaging of K⁺ on the cell surface, we synthesized twelve PSO derivatives with different types of peptide types and lengths, and oligonucleotide sequences including thrombin-binding aptamer (TBA) sequences with FAM and TAMRA as a FRET chromophore pair, and evaluated their performance. 1 was shown to respond selectively to K⁺, not to most ions present in vivo, and to show reciprocal fluorescence changes in response to K⁺ concentration. For the peptide chains and oligonucleotide sequences examined in this study, the PSO derivatives had K_d values for K⁺ in the range of 5–30 mM. All PSO derivatives showed high K⁺ selectivity even in the presence of excess Na⁺. The PSO derivatives were successfully localized to the cell surface by biotinylated concanavalin A (ConA) or sulfo-NHS-biotin via streptavidin (StAv). Fluorescence imaging of extracellular K⁺ upon addition of apoptosis inducers was successfully achieved by 1 localized to the cell surface.