A peptide-oligonucleotide conjugate (1) was synthesized by the attachment of FAM, TAMRA, and biotin moieties to a telomere DNA sequence of 5'-TAG GGT TAG GGT TAG GGT TAG GG-3'. This conjugate was induced to be an anti-parallel structure in the presence of sodium ion (Na+), whereas a hybrid one was formed under potassium ion (K+) as a monitoring by circular dichromic spectra. The conformation change of this conjugate gave an effective FRET signal change upon the addition of NaCl, compared with the case of KCl. Under 5 mM KCl as an extracellular condition, a FRET change was observed upon addition of NaCl and quantitative FRET change was observed in 0 - 250 mM NaCl. This conjugate was immobilized on the cell surface through a sugar chain on the cell, biotinyl concanavallin A and streptavidin. This conjugate was utilized for Na+ sensing based on anti-parallel tetraplex formation with Na+.
Keywords: FAM; Peptide-oligonucleotide conjugate; TAMRA; antiparallel tetraplex; fluorometric imaging; hybrid tetraplex; potassium ion; sodium ion.