The i-motif is four-stranded DNA structure stabilized by hemiprotonated cytosine base pairs (C:C+). Although this is a very attractive structural motif for the development of devices at a nanometric scale, the requirement of acidic pH for its formation makes the i-motif occurrence in vivo controversial.

In a recent study, scientists of the Rocasolano Institute of Physical Chemistry and its associated unit with the University of Barcelona (BIOESTRAN), together with collaborators of the IRB, have found i-motif like structures in repetitive DNA sequences that are prevalent in the human genome. Most importantly, these structures are stable at physiological conditions. This is due to the particular arrangement of the C:C+ base pairs and other secondary structure elements (minor groove tetrads) which favors the cytosine protonation at neutral pH.

B.Mir, I. Serrano, D. Buitrago, M. Orozco, N. Escaja, and C. González.Prevalent sequences in the human genome can form mini i-motifs structures at physiological pH. J. Am. Chem. Soc., 139, 13985-13988, 2017. doi: 10.1021/jacs.7b07383