Transition and Regulation of MicroRNA Let-7a Conformation at the Membrane Interface by Different Ionic Solutions

The Lethal 7 (Let-7) miRNA family is attracting more and more attention in recent decades due to its capability in post-transcriptional regulation and the modulation of various physiological and pathological processes. Yet, the underlying mechanism that controls the conformation and biofunctions of Let-7 molecules during their translocation in and out of the cell membrane is still elusive. In the present study, the sum frequency generation vibrational spectroscopy (SFG-VS), a second-order nonlinear spectroscopic technique, was applied to examine the interfacial behavior of Let-7a at the lipid membrane interface. By creating the lamellar membrane environment <i>in vitro</i> with different ionic solutions, we were able to capture conformational changes in the Let-7a molecule based on the SFG spectra collected from the membrane interface after the miRNA-membrane interaction. Our results indicate that the ribose guanosine (rG) residues and ribose uridine (rU) residues of the Let-7a molecule show versatile changes as the concentration of ionic solutions increases. The analysis results also indicate that the hydrogen-bonding networks around the Let-7a molecules are greatly changed by the salt as the concentration of the NaCl and CaCl₂ solutions increases. As NaCl and CaCl₂ solution concentrations rose during experiments, we noted a marked reconfiguration of the hydrogen-bonding network around Let-7a molecules, driven by strengthened interactions between salt ions, water molecules, and Let-7a's functional groups, disrupting the original network and altering its connectivity/stability. This research offers valuable molecular-level insights into the salt-dependent conformation and behavior changes of miRNA at the lamellar lipid membrane interface. These findings also provide new perspectives for miRNA-related therapy and may help researchers in the improvement of innovative and pertinent drug delivery systems.