(349h) Regulation of Nucleic Acid Conformation on Liposomal Membrane Surface

Nucleic acid molecules can be used as therapeutic agents in genetic level. Because of their unstable molecular properties in vivo, thus it would be impossible to administer nucleic acid molecules directly as drugs. Liposomes are usually employed as cargo for nucleic acid, but most of reported works have focused only on “delivery” to the target site. Recently, it has been reported that liposomes accumulate biopolymers such as nucleic acid molecules in the surface layer and act as a field to change their structure and function. The conformation of nucleic acids composed only of cytosine bases, called i-motif, can be also used in controlling gene expression.

The aim of this research is to investigate the detail interaction between liposomes and nucleic acid molecules. To achieve this, the interaction between nucleic acid molecules that forms "i-motif" were studied. Isothermal titration calorimetry (ITC) was used to measure the caloric change associated with the interaction of nucleic acid molecules. It was proven that the adsorption of Cytosine bases (polyC) onto the liposome membrane was only observed while no adsorption of other bases (A, T, G). The i-motif of Cytosine bases are formed by 4 strands in equilibrium. Focusing on polyC, the effect of nucleic acid chain length was estimated. It is reported that i-motif of polyC can be formed in acidic pH condition. Based on circular dichroism spectroscopy, it was estimated that the i-motif structures of polyC_[10mer], polyC_[25mer], and polyC_[50mer] were formed at the pH < 6.23, pH < 7.42, and pH < 7.50, respectively. Furthermore, the interaction between polyC_[10mer] and DOPC liposomes could be confirmed by the decrease of membrane fluidity. As conclusion, the conformation of nucleic acid molecules can be varied at the liposomal membrane surface, which can be a novel strategy to control the function of nuclei acid molecules in gene therapy.

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