Synthetic Mitochondria-Targeting Peptides Incorporating α-Aminoisobutyric Acid with a Stable Amphiphilic Helix Conformation in Plant Cells

In the genetic modification of plant cells, the mitochondrion is an important target in addition to the nucleus and plastid. However, gene delivery into the mitochondria of plant cells has yet to be established by conventional methods, such as particle bombardment, because of the small size and high mobility of mitochondria. To develop an efficient mitochondria-targeting signal (MTS) that functions in plant cells, we designed the artificial peptide (LURL)₃ and its analogues, which periodically feature hydrophobic α-aminoisobutyric acid (Aib, U) and cationic arginine (R), considering the consensus motif recognized by the mitochondrial import receptor Tom20. Circular dichroism measurements and molecular dynamics simulation studies revealed that (LURL)₃ had a propensity to form a stable α-helix in 0.1 M phosphate buffer solution containing 1.0 wt % sodium dodecyl sulfate. After internalization into plant cells via particle bombardment, (LURL)₃ revealed highly selective accumulation in the mitochondria, whereas its analogue (LARL)₃ was predominantly located in the vacuoles in addition to mitochondria. The high selectivity of (LURL)₃ can be attributed to the incorporation of Aib, which promotes the hydrophobic interaction between the MTS and Tom20 by increasing the hydrophobicity and helicity of (LURL)₃. The present study provided a prospective mitochondrial targeting system using the simple design of artificial peptides.