Artificial Cell-Penetrating Peptide Containing Periodic α-Aminoisobutyric Acid with Long-Term Internalization Efficiency in Human and Plant Cells

Cell-penetrating peptides (CPPs) have been widely utilized as efficient molecular tools for the delivery of bioactive cargoes such as peptides, proteins, and genetic material. However, to improve their versatility as tools in biological environments, the resistance of CPPs to enzymatic degradation and their structural stability must be improved to achieve long-term efficacy. Here we designed and synthesized novel artificial CPPs, poly(LysAibXaa), containing periodic alpha-aminoisobutyric acid (Aib) and L-lysine by chemoenzymatic polymerization. Poly(LysAibAla) tended to form 3(10)- and alpha-helical structures under the amphiphilic cell-membrane-mimicking environment. Poly(LysAibXaa) exhibited long-term internalization and thus high accumulation in live cells, which is attributed to the improvement in the resistance to proteolytic digestion as a result of the incorporation of Aib residues into the peptide backbone. We presented a simple molecular design and synthesis of efficient CPPs applicable to both human and plant cells with long-term stability and negligible cytotoxicity.