Identification and Evaluation of the Minimum Unit of a KALA Peptide Required for Gene Delivery and Immune Activation

The KALA peptide (WEAKLAKALAKALAKHLAKALAKALKA) is an amphiphilic peptide that forms an α-helical structure at physiological pH. We previously reported that, when a plasmid DNA-encapsulating liposomal membrane is modified with the KALA peptide, transgene expression and immune activation are facilitated in bone marrow-derived dendritic cells (BMDCs). However, the minimum unit of the KALA peptide and the importance of its secondary structure for these activities are not completely known at this time. We herein report on the identification of the minimum unit of the KALA peptide (short-KALA) required for activity, as determined by the stepwise removal of "K-A-L-A" units. We evaluated the activities of 4 types of short-KALAs by modifying plasmid DNA-encapsulating multi-functional envelop-type nano devices. Among the peptides tested, a short-KALA3 (WEAKLAKALAKALA) was the shortest KALA peptide that could form an α-helical structure, as well as to elicit transgene expression and immune activation in BMDCs. Furthermore, the function of the short-KALA3 as an inducer of cellular uptake was retained, while uptake was completely lost in more shortened versions of KALA (short KALA4), in that transgene expression and immunological activation were both completely lost. These collective data show that the KALA peptide must form an α-helical structure to induce cellular uptake in BMDCs.