Tat (transactivator of transcription), a cell penetrating peptide (CPP) is commonly used to deliver DNA across membranes in order to overcome the issues proposed by low transfection efficiency in cell culture [1]. It consists of up to 35 amino acids of the HIV-1 full length protein Tat, whose penetrating activity is supposed to be induced by guanidinium groups [2].

TAT-LK15 is a short fusion peptide comprised of Tat and the synthetic LK15 peptide [1]. Adding LK15 results in improved transport efficiency across the cell membrane. LK15 consists of 15 amino acids, which are all either leucine (L) or lysine (K) residue, resulting in an amphipathic protein [1].

Tat-LK15 has been reported to significantly increase the transport of nucleic acids through membranes, which allows for novel transfection protocols [1]. Moreover, Saleh et al. (2010) demonstrated that Tat-LK15/DNA complex treatment results in stronger leakage of the membrane, which could be causing the increased transfection activity [1].

With introducing Tat-LK15 to the iGEM registry, we have improved Tat (BBa_K1202006). Furthermore, using our software tool C3Pred (Software), we confirmed that the improvement confers to a higher penetrability. Exemplarily chosen cell penetrating peptides were evaluated for their penetrability (Fig. 1). Our tool shows that the penetrative activity of Tat is about 45.97, while Tat-LK15 has an activity of 228.81, a large improvement.