Design and evaluation of variants of the protein transduction domain originated from translationally controlled tumor protein

Protein transduction domains (PTDs) have been successfully employed to deliver therapeutic cargos both in vitro and in vivo because of their cellular penetrating ability. We previously reported that a 10-amino acid peptide (MIIYRDLISH) derived from the NH₂-terminus of human translationally controlled tumor protein (TCTP) functions as a PTD. TCTP-PTD is quite different from other well-known PTDs in its hydrophobic composition and structural character, and the sequence requirements for transduction remain unknown. To identify the role of each residue, we compared the cellular uptake of various deletion mutants and Ala substituents of TCTP-PTD. The results showed that the amino terminal residues and the hydrophobic nature of the peptide, with a minimal length of nine residues, were necessary for transduction. Based on the elucidated sequence requirements, we designed and evaluated variants to improve the efficiency and solubility through sequential modification of TCTP-PTD. During the optimization process, we also delineated the contribution of residues and the advantageous composition of sequences for cellular uptake.