Protein transduction domain of translationally controlled tumor protein: characterization and application in drug delivery

Figures & data

Figure 1. The N-terminal location of TCTP-PTD in the solution structure of human TCTP (hTCTP). NMR structure of hTCTP (Feng et al., 2007) was obtained from the ExPasy website (PDB ID: 2HR9, https://swissmodel.expasy.org), SWISS-MODEL repository (Bienert et al., 2017). The major domains of hTCTP is indicated such as flexible loop, α-helical domain, and β-stranded core domain. TCTP-PTD (1-MIIYRDLISH-10) is located at N-terminus of TCTP, as highlighted with colored box.

Figure 2. Studies using the TCTP-PTD with various cargos. TCTP-PTD or its variants were complexed with various cargos by simple mixing (for insulin, exendin-4, ovalbumin, and rAd/3XG), covalent conjugation (for KLA and cyclin B1 siRNA), or fusion protein (SOD and TCTP). TCTP-PTD and their effectiveness in the delivery of therapeutics for diabetes, cancer and brain damage, and of antigens for immunization were studied.

Table 1. Examples of use of TCTP-PTD and its variants in the delivery of various cargos.

Name	Sequence	pI^a	Cargo	Method	Reference
TCTP-PTD	MIIYRDLISH	6.50	rAd/3XG	simple mixing	(Kim et al., 2011b)
			KLA	conjugation	(Kim et al., 2011a)
			Cyclin B1 siRNA	conjugation	(Jeon et al., 2019)
			SOD	fusion protein	(Lee et al., 2011)
			TCTP	fusion protein	(Maeng et al., 2013)
TCTP-PTD13	MIIFRALISHKK	11.17	insulin	simple mixing	(Bae & Lee, 2013)
			OVA	simple mixing	(Bae et al., 2016)
TCTP-PTD13M2	MIIFRLLASHKK	11.17	Exendin-4	simple mixing	(Bae et al., 2018a)
			insulin	simple mixing	(Bae et al., 2018b)

^aThe theoretical isoelectric point was calculated using the tool of the ExPasy server.

Figure 3. Role of TCTP-PTD in the regulation of intracellular and extracellular actions. TCTP itself can translocate into cells and retains its intracellular activity. Following secretion of TCTP from cells via a non-classical pathway (Amzallag et al., 2004), TCTP is subjected to proteolytic cleavage, resulting in the truncated product TCTP-PTD (1-10), liberating N11TCTP (11-172). N11TCTP is then dimerized under the specific pathologic conditions to form the histamine-releasing factor (HRF), the critical moiety responsible for the extracellular functions of TCTP (Kim et al., 2013). TCTP-PTD-truncated forms, such as N11-TCTP and dTCTP (HRF) cannot cross the plasma membrane, indicating the TCTP-PTD’s role in the plethora of TCTP functions in and out of the cell.

Table 2. Comparison of TCTP-PTD with TAT-PTD.

	TCTP-PTD	TAT-PTD
Sequence	MIIYRDLISH (TCTP 1-10)	GRKKRRQRRR (Tat 48-57)
Class	Hydrophobic PTD	Cationic PTD
Origin	Human TCTP (a housekeeping protein)	HIV-1 Tat (a transactivator of transcription)
Mechanism (Unconjugated)	Lipid-raft/caveolae-mediated endocytosis and pinocytosis (Kim et al. 2011b, 2015)	Clathrin-mediated endocytosis (Richard et al., 2005)
Cell-surface binding (Kim et al., 2011b)	Heparan sulfate-independent uptake	Heparan sulfate-dependent uptake
Localization	Non-nuclear localization (Cytoplasm/Cytoskeleton) (Kim et al. 2011b, 2015)	Nuclear localization (Chauhan et al., 2007)
Kinetics (Kim et al., 2011b)	Relatively efficient at higher concentration in later time points	Relatively efficient at lower concentration in earlier time points

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