Cell-penetrating peptides (CPPs) are short peptides that can cross cell membranes. CPPs enable the delivery of biomolecules into cells and can act as drug-delivery vectors. Because recombinant production of CPPs as fusions to protein “cargo” leads to low yields for some CPP-cargo fusions, approaches to enhance the recombinant expression of peptide-cargo fusions need to be identified. We optimized expression conditions in Escherichia coli for fusions of CPPs (SynB, histatin-5, and MPG) to the cargo proteins biotin carboxyl carrier protein, maltose-binding protein, and green fluorescent protein. We used Western blotting to evaluate induction temperatures of 37, 30, and 20°C, and induction times of 6, 10, and 24 h. Glutathione-S-transferase was incorporated as a fusion partner to improve expression. In general, expression at 37°C for 6 and 10 h led to the highest levels of expression for the different CPP-cargo constructs. The improvements in expression of CPP-cargo fusions will allow higher yields of CPP-cargo fusions for studies of their translocation into cells.

1.
Albarran B, To R, Stayton PS: A TAT-streptavidin fusion protein directs uptake of biotinylated cargo into mammalian cells. Protein Eng Des Sel 2005; 18: 147–152.
2.
Alhakamy NA, Nigatu AS, Berkland CJ, Ramsey JD: Noncovalently associated cell-penetrating peptides for gene delivery applications. Ther Deliv 2013; 4: 741–757.
3.
Beloor J, Zeller S, Choi CS, Lee SK, Kumar P: Cationic cell-penetrating peptides as vehicles for siRNA delivery. Ther Deliv 2015; 6: 491–507.
4.
Chalfie M, Tu Y, Euskirchen G, Ward WW, Prasher DC: Green fluorescent protein as a marker for gene expression. Science 1994; 263: 802–805.
5.
Choi-Rhee E, Cronan JE: The biotin carboxylase-biotin carboxyl carrier protein complex of Escherichia coli acetyl-CoA carboxylase. J Biol Chem 2003; 278: 30806–30812.
6.
Copolovici DM, Langel K, Eriste E, Langel U: Cell-penetrating peptides: design, synthesis, and applications. ACS Nano 2014; 8: 1972–1994.
7.
Derossi D, Joliot AH, Chassaing G, Prochiantz A: The third helix of the antennapedia homeodomain translocates through biological membranes. J Biol Chem 1994; 269: 10444–10450.
8.
di Guan C, Li P, Riggs PD, Inouye H: Vectors that facilitate the expression and purification of foreign peptides in Escherichia coli by fusion to maltose-binding protein. Gene 1988; 67: 21–30.
9.
Drin G, Cottin S, Blanc E, Rees AR, Temsamani J: Studies on the internalization mechanism of cationic cell-penetrating peptides. J Biol Chem 2003; 278: 31192–31201.
10.
Du H, Puri S, McCall A, Norris HL, Russo T, Edgerton M: Human salivary protein histatin 5 has potent bactericidal activity against ESKAPE pathogens. Front Cell Infect Microbiol 2017; 7: 41.
11.
Esposito D, Chatterjee DK: Enhancement of soluble protein expression through the use of fusion tags. Curr Opin Biotechnol 2006; 17: 353–358.
12.
Frankel AD, Pabo CO: Cellular uptake of the TAT protein from human immunodeficiency virus. Cell 1988; 55: 1189–1193.
13.
Gong Z, Ikonomova SP, Karlsson AJ: Secondary structure of cell-penetrating peptides during interaction with fungal cells. Protein Sci 2018; 27: 702–713.
14.
Gong Z, Karlsson AJ: Translocation of cell-penetrating peptides into Candida fungal pathogens. Protein Sci 2017; 26: 1714–1725.
15.
Gong Z, Walls MT, Karley AN, Karlsson AJ: Effect of a flexible linker on recombinant expression of cell-penetrating peptide fusion proteins and their translocation into fungal cells. Mol Biotechnol 2016; 58: 838–849.
16.
Green M, Loewenstein PM: Autonomous functional domains of chemically synthesized human immunodeficiency virus TAT trans-activator protein. Cell 1988; 55: 1179–1188.
17.
Gupta B, Levchenko TS, Torchilin VP: Intracellular delivery of large molecules and small particles by cell-penetrating proteins and peptides. Adv Drug Deliv Rev 2005; 57: 637–651.
18.
Helmerhorst EJ, Breeuwer P, van’t Hof W, Walgreen-Weterings E, Oomen LC, Veerman EC, Amerongen AV, Abee T: The cellular target of histatin 5 on Candida albicans is the energized mitochondrion. J Biol Chem 1999; 274: 7286–7291.
19.
Ilsen CYTZ, Onsan BK: Optimization of starting time and period of induction and inducer concentration in the production of the restriction enzyme EcoRI from recombinant E. coli. Turk J Chem 1998; 22: 221–226.
20.
Kapust RB, Waugh DS: Escherichia coli maltose-binding protein is uncommonly effective at promoting the solubility of polypeptides to which it is fused. Protein Sci 1999; 8: 1668–1674.
21.
Koren E, Torchilin VP: Cell-penetrating peptides: breaking through to the other side. Trends Mol Med 2012; 18: 385–393.
22.
Kristensen M, Birch D, Morck Nielsen H: Applications and challenges for use of cell-penetrating peptides as delivery vectors for peptide and protein cargos. Int J Mol Sci 2016; 17: 185.
23.
Lee CH, Chou CC, Hsu MF, Wang AH: Determining the N-terminal orientations of recombinant transmembrane proteins in the Esche­richia coli plasma membrane. Sci Rep 2015; 5: 15086.
24.
Mae M, Langel U: Cell-penetrating peptides as vectors for peptide, protein and oligonucleotide delivery. Curr Opin Pharmacol 2006; 6: 509–514.
25.
Marini G, Luchese MD, Argondizzo AP, de Goes AC, Galler R, Alves TL, Medeiros MA, Larentis AL: Experimental design approach in recombinant protein expression: determining medium composition and induction conditions for expression of pneumolysin from Streptococcus pneumoniae in Escherichia coli and preliminary purification process. BMC Biotechnol 2014; 14: 1.
26.
Mochon AB, Liu H: The antimicrobial peptide histatin-5 causes a spatially restricted disruption on the Candida albicans surface, allowing rapid entry of the peptide into the cytoplasm. PLoS Pathog 2008; 4:e1000190.
27.
Morris MC, Deshayes S, Heitz F, Divita G: Cell-penetrating peptides: from molecular mechanisms to therapeutics. Biol Cell 2008; 100: 201–217.
28.
Morris MC, Vidal P, Chaloin L, Heitz F, Divita G: A new peptide vector for efficient delivery of oligonucleotides into mammalian cells. Nucleic Acids Res 1997; 25: 2730–2736.
29.
Nallamsetty S, Austin BP, Penrose KJ, Waugh DS: Gateway vectors for the production of combinatorially-tagged His6-MBP fusion proteins in the cytoplasm and periplasm of Escherichia coli. Protein Sci 2005; 14: 2964–2971.
30.
Niwa H, Inouye S, Hirano T, Matsuno T, Kojima S, Kubota M, Ohashi M, Tsuji FI: Chemical nature of the light emitter of the Aequorea green fluorescent protein. Proc Natl Acad Sci USA 1996; 93: 13617–13622.
31.
Ormo M, Cubitt AB, Kallio K, Gross LA, Tsien RY, Remington SJ: Crystal structure of the Aequorea victoria green fluorescent protein. Science 1996; 273: 1392–1395.
32.
Puri S, Edgerton M: How does it kill? Understanding the candidacidal mechanism of salivary histatin 5. Eukaryot Cell 2014; 13: 958–964.
33.
Rajarao GK, Nekhotiaeva N, Good L: Peptide-mediated delivery of green fluorescent protein into yeasts and bacteria. FEMS Microbiol Lett 2002; 215: 267–272.
34.
Rajarao GK, Nekhotiaeva N, Good L: The signal peptide NPFSD fused to ricin A chain enhances cell uptake and cytotoxicity in Candida albicans. Biochem Biophys Res Commun 2003; 301: 529–534.
35.
Raran-Kurussi S, Waugh DS: The ability to enhance the solubility of its fusion partners is an intrinsic property of maltose-binding protein but their folding is either spontaneous or chaperone-mediated. PLoS One 2012; 7: e49589.
36.
Rosano GL, Ceccarelli EA: Recombinant protein expression in Escherichia coli: advances and challenges. Front Microbiol 2014; 5: 172.
37.
Sadler K, Eom KD, Yang JL, Dimitrova Y, Tam JP: Translocating proline-rich peptides from the antimicrobial peptide bactenecin 7. Biochemistry 2002; 41: 14150–14157.
38.
Shin MC, Zhang J, Min KA, Lee K, Byun Y, David AE, He H, Yang VC: Cell-penetrating peptides: achievements and challenges in application for cancer treatment. J Biomed Mater Res A 2014; 102: 575–587.
39.
Smith DB: Generating fusions to glutathione S-transferase for protein studies. Methods Enzymol 2000; 326: 254–270.
40.
Smith DB, Johnson KS: Single-step purification of polypeptides expressed in Escherichia coli as fusions with glutathione S-transferase. Gene 1988; 67: 31–40.
41.
SØrensen HP, Mortensen KK: Soluble expression of recombinant proteins in the cytoplasm of Escherichia coli. Microb Cell Fact 2005; 4: 1.
42.
Tan PK, Howard JP, Payne GS: The sequence NPFXD defines a new class of endocytosis signal in Saccharomyces cerevisiae. J Cell Biol 1996; 135: 1789–1800.
43.
Temsamani J, Laruelle C: SynB peptide vectors: a new approach to drug delivery. Chimica Oggi 2010; 28: 18–20.
44.
Tsien RY: The green fluorescent protein. Annu Rev Biochem 1998; 67: 509–544.
45.
Xiang S, Tong L: Crystal structures of human and Staphylococcus aureus pyruvate carboxylase and molecular insights into the carboxyltransfer reaction. Nat Struct Mol Biol 2008; 15: 295–302.
46.
Yu K, Liu C, Kim BG, Lee DY: Synthetic fusion protein design and applications. Biotechnol Adv 2015; 33: 155–164.
47.
Zhang JH, Yun J, Shang ZG, Zhang XH, Pan BR: Design and optimization of a linker for fusion protein construction. Prog Nat Sci 2009; 19: 1197–1200.
You do not currently have access to this content.