Semi-synthetic cell

Type IV system. Protein synthesis inside lipid vesicles. The field of protein expression inside compartments is certainly the most advanced one in context of compartmentalized reactions. To date, in fact, it represents the state of the art in the construction of synthetic cells (more properly, semi-synthetic cells). This interest is due to the above mentioned convergence of some aspects of synthetic biology and experimental studies on the origins of Ufe. A comprehensive review of studies on semi-synthetic cells has been recently published by us, and other reviews have discussed this subject " here we will comment on a couple of relevant examples and highhghting some trends and future perspectives. The complete Ust of pubUshed works can be found in Table 17.1. 

The importance of compartmentalized reactions is constantly growing and evolving. After about 20 years from the first reports on enzymes inside liposomes, current research deals also with the assembly of semi-synthetic cells. 

Finally, the assembly of more complex systems requires that the exact supramolecular reaction site be known. For this purpose, micelles and liposomes are very attractive due to the sequestering of reagents, the possibility of conducting various reactions in a confined space, and the similarity with living cells. These particular organized media are examined in detail in chapter 15, which describes the catalytic effect of micelles and supramolecular systems based on cyclophanes. In addition, the encapsulation process of vesicles and their catalytic effect on organic reactions is outlined in chapter 16. And, finally, chapter 17 previews efforts to assemble a semi-synthetic cell. 

Knight, M. R., Read, N. D., Campbell, A. K., and Trewavas, A. J. (1993). Imaging calcium dynamics in living plants using semi-synthetic recombinant aequorins. J. Cell Biol. 121 83-90. 

Shimomura, O., Musicki, B., Kishi, Y., and Inouye, S. (1993a). Light-emitting properties of recombinant semi-synthetic aequorins and recombinant fluorescein-conjugated aequorin for measuring cellular calcium. Cell Calcium 14 373-378. 

Figure 12.4 The molecular structure of a taxane [114]. Taxotere is the semi-synthetic congener of Taxol. (Reproduced by permission from Macmillan Publishers Ltd Susan C. Roberts. Production and engineering of terpenoids in plant cell culture. Nature Chemical Biology 3 (7) 387-395. London Nature Publishing Group. 2007 Macmillan)...

Addition of the modified gene to a cell-free system containing the appropriate RNA polymerase and semi-synthetic suppressor tRNA. 

Pimecrolimus (58 Elidel ) Ascomycin Macrolactum antibiotic Semi-synthetic NP Microbial Inflammatory skin diseases and atopic dermatitis Blocks T-cell activation 505-517... 

Micafungin (21 Mycamine / Funguard ) FR901379 Macrocyclic lipopeptido- lactone Semi-synthetic NP Microbial Antifungal Inhibits fungal cell wall synthesis 186, 208-210, 248-260... 

Zotarolimus (53 Endeavor stent) Sirolimus (33) Macrolide antibiotic Semi-synthetic NP Microbial Cardiovascular surgery Inhibits cell proliferation, preventing scar tissue formation and minimizes restenosis in angioplasty patients 467 74... 

Anidulafimgin (23 Echinocandin B (24) Lipopeptide Semi-synthetic Microbial Antifungal Inhibits fungal cell wall 279-293... 

Temsirolimus (35 Sirolimus (34) Macrolide Semi-synthetic Microbial Anticancer Leads to cell cycle 337-350... 

Telavancin (28 Vibativ ) Vancomycin (27) Antibiotic Semi-synthetic NP Microbial Antibacterial Inhibits bacterial cell wall synhiesis 304-311... 

Temsirolimus (35 ToriseF, CCI-779 Wyeth, 2007), a semi-synthetic derivative of sirolimus (34), is an intravenous drug for the treatment of renal cell carcinoma (RCC) ° developed by Wyeth Pharmaceuticals... 

Ixabepilone (38 Ixempra, BMS-247550 Bristol-Myers Squibb, 2007), a semi-synthetic derivative of epothilone B (39) produced by Sorangium cellulosum, was developed by Bristol-Myers Squibb (BMS) as an anticancer drug (administered through injection) that binds directly to (3-tubulin subunits on microtubules, leading to suppression of microtubule dynamics, blocking of cells in the mitotic phase and ultimately leading to... 

DRF 3188 a novel semi-synthetic analog of andrographolide Cellnlar response to MCF 7 breast cancer cells. BMC Cancer 4 1-8. 

Etoposide is an effective anticancer drug used in the treatment of small-cell lung cancer, testicular cancer and lymphomas. It is a semi-synthetic modification of the natural lignan podophyllotoxin, and contains three acetal linkages. Can you identify them ... 

Posner and coworkers have prepared a series of semi-synthetic and synthetic ether and ester-linked dimers that were found to have potent anti-proliferative and antitumour activities in vitro. Some of these trioxane dimers were found to be as antiproliferative as calcitriol, the hormonally active form of vitamin D, which is used to treat psoriasis, a skin disorder characterized by uncontrolled cell prohferation. Of the semi synthetic dimers, a polyethylene glycol-linked dimer 107, with S-stereochemistry at both of the lactol acetal positions, was found to be very anti-proliferative and showed activity against leukaemia and colon cancer cell hues in the National Cancer Institute (NCI), USA 60-cell line assay. 

Rifabutin, a semi-synthetic derivative of rifamy-cin S, is a bactericidal antibiotic primarily used in the treatment of tuberculosis. Its effect is based on blocking the DNA-dependend RNA-polymerase of the bacteria. Rifabutin is used in the treatment of infections with Mycobacterium avium intracellulare. Rifabutin is well tolerated in patients with HIV-related tuberculosis, but patients with low CD4 cell counts have a high risk of treatment failure or relapse due to acquired rifamycin resistance. 

Figure 11.1 The semi-synthetic approach to the construction of the minimal cell.

If all these three properties are fulfilled, we have fully fledged cellular life. Of course in semi-synthetic systems the implementation can be less than perfect, and then several kinds of approximation to cellular life can be envisaged. For example, we can have protocells capable of self-maintenance but deprived of selfreproduction or vice versa. Or we can have protocells in which self-reproduction is active for only a few generations or systems that do not have the capability to evolve. Even in a given type of minimal cell - for example one with all three attributes - there might be quite different ways of implementation. 

Are you confident that semi-synthetic living cells can be created in the laboratory... 

Going back to the synthetic biology discussed in this book, I mentioned also that the construction in the laboratory of the early cell using the bottom-up approach is made difficult by the clouds of contingency, and added that there is instead confidence in a different approach to the minimal cell. This is the semi-synthetic approach seen in the previous chapter, which utilizes extant enzymes and/or genes. 

Luisi, P. L., Ferri, F, and Stano, P. (2006). Approaches to semi-synthetic minimal cells a review. Naturwissenschaften, 93, 1-13. 

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