Clove (dried flower bud of Eugenia caryophyllata) has been used as a spice, fragrance and medicinal plant for many years. Eugenol is the main bioactive compound of clove which is derived from the Eugenia caryophyllata in a high level (45–90%) but has been identified in several aromatic plants such as Ocimum basilicum L. (sweet basil). It is now used in cosmetics, industry and pharmaceutical and dental preparations (Kamatou, Vermaak et al. 2012).
Eugenol (C10H12O2) is a simple molecule that has attracted researchers’ attention due to its versatile pharmacological and biological properties. Many studies about its biological activities suggest the development of medicinal products for human and animals uses (Rojas, Souza et al. 2014). Its antimicrobial, anti-inflammatory, analgesic, antioxidant and anticancer activity has been studied (Kamatou, Vermaak et al. 2012). Eugenol (and its derivatives) role in the prevention of chronic disease due to its antioxidant and anti-inflammatory activities has been studied, too (Fujisawa and Murakami 2016). In addition, a difference in concentration of eugenol or small changes in its structure may have a large effect on its activity (Kamatou, Vermaak et al. 2012). Coniferyl alcohol acyltransferase (CFAT) and eugenol synthase (EGS) are two key enzymes for eugenol biosynthesis in plants.
First, coniferyl alcohol is acetylated by CFAT activity. In the second step, EGS catalyzes eugenol formation from acetylated coniferyl alcohol (coniferyl acetate) (Koeduka, Fridman et al. 2006) (Koeduka, Suzuki et al. 2013) through. Eugenol has been identified in several aromatic plants such as Ocimum basilicum L. (sweet basil). Ocimum basilicum synthesizes and accumulates eugenol in the peltate glandular trichomes (glands) on the surface of its leaves. Based on previous studies, DNA sequence of basil eugenol synthase 1 (EGS1) which encodes a 314 residue protein, catalyzing the formation of eugenol from coniferyl acetate, was successfully identified and expressed in Escherichia coli to produce eugenol (Koeduka, Fridman et al. 2006). Additionally, eugenol level in different tissues of five Ocimum species including Ocimum basilicum (subtypes I, II, III and IV) was determined (Anand, Jayaramaiah et al. 2016). However, Based on our knowledge there is not any report of in silico evaluation of different signal peptides linked to basil eugenol synthase 1 (EGS1) or using any signal peptide for secretory production of basil eugenol synthase 1.
Considering several key advantageous features, E.coli has been used much more than any other microorganism in cloning and expression of recombinant proteins. Nevertheless, there are a number of limitations using this organism including intracellular host protease degradation of recombinant proteins and inclusion body formation which means the formation of insoluble aggregates of misfolded recombinant proteins (Jone, Mahadi et al. 2012, Fakruddin, Mohammad Mazumdar et al. 2013). Target protein recovery from these aggregates is a great problem that needs extensive further processing (Singh, Upadhyay et al. 2015).
Confronting these obstacles, secretory production of recombinant proteins in periplasmic space or culture medium may be performed. Secretory production of recombinant proteins is favorable due to its significant advantages. Excretory recombinant protein detection and purification are simpler while there is no need for cytoplasmic protein extraction processes. Additionally, correct formation of disulfide bonds and less protease activity allows better protein folding and improves protein biological activity. Reducing the effects of toxic proteins on cell physiology, increasing recombinant enzymes accessibility to extracellular substrates, removal of N-terminal methionine and higher product stability and solubility are the other advantages (Choi and Lee 2004, Mergulha˜o, Summers et al. 2005, Ni and Chen 2009). Various strategies may be implemented to produce extracellular proteins (Ni and Chen 2009).
Signal sequences are short specific amino acid sequences consisting of three main regions (namely N-region, H-region, and C-region) that use host natural secretory systems help the protein to be exported outside the cytoplasm. By targeting the protein to a translocation system and then signal peptide cleavage by signal peptidase, mature protein can pass through the membrane and reach the periplasmic or extracellular space. PelB, OmpA, PhoA are among popular signal peptides used for the efficient secretory production of recombinant proteins in E. coli in many studies (Choi and Lee 2004, Yoon, Kim et al. 2010). Selection of an optimum signal sequence is a very important step for efficient production therefore different available bioinformatic tools may help us to evaluate signal peptides providing a beneficial basis for further protein expression process.
In this study, using different bioinformatic tools, we analyzed several confirmed signal peptides from signal peptide database in addition to pelB (a frequently used signal peptide but not confirmed in signal peptide database) for secretory production of EGS1 in E.coli.
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