Modeling and Simulation of Production of Metallothionein and Red Fluorescent Fusion Protein by Recombinant Escherichia Coli Using Graphical Programming

Abstract

Metallothioneins (MTs) are a family of low molecular weight, cysteine rich, metal binding proteins, and exist in a variety of organisms ranging from bacteria to mammals (Moffatt & Denizeau, 1997). MTs play significant roles in clearance of free radical against oxidative damage (Masters et al., 1994), trace element metabolism and heavy metal detoxification (Feldman & Cousins, 1976), cell metabolism (Cherian & Apostolova, 2000), disease processes (Sens et al., 2001; Velazquez et al., 1999), rare metal accumulation (Nordberg, 1998), heavy metal removal and environment protection et al. (Nordberg, 1998; Elinder et al., 1981). The important applications stimulate the interest of large scale production of MT. Compared with the conventional method by extraction from animal organs, MT production by using recombinant E. coli has obvious advantages in reducing cost, increasing efficiency and product quality. However, recombinant MT is easily hydrolyzed and unstable for the thiol group of cysteine when produced by recombinant microorganism (Saito & Hunziker, 1996). By integrating the MT gene with fusion tags, MT was successfully expressed in E. coli (Hong et al., 2001; Yang et al., 2007). On the other hand, rapid measurement of MT production is important for optimization of fermentation process. MT was reported to have light absorption at the wave length of 250 nm after binding with Cd (Onosaka & Cherian, 1982), which could be used for MT measurement. But, according to our experience, this method has low accuracy and poor reproducibility. In order to detect MT production in an easy and rapid way during fermentation process, in this study, MT gene is fused with red fluorescent protein (RFP) gene and coexpressed in recombinant E. coli. Modeling and simulation is a powerful tool for the analysis of the mechanism and dynamic responses of the fermentation process, and for process optimization and automatic control. The production of recombinant protein using recombinant E. coli involves the regulations of aimed gene transcription and translation, which process can be well described by using the white box structured model involing operon regulation and is done in this research. But, the structured model has the disadvantage of extreme complex not suitable for the purpose of process optimization.