Add new documentation to an existing Part β-casein(β-CN) is a protein which could self-associate as a macroscopic flocculent emulsion. The condition that promotes the self-association process is adjustable. In a newly published paper we cited below, researchers found that both temperature (5–55 °C) and divalent cation addition (Ca2+ or Mg2+) can have influence on β-CN-stabilized emulsions and this influence is reversible. The detailed method is to measure the particle size of 0.5% (w/w) β-CN in 10 mM imidazole/HCl buffer (pH 6.8), in a condition of adjusting temperature and divalent cations. The result shows that Ca2+ has a stronger force to promote the formation of emulsion. Furthermore, β-CN/Ca flocculated after incubation at 55 °C for 20 min and displayed significantly different physical properties compared to emulsions in β-CN solution or β-CN/Mg solution when temperature ranged from 5–55°C. This phenomenon is attributed to the interaction of adsorbed β-CN between droplets and the interaction of adsorbed and non-adsorbed β-CN aggregates in the aqueous phase via calcium bridges. Based on this paper, we could predict the self-association process and adjust the feature of β-casein.
S Li, M. , O'Mahony, J. A. , Kelly, A. L. , & André Brodkorb. (2019). The influence of temperature- and divalent-cation-mediated aggregation of β-casein on the physical and microstructural properties of β-casein-stabilised emulsions. Colloids and surfaces B: Biointerfaces, 187, 110620.
Firstly, as we used IPTG to induce the expression of target protein, we noticed the IPTG-inducing expression protocol in our lab are not sufficient. So we did a gradient concentration experiment to find a proper concentration. We noticed that the more IPTG added, the less OD600 is measured in the same time, which means IPTG brings some toxicity to bacteria. The concentration less than 1.0mM could leave bacteria in an active condition, more than 1.0mM, the growth rate of bacteria will be repressed. We found the band of 1.0mM IPTG is the most clear in our experiment, so we suggest the future iGEM team to pay attention to the OD600 of bacteria and use 1.0mM IPTG as a test.