Real-time monitoring of artemin in vivo chaperone activity using luciferase as an intracellular reporter.

Artemin is an abundant thermostable protein in Artemia encysted embryos and considered as a stress protein, as its highly regulated expression is associated with stress resistance. Artemin cDNA was previously isolated and cloned from Artemia urmiana and artemin was found as an efficient molecular chaperone in vitro. Here, co-transformation of E. coli was performed with two expression vectors containing artemin and firefly luciferase for in vivo studies. The time-course of luciferase inactivation at low and elevated temperatures showed that luciferase was rapidly inactivated in control cells, but it was found that luciferase was protected significantly in artemin expressing cells. More interestingly, luciferase activity was completely regained in heat treated artemin expressing cells at room temperature. In addition, in both stress conditions, similar to residual activity of luciferase, cell viability in induced cultures over-expressing artemin was significantly higher than non-expressed artemin cells. It can be suggested that artemin confers impressive resistance in stressful conditions when introduced into E. coli cells, which is due to that it protects proteins against aggregation. Such luciferase co-expression system can be used as a real-time reporter to investigate the activity of chaperone proteins in vivo and provide a rapid and simple test for molecular chaperones.