Coupled selection of protein solubility in E. coli using uroporphyrinogen III methyltransferase as red fluorescent reporter

Uroporphyrinogen III methyltransferase (UMT) is a novel reporter owing to the catalytic products accumulated in cells emitting red florescence. Overexpression of UMT confers resistance of the Escherichia coli cells to potassium tellurite that inhibits cell growth. In this study, we applied UMT reporter for monitoring protein solubility of MBP or TEV protease variants under different expression conditions, as well as 12 maize proteins with either the designed linker or N-terminal SUMO tag. Effects of five enzymes involved in heme and siroheme biosynthesis on the reporter were also investigated. With increasing concentrations of potassium tellurite, colony numbers of the mixed cells expressing the selected five proteins with different solubility were decreased, but colonies displaying red fluorescence was identified to be produced the protein with relatively high solubility. The developed UMT reporter system is sensitive for monitoring protein solubility based on coupled fluorescence and chemical selection.