Site-Directed Mutagenesis of Position 204 Threonine to Isoleucine Failed to Generate Acid-Tolerant EGFP

Abstract

Protonation of green fluorescent protein (GFP) in acidic conditions prevents the emission of fluorescent light and limits the ability to visualize, localize, and study acidic organelles. Therefore, it is critical to introduce mutations into enhanced GFP (EGFP) to generate acid-tolerant fluorescent proteins. This experiment aimed to replicate a threonine to isoleucine mutation at position 204 in EGFP and identify if acid-stable fluorescent proteins would be produced in the BL21(DE3) Escherichia coli system. Site-directed mutagenesis was utilized to generate T204I mutant EGFP. SDS-PAGE and fluorescence microscopy were employed to analyze induction success and fluorescence. Spectrofluorophotometry was used to determine the excitation and emission spectra of T204I mutant EGFP and whether acid-tolerant proteins were generated. Results illustrated that the mutation of threonine to isoleucine at position 204 produced fluorescent proteins at pH 7. However, at pH 6 and 5, proteins failed to fluoresce. The replication of the T204I mutation failed to generate acid-stable EGFP proteins in the BL21(DE3) E. coli system. There is significance in generating acid-stable cellular markers, as currently, no cellular markers thrive in acidic conditions. This limits the ability to study acidic organelles and acidic cellular processes. Creating acid-tolerant markers will permit a greater range of biological research.