Codon-optimized cloning, expression and characterization of the C-terminal region of human apoptotic protein GADD34 in Escherichia coli

Abstract

The human GADD34 (Growth Arrest and DNA Damage-inducible 34) is the product of an apoptosis- and DNA-damage-inducible gene. The C-terminus domain of GADD34 is highly homologous to HSV-1 γ1 34.5, HSV-2 and the African swine fever virus virulence-associated factor NL-S. Among these viral proteins, HSV-1 γ 34.5 protein is known to prevent apoptosis of viral-infected cells. Because of the difficulty in expressing GADD34 protein or any of its fragments, including the C-terminus (amino acids 533-632) in E. coli, partially due to sub-optimal expression of eukaryotic codons in prokaryotic E. coli, we used a codon-optimized cloning scheme to construct the eukaryotic gene that codes for GADD34533-632. We derived a novel PCR protocol to assemble 20 oligonucleotides into the synthetic GADD34533-632 gene. The clear advantage of using this protocol is that the assembled gene is without the mutation and deletion that are usually of a major problem in constructing synthetic genes. The synthetic GADD34533-632 gene was cloned, expressed, and purified in large quantity. We obtained approximately 50 mg of GADD34533-632 protein per liter minimum-medium culture. To our knowledge, this is the first report of a large-scale production of the C-terminus of GADD34. The production and purification of GADD34 533-632 in large quantity are essential for structure determination as well as for understanding its interactions with other proteins such as phosphatase 1-α using NMR spectroscopy and other biophysical methods.