Purification and Characterization of Glutathione Binding Protein GsiB from Escherichia coli

OBJECTIVES: To purify and characterize the glutathione binding protein GsiB of glutathione importer (GSI) in Escherichia coli (E. coli). RESULTS: The coding sequence of GsiB was cloned from E. coli MG1655 and expressed in BL21(DE3). GsiB protein was expressed and purified to homogeneity using Ni-affinity and gel filtration chromatography. SDS-PAGE of purified GsiB showed a single protein band of molecular mass 56 kDa, while native gel showed two bands around 56 kDa and 110 kDa. Gene knockout showed that GsiB was essential for GSI mediated glutathione import. Interactions of GsiA, B, C, and D were determined using bacterial two-hybrid method. Without glutathione, GsiB showed no direct interaction with the other three proteins. However, GsiB could interact with GsiC and GsiD when using glutathione as sole sulfur source. CONCLUSIONS: GsiB functions in E. coli was characterized which could help elucidate the glutathione import mechanism in gram-negative bacteria.