Heterologous Expression and Purification of the Magnesium Transporter A (MgtA) in Escherichia coli

Abstract

The magnesium transporter A (MgtA) is a magnesium transporting P-type ATPase present in prokaryotes and plants (Subramani et al., 2016). In Salmonella typhimurium and Escherichia coli (E. coli), MgtA is expressed only in magnesium limiting conditions and plays an important role in Mg2+ homeostasis (Groisman et al., 2013). The transcription of mgtA is regulated by the two-component system PhoP/PhoQ (Soncini et al., 1996; Kato et al., 1999). The membrane bound histidine kinase, PhoQ, senses low Mg2+ concentration in the periplasmic space and phosphorylates its cognate response regulator, PhoP, which initiates mgtA transcription (Groisman et al., 2013). MgtA is targeted to the plasma membrane and facilitate the bacterial survival under low Mg2+ condition, by importing Mg2+ into the cytoplasm. The MgtA homolog in petunia (PH1) is found in the vacuolar membrane and involved with the coloration of the flower petals (Faraco et al., 2014). As a first step towards understanding the molecular details of MgtA Mg2+ transport, we describe a detailed protocol for the purification of E. coli MgtA that can be used for biochemical and biophysical studies. Recombinant E. coli MgtA with hexa histidine tag at the N-terminus was cloned from E. coli DH5α and over expressed in the E. coli C43(DE3) by fermentation to an OD > 6. Cell lysis was performed in a high pressure homogenizer and the membranes were isolated by ultracentrifugation. Membrane proteins were solubilized with the detergent dodecyl-β-D maltoside. MgtA was purified by affinity and size exclusion chromatography. Final yields of purified MgtA reach ~1 mg MgtA per 3 g of wet cell pellet.