Structural studies on cytosolic domain of magnesium transporter MgtE from Enterococcus faecalis

Abstract

Magnesium (Mg2+) is an essential element for growth and maintenance of living cells. It acts as a cofactor for many enzymes and is also essential for stability of the plasma membrane. There are two distinct classes of magnesium transporters identified in bacteria that convey Mg2+ from periplasm to cytoplasm (Moncrief and Maguire 1999; Lunin, Dobrovetsky et al. 2006) [ATPase dependent (MgtA and MgtB) and constitutively active (CorA and MgtE)]. Previously published work on Mg2+ transporters yielded structures of full length MgtE from Thermus thermophilus, determined at 3.5A resolution, and its cytoplasmic domain with and without bound Mg2+, determined at 2.3 and 3.9A resolution, respectively (Hattori, Tanaka et al. 2007). Here we report the crystal structure of the Mg2+ bound form of the cytosolic portion of MgtE (residues 6-262) from Enterococcus faecalis at 2.2A resolution. The present structure and magnesium bound cytosolic domain structure from Thermus thermophilus (PDB ID: 2YVY) are structurally similar. Three magnesium binding sites are common to both MgtE full length and the present structure. Our work revealed an additional Mg2+ binding site in the E. faecalis structure. In this report, we discuss the functional significance of Mg2+ binding sites in the cytosolic domains of MgtE transporters.