Co(2+) Selectivity of Thermotoga maritima CorA and Its Inability to Regulate Mg(2+) Homeostasis Present a New Class of CorA Proteins

• Published in: The Journal of biological chemistry 2011-05, Vol.286 (18)
• Main Authors: Xia, Yu, Lundbäck, Anna-Karin, Sahaf, Newsha, Nordlund, Gustav, Brzezinski, Peter, Eshaghi, Said
• Format: Article
• Language: English
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M111.222166

CorA is a family of divalent cation transporters ubiquitously present in bacteria and archaea. Although CorA can transport both Mg(2+) and Co(2+) almost equally well, its main role has been suggested to be that of primary Mg(2+) transporter of prokaryotes and hence the regulator of Mg(2+) homeostasis. The reason is that the affinity of CorA for Co(2+) is relatively low and thus considered non-physiological. Here, we show that Thermotoga maritima CorA (TmCorA) is incapable of regulating the Mg(2+) homeostasis and therefore cannot be the primary Mg(2+) transporter of T. maritima. Further, our in vivo experiments confirm that TmCorA is a highly selective Co(2+) transporter, as it selects Co(2+) over Mg(2+) at > 100 times lower concentrations. In addition, we present data that show TmCorA to be extremely thermostable in the presence of Co(2+). Mg(2+) could not stabilize the protein to the same extent, even at high concentrations. We also show that addition of Co(2+), but not Mg(2+), specifically induces structural changes to the protein. Altogether, these data show that TmCorA has the role of being the transporter of Co(2+) but not Mg(2+). The physiological relevance and requirements of Co(2+) in T. maritima is discussed and highlighted. We suggest that CorA may have different roles in different organisms. Such functional diversity is presumably a reflection of minor, but important structural differences within the CorA family that regulate the gating, substrate selection, and transport.