Abstract
The CorA Mg(2+) channel is a homopentamer with five-fold symmetry. Each monomer consists of a large cytoplasmic domain and two transmembrane helices connected via a short periplasmic loop. In the Thermotoga maritima CorA crystal structure, a Mg(2+) is bound between D89 of one monomer and D253 of the adjacent monomer (M1 binding site). Release of Mg(2+) from these sites has been hypothesized to cause opening of the channel. We generated mutants to disrupt Mg(2+) interaction with the M1 site. Crystal structures of the D89K/D253K and D89R/D253R mutants, determined to 3.05 and 3.3 Å, respectively, showed no significant structural differences with the wild type structure despite absence of Mg(2+) at the M1 sites. Both mutants still appear to be in the closed state. All three mutant CorA proteins exhibited transport of (63)Ni(2+), indicating functionality. Thus, absence of Mg(2+) from the M1 sites neither causes channel opening nor prevents function. We also provide evidence that the T. maritima CorA is a Mg(2+) channel and not a Co(2+) channel.