Center for Biomembrane Research, Department of Biochemistry and Biophysics, Stockholm University, 10691 Stockholm, Sweden.
J Biol Chem. 2012 Aug 10;287(33):27547-55. doi: 10.1074/jbc.M112.371484. Epub 2012 Jun 21.
Crystal structures of the CorA Mg(2+) channel have suggested that metal binding in the cytoplasmic domain stabilizes the pentamer in a closed conformation. The open "metal free" state of the channel is, however, still structurally uncharacterized. Here, we have attempted to map conformational states of CorA from Thermotoga maritima by determining which residues support the pentameric structure in the presence or absence of Mg(2+). We find that when Mg(2+) is present, the pentamer is stabilized by the putative gating sites (M1/M2) in the cytoplasmic domain. Strikingly however, we find that the conserved and functionally important periplasmic loop is vital for the integrity of the pentamer when Mg(2+) is absent from the M1/M2 sites. Thus, although the periplasmic loops were largely disordered in the x-ray structures of the closed channel, our data suggests a prominent role for the loops in stabilizing the open conformation of the CorA channels.
晶体结构的 CorA Mg(2+) 通道表明，金属结合在细胞质域稳定五聚体在一个封闭的构象。然而，通道的“无金属”开放状态仍然没有结构特征。在这里，我们试图通过确定哪些残基在存在或不存在 Mg(2+)的情况下支持五聚体结构来描绘来自 Thermotoga maritima 的 CorA 的构象状态。我们发现，当 Mg(2+)存在时，五聚体由细胞质域中的假定门控位点 (M1/M2) 稳定。然而，令人惊讶的是，我们发现，当 M1/M2 位点没有 Mg(2+)时，保守且功能重要的周质环对于五聚体的完整性至关重要。因此，尽管在封闭通道的 X 射线结构中，周质环大部分是无序的，但我们的数据表明，环在稳定 CorA 通道的开放构象中起着重要作用。
