Article ; Online: Cation selectivity by the CorA Mg2+ channel requires a fully hydrated cation.
2010 Volume 49, Issue 29, Page(s) 5998–6008
Abstract: The CorA Mg(2+) channel is the primary uptake system in about half of all bacteria and archaea. However, the basis for its Mg(2+) selectivity is unknown. Previous data suggested that CorA binds a fully hydrated Mg(2+) ion, unlike other ion channels. The ... ...
| Abstract | The CorA Mg(2+) channel is the primary uptake system in about half of all bacteria and archaea. However, the basis for its Mg(2+) selectivity is unknown. Previous data suggested that CorA binds a fully hydrated Mg(2+) ion, unlike other ion channels. The crystal structure of Thermotoga maritima CorA shows a homopentamer with two transmembrane segments per monomer connected by a short periplasmic loop. This highly conserved loop, (281)EFMPELKWS(289) in Salmonella enterica serovar Typhimurium CorA, is the only portion of the channel outside of the cell, suggesting a role in cation selectivity. Mutation of charged residues in the loop, E281 and K287, to any of several amino acids had little effect, demonstrating that despite conservation electrostatic interactions with these residues are not essential. While mutation of the universally conserved E285 gave a minimally functional channel, E285A and E285K mutants were the most functional, again indicating that the negative charge at this position is not a determining factor. Several mutations at K287 and W288 behaved anomalously in a transport assay. Analysis indicated that mutation of K287 and W288 disrupts cooperative interactions between distinct Mg(2+) binding sites. Overall, these results are not compatible with electrostatic interaction of the Mg(2+) ion with the periplasmic loop. Instead, the loop appears to form an initial binding site for hydrated Mg(2+), not for the dehydrated cation. The loop residues may function to accelerate dehydration of the before entry of Mg(2+) into the pore of the channel. |
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| MeSH term(s) | Amino Acid Sequence ; Bacterial Proteins/chemistry ; Bacterial Proteins/genetics ; Bacterial Proteins/metabolism ; Binding Sites/genetics ; Cation Transport Proteins/chemistry ; Cation Transport Proteins/genetics ; Cation Transport Proteins/metabolism ; Cations, Divalent/metabolism ; Conserved Sequence ; Magnesium/chemistry ; Magnesium/metabolism ; Mutation ; Protein Conformation ; Salmonella typhimurium/metabolism ; Thermotoga maritima/metabolism ; Water/chemistry ; Water/metabolism |
| Chemical Substances | Bacterial Proteins ; Cation Transport Proteins ; Cations, Divalent ; CorA protein, Salmonella ; Water (059QF0KO0R) ; Magnesium (I38ZP9992A) |
| Language | English |
| Publishing date | 2010-06-21 |
| Publishing country | United States |
| Document type | Journal Article ; Research Support, N.I.H., Extramural ; Research Support, Non-U.S. Gov't |
| ZDB-ID | 1108-3 |
| ISSN | 1520-4995 ; 0006-2960 |
| ISSN (online) | 1520-4995 |
| ISSN | 0006-2960 |
| DOI | 10.1021/bi1005656 |
| Database | MEDical Literature Analysis and Retrieval System OnLINE |
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