The CorA Mg2+ transporter is a homotetramer.
CorA is a primary Mg2+ transporter for Bacteria and Archaea. The C-terminal domain of approximately 80 amino acids forms three transmembrane (TM) segments, which suggests that CorA is a homo-oligomer. A Cys residue was added to the cytoplasmic C terminus (C317) of Salmonella enterica serovar Typhimurium CorA with or without mutation of the single periplasmic Cys191 to Ser; each mutant retained function. Oxidation of the Cys191Ser Cys317 CorA gave a dimer. Oxidation of Cys317 CorA showed a dimer plus an additional band, apparently cross-linked via both Cys317 and C191. To determine oligomer order, intact cells or purified membranes were treated with formaldehyde or carbon disulfide. Higher-molecular-mass bands formed, consistent with the presence of a tetramer. Cross-linking of the Bacillus subtilis CorA expressed in Salmonella serovar Typhimurium similarly indicated a tetramer. CorA periplasmic soluble domains from both Salmonella serovar Typhimurium and the archaeon Methanococcus jannaschii were purified and shown to retain structure. Formaldehyde treatment showed formation of a tetramer. Finally, previous mutagenesis of the CorA membrane domain identified six intramembrane residues forming an apparent pore that interacts with Mg2+ during transport. Each was mutated to Cys. In mutants carrying a single intramembrane Cys residue, spontaneous disulfide bond formation that was enhanced by oxidation with Cu(II)-1,10-phenanthroline was observed between monomers, indicating that these Mg2+-interacting residues within the membrane are very close to their cognate residue on another monomer. Thus, CorA appears to be a homotetramer with a TM segment of one monomer physically close to the same TM segment of another monomer.
Warren
Mary Ann
MA
Department of Pharmacology, School of Medicine, Case Western Reserve University, 10900 Euclid Ave., Cleveland, OH 44106-4965, USA.
Kucharski
Lisa M
LM
Veenstra
Alexander
A
Shi
Liang
L
Grulich
Paul F
PF
Maguire
Michael E
ME
D019943:Amino Acid Substitution; D001105:Archaea / Q000201:enzymology; D001412:Bacillus subtilis / Q000201:enzymology*; D001419:Bacteria / Q000201:enzymology; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D027682:Cation Transport Proteins / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D003545:Cysteine / Q000378:metabolism; D008274:Magnesium / Q000378:metabolism*; D017017:Methanococcus / Q000201:enzymology*; D008970:Molecular Weight; D020125:Mutation, Missense; D010084:Oxidation-Reduction; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D021122:Protein Subunits / Q000737:chemistry*; D012486:Salmonella typhimurium / Q000201:enzymology*
D001426:Bacterial Proteins; D027682:Cation Transport Proteins; D021122:Protein Subunits; D008274:Magnesium; D003545:Cysteine