FUNCTIONAL SIMILARITY BETWEEN ARCHAEAL AND BACTERIAL CORA MAGNESIUM TRANSPORTERS

The constitutively expressed CorA Mg2+ transporter is the major Mg2+ i nflux system of Salmonella typhimurium and Escherichia coli. Genomic s equence data indicated the presence of a homolog in the archaeal organ ism Methanococcus jannaschii. The putative M. jannaschii CorA was expr essed in an Mg2+-transport-deficient strain of S. typhimurium to deter mine its functional characteristics. The archaeal CorA. homolog is a f unctional Mg2+ uptake system when expressed in S. typhimurium and has properties which are highly similar to those of the normal CorA transp orter of S. typhimurium despite having a low level of sequence identit y with the protein and being expressed in a lipid membrane of quite di fferent composition than normal. This implies that the overall functio n of the proteins is the same and further suggests that their structur es are very similar.