NhaA antiporters

Fluorescein-5-maleimide also has been used to study the assembly dynamics of mycobacterium tuberculosis (Chen et al., 2007), to study monomers and dimers of nhaa Na+/H+ antiporter of E. coli (Rimon et al., 2007), and to investigate the regulation of the protein disulfide proteome by mitochondria (Yang et al., 2007). 

Rimon, A., Tzubery, T., and Padan, E. (2007) Monomers of nhaa NA+/H+ antiporter of Escherichia coli are fully functional yet dimers are beneficial under extreme stress conditions at alkaline ph in the presence of NA+ or LI+. /. Biol. Chem. 10.1074/jbc.M704469200. 

The melibiose carrier MelB of E. coli is a well-studied sodium symport system. This carrier is of special interest, because it can also use protons or lithium ions for cotransport. The projection structure of MelB has been solved at 8 A resolution [107]. The 12 TM helices are arranged in an asymmetrical pattern similar to the previously solved structure of NhaA, which, however, follows an antiport mechanism (Na+ ions out of the cell and H+ into the cell). 

The three-dimensional structure of OxlT, an oxalate/formate antiporter from Oxalobacter formigenes, most recently solved [124], is explicitly different from that of both antiporter NhaA and symporter MelB (see above). There is an obvious twofold symmetry in the organisation of the 12 transmembrane helices. This supports the previous idea that the MFS proteins evolved from a duplication of a 6-TM protein to form a 12-TM protein. Moreover, it is possible that the 6-TM predecessor was created from a duplication of an ancestral 3-TM protein. 

Hilger D, Jung H, Padan E, Wegener C, Vogel KP, Steinhoff HJ, Jeschke G. Assessing oligomerization of membrane proteins by four-pulse DEER pH-dependent dimerization of NhaA Na- -/H- -antiporter of E. cob. Biophys. J. 2005 89 1328-1338. 

Ivey DM, Guffanti AA, Shen Z, Kudyan N, Krulwich TA (1992) The CadC gene product of alkaliphilic Bacillus firmus OF4 partially restores Na resistance to an Escherichia coli strain lacking an Na /H antiporter (NhaA). J Bacteriol 174 4878-4884... 

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