10th International Magnesium Symposium Schedule of Events

21
The CorA-Mrs2 superfamily of Mg2+ transport proteins in bacteria and
mitochondria
Elisabeth Froschauer 1 , Martin Kolisek 1 , Martin Piskacek 1 , Gabor Zsurka 1 , Julian
Weghuber 1 , Monika Schweigel 2 , Rudolf J. Schweyen 1 . 1 Max Perutz Laboratories,
Department of Microbiology and Genetics / University of Vienna, Campus Vienna
Biocenter Dr. Bohrgasse 9, A-1030 Vienna, Austria; 2 Free University Berlin,
Institute of Veterinary-Physiology, Oertzenweg 19b, D-14163 Berlin, Germany.
rudolf.schweyen@univie.ac.at
The CorA proteins of bacteria and the Mrs2 proteins of mitochondria are
characterized by the presence of two adjacent transmembrane domains. The only
sequence conserved among them (Y/F-G-M-N) is a short motif at the end of one of
these domains. Functional homology of these proteins is evident from the fact that
mitochondrial defects of Mrs2p lacking yeast cells (mrs2D mutants) are cured by the
expression of either the bacterial CorA protein or the human Mrs2 protein. Growth of
CorA mutant bacterial cells are Mg2+ -dependent, mrs2D yeast cells show
unconditional mitochondrial defects, but stay viable, while human mrs2D cells are
unviable.
Similarity between CorA and Mrs2 proteins further extends to the Mg2+ fluxes across
membranes. By use of the fluorescent, Mg2+ -sensitive dye mag-fura 2 we have
recently determined Mg2+ fluxes across bacterial plasma membranes as well as
across yeast and human mitochondrial membranes. The CorA and Mrs2 proteins
mediate rapid, high- capacity influx into bacterial cells and into isolated mitochondria,
respectively. Addition of 10 mM Mg2+ to isolated mitochondria can result in an
increase of intramitochondrial free Mg2+ by as much as 50% per second, with a
pronounced saturation at about 5 mM in yeast mitochondria. The driving force for
Mg2+ influx by both, CorA and Mrs2 proteins is the high (inside negative) membrane
potential of mitochondria and bacteria. Mg2+ influx studies suggest the presence of
Mg2+ channels in the bacterial and mitochondrial membranes. This notion is
supported by cross-linking studies in yeast and human mitochondrial membranes,
revealing the presence of homo-oligomeric Mrs2 protein complexes.