Mrs2p is an essential component of the major electrophoretic Mg2+ influx system in mitochondria

Abstract

Steady-state concentrations of mitochondrial Mg 2+ previously have been shown to vary with the expression of Mrs2p, a component of the inner mitochondrial membrane with two transmembrane domains. While its structural and functional similarity to the bacterial Mg 2+ transport protein CorA suggested a role for Mrs2p in Mg 2+ in¯ux into the organelle, other functions in cation homeostasis could not be excluded. Making use of the¯uorescent dye mag-fura 2 to measure free Mg 2+ concentrations continuously, we describe here a high capacity, rapid Mg 2+ in¯ux system in isolated yeast mitochondria, driven by the mitochondrial membrane potential Dy and inhibited by cobalt(III)hexaammine. Overexpression of Mrs2p increases in¯ux rates 5-fold, while the deletion of the MRS2 gene abolishes this high capacity Mg 2+ in¯ux. Mg 2+ ef¯ux from isolated mitochondria, observed with low Dy only, also requires the presence of Mrs2p. Cross-linking experiments revealed the presence of Mrs2p-containing complexes in the mitochondrial membrane, probably constituting Mrs2p homooligomers. Taken together, these ®ndings characterize Mrs2p as the ®rst molecularly identi®ed metal ion channel protein in the inner mitochondrial membrane.

The LETM1/YOL027 Gene Family Encodes a Factor of the Mitochondrial K+ Homeostasis with a Potential Role in the Wolf-Hirschhorn Syndrome

“…The genome of the yeast S. cerevisiae harbors two homologs, MRS7 (YPR125) and YOL027. MRS7 was isolated as a multi-copy suppressor of a mutant defective in mitochondrial Mg 2ϩ influx (3,10). Deletion of YOL027 has been shown to cause changes in mitochondrial morphology and suggested a mitochondrial location of the YOL027 gene product (29).…”

“…Several cation channels have been characterized physiologically (reviewed in Refs. 1 and 2), and recently, a single one has been identified molecularly (3). These transport systems seem to have intrinsic control mechanisms which ensure that the matrix cation concentrations stay within physiological ranges, far below chemical equilibrium.…”

A Screen for Nigericin-Resistant Yeast Mutants Revealed Genes Controlling Mitochondrial Volume and Mitochondrial Cation Homeostasis

“…The two-to threefold increase of magnesium levels in mitochondrial extracts from mdm31 and mdm32 mutants is extraordinary. In comparison, yeast strains with the overexpressed mitochondrial magnesium channels Mrs2 or Lpe10 exhibit no greater than a 50% increase in mitochondrial magnesium (Bui et al 1999;Gregan et al 2001a,b;Kolisek et al 2003). Hence, Mdm31p and Mdm32p seem to be involved in mitochondrial magnesium homeostasis either directly or indirectly in a regulatory capacity.…”

“…Hence, Mdm31p and Mdm32p seem to be involved in mitochondrial magnesium homeostasis either directly or indirectly in a regulatory capacity. Since magnesium export is negligible in yeast mitochondria (Kolisek et al 2003), Mdm31p and Mdm32p proteins are more likely involved in regulation of mitochondrial magnesium influx. Alternatively, Mdm31p and Mdm32p may regulate levels of magnesium-binding ligands (e.g., phosphate, nucleotides, or citrate) in mitochondria, thus affecting magnesium content indirectly.…”

“…Whereas magnesium export was detected in rat heart mitochondria in the presence of respiratory substrates (Rutter et al 1990), mitochondria from Saccharomyces cerevisiae exhibited only negligible magnesium export (Kolisek et al 2003). DC-driven magnesium import is mediated by a channel encoded by the MRS2 gene and presumably by its functional homolog, Lpe10p (Gregan et al 2001a;Kolisek et al 2003). The Mrs2p-mediated 1 transport activity seems to be tightly regulated since overexpression of the channel elicits only a moderate increase in mitochondrial magnesium content (Bui et al 1999).…”