Mrs2p Forms a High Conductance Mg2+ Selective Channel in Mitochondria

Members of the CorA-Mrs2-Alr1 superfamily of Mg2+ transporters are ubiquitous among pro- and eukaryotes. The crystal structure of a bacterial CorA protein has recently been solved, but the mode of ion transport of this protein family remained obscure. Using single channel patch clamping we unequivocally show here that the mitochondrial Mrs2 protein forms a Mg2+-selective channel of high conductance (155 pS). It has an open probability of ∼60% in the absence of Mg2+ at the matrix site, which decreases to ∼20% in its presence. With a lower conductance (∼45 pS) the Mrs2 channel is also permeable for Ni2+, whereas no permeability has been observed for either Ca2+, Mn2+, or Co2+. Mutational changes in key domains of Mrs2p are shown either to abolish its Mg2+ transport or to change its characteristics toward more open and partly deregulated states. We conclude that Mrs2p forms a high conductance Mg2+ selective channel that controls Mg2+ influx into mitochondria by an intrinsic negative feedback mechanism

Mdm38 protein depletion causes loss of mitochondrial K+/H+ exchange activity, osmotic swelling and mitophagy

Loss of the MDM38 gene product in yeast mitochondria results in a variety of phenotypic effects including reduced content of respiratory chain complexes, altered mitochondrial morphology and loss of mitochondrial K+/H+ exchange activity resulting in osmotic swelling. By use of doxycycline-regulated shut-off of MDM38 gene expression, we show here that loss of K+/H+ exchange activity and mitochondrial swelling are early events, associated with a reduction in membrane potential and fragmentation of the mitochondrial reticulum. Changes in the pattern of mitochondrially encoded proteins are likely to be secondary to the loss of K+/H+ exchange activity. The use of a novel fluorescent biosensor directed to the mitochondrial matrix revealed that the loss of K+/H+ exchange activity was immediately followed by morphological changes of mitochondria and vacuoles, the close association of these organelles and finally uptake of mitochondrial material by vacuoles. Nigericin, a K+/H+ ionophore, fully prevented these effects of Mdm38p depletion. We conclude that osmotic swelling of mitochondria triggers selective mitochondrial autophagy or mitophagy

DNA Sequence Data Indicates the Polyphyly of the Family Ctenidae (Araneae)

Volume: 21Start Page: 194End Page: 20