27
views
0
recommends
+1 Recommend
0 collections
    0
    shares
      • Record: found
      • Abstract: found
      • Article: found
      Is Open Access

      Mrs2p Forms a High Conductance Mg 2+ Selective Channel in Mitochondria

      research-article

      Read this article at

      Bookmark
          There is no author summary for this article yet. Authors can add summaries to their articles on ScienceOpen to make them more accessible to a non-specialist audience.

          Abstract

          Members of the CorA-Mrs2-Alr1 superfamily of Mg 2+ 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 Mg 2+-selective channel of high conductance (155 pS). It has an open probability of ∼60% in the absence of Mg 2+ at the matrix site, which decreases to ∼20% in its presence. With a lower conductance (∼45 pS) the Mrs2 channel is also permeable for Ni 2+, whereas no permeability has been observed for either Ca 2+, Mn 2+, or Co 2+. Mutational changes in key domains of Mrs2p are shown either to abolish its Mg 2+ transport or to change its characteristics toward more open and partly deregulated states. We conclude that Mrs2p forms a high conductance Mg 2+ selective channel that controls Mg 2+ influx into mitochondria by an intrinsic negative feedback mechanism.

          Related collections

          Most cited references34

          • Record: found
          • Abstract: found
          • Article: not found

          Improved patch-clamp techniques for high-resolution current recording from cells and cell-free membrane patches.

          1. The extracellular patch clamp method, which first allowed the detection of single channel currents in biological membranes, has been further refined to enable higher current resolution, direct membrane patch potential control, and physical isolation of membrane patches. 2. A description of a convenient method for the fabrication of patch recording pipettes is given together with procedures followed to achieve giga-seals i.e. pipette-membrane seals with resistances of 10(9) - 10(11) omega. 3. The basic patch clamp recording circuit, and designs for improved frequency response are described along with the present limitations in recording the currents from single channels. 4. Procedures for preparation and recording from three representative cell types are given. Some properties of single acetylcholine-activated channels in muscle membrane are described to illustrate the improved current and time resolution achieved with giga-seals. 5. A description is given of the various ways that patches of membrane can be physically isolated from cells. This isolation enables the recording of single channel currents with well-defined solutions on both sides of the membrane. Two types of isolated cell-free patch configurations can be formed: an inside-out patch with its cytoplasmic membrane face exposed to the bath solution, and an outside-out patch with its extracellular membrane face exposed to the bath solution. 6. The application of the method for the recording of ionic currents and internal dialysis of small cells is considered. Single channel resolution can be achieved when recording from whole cells, if the cell diameter is small (less than 20 micrometer). 7. The wide range of cell types amenable to giga-seal formation is discussed.
            Bookmark
            • Record: found
            • Abstract: found
            • Article: not found

            TRPM7 Provides an Ion Channel Mechanism for Cellular Entry of Trace Metal Ions

            Trace metal ions such as Zn2+, Fe2+, Cu2+, Mn2+, and Co2+ are required cofactors for many essential cellular enzymes, yet little is known about the mechanisms through which they enter into cells. We have shown previously that the widely expressed ion channel TRPM7 (LTRPC7, ChaK1, TRP-PLIK) functions as a Ca2+- and Mg2+-permeable cation channel, whose activity is regulated by intracellular Mg2+ and Mg2+·ATP and have designated native TRPM7-mediated currents as magnesium-nucleotide–regulated metal ion currents (MagNuM). Here we report that heterologously overexpressed TRPM7 in HEK-293 cells conducts a range of essential and toxic divalent metal ions with strong preference for Zn2+ and Ni2+, which both permeate TRPM7 up to four times better than Ca2+. Similarly, native MagNuM currents are also able to support Zn2+ entry. Furthermore, TRPM7 allows other essential metals such as Mn2+ and Co2+ to permeate, and permits significant entry of nonphysiologic or toxic metals such as Cd2+, Ba2+, and Sr2+. Equimolar replacement studies substituting 10 mM Ca2+ with the respective divalent ions reveal a unique permeation profile for TRPM7 with a permeability sequence of Zn2+ ≈ Ni2+ >> Ba2+ > Co2+ > Mg2+ ≥ Mn2+ ≥ Sr2+ ≥ Cd2+ ≥ Ca2+, while trivalent ions such as La3+ and Gd3+ are not measurably permeable. With the exception of Mg2+, which exerts strong negative feedback from the intracellular side of the pore, this sequence is faithfully maintained when isotonic solutions of these divalent cations are used. Fura-2 quenching experiments with Mn2+, Co2+, or Ni2+ suggest that these can be transported by TRPM7 in the presence of physiological levels of Ca2+ and Mg2+, suggesting that TRPM7 represents a novel ion-channel mechanism for cellular metal ion entry into vertebrate cells.
              Bookmark
              • Record: found
              • Abstract: found
              • Article: not found

              Crystal structure of the CorA Mg2+ transporter.

              The magnesium ion, Mg2+, is essential for myriad biochemical processes and remains the only major biological ion whose transport mechanisms remain unknown. The CorA family of magnesium transporters is the primary Mg2+ uptake system of most prokaryotes and a functional homologue of the eukaryotic mitochondrial magnesium transporter. Here we determine crystal structures of the full-length Thermotoga maritima CorA in an apparent closed state and its isolated cytoplasmic domain at 3.9 A and 1.85 A resolution, respectively. The transporter is a funnel-shaped homopentamer with two transmembrane helices per monomer. The channel is formed by an inner group of five helices and putatively gated by bulky hydrophobic residues. The large cytoplasmic domain forms a funnel whose wide mouth points into the cell and whose walls are formed by five long helices that are extensions of the transmembrane helices. The cytoplasmic neck of the pore is surrounded, on the outside of the funnel, by a ring of highly conserved positively charged residues. Two negatively charged helices in the cytoplasmic domain extend back towards the membrane on the outside of the funnel and abut the ring of positive charge. An apparent Mg2+ ion was bound between monomers at a conserved site in the cytoplasmic domain, suggesting a mechanism to link gating of the pore to the intracellular concentration of Mg2+.
                Bookmark

                Author and article information

                Journal
                Biophys J
                biophysj
                Biophysical Journal
                The Biophysical Society
                0006-3495
                1542-0086
                1 December 2007
                7 September 2007
                1 December 2007
                : 93
                : 11
                : 3872-3883
                Affiliations
                [* ]Institute for Biophysics, University of Linz, Linz, Austria; and []Max F. Perutz Laboratories, Department of Genetics, University of Vienna, Vienna, Austria
                Author notes

                Address reprint requests to Christoph Romanin, University of Linz, Linz, Austria. Tel.: 4373224689272; E-mail: christoph.romanin@ 123456jku.at ; or to Rudolf J. Schweyen, MFPL, University of Vienna, Vienna, Austria. Tel.: 431427754604; E-mail: rudolf.schweyen@ 123456univie.ac.at .

                Article
                112318
                10.1529/biophysj.107.112318
                2099211
                17827224
                eda72cbc-8c40-4ea1-bae4-1f86482b308e
                Copyright © 2007, Biophysical Society

                This is an Open Access article distributed under the terms of the Creative Commons-Attribution Noncommercial License ( http://creativecommons.org/licenses/by-nc/2.0/), which permits unrestricted noncommercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

                History
                : 8 May 2007
                : 29 June 2007
                Categories
                Channels, Receptors, and Electrical Signaling

                Biophysics
                Biophysics

                Comments

                Comment on this article