Camila Cimadamore-Werthein

• Kunji, Edmund R.S.; Mavridou, Vasiliki; King, Martin S.; Cimadamore-Werthein, Camila; Baron, Stephany Jaiquel & Jones, Scott A. [Vis alle 13 forfattere av denne artikkelen] (2025). The peculiar properties of mitochondrial carriers of the SLC25 family. Biochemical Journal. ISSN 0264-6021. 482(15), s. 1047–1078. doi: 10.1042/bcj20253171. Fulltekst i vitenarkiv Vis sammendrag

  With 53 members, the SLC25 mitochondrial carriers form the largest solute carrier family in humans. They transport a wide variety of substrates across the mitochondrial inner membrane to generate chemical energy and to supply molecules and ions for growth and maintenance of cells. They are among the smallest transporters in nature, yet they translocate some of the largest molecules without proton leak. With one exception, they are monomeric and have an unusual three-fold pseudo-symmetric structure. These carriers also have a unique transport mechanism, which is facilitated by six structural elements, meaning that all transmembrane helices move separately, but in a co-ordinated way. In addition, there are three functional elements that are an integral part of the alternating access mechanism, which opens and closes the carrier to the mitochondrial matrix or the intermembrane space. The first is a matrix gate, comprising the matrix salt bridge network and glutamine braces on transmembrane helices H1, H3 and H5. The second is a cytoplasmic gate, containing the cytoplasmic salt bridge network and tyrosine braces on transmembrane helices H2, H4 and H6. The third functional element is a single central substrate-binding site, the access to which is controlled by the opening and closing of the two gates in an alternating way. The electrostatic properties of the binding site facilitate the exchange of charged substrates across the inner membrane in the presence of a high membrane potential. Here, we discuss the extraordinary features of mitochondrial carriers, providing new insights into one of the most complex and dynamic transport mechanisms in nature.

• Cimadamore-Werthein, Camila; King, Martin S; Lacabanne, Denis; Pyrihová, Eva; Baron, Stephany Jaiquel & Kunji, Edmund RS (2024). Human mitochondrial carriers of the SLC25 family function as monomers exchanging substrates with a ping-pong kinetic mechanism. EMBO Journal. ISSN 0261-4189. 43(16). doi: 10.1038/s44318-024-00150-0. Fulltekst i vitenarkiv Vis sammendrag

  Members of the SLC25 mitochondrial carrier family link cytosolic and mitochondrial metabolism and support cellular maintenance and growth by transporting compounds across the mitochondrial inner membrane. Their monomeric or dimeric state and kinetic mechanism have been a matter of long-standing debate. It is believed by some that they exist as homodimers and transport substrates with a sequential kinetic mechanism, forming a ternary complex where both exchanged substrates are bound simultaneously. Some studies, in contrast, have provided evidence indicating that the mitochondrial ADP/ATP carrier (SLC25A4) functions as a monomer, has a single substrate binding site, and operates with a ping-pong kinetic mechanism, whereby ADP is imported before ATP is exported. Here we reanalyze the oligomeric state and kinetic properties of the human mitochondrial citrate carrier (SLC25A1), dicarboxylate carrier (SLC25A10), oxoglutarate carrier (SLC25A11), and aspartate/glutamate carrier (SLC25A13), all previously reported to be dimers with a sequential kinetic mechanism. We demonstrate that they are monomers, except for dimeric SLC25A13, and operate with a ping-pong kinetic mechanism in which the substrate import and export steps occur consecutively. These observations are consistent with a common transport mechanism, based on a functional monomer, in which a single central substrate-binding site is alternately accessible.

• Høyland, Lena Elise; Linden, Magali R Van; Niere, Marc; Strømland, Øyvind; Sharma, Suraj & Dietze, Jörn Lukas Franz [Vis alle 24 forfattere av denne artikkelen] (2024). Subcellular NAD+ pools are interconnected and buffered by mitochondrial NAD+. Nature Metabolism. 6(12), s. 2319–2337. doi: 10.1038/s42255-024-01174-w. Fulltekst i vitenarkiv Vis sammendrag

  The coenzyme NAD+ is consumed by signaling enzymes, including poly-ADP-ribosyltransferases (PARPs) and sirtuins. Aging is associated with a decrease in cellular NAD+ levels but how cells cope with persistently decreased NAD+ concentrations is unclear. Here, we show that subcellular NAD+ pools are interconnected, with mitochondria acting as a rheostat to maintain NAD+ levels upon excessive consumption. To evoke chronic, compartment-specific over-consumption of NAD+, we engineered cell lines stably expressing PARP activity in mitochondria, the cytosol, endoplasmic reticulum, or peroxisomes, resulting in a decline of cellular NAD+ concentrations by up to 50%. Isotope-tracer flux measurements and mathematical modeling show that the lowered NAD+ concentration kinetically restricts NAD+ consumption to maintain a balance with the NAD+ biosynthesis rate, which remains unchanged. Chronic NAD+ deficiency is well tolerated unless mitochondria are directly targeted. Mitochondria maintain NAD+ by import through SLC25A51, and reversibly cleave NAD+ to NMN and ATP, when NMNAT3 is present. Thereby, these organelles can maintain an additional, virtual NAD+ pool. Our results are consistent with a well-tolerated aging-related NAD+ decline as long as the vulnerable mitochondrial pool is not directly affected.

• Cimadamore-Werthein, Camila; Baron, Stephany Jaiquel; King, Martin S; Springett, Roger & Kunji, Edmund RS (2023). Human mitochondrial ADP/ATP carrier SLC25A4 operates with a ping‐pong kinetic mechanism. EMBO Reports. ISSN 1469-221X. 24(8). doi: 10.15252/embr.202357127. Fulltekst i vitenarkiv Vis sammendrag

  The mitochondrial ADP/ATP carrier (SLC25A4), also called the adenine nucleotide translocase, imports ADP into the mitochondrial matrix and exports ATP, which are key steps in oxidative phosphorylation. Historically, the carrier was thought to form a homodimer and to operate by a sequential kinetic mechanism, which involves the formation of a ternary complex with the two exchanged substrates bound simultaneously. However, recent structural and functional data have demonstrated that the mitochondrial ADP/ATP carrier works as a monomer and has a single substrate binding site, which cannot be reconciled with a sequential kinetic mechanism. Here, we study the kinetic properties of the human mitochondrial ADP/ATP carrier by using proteoliposomes and transport robotics. We show that the Km/Vmax ratio is constant for all of the measured internal concentrations. Thus, in contrast to earlier claims, we conclude that the carrier operates with a ping‐pong kinetic mechanism in which substrate exchange across the membrane occurs consecutively rather than simultaneously. These data unite the kinetic and structural models, showing that the carrier operates with an alternating access mechanism.

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