1.A.77 The Mg2+/Ca2+ Uniporter (MCU) Family

Mitochondrial Ca2+ homeostasis plays a key role in the regulation of aerobic metabolism and cell survival. Mitochondrial Ca2+ uptake occurs via the ruthenium red sensitive Ca2+ uniporter (MCU), and efflux occurs via a Na+/Ca2+ exchanger (mNCX). De Stefani et al. (2011) and Baughman et al. (2011) simultaneously reported the identity of a protein (named MCU) that shares tissue distribution with MICU1 (also known as CBARA1), a   uniporter regulator that is present in organisms in which mitochondrial Ca2+ uptake was demonstrated and whose sequence includes two transmembrane domains.  Short interfering RNA (siRNA) silencing of MCU reduced mitochondrial Ca2+ uptake, and MCU overproduction increased the matrix Ca2+ concentration evoked by inositol 1,4,5-trisphosphate-generating agonists. The purified MCU protein showed channel activity in planar lipid bilayers, with electrophysiological properties and inhibitor sensitivities of the uniporter 90. A mutant MCU, in which two negatively charged residues of the putative pore-forming region were replaced, had no channel activity and reduced agonist-dependent matrix Ca2+ concentration transients when overexpressed. Thus, MCU is the channel responsible for ruthenium-red-sensitive mitochondrial Ca2+ uptake. Distant prokaryotic homologues have been identified (A. Lee and MH Saier, unpublished results).  A small (10 KDa) protein with 1 TMS, EMRE, is required for interaction of MCU with MICU1 and 2 (see figure4F in Sancak et al. 2013).  The entire complex includes MICU1, MICU2, EMRE and MCU, and has a molecular size of 480,000 Daltons.  The MICU family has TC# 8.A.44 and functions in regulation.  The EMRE family has TC# 8.A.45 and funtions to interconnect MUC and MICU in the complex (Sancak et al. 2013).

Mitochondrial calcium uniporter, MCU, forms oligomers in the mitochondrial inner membrane, physically interacts with MICU1 (1.A.76.1.1), and resides within a large molecular weight complex. Silencing MCU in cultured cells or in vivo in mouse liver severely abrogates mitochondrial Ca2+ uptake, whereas mitochondrial respiration and membrane potential remain fully intact. MICU1 (TC# 8.A.44.1.1) is an essential component of the MCU system, and serves as the gatekeeper of MCU-mediated Ca2+ uptake that is essnetial to prevent Ca2+ overload and associated stress (Mallilankaraman et al., 2012a; Mallilankaraman et al., 2012b). The oligomeric channel can incorporate an inhibitory subunit, MCUb, that exerts a dominant-negative effect on channel formation (Raffaello et al., 2013). Also essential is the EMRE subunit (TC# 8.A.45.1.1) which binds MICU1 via transmembrane helices to control Ca2+ transport activity (Tsai et al. 2016). MCUs interact with Miro1 (Q8IXI2), a mitochondrial Rho GTPase that seems to regulate MCU activities (Niescier et al. 2018). Carboxylate-Capped Analogues of Ru265 are prodrugs that inhibit mitochondrial calcium uptake in intact, nonpermeabilized cells, revealing their value as tools and potential therapeutic agents for mitochondrial calcium-related disorders (Bigham et al. 2022)

MCU has two predicted transmembrane helices, which are separated by a highly conserved linker facing the intermembrane space. Acidic residues in this linker are required for its full activity. However, an S259A point mutation retained function but confered resistance to Ru360, the most potent inhibitor of the uniporter (Baughman et al., 2011). MCU homologues and their cytoplasmic regulatory protein partners with two EF-hand motifs, MICU, are both present in many but not all eukaryotes having MCU (Bick et al., 2012). The phylogenies and domain orders of MCU Ca2+ channel homologues have been reported (Bick et al., 2012). MCU is involved in the apoptosis in PC12 cells induced by 1-methyl-4-phenylpyridinium ions (MPP) (Wang et al. 2018).

Ca2+ flux across the inner mitochondrial membrane (IMM) regulates cellular bioenergetics, intra-cellular cytoplasmic Ca2+ signals, and various cell death pathways. Ca2+ entry into the mitochondria occurs due to the highly negative membrane potential (ΔΨm) through a selective inward rectifying MCU channel (Nemani et al. 2018). In addition to being regulated by various mitochondrial matrix resident proteins such as MICUs, MCUb, MCUR1 and EMRE, the channel is transcriptionally regulated by an upstream Ca2+ cascade, post transnational modification and divalent cations. The mode of regulation either inhibits or enhances MCU channel activity and thus regulates mitochondrial metabolism and cell fate (Nemani et al. 2018)

The atp operon of alkaliphilic Bacillus pseudofirmus OF4, as in most prokaryotes, contains the eight structural genes for the F-ATPase (ATP synthase), which are preceded by an atpI gene that encodes a membrane protein with 2 TMSs. A tenth gene, atpZ, has been found in this operon, which is upstream of and overlapping with atpI (Hicks et al., 2003). Most Bacillus species, and some other bacteria, possess atpZ homologues. AtpZ is predicted to be a membrane protein with a hairpin topology. Deletion of atpZ, atpI, or atpZI from B. pseudofirmus OF4 led to a requirement for a greatly increased concentration of Mg2 for growth at pH 7.5. Either atpZ, atpI, or atpZI complemented the similar phenotype of a triple mutant of Salmonella typhimurium(MM281), which is deficient in Mg2+ uptake. atpZ and atpI, separately and together, increased the Mg2+ -sensitive 45Ca2+ uptake by vesicles of an Escherichia coli mutant that is defective in Ca2+ and Na+ efflux. Hicks et al. (2003) hypothesized that AtpZ and AtpI, as homooligomers, and perhaps as heterooligomers, are Mg2+ transporters, Ca2+ transporters, probable Mg2+/Ca2+ channel proteins. Such proteins could provide Mg2+ , which is required by ATP synthase, and also support charge compensation, when the enzyme is functioning in the hydrolytic direction e.g., during cytoplasmic pH regulation. AtpZ and AtpI have 2 and 4 TMSs respectively.

The Na+ F1FO ATP synthase of the anaerobic acetogenic bacterium Acetobacterium woodii has a unique hybrid rotor that contains nine copies of a FO-like c subunit with 1 ion binding site in the 2TMS protein, and one copy of a VO-like c(1) subunit with one ion binding site in four transmembrane helices. Brandt et al. (2013) cloned and expressed its Na+ F1FO ATP synthase operon in E. coli. A Δatp mutant of E. coli produced a functional, membrane-bound Na+ F1FO ATP synthase that was purified in a single step after inserting a His(6)-tag to its β subunit. The purified enzyme was competent in Na+ transport and contained the FOVO hybrid rotor in the same stoichiometry as in A. woodii. Deletion of the atpI gene from the A. woodii operon resulted in a loss of the c ring and a mis-assembled Na+ F1FO ATP synthase. AtpI from E. coli did not substitute for AtpI from A. woodii. Thus, the native AtpI is required for assembly of the hybrid rotor.

The uniporter is membrane potential dependent and sensitive to ruthenium red and its derivative Ru360. It has high conductance and selectivity. Ca2+ entry into mitochondria activates the tricarboxylic acid cycle and seems to be crucial for matching the production of ATP in mitochondria with its cytosolic demand. MCU is the pore-forming subunit of the uniporter holocomplex. Oxenoid et al. 2016 reported the structure of the pore domain of MCU from Caenorhabditis elegans, determined using nuclear magnetic resonance (NMR) and electron microscopy (EM). MCU is a homo-oligomer in which the second transmembrane helix forms a hydrophilic pore. The channel assembly displays a unique ion channel architecture and is stabilized by a coiled-coil motif protruding into the mitochondrial matrix. The critical DXXE motif forms the pore entrance, which features two carboxylate rings; these rings appear to form the selectivity filter (Oxenoid et al. 2016).

Ca2+ uptake into mitochondria regulates bioenergetics, apoptosis, and Ca2+ signaling. The primary pathway for mitochondrial Ca2+ uptake is MCU. Mitochondrial Ca2+ uptake is tightly regulated to maintain low matrix [Ca2+] and prevent opening of the permeability transition pore and cell death, while meeting dynamic cellular energy demands. Vais et al. 2020 defined a regulatory mechanism in which cytoplasmic Ca2+ regulation of intermembrane space-localized MICU1/2 is controlled by Ca2+-regulatory mechanisms localized across the membrane in the mitochondrial matrix. Ca2+ that permeates through the channel pore regulates Ca2+ affinities of coupled inhibitory and activating sensors in the matrix. Ca2+ binding to the inhibitory sensor within the MCU amino terminus closes the channel despite Ca2+ binding to MICU1/2. Conversely, disruption of the interaction of MICU1/2 with the MCU complex disables matrix Ca2+ regulation of channel activity. These results demonstrate how Ca2+ influx into mitochondria is tuned by coupled Ca2+-regulatory mechanisms on both sides of the inner mitochondrial membrane (Vais et al. 2020).

As noted above, MCU controls mitochondrial bioenergetics, and its activity varies greatly between tissues. Xue et al. 2023 highlighted a recently identified MCU-EMRE-UCP1 complex, named thermoporter, in the adaptive thermogenesis of brown adipose tissue (BAT). The thermoporter enhances MCU activity to promote thermogenic metabolism, demonstrating a BAT-specific regulation for MCU activity.

The generalized reaction believed to be catalyzed by (AtpZ)n, (AtpI)n and (AtpZ)n-x AtpIx is:

Mg2+ or Ca2+ (out) ⇌ Mg2+ or Ca2+ (in)



Baughman, J.M., F. Perocchi, H.S. Girgis, M. Plovanich, C.A. Belcher-Timme, Y. Sancak, X.R. Bao, L. Strittmatter, O. Goldberger, R.L. Bogorad, V. Koteliansky, and V.K. Mootha. (2011). Integrative genomics identifies MCU as an essential component of the mitochondrial calcium uniporter. Nature 476: 341-345.

Bick, A.G., S.E. Calvo, and V.K. Mootha. (2012). Evolutionary diversity of the mitochondrial calcium uniporter. Science 336: 886.

Bigham, N.P., Z. Huang, J. Spivey, J.J. Woods, S.N. MacMillan, and J.J. Wilson. (2022). Carboxylate-Capped Analogues of Ru265 Are MCU Inhibitor Prodrugs. Inorg Chem 61: 17299-17312.

Brandt, K., D.B. Müller, J. Hoffmann, C. Hübert, B. Brutschy, G. Deckers-Hebestreit, and V. Müller. (2013). Functional production of the Na+ F1F(O) ATP synthase from Acetobacterium woodii in Escherichia coli requires the native AtpI. J. Bioenerg. Biomembr. 45: 15-23.

De Stefani, D., A. Raffaello, E. Teardo, I. Szabò, and R. Rizzuto. (2011). A forty-kilodalton protein of the inner membrane is the mitochondrial calcium uniporter. Nature 476: 336-340.

Docampo R., Moreno SN. and Plattner H. (2014). Intracellular calcium channels in protozoa. Eur J Pharmacol. 739:4-18.

Drago, I., P. Pizzo, and T. Pozzan. (2011). After half a century mitochondrial calcium in- and efflux machineries reveal themselves. EMBO. J. 30: 4119-4125.

Dubinin, M.V., E.Y. Talanov, K.S. Tenkov, V.S. Starinets, I.B. Mikheeva, M.G. Sharapov, and K.N. Belosludtsev. (2020). Duchenne muscular dystrophy is associated with the inhibition of calcium uniport in mitochondria and an increased sensitivity of the organelles to the calcium-induced permeability transition. Biochim. Biophys. Acta. Mol Basis Dis 1866: 165674.

Hicks, D.B., Z. Wang, Y. Wei, R. Kent, A.A. Guffanti, H. Banciu, D.H. Bechhofer, and T.A. Krulwich. (2003). A tenth atp gene and the conserved atpI gene of a Bacillus atp operon have a role in Mg2+ uptake. Proc. Natl. Acad. Sci. USA 100: 10213-10218.

Huang, G. and R. Docampo. (2018). The Mitochondrial Ca Uniporter Complex (MCUC) of Trypanosoma brucei Is a Hetero-oligomer That Contains Novel Subunits Essential for Ca Uptake. MBio 9:.

Huang, G. and R. Docampo. (2020). The Mitochondrial Calcium Uniporter Interacts with Subunit c of the ATP Synthase of Trypanosomes and Humans. mBio 11:.

Islam, M.N., G.A. Gusarova, S.R. Das, L. Li, E. Monma, M. Anjaneyulu, L. Mthunzi, S.K. Quadri, E. Owusu-Ansah, S. Bhattacharya, and J. Bhattacharya. (2022). The mitochondrial calcium uniporter of pulmonary type 2 cells determines severity of acute lung injury. Nat Commun 13: 5837.

Kholmukhamedov, A., R. Janecke, H.J. Choo, and S.M. Jobe. (2018). The mitochondrial calcium uniporter regulates procoagulant platelet formation. J Thromb Haemost. [Epub: Ahead of Print]

MacEwen, M.J., A.L. Markhard, M. Bozbeyoglu, F. Bradford, O. Goldberger, V.K. Mootha, and Y. Sancak. (2020). Evolutionary divergence reveals the molecular basis of EMRE dependence of the human MCU. Life Sci Alliance 3:.

Mallilankaraman, K., C. Cárdenas, P.J. Doonan, H.C. Chandramoorthy, K.M. Irrinki, T. Golenár, G. Csordás, P. Madireddi, J. Yang, M. Müller, R. Miller, J.E. Kolesar, J. Molgó, B. Kaufman, G. Hajnóczky, J.K. Foskett, and M. Madesh. (2012). MCUR1 is an essential component of mitochondrial Ca2+ uptake that regulates cellular metabolism. Nat. Cell Biol. 14: 1336-1343.

Mallilankaraman, K., P. Doonan, C. Cárdenas, H.C. Chandramoorthy, M. Müller, R. Miller, N.E. Hoffman, R.K. Gandhirajan, J. Molgó, M.J. Birnbaum, B.S. Rothberg, D.O. Mak, J.K. Foskett, and M. Madesh. (2012). MICU1 Is an Essential Gatekeeper for MCU-Mediated Mitochondrial Ca2+ Uptake that Regulates Cell Survival. Cell 151: 630-644.

Morales-Rios, E., I.N. Watt, Q. Zhang, S. Ding, I.M. Fearnley, M.G. Montgomery, M.J. Wakelam, and J.E. Walker. (2015). Purification, characterization and crystallization of the F-ATPase from Paracoccus denitrificans. Open Biol 5:.

Nemani, N., S. Shanmughapriya, and M. Madesh. (2018). Molecular regulation of MCU: Implications in physiology and disease. Cell Calcium 74: 86-93.

Nguyen, N.X., J.P. Armache, C. Lee, Y. Yang, W. Zeng, V.K. Mootha, Y. Cheng, X.C. Bai, and Y. Jiang. (2018). Cryo-EM structure of a fungal mitochondrial calcium uniporter. Nature. [Epub: Ahead of Print]

Niescier, R.F., K. Hong, D. Park, and K.T. Min. (2018). MCU Interacts with Miro1 to Modulate Mitochondrial Functions in Neuron.s. J. Neurosci. 38: 4666-4677.

O'Brien, J.E. and M.H. Meisler. (2013). Sodium channel SCN8A (Nav1.6): properties and de novo mutations in epileptic encephalopathy and intellectual disability. Front Genet 4: 213.

Oxenoid, K., Y. Dong, C. Cao, T. Cui, Y. Sancak, A.L. Markhard, Z. Grabarek, L. Kong, Z. Liu, B. Ouyang, Y. Cong, V.K. Mootha, and J.J. Chou. (2016). Architecture of the mitochondrial calcium uniporter. Nature 533: 269-273.

Quan, X., T.T. Nguyen, S.K. Choi, S. Xu, R. Das, S.K. Cha, N. Kim, J. Han, A. Wiederkehr, C.B. Wollheim, and K.S. Park. (2015). Essential role of mitochondrial Ca2+ uniporter in the generation of mitochondrial pH gradient and metabolism-secretion coupling in insulin-releasing cells. J. Biol. Chem. 290: 4086-4096.

Raffaello, A., D. De Stefani, D. Sabbadin, E. Teardo, G. Merli, A. Picard, V. Checchetto, S. Moro, I. Szabò, and R. Rizzuto. (2013). The mitochondrial calcium uniporter is a multimer that can include a dominant-negative pore-forming subunit. EMBO. J. 32: 2362-2376.

Sancak, Y., A.L. Markhard, T. Kitami, E. Kovács-Bogdán, K.J. Kamer, N.D. Udeshi, S.A. Carr, D. Chaudhuri, D.E. Clapham, A.A. Li, S.E. Calvo, O. Goldberger, and V.K. Mootha. (2013). EMRE is an essential component of the mitochondrial calcium uniporter complex. Science 342: 1379-1382.

Soontharapirakkul, K., W. Promden, N. Yamada, H. Kageyama, A. Incharoensakdi, A. Iwamoto-Kihara, and T. Takabe. (2011). Halotolerant cyanobacterium Aphanothece halophytica contains an Na+-dependent F1F0-ATP synthase with a potential role in salt-stress tolerance. J. Biol. Chem. 286: 10169-10176.

Tsai, M.F., C.B. Phillips, M. Ranaghan, C.W. Tsai, Y. Wu, C. Willliams, and C. Miller. (2016). Dual functions of a small regulatory subunit in the mitochondrial calcium uniporter complex. Elife 5:.

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Wang, C., R. Baradaran, and S.B. Long. (2020). Structure and Reconstitution of an MCU-EMRE Mitochondrial Ca Uniporter Complex. J. Mol. Biol. 432: 5632-5648.

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TC#NameOrganismal TypeExample

Inner membrane 40KD Mitochondrial Ca2+ Channel-forming Uniporter, MCU or MICU2 (DUF607; 350 aas; coiled coil domain protein 109 A) (De Stefani et al., 2011; Drago et al., 2011).  It functions with MICU1, and essential component of the system, as well as the gatekeeper for Ca2+ uptake (Mallilankaraman et al. 2012a; Mallilankaraman et al. 2012b).  It contributes to metabolism-insulin secretion coupling in clonal pancreatic beta-cells (Alam et al. 2012).  MCU-mediated Ca2+ uptake in beta cells is essential to establish a nutrient-induced mitochondrial pH gradient which is critical for sustained ATP synthesis and metabolism-secretion coupling in insulin-releasing cells (Quan et al. 2015). The mitochondrial calcium uniporter of pulmonary type 2 cells determines the severity of acute lung injury (Islam et al. 2022).



MCU of Mus musculus (Q3UMR5)


MCU homologue (355 aas; 2 TMSs)


MCU homologue of Chlorobium phaeobacteroides (A1BIL6)


Mitochondrial calcium uniporter, MCU, of 362 aas

Alveolata (Ciliates)

MCU of Tetrahymena thermophila


The mitochondrial calcium uniporter regulatory subunit MCUb of 336 aas; part of the MCU complex (Sancak et al. 2013). MCU regulates procoagulant platelet formation (Kholmukhamedov et al. 2018) and interacts with the c-subunit of the mitochondrial ATPase (Huang and Docampo 2020). It functions in animals (but not in fungi or protozoans) with another protein, EMRE or SMDT1 of 107 aas (TC# 8.A.45.1.1) that interacts with and renders the channel functional (MacEwen et al. 2020). The mitochondrial calcium uniporter of pulmonary type 2 cells determines the severity of acute lung injury (Islam et al. 2022).


MCUb of Homo sapiens


Mitochondrial calcium uniporter of 658 aas (Docampo et al. 2013).


MCU of Monosiga brevicollis


Mitochondrial calcium uniporter of 297 aas.


MCU of Leishmania donovani


MCU of 488 aas and 2 TMSs.  The 3.8 Å cryoEM structure has been solved (Nguyen et al. 2018). The channel is a homotetramer with two-fold symmetry in its amino-terminal domain (NTD) that adopts a structure similar to that of human MCU. The NTD assembles as a dimer of dimers to form a tetrameric ring that connects to the transmembrane domain through an elongated coiled-coil domain. The ion-conducting pore domain maintains four-fold symmetry, with the selectivity filter positioned at the start of the pore-forming TM2 helix. The aspartate and glutamate sidechains of the conserved DIME motif are oriented towards the central axis and separated by one helical turn (Nguyen et al. 2018).

MCU of the fungus, Neosartorya fischeri


Mitochondrial calcium uniporter protein, MCU, of 302 aas and 2 TMSs. It interacts with subunit c of the ATP synthase (Huang and Docampo 2020).

MCU of Trypanosoma cruzi


CMU of 248 aas and 2 TMSs.  It functions together with the EMRE regulatory protein (TC#8.A.45.1.6). MCU and EMRE form the minimal functional unit of the mitochondrial calcium uniporter complex in metazoans. Wang et al. 2020 functionally reconstituted an MCU-EMRE complex from the red flour beetle, Tribolium castaneum, and determined a cryo-EM structure of the complex at 3.5 Å resolution. They demonstrated Ca2+ uptake into proteoliposomes containing the purified complex. Uptake depended on EMRE as well as cardiolipin. The structure revealed a tetrameric channel with a single ion pore. EMRE was located at the periphery of the transmembrane domain and associates primarily with the first TMS of MCU. Coiled-coil and juxtamembrane domains within the matrix portion of the complex adopt markedly different conformations than in a structure of a human MCU-EMRE complex, suggesting that the structures represent different conformations of these functionally similar metazoan channels (Wang et al. 2020).

Mcu of Tribolium castaneum


MCU homologue of 338 aas and 2 TMSs.


MCU homologue of Arabidopsis thaliana (Q1PE15)


Algal MCU homologue (300 aas; 2 TMSs)


MCU homologue of Chlamydomonas reinhardtii (A8J6W0)


Slime mold MCU homologue of 275 aas and 2 TMSs. The structure of the N-terminal domain (NTD) has been solved at 1.7 A resolution (Yuan et al. 2020). The oligomeric DdMCU-NTD contains four helices and two strands arranged in a fold that is completely different from the known structures of other MCU-NTD homologues. This domain may regulate channel activity (Yuan et al. 2020).

Slime molds

MCU homologue of Dictyostellium discoideum (Q54LT0)


Fungal MCU homologue of 493 aas and 2 TMS. The cryo-electron microscopy structure of the full-length MCU to an overall resolution of ~3.7 Å has been determined (Yoo et al. 2018). The structure reveals a tetrameric architecture, with the soluble and transmembrane domains adopting different symmetric arrangements within the channel. The conserved W-D-Phi-Phi-E-P-V-T-Y sequence motif of the MCU pore forms a selectivity filter comprising two acidic rings separated by one helical turn along the central axis of the channel pore (Yoo et al. 2018).


MCU homologue of Neurospora crassa (Q7S4I4)


MCU homologue of 355 aas; 4 TMSs (2+2) (Docampo et al. 2013).


MCU homologue of Trypanosoma cruzi (E7KWU4)


Mitochondrial Ca2+ Uniporter, a channel complex. MCU is a putative 5TMS protein (307 aas) with homology to MCU Ca2+/Mg2+ channels in the C-terminal 2TMS domain. The N-terminal domain is found only in Trypanosoma and Leishmania species. The TbMCU complex possesses four subunits, MCU (307 aas), MCUb (214 aas), MCUc (254 aas) and MCUd (249 aas)), present only in trypanosomatids and required for Ca2+ transport. These four subunits  interact through their transmembrane helices to form hetero-oligomers in a ~380 KDa complex (Huang and Docampo 2018).


Channel homologues of Trypanosoma brucei


Ciliate MCU homologue 362 aas; 2 TMSs

Alveolata (Ciliates)

MCU homologue of Paramecium tetraurelia (A0E7U6)


MCU homologue (766 aas; 2 TMSs)


MCU homologue of Cytophaga hutchinsonii (Q11Z39)


TC#NameOrganismal TypeExample

TC#NameOrganismal TypeExample

TC#NameOrganismal TypeExample

TC#NameOrganismal TypeExample

TC#NameOrganismal TypeExample

TC#NameOrganismal TypeExample

TC#NameOrganismal TypeExample

TC#NameOrganismal TypeExample

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TC#NameOrganismal TypeExample

Putative Mg2+ transporter, AtpZ


AtpZ of Helicobacter pylori (Q1CUJ6)


AtpZ homologue of 87 aas.


AtpZ of Hippea maritima


AtpZ homologue of 90 aas


AtpZ of Campylobacter curvus


AtpZ homologue of 60 aas


AtpZ homologue of Methanothermococcus okinawensis


AtpZ homologue of 80 aas


AtpZ of Geobacter metallireducens


AtpZ homologue of 105 aas


AtpZ of Acidophilium multivorum


AtpZ homologue of 96 aas


AtpZ of Tistrella mobilis


Putative Mg2+ channel of 113 aas and 2 TMSs. Part of the F-type ATPase (Morales-Rios et al. 2015).

Magnesium channel of Paracoccus denitrificans


Putative Mg2+ channel, AtpI, that functions with a Na+-transporting F-type ATPase (Soontharapirakkul et al. 2011).

AtpI of Aphanothece halophytica


AtpZ homologue (125 aas; 2 TMSs)


AtpZ homologue of Anaeromyxobacter sp. Fw109-5 (A7HIX1)


AtpZ of 92 aas


AtpZ of Desulfovibrio vulgaris (A1VF64)


AtpZ of 106 aas


AtpZ of Chlorobium tepidum (Q8KGE5)


AtpZ of 105 aas


AtpZ of Rhodomicrobium vannielii (E3I7U2)


AtpZ of 108 aas


AtpZ of Maricaulis maris (Q0AMJ5)


ATP synthase protein Z of 114 aas


AtpZ of Rhodobacter capsulatus


The Mg2+ uptake channel, AtpZ.  Postulated to form homo- and/or hetero oligomers [(AtpZ)n-x (AtpI)x] (Hicks et al., 2003).  The AtpI homologue (P22475) is in subfamily 1.A.77.3 and has TC# 1.A.77.3.1.


The AtpZI Mg2+/Ca2+ channel of Bacillus pseudofirmus
AtpZ (Q9EXJ9)


AtpZ of 112 aas.



AtpI of Methanosarcina acetivorans (Q8TN54)


TC#NameOrganismal TypeExample

AtpI of 133 aas,  This protein is a part of a two component channel and as such is also listed with TC# 1.A.77.2.8.


AtpI of Bacillus pseudofirmus


AtpI homologue of 126 aas


AtpI of Ferrimonas balearica


AtpI of 126 aas


AtpI of E. coli


AtpI homologue of 185 aas


AtpI of Ralstonia solanacearum

1.A.77.3.13ATP synthase protein I


AtpI of Mycoplasma gallisepticum )


ATP synthase I, AtpI


AtpI of Acetohalobium arabaticum


ATP synthase subunit I


AtpI of Geobacter uraniireducens


ATP synthase I


AtpI of Fervidobacterium pennivorans


AtpI of the Na+ ATPase.  Essential for assembly of the c-ring of the rotor (Brandt et al. 2013).


AtpI of Acetobacterium woodii


AtpI homologue of 122 aas and 4 TMSs


AtpI homologue of Clostridium sticklandii


AtpI homologue of 109 aas


AtpI of Thermatoga thermarum

1.A.77.3.2ATP synthase protein IBacilli

AtpI of Bacillus subtilis


ATP synthase, subunit I of 117 aas and 4 TMSs

AtpI of Staphylococcus aureus



AtpI of Synechococcus sp.


ATP snthase subunit I, AtpI of 147 aas


AtpI of Halothermothrix orenii


ATP synthase, subunit I, AtpI of 153 aas


AtpI of Mycobacterium leprae


AtpI of 255 aas and 4 TM

Red Algae

AtpI of Galdieria sulfuraria


Putative AtpI of 122 aas and 4 TMSs


AtpI of Denitrovibrio acetophilus


Uncharacterized protein of 189 aas and 5 TMSs


UP of Anaeromyxobacter dehalogenans


AtpI homologue of 133 aas


AtpI of Leptotrichia buccalis


AtpI homologue of 126 aas


AtpI of Ilyobacter polytrophus


AtpI homologue of 127 aas


AtpI of Propionigenium modestum


ATP synthase subunit I


AtpI of Desulfococcus oleovorans


AtpI homologue of 135 aas


AtpI of Sebaldella termitidis


AtpI homologue of 164aas and 4 TMSs


AtpI of Mycoplasma fermentans


AtpI homologue of 150 aas


AtpI of Mycoplasma arthritidis


AtpI homologue of 161 aas


AtpI of Mycoplasma synoviae


AtpI of 140 aas and 4 TMSs


AtpI of Desulfotalea psychrophila


Putative AtpI of 129 aas and 4 TMSs


AtpI of Heliobacterium modesticaldum


Putative AtpI of 139 aas and 4 TMSs


AtpI of Candidatus Koribacter versatilis


Putative AtpI of 133 aas and 4 TMSs


AtpI of Desulfobacula toluolica


Putative AtpI of 140 aas and 4 TMSs


AtpI of Syntrophus aciditrophicus


Putative AtpI of 256 aas and 4 or 5 TMSs.  The N-terminus may include a single TMS plus a hydrophilic domain before the C-terminal AtpI domain.

Rhodophyta (Eukaryote)

AtpI of Chondrus crispus

1.A.77.3.4ATP synthase protein IGram-positive bacteria

AtpI of Bacillus megaterium


AtpI of 156 aas and 4 TMSs

Rhizaria (Eukaryote)

AtpI of Paulinella chromatophora


Putative AtpI of 119 aas and 4 TMSs


AtpI of Deferribacter desulfuricans


Putative AtpI of 138 aas and 4 TMSs


AtpI of Granulicella tundricola


Putative AtpI of 121 aas and 4 TMSs


AtpI of Thermodesulfovibrio yellowstonii


Putative AtpI of 160 aas and 4 TMSs


AtpI of Mycoplasma mobile


ATP synthase I-like protein, AtpI, of 385 aas amd 3 - 4 TMSs.

AtpI of Chlamydomonas reinhardtii (Chlamydomonas smithii)


AtpI homologue


AtpI homologue of Coprococcus catus


AtpI homologue of 122aas and 4 TMSs


AtpI homologue of Paenibacillus mucilaginosus

1.A.77.3.7ATP synthase protein I


AtpI of Vibrio cholerae serotype O1


AtpI homologue of 150 aas


AtpI of Klebsiella pneumoniae


AtpI homologue of 135 aas


AtpI of Pseudomonas putida


TC#NameOrganismal TypeExample

Fusion protein with N-terminal 4 TMS AtpI domain and large soluble C-terminal α/β-hydrolase domain.


Fusion protein of Galdieria sulphuraria


Fusion protein with N-terminal 4 TMS AtpI domain and large soluble C-terminal α/β-hydrolase domain.

Slime molds

Fusion protein of Dictyostelium discoideum


Fusion protein with N-terminal 4 TMS AtpI domain and large soluble C-terminal α/β-hydrolase domain.


Fusion protein of Entamoeba histolytica


TC#NameOrganismal TypeExample

AtpI homologue of 147 aas and 4 TMSs.  Deletion of the gene encoding the ortholog, cg1360, affects ATP synthase function and enhances production of L-Valine in Corynebacterium glutamicum (Wang et al. 2019).


AtpI of Corynebacterium diphtheriae


AtpI homologue of 137 aas


AtpI of Streptomyces avermitilis


AtpI homologue of 145 aas


AtpI of Frankia alni


Putative AtpI of 177 aas and 4 TMSs

AtpI of Saccharomonospora cyanea


Putative ATP synthase protein I2 of 161 aas and 4 TMSs

Putative reductase of Actinokineospora spheciospongiae


Uncharacterized protein of 157 aas and 3-4 TMSs

UP of Cellulomonas fimi


TC#NameOrganismal TypeExample

TC#NameOrganismal TypeExample

TC#NameOrganismal TypeExample

TC#NameOrganismal TypeExample