Hmt-1 (CG4225, DmHMT-1) is the Drosophila member of the ABCB6/HMT-1 clade of ATP-binding cassette half-transporters. The single 866-residue product has an N-terminal ABCB6-type membrane extension (TMD0), a six-helix ABC transmembrane domain and a C-terminal ABC nucleotide-binding domain, and is expected to function as a homodimer that couples ATP hydrolysis to translocation of solutes across an organellar membrane. When expressed in fission yeast, DmHMT-1 restores cadmium tolerance to hmt-1 mutants and localizes to the vacuolar membrane, but it does not transport cadmium-phytochelatin complexes, consistent with the absence of phytochelatin synthase from the fly genome; its cadmium-detoxifying role is therefore phytochelatin-independent. Orthologous human ABCB6 transports porphyrins and hemin and binds cadmium-glutathione and cadmium-phytochelatin complexes whose binding stimulates ATP hydrolysis, so heme/porphyrin and thiol-coordinated metal transport are conserved activities of the clade. The endogenous membrane in fly cells and the chemical species that DmHMT-1 moves have not been determined.
Summary: Golgi membrane is one of eleven compartments that an ARBA subcellular-location rule copies from mammalian ABCB6 onto this unreviewed fly entry; there is no fly or heterologous evidence for a Golgi site of action.
Reason: The only experimental localization of DmHMT-1 places it in the vacuolar membrane after expression in S. pombe (PMID:19001374). The ARBA location list mirrors the biosynthetic and endolysosomal itinerary reported for mammalian ABCB6 (PMID:22655043); a Golgi transit stage is not a site where the transporter acts, and PAINT curators placed only vacuolar membrane at the opisthokont ABCB6 node (PTN008609345), not Golgi membrane. Golgi membrane is therefore over-annotation for the fly protein.
heterologously expressed DmHMT-1 suppresses the Cd2+ hypersensitivity of S. pombe hmt-1 mutants and localizes to the vacuolar membrane but does not transport Cd.PC complexes.
Summary: Correct but generic; the ABC nucleotide-binding cassette binds ATP.
Reason: Hmt-1 has a single ABC transporter nucleotide-binding domain (residues 576-810) with the ABC signature motif. The nucleotide bound by this cassette is ATP, which the gene already carries as GO:0005524 ATP binding; that more specific term should replace generic nucleotide binding.
Summary: ATP binding by the ABC nucleotide-binding domain is the energy input of the transport cycle.
Reason: The intact ABC cassette with Walker motifs and ABC signature is diagnostic for ATP binding. In the orthologous human ABCB6, the catalytic glutamate mutant E752Q abolishes substrate-stimulated ATP hydrolysis, showing that the cassette is a functional ATPase in this clade. ATP binding is a molecular-level part of the core transporter activity.
Supporting Evidence:
file:DROME/Hmt-1/Hmt-1-uniprot.txt
DR InterPro; IPR003439; ABC_transporter-like_ATP-bd.
By contrast, the catalytically inactive E752Q mutant displayed little basal activity and no Cd(II):GSH-stimulated ATPase activity, probably due to an inability to hydrolyze ATP
Summary: Hmt-1 is a ten-helix integral membrane protein; the extracellular-region row is a mapping of "Secreted, extracellular exosome" copied from mammalian ABCB6 found in reticulocyte exosomes.
Reason: The SL-0243 mapping derives from the ARBA location rule, whose mammalian basis is ABCB6 carried on exosomes shed by maturing reticulocytes (PMID:22655043). That is a membrane-vesicle observation specific to erythroid maturation, a cell type insects lack, and it does not mean the protein is a soluble extracellular-region component. DmHMT-1 has ten predicted transmembrane helices and localizes to an intracellular vacuolar membrane in the only experimental study (PMID:19001374). There is no biological basis to place it in the extracellular region.
ABCB6 is a glycoprotein present in the membrane of mature erythrocytes and in exosomes released from reticulocytes during the final steps of erythroid maturation
heterologously expressed DmHMT-1 suppresses the Cd2+ hypersensitivity of S. pombe hmt-1 mutants and localizes to the vacuolar membrane but does not transport Cd.PC complexes.
Summary: Mitochondrial outer-membrane localization is contested even for human ABCB6 and is not supported for the fly protein.
Reason: Mitochondrial outer-membrane localization was proposed for mammalian ABCB6 (PMID:17006453) but later work found endogenous ABCB6 in the endo/lysosomal compartment and absent from mitochondria (PMID:22655043). PAINT curators assigned only vacuolar membrane at the opisthokont ABCB6 node and did not propagate a mitochondrial location, and DmHMT-1 itself localizes to the vacuolar membrane in yeast (PMID:19001374). The term is not demonstrably wrong for every family member, but there is no support for it in the fly.
heterologously expressed DmHMT-1 suppresses the Cd2+ hypersensitivity of S. pombe hmt-1 mutants and localizes to the vacuolar membrane but does not transport Cd.PC complexes.
Summary: Lysosomal membrane is plausible for an animal ABCB6 ortholog that targets the yeast vacuole, but the endogenous fly compartment has not been examined.
Reason: Lysosomal membrane is a descendant of the accepted vacuolar membrane term. Human ABCB6 is endo/lysosomal (PMID:22655043), and the animal counterpart of the yeast vacuole is the lysosome, so this is the most likely specific compartment for DmHMT-1. However, the only DmHMT-1 localization was done in S. pombe, and PAINT curators deliberately stopped at vacuolar membrane at the opisthokont node. Without a fly-cell localization this row can be neither accepted nor rejected.
heterologously expressed DmHMT-1 suppresses the Cd2+ hypersensitivity of S. pombe hmt-1 mutants and localizes to the vacuolar membrane but does not transport Cd.PC complexes.
Summary: Vacuolar membrane is the PAINT assignment at the opisthokont ABCB6/HMT-1 node, grounded in part on DmHMT-1's own vacuolar localization.
Reason: PTN008609345 (Opisthokonta) carries vacuolar membrane with fly, rat, human and worm members among its descendant evidence; FBgn0038376 appears among the sources because of the target's own IDA, which is expected and is not circularity. The term is at the level the evidence supports for a lineage spanning yeast vacuoles and animal lysosomes.
heterologously expressed DmHMT-1 suppresses the Cd2+ hypersensitivity of S. pombe hmt-1 mutants and localizes to the vacuolar membrane but does not transport Cd.PC complexes.
IDA PMID:19001374 Drosophila ABC transporter, DmHMT-1, confers tolerance to ca...
ACCEPT
Summary: DmHMT-1 expressed in fission yeast localizes to the vacuolar membrane.
Reason: The abstract directly reports vacuolar-membrane localization of heterologously expressed DmHMT-1. This is a heterologous-system observation (S. pombe), so it shows the protein's targeting capacity rather than its native fly compartment; vacuolar membrane is the appropriate general level, consistent with the IBA at the opisthokont node.
heterologously expressed DmHMT-1 suppresses the Cd2+ hypersensitivity of S. pombe hmt-1 mutants and localizes to the vacuolar membrane but does not transport Cd.PC complexes.
Summary: ER membrane is a biosynthetic transit compartment copied by the ARBA location rule, not a demonstrated site of Hmt-1 activity.
Reason: All integral membrane glycoproteins of the endolysosomal system pass through the ER, but that does not make the ER a functional location. Neither the fly study (PMID:19001374) nor the PAINT opisthokont node supports ER membrane, and mammalian ABCB6 is assigned to endo/lysosomes (PMID:22655043).
heterologously expressed DmHMT-1 suppresses the Cd2+ hypersensitivity of S. pombe hmt-1 mutants and localizes to the vacuolar membrane but does not transport Cd.PC complexes.
Summary: Plasma-membrane ABCB6 is documented chiefly in mammalian erythrocytes; there is no evidence for a plasma-membrane pool of the fly protein.
Reason: The mammalian plasma-membrane observation concerns mature erythrocytes (PMID:22655043), a cell type without an insect counterpart. DmHMT-1 localizes to the vacuolar membrane in the only experimental study (PMID:19001374), and PAINT curators did not propagate plasma membrane at the ABCB6 node. The row is an ARBA transfer that outruns the fly evidence.
ABCB6 is a glycoprotein present in the membrane of mature erythrocytes and in exosomes released from reticulocytes during the final steps of erythroid maturation
heterologously expressed DmHMT-1 suppresses the Cd2+ hypersensitivity of S. pombe hmt-1 mutants and localizes to the vacuolar membrane but does not transport Cd.PC complexes.
Summary: Endosomal membranes are part of the endo/lysosomal system where mammalian ABCB6 resides, but no fly or heterologous experiment addresses them for DmHMT-1.
Reason: Human ABCB6 is endo/lysosomal (PMID:22655043), so an endosomal pool is plausible for an animal ortholog en route to lysosomes. The DmHMT-1 experiment resolves only the yeast vacuolar membrane (PMID:19001374), which does not distinguish endosomal from vacuolar residence. This row is left unresolved rather than accepted or removed.
heterologously expressed DmHMT-1 suppresses the Cd2+ hypersensitivity of S. pombe hmt-1 mutants and localizes to the vacuolar membrane but does not transport Cd.PC complexes.
Summary: ABC-type heme/porphyrin transport is the PAINT assignment at the eumetazoan ABCB6 node, from which Hmt-1 descends; human ABCB6 hemin:GSH-stimulated ATP hydrolysis and substrate-bound structures ground it.
Reason: PTN001199916 is placed at Eumetazoa (taxon 6072) and seeded by human ABCB6 (Q9NP58); Drosophila Hmt-1 is inside that clade (PANTHER subfamily PTHR24221:SF654, ABCB6) and retains the ABCB6-specific N-terminal domain, so the inference is phylogenetic, not a best-hit transfer. Human ABCB6 binds coproporphyrin III and hemin in its central cavity, and hemin in the presence of glutathione stimulates its ATPase about sixfold (PMID:35950458); ABCB6 was first identified as an ATP-dependent porphyrin uptake transporter (PMID:17006453). No fly experiment has tested heme or porphyrin transport, and no evidence for loss of the activity in the fly lineage exists. The activity is accepted as inherited, with the caveat recorded in core_functions that its physiological weight in the fly is unknown.
Here we report the cryo-electron microscopy (cryo-EM) structures of human ABCB6 with its substrates, coproporphyrin III (CPIII) and hemin, at 3.5 and 3.7 Γ resolution, respectively.
metal-centered porphyrins, such as hemin (ferric chloride heme) and cobalt (III) PPIX, markedly stimulated the ATPase activity of ABCB6-βTMD0 approximately 6-fold only when the cellular antioxidant glutathione (GSH; Ξ³-glu-cys-gly) was included in the reaction buffer
Summary: The EC 7.6.2.5 mapping agrees with the phylogenetically grounded IBA for ABC-type heme transport.
Reason: The EC number on this entry is itself an ARBA prediction, so this row adds no independent evidence; it is accepted because the same claim is grounded by the eumetazoan PAINT node and human ABCB6 biochemistry (see the IBA row), and rows sharing a term must be judged consistently.
metal-centered porphyrins, such as hemin (ferric chloride heme) and cobalt (III) PPIX, markedly stimulated the ATPase activity of ABCB6-βTMD0 approximately 6-fold only when the cellular antioxidant glutathione (GSH; Ξ³-glu-cys-gly) was included in the reaction buffer
Summary: Correct but general; the ABCB6 clade moves heme across a membrane, which is heme transmembrane transport, a term this gene already carries.
Reason: GO:0035351 heme transmembrane transport is_a GO:0015886 heme transport. An ABC-type heme transporter by definition carries out the transmembrane step, and the gene already has GO:0035351 by inter-ontology inference from the same molecular function. The specific child is the better term.
Propagation Review
Root cause:TERM SCOPING PROBLEM
Failure modes:GRANULARITY MISMATCH
Sources checked:
PANTHER:PTN001199916SUPPORTS TRANSFER
Eumetazoan ABCB6 node seeded by human ABCB6; Hmt-1 is inside the clade; the node term is correct but its transmembrane child is preferred.
Here we report the cryo-electron microscopy (cryo-EM) structures of human ABCB6 with its substrates, coproporphyrin III (CPIII) and hemin, at 3.5 and 3.7 Γ resolution, respectively.
Summary: Membrane residence is certain from ten predicted transmembrane helices; the experimentally resolved membrane is the vacuolar membrane.
Reason: Membrane is correct but uninformative. Vacuolar membrane, which the gene already carries by IDA and IBA, is the specific supported replacement.
heterologously expressed DmHMT-1 suppresses the Cd2+ hypersensitivity of S. pombe hmt-1 mutants and localizes to the vacuolar membrane but does not transport Cd.PC complexes.
Summary: The ABC cassette hydrolyses ATP to drive transport.
Reason: The intact ABC nucleotide-binding domain carries the catalytic machinery for ATP hydrolysis; in human ABCB6 substrate binding stimulates hydrolysis and the E752Q catalytic mutant abolishes it (PMID:38822018, PMID:35950458). ATP hydrolysis is the energy-coupling activity of the transporter.
Supporting Evidence:
file:DROME/Hmt-1/Hmt-1-uniprot.txt
DR InterPro; IPR003439; ABC_transporter-like_ATP-bd.
By contrast, the catalytically inactive E752Q mutant displayed little basal activity and no Cd(II):GSH-stimulated ATPase activity, probably due to an inability to hydrolyze ATP
metal-centered porphyrins, such as hemin (ferric chloride heme) and cobalt (III) PPIX, markedly stimulated the ATPase activity of ABCB6-βTMD0 approximately 6-fold only when the cellular antioxidant glutathione (GSH; Ξ³-glu-cys-gly) was included in the reaction buffer
Summary: Heme (hemin) binding in the transport cavity is the substrate-recognition step of the inherited heme transporter activity.
Reason: Human ABCB6 binds hemin, as a hemin:glutathione complex, in its central cavity (PMID:35950458), and the PAINT eumetazoan node assigns heme binding. Binding is correct for the clade and is retained, but it is a component of the transporter activity rather than a separate core function.
Here we report the cryo-electron microscopy (cryo-EM) structures of human ABCB6 with its substrates, coproporphyrin III (CPIII) and hemin, at 3.5 and 3.7 Γ resolution, respectively.
Summary: An early-endosome pool is plausible on the route to lysosomes but untested for DmHMT-1.
Reason: Same basis as the endosome membrane row; mammalian ABCB6 is endo/lysosomal (PMID:22655043) but no experiment resolves endosomal sub-compartments for the fly protein (PMID:19001374).
heterologously expressed DmHMT-1 suppresses the Cd2+ hypersensitivity of S. pombe hmt-1 mutants and localizes to the vacuolar membrane but does not transport Cd.PC complexes.
Summary: A late-endosome pool is plausible but untested for DmHMT-1.
Reason: Same basis as the endosome membrane row; mammalian ABCB6 is endo/lysosomal (PMID:22655043) but no experiment resolves endosomal sub-compartments for the fly protein (PMID:19001374).
heterologously expressed DmHMT-1 suppresses the Cd2+ hypersensitivity of S. pombe hmt-1 mutants and localizes to the vacuolar membrane but does not transport Cd.PC complexes.
Summary: A multivesicular-body pool is plausible for an exosome-sorted mammalian ABCB6 but untested for DmHMT-1.
Reason: Mammalian ABCB6 reaches reticulocyte exosomes, implying passage through multivesicular bodies (PMID:22655043). Whether the fly protein is sorted this way has not been examined (PMID:19001374).
ABCB6 is a glycoprotein present in the membrane of mature erythrocytes and in exosomes released from reticulocytes during the final steps of erythroid maturation
heterologously expressed DmHMT-1 suppresses the Cd2+ hypersensitivity of S. pombe hmt-1 mutants and localizes to the vacuolar membrane but does not transport Cd.PC complexes.
Summary: Heme transmembrane transport follows from the accepted ABC-type heme transporter activity.
Reason: The row is inferred from GO:0015439, which is accepted on phylogenetic grounds (PAINT eumetazoan ABCB6 node) with human ABCB6 biochemical and structural support (PMID:35950458, PMID:17006453). No fly experiment has measured heme movement.
Here we report the cryo-electron microscopy (cryo-EM) structures of human ABCB6 with its substrates, coproporphyrin III (CPIII) and hemin, at 3.5 and 3.7 Γ resolution, respectively.
Summary: True for any ABC transporter but uninformative; the specific process inherited at the ABCB6 node is heme transmembrane transport.
Reason: PTN000657189 is a deep ABCB node assigning only generic transmembrane transport, which is correct for Hmt-1. The gene carries a specific transmembrane-transport descendant, GO:0035351 heme transmembrane transport (is_a GO:0055085), which is supported at the eumetazoan ABCB6 node. The cadmium-related transport step has no specific term that the evidence supports, because the transported cadmium species is unknown (PMID:19001374); that role is captured by cellular detoxification of cadmium ion.
Propagation Review
Root cause:TERM SCOPING PROBLEM
Failure modes:GRANULARITY MISMATCH
Sources checked:
PANTHER:PTN000657189SUPPORTS TRANSFER
Deep ABCB node assigning generic transmembrane transport; correct for Hmt-1 but less specific than the ABCB6-node heme transmembrane transport.
Here we report the cryo-electron microscopy (cryo-EM) structures of human ABCB6 with its substrates, coproporphyrin III (CPIII) and hemin, at 3.5 and 3.7 Γ resolution, respectively.
heterologously expressed DmHMT-1 suppresses the Cd2+ hypersensitivity of S. pombe hmt-1 mutants and localizes to the vacuolar membrane but does not transport Cd.PC complexes.
Summary: Same claim as the IBA row; generic transmembrane transport should be refined to heme transmembrane transport.
Reason: Consistent with the IBA row for the same term; the ABC transmembrane-domain mapping is correct but general, and GO:0035351 is the supported specific descendant already on the gene.
Here we report the cryo-electron microscopy (cryo-EM) structures of human ABCB6 with its substrates, coproporphyrin III (CPIII) and hemin, at 3.5 and 3.7 Γ resolution, respectively.
IGI PMID:19001374 Drosophila ABC transporter, DmHMT-1, confers tolerance to ca...
ACCEPT
Summary: DmHMT-1 rescues the cadmium hypersensitivity of S. pombe hmt-1 mutants, a phytochelatin-independent detoxification role that the human ABCB6 ortholog shares.
Reason: The complementation experiment directly shows that DmHMT-1 performs the cellular function missing in hmt-1 mutant yeast, and the authors conclude a phytochelatin-independent role in Cd2+ detoxification, consistent with the fly genome lacking phytochelatin synthase. As an ATP-driven transporter that removes cadmium from the cytosol, Hmt-1 performs the detoxifying step itself, so this is participation rather than an indirect phenotype. Human ABCB6 binds Cd(II):glutathione, is stimulated by it, and protects insect Sf9 cells from cadmium only when catalytically active (PMID:38822018), supporting the role as conserved in the clade. The caveat is that the assay is heterologous.
heterologously expressed DmHMT-1 suppresses the Cd2+ hypersensitivity of S. pombe hmt-1 mutants and localizes to the vacuolar membrane but does not transport Cd.PC complexes.
cells infected with baculoviruses carrying the hABCB6core gene exhibited enhanced viability, retaining 40% compared with untreated controls, even at a concentration as high as 50 ΞΌM
By contrast, the catalytically inactive E752Q mutant displayed little basal activity and no Cd(II):GSH-stimulated ATPase activity, probably due to an inability to hydrolyze ATP
Summary: ABC-type transporter activity is the appropriate substrate-neutral term for the transport that underlies cadmium detoxification, whose substrate is unresolved.
Reason: Hmt-1 has a complete ABC half-transporter architecture (TMD0, ABC transmembrane domain and ABC cassette). Its best-supported fly role, cadmium detoxification (PMID:19001374), proceeds by an ABC-type activity whose substrate (free Cd2+, a Cd-glutathione complex or another conjugate) is not determined; DmHMT-1 does not transport Cd-phytochelatin. A more specific heme transporter term is accepted separately, but it would not describe the cadmium role, so the generic term is kept as the precise level the cadmium evidence allows rather than refined.
heterologously expressed DmHMT-1 suppresses the Cd2+ hypersensitivity of S. pombe hmt-1 mutants and localizes to the vacuolar membrane but does not transport Cd.PC complexes.
file:DROME/Hmt-1/Hmt-1-uniprot.txt
DR InterPro; IPR032410; ABCB6_N.
file:DROME/Hmt-1/Hmt-1-uniprot.txt
DR InterPro; IPR003439; ABC_transporter-like_ATP-bd.
ATP-driven ABC half-transporter that protects cells from cadmium by a phytochelatin-independent mechanism, acting at a vacuolar (lysosome-like) membrane in the heterologous assay; the transported cadmium species is unresolved, and thiol-coordinated Cd(II) is the leading candidate from the human ortholog.
heterologously expressed DmHMT-1 suppresses the Cd2+ hypersensitivity of S. pombe hmt-1 mutants and localizes to the vacuolar membrane but does not transport Cd.PC complexes.
cells infected with baculoviruses carrying the hABCB6core gene exhibited enhanced viability, retaining 40% compared with untreated controls, even at a concentration as high as 50 ΞΌM
By contrast, the catalytically inactive E752Q mutant displayed little basal activity and no Cd(II):GSH-stimulated ATPase activity, probably due to an inability to hydrolyze ATP
Inherited ABCB6-clade ATP-dependent transport of heme and porphyrins across an organellar membrane. Assigned by PAINT at the eumetazoan ABCB6 node and grounded in human ABCB6 biochemistry and structures; not yet tested for the fly protein, and its physiological importance in Drosophila is unknown.
Here we report the cryo-electron microscopy (cryo-EM) structures of human ABCB6 with its substrates, coproporphyrin III (CPIII) and hemin, at 3.5 and 3.7 Γ resolution, respectively.
metal-centered porphyrins, such as hemin (ferric chloride heme) and cobalt (III) PPIX, markedly stimulated the ATPase activity of ABCB6-βTMD0 approximately 6-fold only when the cellular antioxidant glutathione (GSH; Ξ³-glu-cys-gly) was included in the reaction buffer
Q: Where does endogenous Hmt-1 reside in fly cells (lysosome, endosomes, or another membrane), and does its location change with cadmium exposure?
Q: Which cadmium species does DmHMT-1 transport in the absence of phytochelatins; is Cd(II)-bis-glutathione a substrate, as for human ABCB6?
Q: Does Drosophila Hmt-1 transport heme or porphyrins in vivo, and does loss of Hmt-1 alter porphyrin accumulation or heme-dependent processes?
Suggested Experiments
Experiment: Purify DmHMT-1 (or its TMD0-deleted core) and measure ATPase stimulation by Cd(II):GSH, hemin:GSH and coproporphyrin III, with a Walker B glutamate-to-glutamine mutant as control.
Type: biochemical reconstitution
Experiment: Tag endogenous Hmt-1 by CRISPR knock-in and co-localize with lysosomal (LAMP1, Spinster) and endosomal (Rab5, Rab7) markers in fat body and Malpighian tubule, with and without dietary cadmium.
Type: localization
Experiment: Compare cadmium survival and tissue cadmium content in Hmt-1 null versus control flies, with rescue by wild-type and ATPase-dead transgenes, to test whether the yeast complementation result reflects an in vivo role.
Type: genetic loss of function
External Prediction Reviews
These computational predictions are reviewed separately from the GOA annotation set used for this review. The assessments below are from this project and do not constitute official GO annotations or endorsement by GO/UniProt. They are not included in the existing annotation review above.
The single ABC-type transporter activity prediction is biologically supported by the complete ABCB6-type half-transporter architecture and phytochelatin-independent cadmium-tolerance function of DmHMT-1, and the identical term is already annotated to the gene and accepted as its core activity.
Prediction method: ProtNLM2 Β· Version: UniProt API snapshot 2026-09-08
Review rationale: ABC-type transporter activity is supported by the complete ABCB6-type architecture of Hmt-1 (TMD0, ABC transmembrane domain and ABC nucleotide-binding cassette) and by functional rescue of the fission-yeast hmt-1 cadmium-hypersensitivity phenotype by DmHMT-1, which acts without transporting Cd-phytochelatin complexes; the human ortholog ABCB6 is an ATP-driven porphyrin/heme transporter and heavy-metal efflux pump. The identical term GO:0140359 is already annotated to Hmt-1 (InterPro2GO IEA) and the gene review accepts it as the core molecular function, the precise level the cadmium evidence allows because the transported cadmium species is unresolved. The more specific ABC-type heme transporter activity is also carried (IBA, eumetazoan ABCB6 PAINT node), but it does not describe the cadmium role, so the prediction is not materially less precise than the curated core function. Not novel.
Supporting Evidence:
PMID:19001374: "heterologously expressed DmHMT-1 suppresses the Cd2+ hypersensitivity of S. pombe hmt-1 mutants and localizes to the vacuolar membrane but does not transport Cd.PC complexes."
PMID:35950458: "Here we report the cryo-electron microscopy (cryo-EM) structures of human ABCB6 with its substrates, coproporphyrin III (CPIII) and hemin, at 3.5 and 3.7 Γ resolution, respectively."
PMID:38822018: "also functions as a heavy metal efflux pump"