Dic4 (CG18363) is a Drosophila melanogaster member of the mitochondrial carrier (SLC25) family, placed with Dic1-Dic3 and the mammalian dicarboxylate carrier SLC25A10 in the dicarboxylate-carrier subfamily (PANTHER PTHR45618:SF13). The 302-residue protein has the three repeated Mito_carr domains of an inner-membrane carrier, is expressed mainly at the pupal stage and localizes to mitochondria. Unlike its paralogs Dic1 (dicarboxylate/phosphate antiporter) and Dic3 (phosphate/sulfate/thiosulfate antiporter), recombinant Dic4 reconstituted into liposomes catalysed no homo- or hetero-exchange of dicarboxylates or phosphate. Substitutions at conserved substrate contact points CP1 and CP2 have been proposed to explain this, consistent with a duplicated, fast-evolving paralog. Whether Dic4 transports an untested substrate, or has lost transport activity, is unknown.
IDANOT PMID:21130726 A novel subfamily of mitochondrial dicarboxylate carriers fr...
ACCEPT
Summary: Experimental NOT: reconstituted Dic4 showed no dicarboxylate transport.
Reason: Recombinant Dic4 reconstituted into liposomes catalysed no homo- or hetero-exchange, in an assay in which paralogs Dic1 and Dic3 were active. The NOT annotation records this well. It is consistent with the PAINT NOT node PTN000640888, which removes the dicarboxylate terms from the Dic4 lineage.
IDA PMID:21130726 A novel subfamily of mitochondrial dicarboxylate carriers fr...
ACCEPT
Summary: Mitochondrial localization of Dic4 was shown directly.
Reason: The primary study reports that all expressed fly Dic proteins, including Dic4, are localized in mitochondria. The inner-membrane annotations add the sub-mitochondrial compartment.
Summary: Inner mitochondrial membrane, the location of mitochondrial carrier-family proteins.
Reason: PAINT placed inner-membrane location at the family-level node PTN002515516, with many experimentally located members. Dic4 has the three Mito_carr repeats of an inner-membrane carrier, and it is mitochondrial by direct observation. Loss of transport activity would not remove the membrane location of the carrier fold.
TAS PMID:21130726 A novel subfamily of mitochondrial dicarboxylate carriers fr...
ACCEPT
Summary: Inner mitochondrial membrane, the location of mitochondrial carrier-family proteins.
Reason: The primary paper treats Dic4 as a mitochondrial carrier-family member and shows it is mitochondrial. Members of this family reside in the inner membrane, which the IBA row supports by phylogeny.
IDANOT PMID:21130726 A novel subfamily of mitochondrial dicarboxylate carriers fr...
ACCEPT
Summary: Experimental NOT: reconstituted Dic4 showed no dicarboxylate transport.
Reason: Recombinant Dic4 reconstituted into liposomes catalysed no homo- or hetero-exchange, in an assay in which paralogs Dic1 and Dic3 were active. The NOT annotation records this well. It is consistent with the PAINT NOT node PTN000640888, which removes the dicarboxylate terms from the Dic4 lineage.
Summary: Ancestral anion-transport IBA, contradicted by the negative Dic4 reconstitution and its substituted contact points.
Reason: PAINT placed phosphate, sulfate and thiosulfate transport at the eukaryote-level node PTN000756618, seeded by Dic1 and Dic3, and Dic4 is a member of the same PANTHER subfamily (SF13), so the transfer is phylogenetically grounded. The PAINT curator has already added a fly-lineage NOT node (PTN000640888) that removes the dicarboxylate terms from Dic4, while leaving the phosphate/sulfur-anion terms in place. Target-specific evidence argues against these remaining terms. Dic4 itself was reconstituted in the same assay system in which Dic1 and Dic3 were active, and it catalysed neither homo- nor hetero-exchange; the authors state that it cannot transport dicarboxylates or phosphate. They attribute this to substitutions at substrate contact points CP1 and CP2 in a duplicated, fast-evolving copy, and Dic4 has the longest branch among the fly Dic paralogs in our tree. The refolded inclusion-body assay cannot exclude an untested substrate or condition, and the abstract-only primary paper does not list every substrate tested, so this is marked as over-annotation rather than removed.
Propagation Review
Root cause:PROPAGATION BAD
Failure modes:FUNCTIONAL DIVERGENCEPSEUDO OR SUBACTIVITY LOSS
Sources checked:
PANTHER:PTN000756618 · PTN000756618 SUPPORTS SOURCE BUT NOT TARGET
Activity is supported for donors Dic1 and Dic3; the Dic4 reconstitution was negative and its contact points are substituted.
Its gene could be derived from a duplication of the DmDIC ancestral gene, but the lack of selective pressure upon this gene copy would have allowed mutations impairing DmDic4p’s transport function
Summary: Ancestral anion-transport IBA, contradicted by the negative Dic4 reconstitution and its substituted contact points.
Reason: PAINT placed phosphate, sulfate and thiosulfate transport at the eukaryote-level node PTN000756618, seeded by Dic1 and Dic3, and Dic4 is a member of the same PANTHER subfamily (SF13), so the transfer is phylogenetically grounded. The PAINT curator has already added a fly-lineage NOT node (PTN000640888) that removes the dicarboxylate terms from Dic4, while leaving the phosphate/sulfur-anion terms in place. Target-specific evidence argues against these remaining terms. Dic4 itself was reconstituted in the same assay system in which Dic1 and Dic3 were active, and it catalysed neither homo- nor hetero-exchange; the authors state that it cannot transport dicarboxylates or phosphate. They attribute this to substitutions at substrate contact points CP1 and CP2 in a duplicated, fast-evolving copy, and Dic4 has the longest branch among the fly Dic paralogs in our tree. The refolded inclusion-body assay cannot exclude an untested substrate or condition, and the abstract-only primary paper does not list every substrate tested, so this is marked as over-annotation rather than removed.
Propagation Review
Root cause:PROPAGATION BAD
Failure modes:FUNCTIONAL DIVERGENCEPSEUDO OR SUBACTIVITY LOSS
Sources checked:
PANTHER:PTN000756618 · PTN000756618 SUPPORTS SOURCE BUT NOT TARGET
Activity is supported for donors Dic1 and Dic3; the Dic4 reconstitution was negative and its contact points are substituted.
Its gene could be derived from a duplication of the DmDIC ancestral gene, but the lack of selective pressure upon this gene copy would have allowed mutations impairing DmDic4p’s transport function
Summary: Ancestral anion-transport IBA, contradicted by the negative Dic4 reconstitution and its substituted contact points.
Reason: PAINT placed phosphate, sulfate and thiosulfate transport at the eukaryote-level node PTN000756618, seeded by Dic1 and Dic3, and Dic4 is a member of the same PANTHER subfamily (SF13), so the transfer is phylogenetically grounded. The PAINT curator has already added a fly-lineage NOT node (PTN000640888) that removes the dicarboxylate terms from Dic4, while leaving the phosphate/sulfur-anion terms in place. Target-specific evidence argues against these remaining terms. Dic4 itself was reconstituted in the same assay system in which Dic1 and Dic3 were active, and it catalysed neither homo- nor hetero-exchange; the authors state that it cannot transport dicarboxylates or phosphate. They attribute this to substitutions at substrate contact points CP1 and CP2 in a duplicated, fast-evolving copy, and Dic4 has the longest branch among the fly Dic paralogs in our tree. The refolded inclusion-body assay cannot exclude an untested substrate or condition, and the abstract-only primary paper does not list every substrate tested, so this is marked as over-annotation rather than removed.
Propagation Review
Root cause:PROPAGATION BAD
Failure modes:FUNCTIONAL DIVERGENCEPSEUDO OR SUBACTIVITY LOSS
Sources checked:
PANTHER:PTN000756618 · PTN000756618 SUPPORTS SOURCE BUT NOT TARGET
Activity is supported for donors Dic1 and Dic3; the Dic4 reconstitution was negative and its contact points are substituted.
Its gene could be derived from a duplication of the DmDIC ancestral gene, but the lack of selective pressure upon this gene copy would have allowed mutations impairing DmDic4p’s transport function
Summary: Membrane is correct but general; mitochondrial inner membrane is supported.
Reason: Dic4 is a multi-pass carrier-family protein localized in mitochondria. The more specific term mitochondrial inner membrane (GO:0005743), already carried by Dic4 (IBA and TAS), is supported.
Summary: Ancestral anion-transport IBA, contradicted by the negative Dic4 reconstitution and its substituted contact points.
Reason: PAINT placed phosphate, sulfate and thiosulfate transport at the eukaryote-level node PTN000756618, seeded by Dic1 and Dic3, and Dic4 is a member of the same PANTHER subfamily (SF13), so the transfer is phylogenetically grounded. The PAINT curator has already added a fly-lineage NOT node (PTN000640888) that removes the dicarboxylate terms from Dic4, while leaving the phosphate/sulfur-anion terms in place. Target-specific evidence argues against these remaining terms. Dic4 itself was reconstituted in the same assay system in which Dic1 and Dic3 were active, and it catalysed neither homo- nor hetero-exchange; the authors state that it cannot transport dicarboxylates or phosphate. They attribute this to substitutions at substrate contact points CP1 and CP2 in a duplicated, fast-evolving copy, and Dic4 has the longest branch among the fly Dic paralogs in our tree. The refolded inclusion-body assay cannot exclude an untested substrate or condition, and the abstract-only primary paper does not list every substrate tested, so this is marked as over-annotation rather than removed.
Propagation Review
Root cause:PROPAGATION BAD
Failure modes:FUNCTIONAL DIVERGENCEPSEUDO OR SUBACTIVITY LOSS
Sources checked:
PANTHER:PTN000756618 · PTN000756618 SUPPORTS SOURCE BUT NOT TARGET
Activity is supported for donors Dic1 and Dic3; the Dic4 reconstitution was negative and its contact points are substituted.
Its gene could be derived from a duplication of the DmDIC ancestral gene, but the lack of selective pressure upon this gene copy would have allowed mutations impairing DmDic4p’s transport function
Summary: Generic transport predicted from the carrier domain; unresolved because the only direct test was negative.
Reason: The InterPro carrier signature predicts transmembrane transport. However, the only direct test found no exchange activity for Dic4, and the authors suggest loss of activity in a duplicated copy. No transported substrate is known. An untested substrate cannot be excluded, so the generic term is neither confirmed nor refuted.
Summary: Ancestral anion-transport IBA, contradicted by the negative Dic4 reconstitution and its substituted contact points.
Reason: PAINT placed phosphate, sulfate and thiosulfate transport at the eukaryote-level node PTN000756618, seeded by Dic1 and Dic3, and Dic4 is a member of the same PANTHER subfamily (SF13), so the transfer is phylogenetically grounded. The PAINT curator has already added a fly-lineage NOT node (PTN000640888) that removes the dicarboxylate terms from Dic4, while leaving the phosphate/sulfur-anion terms in place. Target-specific evidence argues against these remaining terms. Dic4 itself was reconstituted in the same assay system in which Dic1 and Dic3 were active, and it catalysed neither homo- nor hetero-exchange; the authors state that it cannot transport dicarboxylates or phosphate. They attribute this to substitutions at substrate contact points CP1 and CP2 in a duplicated, fast-evolving copy, and Dic4 has the longest branch among the fly Dic paralogs in our tree. The refolded inclusion-body assay cannot exclude an untested substrate or condition, and the abstract-only primary paper does not list every substrate tested, so this is marked as over-annotation rather than removed.
Propagation Review
Root cause:PROPAGATION BAD
Failure modes:FUNCTIONAL DIVERGENCEPSEUDO OR SUBACTIVITY LOSS
Sources checked:
PANTHER:PTN000756618 · PTN000756618 SUPPORTS SOURCE BUT NOT TARGET
Activity is supported for donors Dic1 and Dic3; the Dic4 reconstitution was negative and its contact points are substituted.
Its gene could be derived from a duplication of the DmDIC ancestral gene, but the lack of selective pressure upon this gene copy would have allowed mutations impairing DmDic4p’s transport function
The curator therefore deliberately withdrew dicarboxylate transport from the Dic4 lineage but left the phosphate/sulfur-anion terms in place.
Core Functions
Mitochondrial inner-membrane carrier-family protein of the dicarboxylate-carrier subfamily with no transport activity detected in reconstitution assays; its substrate, if any, is unknown.
Q: Should PAINT extend the fly-lineage NOT node PTN000640888 to phosphate, sulfate and thiosulfate transport, given that reconstituted Dic4 catalysed no exchange of any tested substrate?
Q: Does Dic4 have a substrate outside the dicarboxylate/phosphate/sulfur-anion panel, or is it a transport-dead paralog?
Suggested Experiments
Experiment: Reconstitute Dic4 and CP1/CP2-restored variants into proteoliposomes and screen a broad substrate panel, including nucleotides and cofactors, alongside active Dic1 and Dic3 controls.
Experiment: Test pupal-stage phenotypes and mitochondrial metabolite profiles of Dic4 null mutants.
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 ProtNLM2 API snapshot retrieved 2026-09-08 contains no GO-term predictions for Q9VVS1, so there is nothing to score. The absence is assessed against the re-reviewed gene. The terms best supported for Dic4 are mitochondrion (GO:0005739, IDA) and mitochondrial inner membrane (GO:0005743, IBA), both already in GOA and accepted by the gene review, so emitting either would have been CNN rather than a novel prediction. No transport activity is supported: reconstituted Dic4 catalysed no homo- or hetero-exchange of dicarboxylates or phosphate, GOA carries NOT annotations for dicarboxylic acid transmembrane transporter activity and dicarboxylic acid transport, and the gene review marks the IBA sulfate, thiosulfate and phosphate transport terms as over-annotations. Omitting a transport-activity term is therefore appropriate. The separate FUNCTION-text proposal of mitochondrial thiamine pyrophosphate uptake has no positive support and remains UNC; that activity belongs to the characterized carrier Tpc1. A PubMed search for Dic4, DmDic4p and CG18363 returned only the primary characterization study. predictions is empty because no GO or EC prediction was emitted; the narrative judgment remains in the linked function review and is not a score assigned to the omission.
Dicarboxylate carrier 4 (Dic4) encodes a protein of the inner mitochondrial membrane. It belongs to a subfamily of mitochondrial dicarboxylate carriers but it doesn't catalyse an exchange for malate or phosphate.