MDJ1 encodes the major mitochondrial matrix DnaJ/Hsp40 cochaperone for the mtHsp70 Ssc1 system. Mdj1 stimulates Hsp70-dependent folding/refolding cycles, protects mitochondrial matrix proteins from misfolding and heat-induced aggregation, and is enriched at mitochondrial nucleoids where it supports maintenance of functional mitochondrial DNA.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005737 cytoplasm | IBA GO_REF:0000033 | MODIFY | Summary: The cytoplasm IBA is correct but too broad for a mitochondrial matrix DnaJ and should be refined to mitochondrial matrix. Reason: Mdj1 is imported into mitochondria and acts with Ssc1 in the matrix. The PTN002454318 cytoplasm IBD is not wrong because mitochondrion is part_of cytoplasm, and the node is seeded by the yeast MDJ1 matrix evidence itself, but the existing GO:0005759 mitochondrial matrix annotations state the direct compartment more precisely. Propagation Review Root cause: TERM SCOPING PROBLEM Failure modes: GRANULARITY MISMATCH Sources checked: PANTHER:PTN002454318 SUPPORTS TRANSFER The broad ancestral cytoplasm call is supported and includes MDJ1 itself among its experimental descendants, but it is less precise than mitochondrial matrix for the target. Proposed replacements: mitochondrial matrix Supporting Evidence: PMID:8943361 Mdj1p, a DnaJ homolog in the mitochondria of Saccharomyces cerevisiae, is involved in the folding of proteins in the mitochondrial matrix. |
| GO:0042026 protein refolding | IBA GO_REF:0000033 | ACCEPT | Summary: The refolding IBA matches Mdj1's conserved mitochondrial Hsp70 cochaperone role. Reason: The PTN002454318 refolding IBD sits on the current MDJ1 lineage and is supported directly by yeast Mdj1 experiments showing impaired folding of newly imported proteins and purified Ssc1/Mdj1/Yge1-dependent luciferase reactivation. Propagation Review Root cause: NO FAILURE CORE Sources checked: PANTHER:PTN002454318 SUPPORTS TRANSFER Current PTHR43096 PAINT retains protein refolding at PTN002454318; MDJ1 descends from that node and is itself one of the experimental descendants supporting the IBD. Supporting Evidence: PMID:8168133 The efficiency of refolding of a tester protein, dihydrofolate reductase, was significantly reduced in mitochondria lacking Mdj1p after incubation at elevated temperature. PMID:9973563 Luciferase denatured at 42 degreesC is actively reactivated by Ssc1p, Mdj1p and/or Yge1p after lowering the temperature to 25 degreesC. |
| GO:0051082 unfolded protein binding | IBA GO_REF:0000033 | MODIFY | Summary: Obsolete unfolded protein binding should be replaced with the chaperone activity that Mdj1 performs. Reason: Mdj1 executes a DnaJ/Hsp40 protein-folding cochaperone function with mitochondrial Hsp70. GO:0051082 is obsolete; GO:0044183 better captures this client-folding chaperone activity without asserting a standalone ATPase. Propagation Review Root cause: TERM SCOPING PROBLEM Failure modes: GRANULARITY MISMATCH Sources checked: PANTHER:PTN002454318 SOURCE STALE OR MISSING GOA records the MDJ1 IBA at PTN002454318, but the current PTHR43096 snapshot retains this node for GO:0042026 protein refolding and no longer carries GO:0051082. Proposed replacements: protein folding chaperone Supporting Evidence: PMID:7957078 Mdj1p is shown to regulate the ATP dependent association of an unfolded polypeptide chain with mt-hsp70 affecting binding to as well as release from mt-hsp70. |
| GO:0005524 ATP binding | IEA GO_REF:0000002 | REMOVE | Summary: ATP binding is a domain-transfer overreach for a J-domain cochaperone. Reason: Mdj1 is a DnaJ/Hsp40 cochaperone for the ATPase Ssc1. It stimulates the Hsp70 cycle but has no Hsp70 nucleotide-binding domain, so the existing ATPase activator annotation captures the supported molecular function and ATP binding should not be retained as an MDJ1 activity. Supporting Evidence: PMID:9973563 The yeast mitochondrial Hsp70, Ssc1p, functions as a molecular chaperone with its partner proteins, Mdj1p (DnaJ homologue) and Yge1p (GrpE homologue). |
| GO:0005739 mitochondrion | IEA GO_REF:0000044 | ACCEPT | Summary: Mitochondrion is the organelle where Mdj1 performs its chaperone role. Reason: Mdj1 is imported into mitochondria and carries out Ssc1-dependent folding and refolding in the matrix. Supporting Evidence: PMID:8943361 Mdj1p, a DnaJ homolog in the mitochondria of Saccharomyces cerevisiae, is involved in the folding of proteins in the mitochondrial matrix. |
| GO:0006457 protein folding | IEA GO_REF:0000002 | ACCEPT | Summary: Protein folding is supported by Mdj1 loss-of-function experiments. Reason: Loss of Mdj1 impairs folding of newly imported matrix proteins, and later biochemical work reconstituted the Ssc1/Mdj1/Yge1p chaperone system in vitro. Supporting Evidence: PMID:8168133 Import of precursor proteins was not affected by a lack of Mdj1p, but folding of newly imported proteins was markedly impaired. |
| GO:0008270 zinc ion binding | IEA GO_REF:0000043 | ACCEPT | Summary: Manual review: zinc ion binding is consistent with known biology of MDJ1. Reason: Retained as supported or plausible for this gene and evidence context. |
| GO:0009408 response to heat | IEA GO_REF:0000002 | ACCEPT | Summary: Heat-response annotation is consistent with Mdj1 protection against thermal aggregation. Reason: Mdj1 protects mitochondrial proteins from heat-induced aggregation in isolated-mitochondrion assays, so retaining a heat-response process mapping is biologically sound. Supporting Evidence: PMID:8603724 Only the absence of Mdj1p led to enhanced protein aggregation. Thus, a central role in the transient protection against heat stress is attributed to this mitochondrial DnaJ homologue. |
| GO:0031072 heat shock protein binding | IEA GO_REF:0000002 | ACCEPT | Summary: Mdj1 functions through interaction with mitochondrial Hsp70. Reason: Interaction with mt-Hsp70/Ssc1 is central to Mdj1 function, including association and release of unfolded polypeptide chains in the PIM1 quality-control pathway. Supporting Evidence: PMID:7957078 Mdj1p is shown to regulate the ATP dependent association of an unfolded polypeptide chain with mt-hsp70 affecting binding to as well as release from mt-hsp70. |
| GO:0046872 metal ion binding | IEA GO_REF:0000043 | ACCEPT | Summary: Manual review: metal ion binding is consistent with known biology of MDJ1. Reason: Retained as supported or plausible for this gene and evidence context. |
| GO:0051082 unfolded protein binding | IEA GO_REF:0000002 | MODIFY | Summary: Obsolete unfolded protein binding should be replaced with protein folding chaperone. Reason: GO:0051082 is obsolete. The InterPro-derived assertion reflects the real client-binding DnaJ/Hsp40 cochaperone role, which is captured more appropriately by GO:0044183 protein folding chaperone. Proposed replacements: protein folding chaperone Supporting Evidence: PMID:8943361 precursor proteins in transit which had further entered the matrix were found in a complex with Mdj1p. |
| GO:0005515 protein binding | IPI PMID:16554755 Global landscape of protein complexes in the yeast Saccharom... | MARK AS OVER ANNOTATED | Summary: Generic protein binding adds no specific functional assertion for Mdj1. Reason: This high-throughput complex survey may report a real interaction, but GO:0005515 is too generic to represent Mdj1's DnaJ cochaperone activity or a specific client-folding function. No more informative molecular-function replacement is supported by this evidence alone. |
| GO:0005515 protein binding | IPI PMID:19536198 An atlas of chaperone-protein interactions in Saccharomyces ... | MARK AS OVER ANNOTATED | Summary: Generic protein binding adds no specific functional assertion for Mdj1. Reason: The chaperone-interaction atlas supports many TAP-tag based associations, including candidate chaperone substrates, but GO:0005515 does not say what Mdj1 does and should not be retained for this generic physical-interaction evidence. Supporting Evidence: PMID:19536198 It should be emphasized that the interactions presented are indirect TAP-tag based interactions and not direct binary interactions. |
| GO:0005515 protein binding | IPI PMID:27107014 An inter-species protein-protein interaction network across ... | MARK AS OVER ANNOTATED | Summary: Generic protein binding adds no specific functional assertion for Mdj1. Reason: The inter-species interactome assay was designed to map cross-species physical contacts, not to establish a specific Mdj1 molecular activity. GO:0005515 is therefore uninformative and no narrower replacement term is warranted from this screen. |
| GO:0008270 zinc ion binding | RCA PMID:30358795 The cellular economy of the Saccharomyces cerevisiae zinc pr... | ACCEPT | Summary: Manual review: zinc ion binding is consistent with known biology of MDJ1. Reason: Retained as supported or plausible for this gene and evidence context. |
| GO:0005739 mitochondrion | HDA PMID:24769239 Quantitative variations of the mitochondrial proteome and ph... | ACCEPT | Summary: Mitochondrion is the correct organellar localization for Mdj1. Reason: Mdj1 is a mitochondrial matrix cochaperone, so its detection in isolated yeast mitochondria is consistent with the core compartment rather than a peripheral or condition-specific location. Supporting Evidence: PMID:8943361 Mdj1p, a DnaJ homolog in the mitochondria of Saccharomyces cerevisiae, is involved in the folding of proteins in the mitochondrial matrix. |
| GO:0005739 mitochondrion | HDA PMID:16823961 Toward the complete yeast mitochondrial proteome: multidimen... | ACCEPT | Summary: Mitochondrion is the correct organellar localization for Mdj1. Reason: Mdj1 is a mitochondrial matrix cochaperone, so its detection in the PROMITO yeast mitochondrial proteome supports the established core localization. Supporting Evidence: PMID:8943361 Mdj1p, a DnaJ homolog in the mitochondria of Saccharomyces cerevisiae, is involved in the folding of proteins in the mitochondrial matrix. |
| GO:0001671 ATPase activator activity | IDA PMID:9973563 Two distinct mechanisms operate in the reactivation of heat-... | ACCEPT | Summary: Mdj1 activates the Ssc1 mitochondrial Hsp70 chaperone system. Reason: Purified mature Ssc1p, Mdj1p and Yge1p reconstitute mitochondrial Hsp70 chaperone-mediated protection and refolding of heat-denatured luciferase; retaining the curated ATPase activator activity is consistent with Mdj1's J-domain cochaperone role. Supporting Evidence: PMID:9973563 With these purified components of the mitochondrial Hsp70 chaperone system, we have succeeded in reconstituting their chaperone functions in the protection of firefly luciferase against thermal damage in vitro. |
| GO:0005759 mitochondrial matrix | IDA PMID:15383543 Zim17, a novel zinc finger protein essential for protein imp... | ACCEPT | Summary: Mitochondrial matrix is the established compartment of Mdj1 action. Reason: Although the cached Zim17 abstract does not describe its Mdj1 assay, independent Mdj1 publications establish matrix-localized folding and refolding, so the SGD IDA annotation is consistent with the gene's core compartment. Supporting Evidence: PMID:8943361 Mdj1p, a DnaJ homolog in the mitochondria of Saccharomyces cerevisiae, is involved in the folding of proteins in the mitochondrial matrix. |
| GO:0006458 'de novo' protein folding | IMP PMID:8168133 Mdj1p, a novel chaperone of the DnaJ family, is involved in ... | ACCEPT | Summary: Mdj1 is needed for folding newly imported mitochondrial proteins. Reason: MDJ1 disruption specifically impaired folding of imported precursor proteins without blocking their import, supporting a direct role in de novo matrix protein folding. Supporting Evidence: PMID:8168133 Import of precursor proteins was not affected by a lack of Mdj1p, but folding of newly imported proteins was markedly impaired. |
| GO:0006515 protein quality control for misfolded or incompletely synthesized proteins | IMP PMID:7957078 Molecular chaperones cooperate with PIM1 protease in the deg... | ACCEPT | Summary: Mdj1 keeps mitochondrial misfolded proteins competent for PIM1 degradation. Reason: Mdj1 and mt-Hsp70 maintain misfolded matrix proteins in a soluble state that allows PIM1 protease-mediated turnover, so the protein-quality-control annotation is directly supported. Supporting Evidence: PMID:7957078 ATP dependent proteolytic degradation of misfolded proteins in the mitochondrial matrix is mediated by the PIM1 protease and depends on the molecular chaperone proteins mt-hsp70 and Mdj1p. |
| GO:0009408 response to heat | IMP PMID:8603724 Role of the mitochondrial DnaJ homologue, Mdj1p, in the prev... | ACCEPT | Summary: Mdj1 prevents heat-induced aggregation in mitochondria. Reason: Isolated-mitochondrion assays with firefly luciferase showed that loss of Mdj1, unlike tested mt-Hsp70 or Mge1 mutations, enhanced aggregation after a 40 degrees Celsius temperature shift. Supporting Evidence: PMID:8603724 Only the absence of Mdj1p led to enhanced protein aggregation. Thus, a central role in the transient protection against heat stress is attributed to this mitochondrial DnaJ homologue. |
| GO:0042026 protein refolding | IMP PMID:8168133 Mdj1p, a novel chaperone of the DnaJ family, is involved in ... | ACCEPT | Summary: Mdj1 protects heat-denatured proteins for mitochondrial refolding. Reason: Mitochondria lacking Mdj1 had reduced refolding of dihydrofolate reductase after elevated-temperature incubation, supporting this process annotation. Supporting Evidence: PMID:8168133 The efficiency of refolding of a tester protein, dihydrofolate reductase, was significantly reduced in mitochondria lacking Mdj1p after incubation at elevated temperature. |
| GO:0042026 protein refolding | IDA PMID:9973563 Two distinct mechanisms operate in the reactivation of heat-... | ACCEPT | Summary: Purified Mdj1 participates in Hsp70-dependent luciferase refolding in vitro. Reason: Purified mature Mdj1, Ssc1 and Yge1 reconstitute protection and active reactivation of heat-denatured luciferase, directly supporting the protein-refolding annotation. Supporting Evidence: PMID:9973563 Luciferase denatured at 42 degreesC is actively reactivated by Ssc1p, Mdj1p and/or Yge1p after lowering the temperature to 25 degreesC. |
| GO:0051082 unfolded protein binding | IMP PMID:8943361 Role of the mitochondrial DnaJ homolog Mdj1p as a chaperone ... | MODIFY | Summary: Obsolete unfolded protein binding should be replaced with protein folding chaperone. Reason: GO:0051082 is obsolete. The Mdj1 mutant data support a client-binding Hsp40 cochaperone that protects newly synthesized and newly imported matrix proteins, so GO:0044183 is the closest current molecular-function term. Proposed replacements: protein folding chaperone Supporting Evidence: PMID:8943361 Mdj1p and mt-Hsp70 were found in a complex with nascent polypeptide chains on mitochondrial ribosomes. |
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Download this section (compressed HTML)Q: Should MDJ1 receive an explicit mitochondrial genome maintenance process annotation based on nucleoid localization and mtDNA-loss phenotypes?
Q: Is direct DNA-binding/nucleoid association sufficiently represented by current GO cellular-component and process annotations?
Experiment: Test whether Mdj1 client-binding domain mutants separate mitochondrial protein-refolding activity from mtDNA maintenance in the same strain background.
Experiment: Map nucleoid-associated Mdj1 clients by proximity labeling under respiratory growth and heat-stress conditions.
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Download this section (compressed HTML)Co-chaperone that stimulates HSP70 protein Ssc1p ATPase activity; involved in protein folding/refolding in the mitochodrial matrix; required for proteolysis of misfolded proteins; member of the HSP40 (DnaJ) family of chaperones
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