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Showing PAM16 — TIMM16 is a alias.

PAM16

Mitochondrial import inner membrane translocase subunit TIM16 · UniProt Q9Y3D7

Length
125 aa
Mass
13.8 kDa
Annotated
2026-06-10
40 papers in source corpus 17 papers cited in narrative 17 extracted findings
Cross-family judge vs UniProt: Affinage preferred faithfulness: 7/7 claims corpus-supported (100%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

PAM16 (Magmas/Tim16) is an essential peripheral inner-membrane subunit of the mitochondrial presequence translocase-associated import motor (PAM), selectively required for translocation of preproteins into the matrix but not for inner-membrane insertion (PMID:14981507, PMID:14981506). It functions as a J-like co-chaperone that forms an obligate, thermally stabilized heterodimer with the J-protein Pam18/Tim14 through their respective J and degenerate-J domains, an interaction whose integrity is essential for viability and protein import (PMID:16977310, PMID:18003975, PMID:17242434). Rather than acting as a typical J-domain protein, PAM16 modulates Pam18-mediated stimulation of mtHsp70 ATPase activity and, most critically, tethers Pam18 to the TIM23 translocon; recruitment of the heterodimer is governed chiefly by the N-terminal hydrophobic segment of PAM16, which engages the matrix face of the translocon (PMID:15218029, PMID:18003975, PMID:17452317, PMID:22031295). This coupling additionally partitions Pam18's dual roles: PAM16 directs Pam18 to TIM23 for import while attenuating its function in mtHsp70-dependent respiratory chain supercomplex assembly, such that heterodimer disruption redistributes Pam18 to respiratory complexes (PMID:35385740). The human ortholog Magmas complements yeast Δpam16, assembles with the J-proteins DnaJC19 and DnaJC15 in distinct TIM23 import motors via constitutive Magmas variants, and carries out an import-independent role in regulating mitochondrial ROS balance through its J-like domain (PMID:20053669, PMID:25165880, PMID:34715125). A homozygous MAGMAS mutation that destabilizes the protein and impairs matrix import causes a severe human skeletal dysplasia (PMID:24786642). PAM16 levels are further controlled by degradation through the matrix Lon/Pim1 protease (PMID:41099349).

Mechanistic history

Synthesis pass · year-by-year structured walk · 12 steps
  1. 2004 High

    Established PAM16 as an essential, dedicated motor subunit by showing it is specifically required for matrix preprotein import and for recruiting the J-protein Pam18 to the presequence translocase.

    Evidence Genetic depletion, reciprocal Co-IP, and in vitro import assays in S. cerevisiae (two companion studies)

    PMID:14981506 PMID:14981507

    Open questions at the time
    • Did not resolve the structural basis of the Pam16-Pam18 interaction
    • Mechanism of translocon tethering not yet mapped
  2. 2004 High

    Clarified that PAM16 is not a canonical J-protein but instead antagonizes Pam18-mediated stimulation of mtHsp70 ATPase activity, defining it as a regulatory rather than stimulatory cofactor.

    Evidence In vitro ATPase stimulation assays, HPD-motif site-directed mutagenesis, and yeast complementation

    PMID:15218029

    Open questions at the time
    • Whether ATPase inhibition is the physiologically critical function was unresolved
    • Structural distinction between J and J-like domains not yet shown
  3. 2005 High

    Showed via genetic suppressor analysis that heterodimer stability per se — not the altered ATPase activity — is the functionally critical property of the Pam16:Pam18 pair.

    Evidence Yeast genetics, intragenic suppressor analysis, in vitro ATPase and growth assays

    PMID:16105940

    Open questions at the time
    • The molecular interface stabilizing the heterodimer remained structurally undefined
    • Did not address how the dimer engages the translocon
  4. 2006 High

    Provided the structural basis for the heterodimer, revealing that the J and J-like domains share a fold but differ in surface, and that the dimer is essential for viability.

    Evidence X-ray crystallography of the Tim14-Tim16 complex with mutagenesis and ATPase/viability assays

    PMID:16977310

    Open questions at the time
    • Structure did not include the N-terminal translocon-tethering segment
    • Mammalian complex structure not determined
  5. 2007 High

    Defined the multipartite tethering of the heterodimer to TIM23 and established that PAM16's N-terminal hydrophobic segment is the dominant determinant of translocon association.

    Evidence Co-IP, deletion/mutagenesis, suppressor mapping (to TIM44), in vitro import, and biophysical denaturation assays in yeast and recombinant proteins

    PMID:17242434 PMID:17452317 PMID:18003975

    Open questions at the time
    • The matrix-side translocon partner directly contacted by the Pam16 N-terminus was not identified
    • Quantitative contribution of each tethering contact not fully separated
  6. 2009 Medium

    Demonstrated cross-species conservation of the import motor by reconstituting functional human-yeast hybrid heterodimers that bind mtHsp70.

    Evidence In vitro pulldown and mtHsp70 binding assays with purified recombinant human and yeast proteins

    PMID:19564938

    Open questions at the time
    • In vitro reconstitution only, no functional import readout
    • Single lab, limited functional follow-up
  7. 2010 High

    Established human Magmas as a bona fide PAM16 ortholog that complements yeast, localizes to the inner membrane, and assembles with DnaJC19 at the TIM23 complex.

    Evidence Yeast complementation, Co-IP, subcellular fractionation, in vivo import assays, mutagenesis

    PMID:20053669

    Open questions at the time
    • Did not address alternative J-protein partners (DnaJC15) or Magmas variants
    • Import-independent functions not examined
  8. 2011 Medium

    Reinterpreted the heterodimer's primary purpose as physical tethering of Pam18 to the translocon rather than ATPase inhibition, and identified an uncharacterized Pam16 region needed for an active complex.

    Evidence ATPase assays, genetic interaction analysis, growth assays, and mutagenesis in yeast

    PMID:22031295

    Open questions at the time
    • The uncharacterized Pam16 region required for active-complex formation was not defined
    • Single lab reinterpretation
  9. 2014 High

    Connected PAM16 directly to human disease and uncovered an import-independent role in mitochondrial redox homeostasis.

    Evidence Human genetics with yeast complementation/import/stability assays (skeletal dysplasia); RNAi/overexpression, ETC and antioxidant enzyme assays, ROS measurements, domain mutagenesis (redox)

    PMID:24786642 PMID:25165880

    Open questions at the time
    • Molecular mechanism by which the J-like domain controls ROS production and scavenging is undefined
    • How the disease mutation links import defect to skeletal phenotype not established
  10. 2021 Medium

    Revealed mammalian diversification of the motor, with distinct constitutive Magmas variants preferentially partnering DnaJC19- versus DnaJC15-containing TIM23 motors and differing in inhibitory activity.

    Evidence Yeast complementation, Co-IP, subcellular fractionation, ATPase inhibition assays

    PMID:34715125

    Open questions at the time
    • Functional consequences of the two motor variants for distinct substrate sets unknown
    • Single lab study
  11. 2022 High

    Showed that PAM16-Pam18 coupling partitions Pam18 between import and respiratory chain supercomplex assembly, defining a moonlighting branch point controlled by heterodimer integrity.

    Evidence Yeast genetics, Co-IP, in vitro import assays, respiratory chain assembly assays, blue-native PAGE

    PMID:35385740

    Open questions at the time
    • How cells dynamically regulate this partitioning is unknown
    • Whether mammalian Magmas variants similarly partition Pam18 not tested
  12. 2025 Medium

    Identified post-translational regulation of PAM complex levels through Lon/Pim1 protease-mediated turnover of both Pam16 and Pam18.

    Evidence In vitro Lon degradation assays and in vivo overexpression in Δpim1 yeast with growth assays

    PMID:41099349

    Open questions at the time
    • Signals targeting Pam16 for degradation are unknown
    • Physiological conditions triggering turnover not defined

Open questions

Synthesis pass · forward-looking unresolved questions
  • It remains unknown how PAM16's import, ROS-regulatory, and respiratory-assembly functions are integrated and dynamically balanced in vivo, and what the matrix-side translocon partner of its N-terminus is.
  • Direct matrix-side translocon contact unidentified
  • Mechanism coupling redox control to the J-like domain undefined
  • Regulatory logic governing partition of Pam18 between import and respiratory assembly unknown

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0098772 molecular function regulator activity 4 GO:0060090 molecular adaptor activity 3 GO:0140096 catalytic activity, acting on a protein 3
Localization
GO:0005739 mitochondrion 2
Pathway
R-HSA-9609507 Protein localization 3 R-HSA-392499 Metabolism of proteins 2
Partners
DNAJC15DNAJC19MTHSP70PAM18TIM17TIM44
Complex memberships
PAM (presequence translocase-associated motor)Pam16-Pam18 heterodimerTIM23 translocase

Evidence

Reading pass · 17 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2004 Pam16 (yeast ortholog of PAM16/Magmas) is an essential fifth subunit of the presequence translocase-associated protein import motor (PAM). It is selectively required for preprotein translocation into the mitochondrial matrix (but not for protein insertion into the inner membrane), interacts with Pam18, and is needed for association of Pam18 with the presequence translocase and for formation of a mtHsp70-Tim44 complex. Genetic depletion, co-immunoprecipitation, in vitro import assays in Saccharomyces cerevisiae Nature structural & molecular biology High 14981507
2004 Tim16 (Pam16 ortholog; yeast) is an essential cochaperone of the TIM23 translocase that forms a stable subcomplex with the J-protein Tim14 (Pam18). Depletion of Tim16 markedly impairs matrix protein import, disrupts interaction of Tim14 with the TIM23 complex, and causes severe structural changes in the import motor. Genetic depletion, co-immunoprecipitation, in vitro import assays in Saccharomyces cerevisiae Nature structural & molecular biology High 14981506
2004 Pam16 does not function as a typical J-domain protein but antagonizes the function of Pam18: it specifically inhibits the Pam18-mediated stimulation of the ATPase activity of mtHsp70. Introduction of the canonical HPD motif into Pam16 does not confer ability to stimulate mtHsp70 activity, and Pam16-HPD fully substitutes for wild-type Pam16 in vitro and in vivo but cannot replace Pam18. In vitro ATPase stimulation assays, yeast complementation assays, site-directed mutagenesis The Journal of biological chemistry High 15218029
2006 Crystal structure of the Tim14 (Pam18)–Tim16 (Pam16) complex reveals that the conserved J and J-like domains have virtually identical folds but completely different surface properties. The dimer represents a previously undescribed arrangement of J and J-like domains. Tim16 tightly regulates the cochaperone (ATPase-stimulatory) activity of Tim14. Mutations that destroy the Tim14–Tim16 complex are lethal in yeast. X-ray crystallography, mutagenesis, in vitro ATPase assays, yeast viability assays The EMBO journal High 16977310
2005 A stable heterodimer interaction between Pam16's degenerate J domain and Pam18's J domain is critical for mitochondrial protein import function. Alterations destabilizing the Pam16:Pam18 heterodimer cause growth defects and import defects; intragenic suppressors that restore robust growth also restore heterodimer stability. Pam16's inability to stimulate Hsp70 ATPase activity and the reduced stimulatory activity of the heterodimer compared to Pam18 alone are not critical for function. Yeast genetics, in vitro ATPase assays, intragenic suppressor analysis, growth assays Proceedings of the National Academy of Sciences of the United States of America High 16105940
2007 Three distinct interactions tether the Pam18:Pam16 heterodimer to the TIM23 translocon: (1) the N-terminus of Pam16 interacts with the matrix side of the translocon; (2) the intermembrane space domain of Pam18 interacts with Tim17; and (3) the direct interaction of Pam18's J domain with Pam16's J-like domain. Pam16 plays the major role in translocon association, as alterations in the heterodimer stability dramatically affect Pam18 (but not Pam16) association with the translocon. Suppressors mapping to TIM44 restore function, suggesting Tim44 scaffolds precise positioning of mtHsp70 and Pam18 at the translocon. Co-immunoprecipitation, yeast genetics, suppressor analysis, deletion/mutagenesis Molecular biology of the cell High 18003975
2007 The N-terminal hydrophobic segment of Tim16 (Pam16) is crucial for association of the Tim14·Tim16 complex with the core TIM23 translocase. Yeast lacking the N-terminal hydrophobic segment of Tim16 are viable but show growth defects and decreased matrix protein import. Deletion of hydrophobic segments in both Tim16 and Tim14 is lethal. Yeast genetics, co-immunoprecipitation, in vitro import assays, deletion mutagenesis The Journal of biological chemistry High 17452317
2007 The soluble domains of Pam18 (Tim14) and Pam16 (Tim16) form a heterodimer that is thermally more stable (Tm ~41°C) than either individual protein alone (Tm 16.5°C and 29°C respectively). Heterodimer formation is the limiting step for full denaturation. CD spectroscopy, DSS cross-linking, GdnHCl denaturation of recombinant purified proteins Protein science Medium 17242434
2009 The soluble domains of human Tim14/Pam18 and human Tim16/Pam16 interact with their yeast counterparts to form heterodimeric complexes, and these human-yeast hybrid complexes interact with yeast mtHsp70, demonstrating structural conservation of the mitochondrial translocation motor between humans and yeast. In vitro pulldown/interaction assays with purified recombinant proteins, mtHsp70 binding assay International journal of molecular sciences Medium 19564938
2010 Human Magmas (PAM16) is a functional ortholog of yeast Pam16: it completely complements the Δpam16 yeast strain, localizes to mitochondria as a peripheral inner membrane protein in both yeast and humans, forms a stable subcomplex with J-proteins Pam18 (yeast) or DnaJC19 (human) through its C-terminal region, and is tethered to the TIM23 complex in both organisms. Amino acid alterations in Magmas that reduce Magmas:Pam18 subcomplex stability result in temperature sensitivity and protein translocation defects in vivo. Yeast complementation, co-immunoprecipitation, subcellular fractionation, in vivo import assays, site-directed mutagenesis Human molecular genetics High 20053669
2011 Reevaluation revealed that the primary function of the Pam18:Pam16 interaction is physical tethering of Pam18 to the translocon via Pam16, rather than inhibition of Pam18's ATPase stimulatory activity as previously proposed. An uncharacterized region of Pam16 is required for formation of an active Pam18:Pam16 complex able to stimulate Hsp70 ATPase activity. Biochemical ATPase assays, genetic interaction analysis, yeast growth assays, mutagenesis Molecular biology of the cell Medium 22031295
2014 A homozygous mutation in MAGMAS causes a severe skeletal dysplasia in humans. The mutation leads to protein instability, temperature-sensitive growth in yeast, impaired mitochondrial matrix preprotein import, and cell death, confirming MAGMAS/PAM16 is essential for mitochondrial protein import in humans. Human genetics, yeast functional complementation, in vivo import assays, protein stability assays PLoS genetics High 24786642
2014 The J-like domain of Magmas (PAM16) is essential for maintenance of cellular redox balance. Magmas regulates cellular ROS levels by controlling both ROS production and scavenging: it enhances electron transport chain complex activity (reducing ROS production) and promotes antioxidant enzyme activity. This ROS regulatory function operates independently of its role in protein import. RNAi knockdown and overexpression in mammalian cells, ETC complex activity assays, antioxidant enzyme assays, ROS measurements, domain mutagenesis, yeast model validation Cell death & disease Medium 25165880
2022 Disruption of the Pam16-Pam18 heterodimer causes redistribution of Pam18 from the TIM23 complex to respiratory chain supercomplexes, where it forms a homodimer. This redistribution decreases protein import into mitochondria but stimulates mtHsp70-dependent assembly of respiratory chain complexes. Thus, Pam16 coupling to Pam18 differentially controls dual function: recruiting Pam18 to TIM23 for protein import while attenuating Pam18 function in respiratory chain complex assembly. Yeast genetics, co-immunoprecipitation, in vitro import assays, respiratory chain complex assembly assays, blue-native PAGE Cell reports High 35385740
2021 Two additional Magmas variants (Magmas-1 and Magmas-2) are constitutively expressed in mammals; both are functional orthologs of yeast Pam16 with conserved J-like domains essential for cell survival. Magmas-1 is predominantly recruited to TIM23 translocase B (containing DnaJC19), while Magmas-2 is majorly associated with translocase A (containing DnaJC15). The two variants exhibit differential J-protein inhibitory activity in modulating import motor function. Yeast complementation, co-immunoprecipitation, subcellular fractionation, ATPase inhibition assays The Journal of biological chemistry Medium 34715125
2025 Pam16 and Pam18 are substrates of the mitochondrial matrix Lon protease (Pim1 in yeast), which degrades both proteins both in vitro and in vivo. Overexpression of Pam18 and Pam16 exacerbates the growth defect of the Δpim1 strain, indicating that Lon/Pim1-mediated proteolysis regulates PAM complex component levels and thereby mitochondrial protein import. In vitro Lon protease degradation assays, in vivo overexpression in Δpim1 yeast, growth assays The Biochemical journal Medium 41099349
2011 A small molecule Magmas inhibitor (compound 9) binds directly to Magmas protein with Kd = 33 μM as demonstrated by fluorometric titration, and inhibits yeast growth at 4 μM. Target specificity was established by direct binding and genetic studies. Fluorometric titration, yeast growth inhibition assay, molecular modeling, genetic validation Bioorganic & medicinal chemistry letters Low 21514823

Source papers

Stage 0 corpus · 40 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2004 Pam16 has an essential role in the mitochondrial protein import motor. Nature structural & molecular biology 165 14981507
2004 The J domain-related cochaperone Tim16 is a constituent of the mitochondrial TIM23 preprotein translocase. Nature structural & molecular biology 133 14981506
2006 Structure and function of Tim14 and Tim16, the J and J-like components of the mitochondrial protein import motor. The EMBO journal 99 16977310
2004 The presequence translocase-associated protein import motor of mitochondria. Pam16 functions in an antagonistic manner to Pam18. The Journal of biological chemistry 98 15218029
2005 Role of Pam16's degenerate J domain in protein import across the mitochondrial inner membrane. Proceedings of the National Academy of Sciences of the United States of America 77 16105940
2007 Interaction of the J-protein heterodimer Pam18/Pam16 of the mitochondrial import motor with the translocon of the inner membrane. Molecular biology of the cell 67 18003975
2010 Role of Magmas in protein transport and human mitochondria biogenesis. Human molecular genetics 57 20053669
2020 Ovarian Cancer, Cancer Stem Cells and Current Treatment Strategies: A Potential Role of Magmas in the Current Treatment Methods. Cells 52 32183385
2014 Magmas functions as a ROS regulator and provides cytoprotection against oxidative stress-mediated damages. Cell death & disease 41 25165880
2011 Reevaluation of the role of the Pam18:Pam16 interaction in translocation of proteins by the mitochondrial Hsp70-based import motor. Molecular biology of the cell 38 22031295
2007 Association of the Tim14.Tim16 subcomplex with the TIM23 translocase is crucial for function of the mitochondrial protein import motor. The Journal of biological chemistry 38 17452317
2014 The impairment of MAGMAS function in human is responsible for a severe skeletal dysplasia. PLoS genetics 37 24786642
2010 Magmas, a gene newly identified as overexpressed in human and mouse ACTH-secreting pituitary adenomas, protects pituitary cells from apoptotic stimuli. Endocrinology 30 20719856
2005 Magmas expression in neoplastic human prostate. Journal of molecular histology 28 15704001
2001 Identification and characterization of Magmas, a novel mitochondria-associated protein involved in granulocyte-macrophage colony-stimulating factor signal transduction. Experimental hematology 26 11750097
2022 Coupling to Pam16 differentially controls the dual role of Pam18 in protein import and respiratory chain formation. Cell reports 16 35385740
2009 The mitochondrial protein translocation motor: structural conservation between the human and yeast Tim14/Pam18-Tim16/Pam16 co-chaperones. International journal of molecular sciences 16 19564938
2011 Design, synthesis, and biological activity of novel Magmas inhibitors. Bioorganic & medicinal chemistry letters 15 21514823
2007 The Pam18/Tim14-Pam16/Tim16 complex of the mitochondrial translocation motor: the formation of a stable complex from marginally stable proteins. Protein science : a publication of the Protein Society 14 17242434
2003 Developmental expression of Magmas in murine tissues and its co-expression with the GM-CSF receptor. The journal of histochemistry and cytochemistry : official journal of the Histochemistry Society 14 12704206
2018 Magmas inhibition as a potential treatment strategy in malignant glioma. Journal of neuro-oncology 13 30414099
2013 Magmas overexpression inhibits staurosporine induced apoptosis in rat pituitary adenoma cell lines. PloS one 13 24069394
2018 Crystallisation in basaltic magmas revealed via in situ 4D synchrotron X-ray microtomography. Scientific reports 12 29849174
2005 Magmas gene structure and evolution. In silico biology 12 15984936
2013 Comparative analysis of putative orthologues of mitochondrial import motor subunit: Pam18 and Pam16 in plants. PloS one 11 24194927
2012 The yeast magmas ortholog pam16 has an essential function in fermentative growth that involves sphingolipid metabolism. PloS one 10 22808036
2022 Magmas Inhibition in Prostate Cancer: A Novel Target for Treatment-Resistant Disease. Cancers 7 35681713
2021 Multiple variants of the human presequence translocase motor subunit Magmas govern the mitochondrial import. The Journal of biological chemistry 7 34715125
2023 Transition from carbonatitic magmas to hydrothermal brines: Continuous dilution or fluid exsolution? Science advances 5 37467324
2013 Correction: Magmas Overexpression Inhibits Staurosporine Induced Apoptosis in Rat Pituitary Adenoma Cell Lines. PloS one 5 24116255
2014 N-carbamidoyl-4-((3-ethyl-2,4,4-trimethylcyclohexyl)methyl)benzamide enhances staurosporine cytotoxic effects likely inhibiting the protective action of Magmas toward cell apoptosis. Journal of medicinal chemistry 4 24761782
2024 Pam16 and Pam18 were repurposed during Trypanosoma brucei evolution to regulate the replication of mitochondrial DNA. PLoS biology 3 39146359
2025 Enhanced Expression of Mitochondrial Magmas Protein in Ovarian Carcinomas: Magmas Inhibition Facilitates Antitumour Effects, Signifying a Novel Approach for Ovarian Cancer Treatment. Cells 1 40358179
2025 Inhibition of Mitochondrial-Associated Protein MAGMAS Resensitizes Chemoresistant Prostate Cancer Cells to Docetaxel. Cancers 1 40361461
2025 Lon/Pim1-mediated degradation of presequence translocase-associated motor components Pam16 and Pam18 in Saccharomyces cerevisiae. The Biochemical journal 1 41099349
2024 Preclinical assessment of MAGMAS inhibitor as a potential therapy for pediatric medulloblastoma. PloS one 1 39436961
2023 Identification of new hit to lead magmas inhibitors as potential therapeutics for glioblastoma. Bioorganic & medicinal chemistry letters 1 37201660
2019 Identifying the ingredients of hydrous arc magmas: insights from Mt Lamington, Papua New Guinea. Philosophical transactions. Series A, Mathematical, physical, and engineering sciences 1 30966932
2026 MAGMAS Inhibition Enhances Temozolomide Efficacy in Chemotherapy-Resistant Glioblastoma Models. Cancer research communications 0 42090721
2024 Preclinical assessment of MAGMAS inhibitor as a potential therapy for pediatric medulloblastoma. bioRxiv : the preprint server for biology 0 38464047

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