Affinage

METTL15

12S rRNA N(4)-cytidine methyltransferase METTL15 · UniProt A6NJ78

Length
407 aa
Mass
46.1 kDa
Annotated
2026-04-28
14 papers in source corpus 7 papers cited in narrative 7 extracted findings

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

METTL15 is a mitochondria-localized methyltransferase that functions primarily as a chaperone-like assembly factor essential for biogenesis of the mitoribosomal small subunit (SSU). It catalyzes N4-methylcytidine (m4C) modification at position C839 of human mitochondrial 12S rRNA, yet its catalytic activity is dispensable for SSU assembly—its structural presence on the pre-SSU intermediate is the critical requirement (PMID:31665743, PMID:38913872). Cryo-EM structures show that METTL15 binds an RBFA-containing SSU assembly intermediate, induces a large conformational change in RBFA that permits initiation factor mtIF3 to access the subunit interface, thereby coupling rRNA maturation to the early-to-late SSU assembly transition (PMID:35676484). Loss of METTL15 impairs mitochondrial translation, reduces OXPHOS complex protein levels, and in mice causes diminished oxidative muscle performance and decreased learning capability (PMID:31665743, PMID:35682734).

Mechanistic history

Synthesis pass · year-by-year structured walk · 5 steps
  1. 2019 High

    Identifying METTL15 as the m4C methyltransferase for mitochondrial 12S rRNA established the enzyme responsible for a conserved rRNA modification and linked it to mitoribosome SSU assembly and mitochondrial translation.

    Evidence Knockout/knockdown cell lines with bisulfite mapping, in vitro methylation, ribosome fractionation, and proteomics in human cells

    PMID:31665743

    Open questions at the time
    • Structural basis of METTL15 interaction with pre-SSU not resolved
    • Whether catalytic activity or physical presence drives assembly defect unclear
    • In vivo organismal phenotype not assessed
  2. 2020 High

    Independent replication confirmed the m4C839 methyltransferase activity and functional consequences of METTL15 loss, while identification of RBFA-containing assembly intermediates as the likely substrate defined the stage of SSU biogenesis at which METTL15 acts.

    Evidence In vitro methylation assays, oxygen consumption measurements in human cells; co-immunoprecipitation and MS-based partner identification in murine cells with Mettl15 KO

    PMID:32371392 PMID:32573735

    Open questions at the time
    • Structural mechanism by which METTL15 promotes late-factor incorporation unknown
    • Relationship between METTL15 and other SSU assembly factors unresolved
  3. 2022 High

    Cryo-EM visualization of sequential SSU assembly intermediates revealed that METTL15 binding induces a conformational switch in RBFA that opens the subunit interface for mtIF3, establishing the structural mechanism coupling rRNA modification to assembly progression.

    Evidence Cryo-EM of human mitoribosomal SSU assembly intermediates with bound auxiliary factors

    PMID:35676484

    Open questions at the time
    • Whether METTL15 catalytic activity is required for assembly or only its physical presence not distinguished
    • How METTL15 is recruited to the pre-SSU intermediate not determined
  4. 2022 Medium

    In vivo knockout in mice demonstrated that loss of Mettl15 is survivable but causes RBFA accumulation on 55S mitoribosomes, reduced Cox3, impaired muscle performance, and decreased learning, linking the assembly defect to systemic physiology.

    Evidence Mettl15−/− mouse knockout with mitoribosome fractionation, western blot, behavioral and exercise testing

    PMID:35682734

    Open questions at the time
    • Tissue-specific severity of assembly defects not mapped
    • Single-laboratory study awaits independent replication
    • Human disease association not established
  5. 2024 Medium

    Separation-of-function experiments showed the m4C modification itself is dispensable for SSU biogenesis, redefining METTL15 as a chaperone-like assembly factor whose physical presence—not catalytic output—is essential.

    Evidence Catalytic-dead METTL15 mutant rescue of SSU assembly and mitochondrial translation in human cells

    PMID:38913872

    Open questions at the time
    • Single-laboratory study; independent confirmation needed
    • Whether m4C has a distinct quality-control or translational-fidelity role not tested
    • Structural basis for chaperone function versus catalytic function not resolved

Open questions

Synthesis pass · forward-looking unresolved questions
  • The mechanism by which METTL15 is recruited to the pre-SSU and subsequently released, and whether the m4C mark serves a fidelity or quality-control function distinct from assembly, remain open questions.
  • Recruitment mechanism via Mettl17 proposed from trypanosome structural data but not confirmed in mammalian systems
  • No human disease-causing mutations in METTL15 reported
  • Potential role of m4C in translational accuracy not investigated

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0016740 transferase activity 3 GO:0044183 protein folding chaperone 2
Localization
GO:0005739 mitochondrion 3
Pathway
R-HSA-1852241 Organelle biogenesis and maintenance 4 GO:0005840 ribosome 3
Partners
MTIF3RBFATFB1M
Complex memberships
mitoribosomal SSU assembly intermediate

Evidence

Reading pass · 7 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2019 METTL15 is the main N4-methylcytidine (m4C) methyltransferase in human cells, responsible for methylation of position C839 in mitochondrial 12S rRNA. Loss of METTL15 reduces mitochondrial de novo protein synthesis, decreases steady-state levels of OXPHOS complex proteins, and impairs mitoribosome small subunit assembly, with late assembly components unable to be efficiently incorporated. Knockout/knockdown cell lines, RNA immunoprecipitation, in vitro methylation assays, bisulfite mapping, mass spectrometry-based proteomics, mitoribosome fractionation Nucleic acids research High 31665743
2020 Human METTL15 methylates 12S mt-rRNA at m4C839 both in vivo and in vitro; METTL15 depletion impairs mitochondrial mRNA translation and decreases mitochondrial respiration capacity. METTL15 shows different substrate preference compared to its bacterial ortholog rsmH. Immunofluorescence (subcellular localization), RNA immunoprecipitation, in vitro methylation assay, bisulfite mapping, mitochondrial translation assay, oxygen consumption rate measurement The Journal of biological chemistry High 32371392
2020 Mouse METTL15 forms the m4C840 residue of murine mitochondrial 12S rRNA, and its likely substrate is an assembly intermediate of the mitochondrial small ribosomal subunit containing the assembly factor RBFA, as identified by co-immunoprecipitation of interaction partners. Mettl15 gene inactivation in murine cell line, mass spectrometry identification of interaction partners, mitochondrial ribosome fractionation Nucleic acids research High 32573735
2022 Cryo-EM structures of mitoribosomal small subunit (SSU) assembly intermediates reveal that METTL15 binds after RBFA promotes partial unfolding of rRNA h45 and TFB1M binding; METTL15 binding promotes further rRNA maturation and induces a large conformational change of RBFA, which allows initiation factor mtIF3 to occupy the subunit interface during assembly. Cryo-electron microscopy of sequential SSU assembly intermediates in complex with auxiliary factors Nature High 35676484
2022 Mettl15 knockout mice are viable but display accumulation of the assembly factor RbfA in the 55S mitoribosome fraction, reduced Cox3 protein in oxidative muscles, lower blood glucose after exercise, suboptimal muscle performance, and decreased learning capability, establishing in vivo roles for Mettl15-mediated rRNA methylation. Mettl15−/− mouse knockout, mitoribosome fractionation, western blot for Cox3, behavioral and exercise performance assays International journal of molecular sciences Medium 35682734
2024 The catalytic methyltransferase activity of METTL15 is dispensable for mitoribosome small subunit biogenesis; the m4C modification itself is not required, but the METTL15 protein acts as a chaperone-like factor essential for SSU assembly. Catalytic-dead METTL15 mutant rescue experiments, mitoribosome assembly assays, mitochondrial translation assays RNA biology Medium 38913872
2025 Structural and molecular dynamics analyses reveal that Mettl17 acts as a platform for Mettl15 recruitment to the early pre-mitoribosome intermediate; subsequent release of Mettl17 allows a conformational change of Mettl15 enabling substrate recognition. After methylation, Mettl15 adopts a loosely bound state and is replaced by initiation factors, linking early-to-late SSU assembly transition. Cryo-EM structural analysis of Trypanosoma brucei SSU intermediates integrated with mammalian homolog data and molecular dynamics simulations bioRxivpreprint Medium bio_10.1101_2024.12.18.629302

Source papers

Stage 0 corpus · 14 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2019 A trans-ancestral meta-analysis of genome-wide association studies reveals loci associated with childhood obesity. Human molecular genetics 89 31504550
2019 METTL15 introduces N4-methylcytidine into human mitochondrial 12S rRNA and is required for mitoribosome biogenesis. Nucleic acids research 82 31665743
2022 Mechanism of mitoribosomal small subunit biogenesis and preinitiation. Nature 74 35676484
2020 The human mitochondrial 12S rRNA m4C methyltransferase METTL15 is required for mitochondrial function. The Journal of biological chemistry 48 32371392
2023 Identification of Novel, Replicable Genetic Risk Loci for Suicidal Thoughts and Behaviors Among US Military Veterans. JAMA psychiatry 46 36515925
2020 METTL15 interacts with the assembly intermediate of murine mitochondrial small ribosomal subunit to form m4C840 12S rRNA residue. Nucleic acids research 34 32573735
2021 Circ-METTL15 contributes to the proliferation, metastasis, immune escape and restrains apoptosis in lung cancer by regulating miR-1299/PDL1 axis. Autoimmunity 19 34796777
2023 Circular RNA METTL15/miR-374a-5p/ESCO2 axis induces colorectal cancer development. Acta biochimica Polonica 9 37715994
2022 Mitochondrial rRNA Methylation by Mettl15 Contributes to the Exercise and Learning Capability in Mice. International journal of molecular sciences 9 35682734
2023 Impact of AKT1 on cell invasion and radiosensitivity in a triple negative breast cancer cell line developing brain metastasis. Frontiers in oncology 7 37483521
2024 The catalytic activity of methyltransferase METTL15 is dispensable for its role in mitochondrial ribosome biogenesis. RNA biology 5 38913872
2024 Identification of Risk Genes for Attention-Deficit/Hyperactivity Disorder During Early Human Brain Development. Journal of the American Academy of Child and Adolescent Psychiatry 4 39510315
2023 Circ-METTL15 stimulates the aggressive behaviors of papillary thyroid cancer cells by coordinating the miR-200c-3p/XIAP axis. Turkish journal of biology = Turk biyoloji dergisi 1 39051062
2025 Deep adversarial learning identifies ADHD-specific associations between apoptotic genes and white matter microstructure in frontal-striatum-cerebellum circuit. Translational psychiatry 0 40858546