Affinage

MRPL32

Large ribosomal subunit protein bL32m · UniProt Q9BYC8

Round 2 corrected
Length
188 aa
Mass
21.4 kDa
Annotated
2026-04-28
43 papers in source corpus 8 papers cited in narrative 8 extracted findings

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

MRPL32 is a structural protein of the mitochondrial ribosomal large subunit (mt-LSU) that is essential for mitochondrial translation and whose maturation is tightly coupled to quality control by mitochondrial proteases. The precursor form of MRPL32 is processed by the m-AAA protease (AFG3L2/paraplegin), which cleaves its N-terminal presequence—a transferable degron—while a conserved CxxC-X(9)-CxxC motif folds into a tightly structured domain that halts degradation and triggers release of the mature protein; this folding is presequence-assisted and sensitive to oxidative stress, linking mitochondrial redox status to translational capacity (PMID:16239145, PMID:21610694, PMID:29932645). Mature MRPL32 incorporates into preassembled ribosomal particles during the final steps of mt-LSU biogenesis, and its C-terminal extension domain supports mitochondrial translation through a separable, trans-acting mechanism distinct from its structural role in the ribosome (PMID:25278503, PMID:28892042, PMID:29343666). MRPL32 levels can also be regulated by the Lon protease independently of nucleic acid binding, and loss of MRPL32 function modulates susceptibility to oxygen-glucose deprivation–induced apoptosis (PMID:28377575, PMID:32618081).

Mechanistic history

Synthesis pass · year-by-year structured walk · 7 steps
  1. 2005 High

    The mechanism by which MRPL32 acquires its mature form was unknown; discovery that the m-AAA protease cleaves its N-terminal presequence established MRPL32 maturation as a protease-dependent step required for mitoribosome assembly and mitochondrial translation, conserved from yeast to mouse.

    Evidence Yeast genetics and biochemical fractionation combined with a paraplegin-knockout mouse model

    PMID:16239145

    Open questions at the time
    • Molecular determinants within MRPL32 that control processing versus complete degradation were unknown
    • Whether additional proteases contribute to MRPL32 turnover was not addressed
    • Structural basis for MRPL32 positioning within the mitoribosome was unresolved
  2. 2011 High

    The question of how the m-AAA protease distinguishes maturation (partial processing) from complete degradation was answered: a tightly folded CxxC-containing domain acts as a stop signal, and folding requires the presequence, coupling complete import to post-translocational processing; oxidative disruption of this fold leads to full degradation and reduced translation.

    Evidence In vitro import/processing assays, CxxC mutagenesis, oxidative stress treatments, and mitochondrial translation readouts in yeast

    PMID:21610694

    Open questions at the time
    • Identity of the metal or disulfide coordination within the CxxC motif was not structurally resolved
    • Whether the redox-sensitivity mechanism operates identically in mammalian cells was not demonstrated
    • Downstream signaling consequences of complete MRPL32 degradation under oxidative stress were not explored
  3. 2014 High

    The position of MRPL32 within the mitoribosomal large subunit was directly resolved at near-atomic resolution, confirming its identity as a bona fide structural component of the 48-protein mt-LSU.

    Evidence Single-particle cryo-EM of the human mt-LSU at 3.4 Å resolution

    PMID:25278503

    Open questions at the time
    • The timing of MRPL32 incorporation during mt-LSU biogenesis was not captured in this mature ribosome structure
    • Whether MRPL32 contacts rRNA or neighboring proteins critical for peptidyl transferase activity was not analyzed functionally
  4. 2017 High

    Analysis of native mt-LSU assembly intermediates revealed that MRPL32 is incorporated during the final maturation steps, establishing when in the biogenesis pathway the protease-processed protein joins the particle.

    Evidence Cryo-EM of late-stage human mt-LSU assembly intermediates at ~3 Å resolution

    PMID:28892042

    Open questions at the time
    • Assembly factors or chaperones that escort mature MRPL32 to the pre-ribosomal particle were not identified
    • Whether defective MRPL32 processing stalls assembly at this specific intermediate was not tested
  5. 2018 High

    The N-terminal presequence of MRPL32 was characterized as a transferable degron for AFG3L2, and the protease's peptidase specificity (P1' residue preference, constrained product length) was defined, revealing the molecular rules governing MRPL32 maturation cleavage.

    Evidence Reconstituted AFG3L2 assays with purified substrates, presequence mutagenesis, mass spectrometry of products, and fluorogenic peptide reporters

    PMID:29932645

    Open questions at the time
    • Whether AFG3L2 homo- versus hetero-hexameric forms (with paraplegin) differ in MRPL32 cleavage specificity was not resolved
    • Structural basis of how the folded CxxC domain physically stalls AFG3L2 translocation remained unknown
  6. 2018 Medium

    The C-terminal extension of yeast MrpL32 was shown to be dispensable for ribosome incorporation but required for mitochondrial translation, and this function could be provided in trans, revealing a separable role beyond structural integration.

    Evidence Yeast C-terminal truncation and trans-complementation assays with growth and mitochondrial translation phenotypes

    PMID:29343666

    Open questions at the time
    • The molecular target or mechanism through which the C-terminal extension promotes translation is unknown
    • Whether this trans-acting function is conserved in mammalian MRPL32 was not tested
    • Whether the C-terminal extension interacts with tRNA, mRNA, or another ribosomal factor was not determined
  7. 2020 Medium

    A functional connection between MRPL32 and cell survival under ischemic stress was established when MRPL32 knockdown increased viability and reduced apoptosis during oxygen-glucose deprivation/reperfusion, suggesting mitochondrial translation contributes to ischemic cell death.

    Evidence Genome-wide CRISPR/Cas9 knockout screen in neuroblastoma cells validated by individual siRNA knockdown

    PMID:32618081

    Open questions at the time
    • Whether the pro-apoptotic effect is specific to MRPL32 or generalizable to other MRPLs (reflecting reduced mitochondrial translation) was not distinguished
    • Mechanism linking mitochondrial translation to OGDR-induced apoptosis was not dissected
    • In vivo relevance to ischemia-reperfusion injury in neuronal tissue was not tested

Open questions

Synthesis pass · forward-looking unresolved questions
  • Key unresolved questions include the structural basis for how the folded CxxC domain arrests m-AAA protease translocation, the molecular mechanism by which the C-terminal extension supports translation in trans, and whether MRPL32 maturation defects directly contribute to human mitochondrial disease.
  • No high-resolution structure of MRPL32 engaged with the m-AAA protease exists
  • No direct link between MRPL32 mutations and a human Mendelian disorder has been reported
  • Trans-acting partners of the C-terminal extension remain unidentified

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0005198 structural molecule activity 3
Localization
GO:0005739 mitochondrion 4 GO:0005840 ribosome 2
Pathway
R-HSA-392499 Metabolism of proteins 4 GO:0005198 structural molecule activity 3
Partners
AFG3L2SPG7
Complex memberships
mitochondrial ribosomal large subunit (mt-LSU)

Evidence

Reading pass · 8 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2005 The mitochondrial ribosomal protein MrpL32 is processed (its N-terminal mitochondrial targeting sequence is cleaved) by the m-AAA protease in yeast mitochondria. This processing is required for MrpL32's association with preassembled ribosomal particles and completion of mitochondrial ribosome assembly near the inner membrane. Maturation of MrpL32 and mitochondrial protein synthesis are also impaired in a HSP mouse model lacking the m-AAA protease subunit paraplegin, demonstrating functional conservation across species. Yeast genetics, biochemical fractionation, in vivo processing assays, mouse model (paraplegin knockout) Cell High 16239145
2011 A tightly folded domain in MrpL32, harboring a conserved CxxC-X(9)-CxxC sequence motif, halts N-terminal degradation initiated by the m-AAA protease and triggers release of mature MrpL32. Oxidative stress impairs this folding, resulting in complete degradation of MrpL32 by the m-AAA protease and decreased mitochondrial translation. Furthermore, folding of MrpL32 depends on its mitochondrial targeting/presequence, which requires complete import of the precursor before maturation, explaining the need for post-translocational (rather than co-translocational) processing. In vitro import and processing assays, mutagenesis of CxxC motif, oxidative stress treatments, mitochondrial translation assays The EMBO journal High 21610694
2017 Human MrpL32 (large ribosomal subunit protein) is actively degraded in vitro by the mitochondrial Lon protease. This degradation is not protected by nucleic acid binding, unlike some other nucleoid-associated proteins, suggesting Lon can regulate MrpL32 levels independently of its nucleic acid association state. In vitro Lon protease digestion assay with purified human MrpL32 Scientific reports Medium 28377575
2018 Conserved residues within the presequence (N-terminal targeting sequence) of MrpL32 constitute a degron that targets the protein to the human AFG3L2 (m-AAA) protease for processing into its mature form. This degron is transferable and can deliver heterologous proteins to AFG3L2 for degradation. AFG3L2's peptidase specificity is constrained in product length and dominated by the P1' residue identity (preference for hydrophobic and small polar residues), validated by fluorogenic peptide cleavage and full polypeptide substrates. Solubilized AFG3L2 protease assays, mass spectrometry of degradation products, mutagenesis of MrpL32 presequence, fluorogenic reporter peptide assays Biochemistry High 29932645
2018 The C-terminal extension (CE) domain of S. cerevisiae MrpL32 is not required for incorporation into the ribosome per se, but is needed for mitochondrial translational activity. When expressed separately (in trans) from a C-terminally truncated MrpL32, the CE domain can rescue the temperature-sensitive mitochondrial translation defect of mrpL32ΔC mutants, demonstrating a non-structural, trans-acting function of the CE in supporting mitochondrial protein synthesis. Yeast genetics, C-terminal truncation constructs, growth on non-fermentable carbon sources, in trans complementation assay, mitochondrial translation assay Genes & genetic systems Medium 29343666
2014 MrpL32 is present as a component of the large subunit of the human mitochondrial ribosome, as revealed by cryo-EM structure determination at 3.4 Å resolution. The structure defines 48 proteins of the mt-LSU, with MrpL32 occupying a defined position within the complex. Single-particle cryo-electron microscopy at 3.4 Å resolution Science (New York, N.Y.) High 25278503
2017 Cryo-EM structures of two late-stage assembly intermediates of the human mitoribosomal large subunit reveal that MRPL32 incorporation is part of the final steps of mt-LSU maturation, and comparison of intermediates provides insight into the timing of rRNA folding and protein incorporation during ribosomal biogenesis. Cryo-EM of native assembly intermediates isolated from human cell lines, ~3 Å resolution Nature structural & molecular biology High 28892042
2020 Knockdown of MRPL32 in SK-N-BE(2) neuroblastoma cells increased cell viability and attenuated oxygen-glucose deprivation/reperfusion (OGDR)-induced apoptosis, identifying MRPL32 as a contributor to OGDR-induced cell death in a genome-wide CRISPR/Cas9 knockout screen. Genome-wide CRISPR/Cas9 pooled knockout screen followed by individual siRNA knockdown, cell viability assay, apoptosis assay Journal of cellular and molecular medicine Medium 32618081

Source papers

Stage 0 corpus · 43 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2002 Generation and initial analysis of more than 15,000 full-length human and mouse cDNA sequences. Proceedings of the National Academy of Sciences of the United States of America 1479 12477932
2015 The BioPlex Network: A Systematic Exploration of the Human Interactome. Cell 1118 26186194
2017 Architecture of the human interactome defines protein communities and disease networks. Nature 1085 28514442
2015 A human interactome in three quantitative dimensions organized by stoichiometries and abundances. Cell 1015 26496610
2012 The mRNA-bound proteome and its global occupancy profile on protein-coding transcripts. Molecular cell 973 22681889
2018 VIRMA mediates preferential m6A mRNA methylation in 3'UTR and near stop codon and associates with alternative polyadenylation. Cell discovery 829 29507755
2021 Dual proteome-scale networks reveal cell-specific remodeling of the human interactome. Cell 705 33961781
2012 A census of human soluble protein complexes. Cell 689 22939629
2011 Phylogenetic-based propagation of functional annotations within the Gene Ontology consortium. Briefings in bioinformatics 656 21873635
2018 High-Density Proximity Mapping Reveals the Subcellular Organization of mRNA-Associated Granules and Bodies. Molecular cell 580 29395067
2004 The status, quality, and expansion of the NIH full-length cDNA project: the Mammalian Gene Collection (MGC). Genome research 438 15489334
2022 OpenCell: Endogenous tagging for the cartography of human cellular organization. Science (New York, N.Y.) 432 35271311
2015 Panorama of ancient metazoan macromolecular complexes. Nature 407 26344197
1996 Normalization and subtraction: two approaches to facilitate gene discovery. Genome research 401 8889548
2010 Dynamics of cullin-RING ubiquitin ligase network revealed by systematic quantitative proteomics. Cell 318 21145461
2005 The m-AAA protease defective in hereditary spastic paraplegia controls ribosome assembly in mitochondria. Cell 313 16239145
2019 Mitochondrial ClpP-Mediated Proteolysis Induces Selective Cancer Cell Lethality. Cancer cell 298 31056398
2014 Structure of the large ribosomal subunit from human mitochondria. Science (New York, N.Y.) 262 25278503
2022 Tau interactome maps synaptic and mitochondrial processes associated with neurodegeneration. Cell 256 35063084
2003 The DNA sequence and analysis of human chromosome 6. Nature 242 14574404
2021 Quantitative high-confidence human mitochondrial proteome and its dynamics in cellular context. Cell metabolism 239 34800366
2007 hORFeome v3.1: a resource of human open reading frames representing over 10,000 human genes. Genomics 222 17207965
2016 Mitochondrial Protein Interaction Mapping Identifies Regulators of Respiratory Chain Function. Molecular cell 220 27499296
2016 Structure and Function of the Mitochondrial Ribosome. Annual review of biochemistry 217 27023846
2018 An AP-MS- and BioID-compatible MAC-tag enables comprehensive mapping of protein interactions and subcellular localizations. Nature communications 201 29568061
2020 Systems analysis of RhoGEF and RhoGAP regulatory proteins reveals spatially organized RAC1 signalling from integrin adhesions. Nature cell biology 194 32203420
2013 Common genetic variation and antidepressant efficacy in major depressive disorder: a meta-analysis of three genome-wide pharmacogenetic studies. The American journal of psychiatry 186 23377640
2010 A functional peptidyl-tRNA hydrolase, ICT1, has been recruited into the human mitochondrial ribosome. The EMBO journal 153 20186120
2020 A High-Density Human Mitochondrial Proximity Interaction Network. Cell metabolism 148 32877691
2017 Structures of the human mitochondrial ribosome in native states of assembly. Nature structural & molecular biology 136 28892042
2017 The human cytoplasmic dynein interactome reveals novel activators of motility. eLife 118 28718761
2020 Expression analysis of mammalian mitochondrial ribosomal protein genes. Gene expression patterns : GEP 82 32987154
2011 Presequence-dependent folding ensures MrpL32 processing by the m-AAA protease in mitochondria. The EMBO journal 66 21610694
2017 The role of Lon-mediated proteolysis in the dynamics of mitochondrial nucleic acid-protein complexes. Scientific reports 30 28377575
2014 Genetic basis for Saccharomyces cerevisiae biofilm in liquid medium. G3 (Bethesda, Md.) 29 25009170
2018 Dissecting Substrate Specificities of the Mitochondrial AFG3L2 Protease. Biochemistry 17 29932645
2014 Import of ribosomal proteins into yeast mitochondria. Biochemistry and cell biology = Biochimie et biologie cellulaire 17 24943357
2020 CRISPR/Cas9-mediated whole genomic wide knockout screening identifies mitochondrial ribosomal proteins involving in oxygen-glucose deprivation/reperfusion resistance. Journal of cellular and molecular medicine 9 32618081
2023 Insight into the mechanism of DNA methylation and miRNA-mRNA regulatory network in ischemic stroke. Mathematical biosciences and engineering : MBE 6 37322932
2023 Testicular Toxicity in Rats Exposed to AlCl3: a Proteomics Study. Biological trace element research 6 37382810
2024 Mitochondrial proteins as therapeutic targets in diabetic ketoacidosis: evidence from Mendelian randomization analysis. Frontiers in pharmacology 4 39469619
2024 MicroRNA-2861 regulates the proliferation and apoptosis of human retinal vascular endothelial cells treated with high glucose by targeting NDUFB7. Heliyon 2 39170385
2018 The C-terminal extension domain of Saccharomyces cerevisiae MrpL32, a homolog of ribosomal protein L32, functions in trans to support mitochondrial translation. Genes & genetic systems 1 29343666