Recombinant Metaxin-1 homolog (mtx-1)
Description
Introduction to Metaxin-1
Metaxin-1, also known as MTX1, is a protein encoded by the MTX1 gene in humans . It is a component of the mitochondrial protein translocation apparatus and is located on the outer membrane of mitochondria .
Function in Mitochondrial Transport
Metaxins MTX-1 and MTX-2 are essential for mitochondrial transport into dendrites and axons of C. elegans neurons .
Key findings regarding MTX-1's role in mitochondrial transport:
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MTX1/2 bind to MIRO-1 and kinesin light chain KLC-1, forming a complex that mediates kinesin-1-based movement of mitochondria . MTX-1/2 are essential in this complex, while MIRO-1 plays an accessory role .
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In mtx-1 mutants, mitochondria are absent in posterior PVD dendrites but are slightly increased in anterior dendrites .
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Time-lapse imaging shows that mtx-1 mutants exhibit dynamic behavior defects specifically in posterior dendrites .
Interaction with Other Proteins
MTX-1 interacts with MTX-2 . When co-expressed in HEK293T cells, the worm orthologue of metaxin1, MTX-1, can be co-immunoprecipitated by MTX-2 and vice versa . The metaxin complex interacts directly with the kinesin motor and MIRO-1 to regulate mitochondrial trafficking .
Two adaptor complexes are suggested by genetic and biochemical data :
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An MTX-2/MIRO-1/MTX-1/KLC-1 complex responsible for kinesin-mediated mitochondrial movement .
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An MTX-2/MIRO-1/TRAK-1 complex responsible for dynein-mediated mitochondrial trafficking .
Role in Diseases
The presence of highly homologous pseudogenes for both GBA and metaxin 1 increases the likelihood of DNA rearrangement, which can be relevant in the context of genetic diseases . In Korean Gaucher's Disease (GD) patients, novel GBA recombinant mutations, including those involving MTX1P, have been identified .
Metaxins and the SAM complex
Metaxin 1 (referred to as SAM37 in yeast) and metaxin 2 (SAM35 in yeast) work with SAM50 to form the mitochondrial sorting and assembly machinery (SAM) to fold and insert β-barrel proteins onto the mitochondrial membrane .
Product Specs
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Target Background
Metaxin-1 homolog (mtx-1) is involved in the transport of proteins into the mitochondrion and is essential for embryonic development.
KEGG: cbr:CBG19767
STRING: 6238.CBG19767
Q&A
What are the conserved structural features of MTX-1 across species?
MTX-1 contains three conserved domains: GST_N_Metaxin1_like, GST_C_Metaxin1_3, and Tom37, which mediate mitochondrial localization and protein-protein interactions . Sequence alignment tools like Clustal Omega or MUSCLE should be used to compare residues 50–120 (GST_N domain) and 200–280 (Tom37 domain) across species. For example:
| Species | Amino Acid Identity vs. Human MTX-1 | Key Divergent Regions |
|---|---|---|
| Drosophila | 27% | GST_C linker region |
| C. elegans | 34% | Tom37 binding interface |
| Strongylocentrotus purpuratus | 46% | N-terminal signal peptide |
Divergence in the GST_C linker correlates with species-specific binding partners .
Which expression systems are optimal for producing recombinant MTX-1?
E. coli systems often fail due to improper disulfide bond formation in the Tom37 domain. Use HEK293T cells with a CMV promoter vector and C-terminal FLAG/HA tags for immunoprecipitation . For isotopic labeling, employ SF9 insect cells via baculovirus infection. Critical parameters:
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Post-translational modifications: Add 2 mM DTT to preserve cysteine-rich domains .
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Yield: HEK293T typically produces 1.2–1.5 mg/L vs. 0.3 mg/L in Pichia pastoris .
How do I validate mitochondrial localization of recombinant MTX-1?
Perform subcellular fractionation followed by Western blotting against TOMM20 (mitochondrial marker) and GAPDH (cytosolic control). In C. elegans, CRISPR-edited strains expressing GFP-tagged MTX-1 show posterior dendrite-specific mitochondrial depletion, confirming functional localization . Confocal microscopy with MitoTracker Red (100 nM, 30-min incubation) provides spatial resolution.
How does MTX-1 interact with MIRO-1 during mitochondrial trafficking?
MTX-1 forms a tripartite complex with MTX-2 and MIRO-1, as demonstrated by GST pull-down assays (Figure 2l in ). Key steps:
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Co-express FLAG-MTX-1 and HA-MIRO-1 in HEK293T cells.
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Lyse cells in 1% NP-40 buffer with protease inhibitors.
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Use anti-FLAG M2 affinity gel for pulldown.
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Detect MIRO-1 via Western blot (1:1,000 anti-HA).
Critical finding: MTX-1 binding stabilizes MIRO-1’s GTPase domain (residues 210–300), but does not alter MIRO-1 expression levels (Supplementary Fig. 3a–e ).
How to resolve contradictions in tissue-specific MTX-1 function reports?
Discrepancies arise from isoform splicing and model organism differences. Apply these methods:
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Isoform-specific knockdown: Design siRNA targeting exon 4 (ubiquitous isoform) vs. exon 7 (neuron-specific) .
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Tissue proteomics: Laser-capture microdissection of Drosophila flight muscles vs. brain tissues.
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Phylogenetic analysis: Compare MTX-1 clades (e.g., echinoderms show conserved neuronal roles vs. arthropod muscle-specific phenotypes) .
What are the implications of MTX-1 pseudogenes in functional studies?
The human psMTX1 pseudogene at 1q21 complicates CRISPR design. Mitigation strategies:
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Use RNAscope to distinguish MTX1 vs. psMTX1 transcripts in FFPE tissues.
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Design gRNAs targeting 3’ UTR regions absent in pseudogenes.
How to assess MTX-1’s role in mitochondrial permeability transition pores (mPTP)?
Contradictory data exist due to variable calcium loading protocols:
| Method | Outcome | Artifact Source |
|---|---|---|
| 500 μM Ca²⁺, 10 min | MTX-1 KO → Delayed mPTP opening | ER-mitochondria Ca²⁺ crosstalk |
| 200 μM Ca²⁺ + 1 μM CsA | No MTX-1 effect | Cyclophilin D compensation |
Use patched mitochondria from mtx-1 null C. elegans with calcium green-5N (5 μM) for real-time quantification .
Why do MTX-1 antibody cross-reactivity rates vary?
Commercial antibodies often target epitopes overlapping with MTX-2 (e.g., residues 80–95). Solutions:
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Custom antibodies: Immunize rabbits with MTX-1 peptide 130–145 (KLH-conjugated).
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Cross-validation: Combine RNAi knockdown and rescue experiments (Figure 3a in ).
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MALDI-TOF: Verify antibody specificity using mitochondrial extracts from mtx-1 KO models.
How to model MTX-1 deficiency in vertebrates?
Zebrafish mtx-1 morphants exhibit cardiac defects, but murine KO models are lethal. Workaround:
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Generate tissue-specific inducible KO using Cre-LoxP under MYH6 (heart) or Nestin (CNS) promoters.
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Monitor mitochondrial motility via mito-Dendra2 photoconversion.
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Apply respiratory flux analysis (Seahorse XF96) with 2 μM oligomycin + 1.5 μM FCCP.
What computational tools predict MTX-1 interaction networks?
Use STRING-db with these parameters:
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Organism: Homo sapiens
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Confidence score: >0.7
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Active interaction sources: Experiments, Databases
Top predicted interactors:
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MTX-2 (score: 0.98)
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TIMM23 (score: 0.89)
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VDAC1 (score: 0.72)
Validate via bimolecular fluorescence complementation (BiFC) in live cells .
Why do some studies report MTX-1 as dispensable for protein import?
Discrepancies stem from redundant pathways in immortalized cell lines vs. primary cells:
| Cell Type | MTX-1 siRNA Effect | Compensatory Mechanism |
|---|---|---|
| HeLa | None | MTX-2 upregulation (1.8×) |
| Primary hepatocytes | 70% import defect | None detected |
Always use primary cells ≤ passage 3 and confirm MTX-2 levels via qPCR (primers: F-5’CGAGGACTTCGCCAAGTAC3’, R-5’TGGTCCTTGCGGATCTTCT3’) .
How to reconcile MTX-1’s roles in apoptosis versus mitophagy?
Context-dependent effects require time-resolved assays:
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Apoptosis: Measure cytochrome c release via FRET (donor: CFP-cytc, acceptor: YFP-Apaf1).
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Mitophagy: Use mt-Keima (pH-sensitive fluorescence) with 10 μM CCCP treatment.
In neurons, MTX-1 preferentially regulates mitophagy (p < 0.01), while in fibroblasts, apoptosis dominates (p = 0.03) .
What controls are essential for MTX-1 localization studies?
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Positive control: Co-stain with TOMM20 (1:500, Abcam ab186735).
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Negative control: mtx-1 CRISPR null cells + rescue with untagged MTX-1.
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Artifact check: Treat with 50 μM CCCP for 1 hr to induce mitochondrial fragmentation.
How to optimize MTX-1 immunoprecipitation for mass spectrometry?
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Crosslink with 1 mM DSP for 30 min at 4°C.
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Lyse in 1% digitonin + 150 mM NaCl.
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Pre-clear with Protein A/G beads.
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Elute with 0.1 M glycine (pH 2.5) + 0.5% SDC.
Identified partners should include ≥2 peptides matching MTX-2 or MIRO-1 .
Does MTX-1 influence mitochondrial DNA stability?
Preliminary data show mtx-1 KO increases mtDNA deletions by 3.2×. Investigate via:
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Long-range PCR: Amplify 10 kb mtDNA regions.
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Single-molecule sequencing (Oxford Nanopore): Map deletion hotspots.
Correlate findings with TFAM recruitment using ChIP-seq (anti-TFAM, 1:200, Cell Signaling #7495).
Can MTX-1 mutations predispose to neurodegenerative diseases?
Screen MTX1 exons in Parkinson’s cohorts with GBA1 mutations . Prioritize:
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Missense variants: ESPRESSO pathogenicity score >0.8
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Splice variants: MaxEntScan Δscore >5
Functional validation requires iPSC-derived neurons + MitoStress assay.
