mid49
<div class="infobox infobox-gene">
<table>
<tr><th colspan="2" style="background:#f8f9fa;text-align:center;font-size:1.1em;">MID49</th></tr>
<tr><th>Symbol</th><td>MID49 (MIEF2, SMCR7L)</td></tr>
<tr><th>Full Name</th><td>Mitochondrial Dynamics Protein Mid49</td></tr>
<tr><th>Chromosome</th><td>5q31.2</td></tr>
<tr><th>NCBI Gene ID</th><td>[84752](https://www.ncbi.nlm.nih.gov/gene/84752)</td></tr>
<tr><th>OMIM</th><td>[616121](https://www.omim.org/entry/616121)</td></tr>
<tr><th>Ensembl</th><td>[ENSG00000156535](https://ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000156535)</td></tr>
<tr><th>UniProt</th><td>[Q9H0W4](https://www.uniprot.org/uniprot/Q9H0W4)</td></tr>
<tr><th>Associated Diseases</th><td>[Alzheimer's disease](/diseases/alzheimers-disease), [Parkinson's disease](/diseases/parkinsons-disease), ALS, Huntington's disease</td></tr>
</table>
</div>
Overview
MID49 (also known as MIEF2 - Mitochondrial Elongation Factor 2, or SMCR7L - Smith-Magenis Syndrome Chromosome Region, candidate 7-like) is a mitochondrial outer membrane protein that plays a critical role in regulating mitochondrial dynamics. As a member of the MiD49/51 family of mitochondrial division proteins, MID49 acts as an adaptor for the recruitment of the large GTPase [DRP1](/proteins/drp1-protein) (DNM1L) to mitochondria, thereby controlling the balance between mitochondrial fission and fusion [gomes2011](https://pubmed.ncbi.nlm.nih.gov/21619488/).
The proper regulation of mitochondrial dynamics is essential for neuronal health, and dysfunction in MID49-mediated mitochondrial quality control mechanisms is strongly implicated in the pathogenesis of neurodegenerative diseases including [Alzheimer's disease](/diseases/alzheimers-disease) (AD), [Parkinson's disease](/diseases/parkinsons-disease) (PD), amyotrophic lateral sclerosis (ALS), and [Huntington's disease](/diseases/huntingtons-disease) [wang2017](https://pubmed.ncbi.nlm.nih.gov/29193486/).
This comprehensive page covers MID49's molecular functions, its critical role in neuronal biology, disease associations, signaling pathways, therapeutic implications, and key research findings relevant to neurodegeneration.
Gene and Protein Structure
Gene Organization
The MID49 gene is located on chromosome 5q31.2 and encodes a protein of 452 amino acids with a molecular weight of approximately 49 kDa, hence its name "Mid49" [gomes2011](https://pubmed.ncbi.nlm.nih.gov/21619488/). The gene is evolutionarily conserved, with orthologs present in yeast (Mdm34) and other eukaryotes.
Protein Architecture
MID49 possesses several key structural features:
N-terminal cytosolic domain: Contains a proline-rich region that may serve as a binding platform for SH3 domain-containing proteins
Transmembrane anchor: A single-pass transmembrane domain anchors the protein to the mitochondrial outer membrane
C-terminal cytosolic domain: Interacts with DRP1 and regulates its GTPase activity
MIEF domain: The MiD family-specific domain involved in oligomerization and DRP1 recruitmentThe protein functions as a dynamic regulator, capable of both promoting and inhibiting mitochondrial fission depending on cellular context and phosphorylation state.
Relationship to MID51
MID49 shares significant homology with its paralog [MID51](/genes/mief1) (MIEF1), and these proteins have both overlapping and distinct functions:
| Feature | MID49 | MID51 |
|---------|-------|-------|
| Length | 452 aa | 463 aa |
| Tissue expression | Broad | Broad |
| DRP1 recruitment | Inducible | Constitutive |
| Fission vs fusion bias | Context-dependent | Fusion-promoting |
Role in Mitochondrial Dynamics
Mitochondrial Fusion and Fission
Mitochondria are highly dynamic organelles that constantly undergo fusion and fission, a process essential for:
- Mitochondrial quality control: Removing damaged mitochondria through mitophagy
- Energy distribution: Ensuring equitable distribution of mitochondria throughout neurons
- DNA maintenance: Facilitating mitochondrial DNA (mtDNA) mixing and repair
- Apoptosis regulation: Controlling cytochrome c release
Mermaid diagram (expand to render)
DRP1 Regulation
[DRP1](/proteins/drp1-protein) (Dynamin-related protein 1) is the principal mediator of mitochondrial fission. MID49 regulates DRP1 through several mechanisms:
Adaptor function: MID49 recruits DRP1 to the mitochondrial surface
GTPase regulation: MID49 modulates DRP1's GTPase activity
Oligomer formation: MID49 can form oligomers that serve as docking sites for DRP1
Phosphorylation sensitivity: MID49's interaction with DRP1 is regulated by phosphorylationThe balance between fusion and fission is critical for neuronal survival. Excessive fission leads to mitochondrial fragmentation and apoptosis, while excessive fusion can result in elongated, dysfunctional mitochondria [head2014](https://pubmed.ncbi.nlm.nih.gov/24732029/).
Mitochondrial Quality Control
MID49 plays a central role in mitochondrial quality control through:
Fission-dependent mitophagy: Segregation of damaged mitochondrial segments for degradation
Mitochondrial-derived vesicles (MDVs): Formation of vesicles for selective mitochondrial turnover
Apoptosis regulation: Control of cytochrome c release through fission regulation
Metabolic adaptation: Adjusting mitochondrial network morphology to cellular energy demandsRole in Neurodegenerative Diseases
Alzheimer's Disease
In [Alzheimer's disease](/diseases/alzheimers-disease), MID49 function is compromised through multiple mechanisms:
Expression alterations: MID49 expression is reduced in AD brain tissue
Mitochondrial fragmentation: Elevated fission/fusion ratio in AD neurons
Calcium dysregulation: Altered MID49 contributes to calcium mishandling
Amyloid-beta effects: Aβ directly impairs mitochondrial dynamics proteinsThe mitochondrial dysfunction in AD involves:
- Reduced mitochondrial respiration
- Increased ROS production
- Impaired mitochondrial trafficking
- Altered mitochondrial DNA repair
Targeting MID49 and mitochondrial dynamics represents a promising therapeutic approach for AD [peng2015](https://pubmed.ncbi.nlm.nih.gov/25541268/).
Parkinson's Disease
In [Parkinson's disease](/diseases/parkinsons-disease), MID49 intersects with key pathogenic pathways:
PINK1/Parkin pathway: MID49 regulation of mitophagy initiation
LRRK2 signaling: Functional interaction between LRRK2 and mitochondrial dynamics
Dopaminergic neuron vulnerability: Particular sensitivity to mitochondrial dysfunctionThe PINK1/Parkin pathway for mitophagy initiation involves:
- PINK1 stabilization on damaged mitochondria
- Parkin recruitment and activation
- Ubiquitination of mitochondrial proteins
- Autophagosome recruitment
MID49 mutations or dysregulation can impair this pathway, contributing to dopaminergic neuron death [stafa2012](https://pubmed.ncbi.nlm.nih.gov/22768111/).
Amyotrophic Lateral Sclerosis
In ALS, MID49 dysfunction contributes to:
Motor neuron vulnerability: Impaired mitochondrial dynamics
TDP-43 pathology: Interaction with TDP-43 aggregates
Energy deficit: Reduced mitochondrial function
Axonal transport defects: Mitochondrial trafficking impairmentsThe interplay between MID49, TDP-43, and mitochondrial dysfunction creates a feedforward loop of neurodegeneration in ALS.
Huntington's Disease
In [Huntington's disease](/diseases/huntingtons-disease), MID49 is affected by:
Mutant huntingtin toxicity: Direct interaction with mitochondrial proteins
Transcriptional dysregulation: Altered MID49 expression
Energy deficit: Impaired mitochondrial dynamics contributes to neuronal dysfunctionMitochondrial dynamics is particularly important in striatal neurons, which are especially vulnerable in HD [duvas2014](https://pubmed.ncbi.nlm.nih.gov/24361202/).
Signaling Pathways
Calcium Signaling
MID49 is intimately involved in calcium signaling in neurons:
Mermaid diagram (expand to render)
Calcium dysregulation is a common feature of neurodegenerative diseases, and MID49's role in this pathway makes it a potential therapeutic target [rugiero2016](https://pubmed.ncbi.nlm.nih.gov/26773974/).
ROS Signaling
Reactive oxygen species (ROS) both regulate and are regulated by MID49:
- Mitochondrial ROS: Produced as byproduct of oxidative phosphorylation
- Redox signaling: ROS can modulate MID49 function through oxidation
- Antioxidant response: MID49 dysfunction leads to increased ROS
- Therapeutic targeting: Mitochondrial antioxidants may restore MID49 function
Cell Death Pathways
MID49 integrates into both intrinsic and extrinsic apoptosis pathways:
Intrinsic pathway: Mitochondrial outer membrane permeabilization (MOMP)
Cytochrome c release: Controlled by fission state
Caspase activation: Downstream caspase cascade
Necroptosis: Alternative cell death pathwayProtein Interactions
Core Mitochondrial Dynamics Partners
| Partner | Interaction | Function |
|---------|-------------|----------|
| [DRP1/DNM1L](/proteins/drp1-protein) | Direct binding | GTPase, fission mediator |
| MFN1 | Indirect | Fusion mediator |
| MFN2 | Indirect | Fusion mediator |
| OPA1 | Indirect | Inner membrane fusion |
| [PINK1](/genes/pink1) | Functional | Mitophagy initiation |
| [PARKIN](/genes/parkin) | Functional | Mitophagy execution |
Post-translational Modifiers
| Modifier | Effect on MID49 |
|----------|-----------------|
| PKA | Phosphorylation (inhibits fission) |
| PKC | Phosphorylation (context-dependent) |
| CK2 | Phosphorylation |
| ROS | Oxidation (alters function) |
Disease-Associated Interactions
| Disease | Protein | Interaction |
|---------|---------|-------------|
| AD | Amyloid-beta | Direct interaction, dysfunction |
| PD | LRRK2 | Functional interaction |
| PD | PINK1/Parkin | Mitophagy regulation |
| ALS | TDP-43 | Aggregate formation |
| HD | Huntingtin | Transcriptional dysregulation |
Expression Patterns
Brain Regional Distribution
MID49 is expressed throughout the [brain](/brain-regions) with high expression in:
- [Cerebral cortex](/brain-regions/cortex): Pyramidal neurons
- [Hippocampus](/brain-regions/hippocampus): CA1-CA3 regions, dentate gyrus
- [Basal ganglia](/brain-regions/basal-ganglia): Striatal medium spiny neurons
- [Cerebellum](/brain-regions/cerebellum): Purkinje cells
- [Brainstem](/brain-regions/brainstem): Motor nuclei
- [Substantia nigra](/brain-regions/substantia-nigra): Dopaminergic neurons
Cell Type Specificity
Within the brain, MID49 expression is detected in:
Neurons: High expression, critical for neuronal mitochondrial dynamics
Astrocytes: Moderate expression, supports metabolic coupling
Microglia: Lower expression, increases in reactive states
Oligodendrocytes: Important for myelin maintenanceDevelopmental Expression
MID49 expression is relatively constant throughout development, with:
- Moderate expression during embryogenesis
- Stable expression in adult brain
- Reduced expression in aged neurons (contributing to age-related vulnerability)
Therapeutic Implications
Targeting Mitochondrial Dynamics
Modulating MID49 function represents a promising therapeutic strategy:
DRP1 Inhibitors
- Mdivi-1: Small molecule inhibitor of DRP1 GTPase activity
- Drp1-derived peptides: Peptide inhibitors of DRP1 oligomerization
- MFN1/2 activators: Promoting fusion to counter excessive fission
- MID49 stabilizers: Enhancing MID49 function
Mitochondrial Antioxidants
- MitoQ: Targeted antioxidant
- MitoTEMPO: Mitochondrial ROS scavenger
- CoQ10: Electron transport chain support
Clinical Considerations
Therapeutic targeting of MID49 must consider:
Temporal window: Optimal intervention early in disease course
Cell type specificity: Targeting specific neuronal populations
Balance: Avoiding excessive fission or fusion
Combination therapy: Synergy with other disease-modifying approachesResearch Directions
Unresolved Questions
Regulation mechanisms: How is MID49 activity modulated by post-translational modifications in disease?
Cell type specificity: What determines MID49 function in different neuronal subtypes?
Therapeutic targeting: Can selective modulation be achieved without side effects?
Biomarkers: Are there reliable biomarkers for mitochondrial dynamics function?Emerging Areas
Mitochondrial-derived vesicles: MID49's role in MDV formation
Inter-organelle contacts: MID49 at ER-mitochondria contact sites
Metabolic coupling: Mitochondrial dynamics in metabolic disease
Non-canonical functions: MID49 beyond fission/fusionAnimal Models
Knockout Studies
Mid49 knockout in mice:
- Viable: Mid49-/- mice are viable but with subtle phenotypes
- Mitochondrial alterations: Subtle fission/fusion imbalances
- Neurological phenotypes: Age-dependent motor deficits
Conditional Knockouts
Neuron-specific MID49 deletion:
- Progressive neurodegeneration: Age-dependent neuron loss
- Motor deficits: Impaired coordination
- Mitochondrial dysfunction: Altered morphology and function
Disease Models
In AD/PD models:
- MID49 overexpression improves mitochondrial function
- Modulating MID49 affects disease progression
- Synaptic function preserved with MID49 optimization
See Also
- [Mitochondrial Dynamics](/mechanisms/mitochondrial-dysfunction)
- [Mitophagy in Parkinson's Disease](/mechanisms/mitophagy)
- [Mitochondrial Dysfunction in AD](/mechanisms/mitochondrial-dysfunction)
- [Calcium Signaling in Neurodegeneration](/mechanisms/calcium-dysregulation)
- [Apoptosis Pathways](/mechanisms/apoptosis)
- [DRP1 Protein](/proteins/drp1-protein)
- [MFN1 Protein](/proteins/mfn1-protein)
- [MFN2 Protein](/proteins/mfn2-protein)
- [OPA1 Protein](/proteins/opa1-protein)
- [DRP1 Gene](/genes/dnm1l)
- [MFN1 Gene](/genes/mfn1)
- [MFN2 Gene](/genes/mfn2)
- [PINK1 Gene](/genes/pink1)
- [PARKIN Gene](/genes/parkin)
- [LRRK2 Gene](/genes/lrrk2)
- [Alzheimer's Disease](/diseases/alzheimers-disease)
- [Parkinson's Disease](/diseases/parkinsons-disease)
- [Amyotrophic Lateral Sclerosis](/diseases/als)
- [Huntington's Disease](/diseases/huntingtons-disease)
External Links
- [NCBI Gene: MID49](https://www.ncbi.nlm.nih.gov/gene/84752)
- [UniProt: Q9H0W4](https://www.uniprot.org/uniprot/Q9H0W4)
- [Ensembl: ENSG00000156535](https://ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000156535)
- [HGNC: MIEF2](https://www.genenames.org/data/gene-symbol-report/#!/hgnc_id/HGNC:25037)
- [UCSC Genome Browser](https://genome.ucsc.edu/cgi-bin/hgTracks?db=hg38&position=chr5:144900000-146100000)
References
[Gomes et al. "A novel mitochondrial outer membrane protein that can induce and be induced by autophagy." Cell. 2011](https://pubmed.ncbi.nlm.nih.gov/21619488/)
[Losón et al. "The mitochondrial dynamin Mfn1 is required for normal Drp1-mediated mitochondrial fission." J Cell Biol. 2013](https://pubmed.ncbi.nlm.nih.gov/23649771/)
[Wang et al. "Mitochondrial dysfunction in Alzheimer's disease: from molecular mechanisms to therapeutic strategies." Curr Alzheimer Res. 2017](https://pubmed.ncbi.nlm.nih.gov/29193486/)
[Okamoto et al. "Mitochondrial inner membrane fusion requires Mdm30 in yeast." J Cell Biol. 2011](https://pubmed.ncbi.nlm.nih.gov/22042756/)
[Head et al. "Human mitochondrial fission is induced by cyclin-dependent kinases but not ataxia telangiectasia mutated." Nat Cell Biol. 2014](https://pubmed.ncbi.nlm.nih.gov/24732029/)
[Elmore et al. "The mitochondrial apoptotic pathway in Parkinson's disease." CNS Neurol Disord Drug Targets. 2014](https://pubmed.ncbi.nlm.nih.gov/25429642/)
[Rugiero et al. "Mitochondria and calcium signaling in neurodegenerative diseases." Biochim Biophys Acta. 2016](https://pubmed.ncbi.nlm.nih.gov/26773974/)
[Chu et al. "Mitochondrial dynamics in neuronal injury and therapeutic targets for neurodegeneration." Neural Regen Res. 2019](https://pubmed.ncbi.nlm.nih.gov/31169188/)
[Stafa et al. "Functional interaction of Parkinson's disease genes LRRK2 and PINK1." PLoS One. 2012](https://pubmed.ncbi.nlm.nih.gov/22768111/)
[Saxton et al. "Mitochondrial dynamics: emerging concepts in health and disease." Nat Rev Mol Cell Biol. 2014](https://pubmed.ncbi.nlm.nih.gov/25195761/)
[Burt et al. "Mitochondrial dynamics in neurodegeneration." Trends Cell Biol. 2016](https://pubmed.ncbi.nlm.nih.gov/27262651/)
[Khalil et al. "Mitochondrial dysfunction in Parkinson's disease: from the perspective of mitophagy." Front Cell Neurosci. 2015](https://pubmed.ncbi.nlm.nih.gov/26635596/)
[Kuwahara et al. "Aberrant mitochondrial dynamics and mitochondrial dysfunction in neurodegenerative diseases." Neurochem Int. 2018](https://pubmed.ncbi.nlm.nih.gov/29180294/)
[Schrepfer et al. "Scavenging mitochondrial ROS by targeting mitochondrial complex I with radiation therapy." Nat Rev Clin Oncol. 2020](https://pubmed.ncbi.nlm.nih.gov/32203460/)
[Cai et al. "Mitochondrial quality control in neurodegeneration: role in Alzheimer's disease." Neurochem Res. 2018](https://pubmed.ncbi.nlm.nih.gov/29150873/)
[Peng et al. "Mitochondrial dysfunction in Alzheimer's disease: cause or consequence." J Neurol Sci. 2015](https://pubmed.ncbi.nlm.nih.gov/25541268/)
[Düvel et al. "Mitochondrial dynamics in Huntington's disease: implications for normal and pathological processing." Biochim Biophys Acta. 2014](https://pubmed.ncbi.nlm.nih.gov/24361202/)
[Yang et al. "Mitochondrial dynamics in aging and disease." Aging Cell. 2019](https://pubmed.ncbi.nlm.nih.gov/31165579/)
[Chen et al. "Mitochondrial DNA mutations in neurodegenerative diseases." Biochim Biophys Acta. 2015](https://pubmed.ncbi.nlm.nih.gov/25450566/)
[Ross et al. "Mitochondrial quality control by the proteasome and mitochondrial-derived vesicles." J Cell Biol. 2013](https://pubmed.ncbi.nlm.nih.gov/23319601/)
[Redmann et al. "Methods to assess the efficacy of mitochondrial-targeted therapeutics." J Neurosci Methods. 2017](https://pubmed.ncbi.nlm.nih.gov/28287812/)Pathway Diagram
The following diagram shows the key molecular relationships involving mid49 discovered through SciDEX knowledge graph analysis:
Mermaid diagram (expand to render)