MARCH5 protein (Membrane Associated Ring-CH-Type Finger 5, also known as MITOL) is a mitochondrial outer membrane E3 ubiquitin ligase encoded by the MARCH5/MARCHF5 gene. MARCH5 is a RING-CH type ubiquitin ligase that spans the outer mitochondrial membrane four times and ubiquitinates misfolded proteins, mitochondrial dynamics regulators (DRP1, MFN1/2), and innate immune signaling components. MARCH5 is a critical component of mitochondrial protein quality control, and its dysfunction leads to mitochondrial fragmentation and neuronal vulnerability in Parkinson's disease and ALS.
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| Protein Name | E3 ubiquitin-protein ligase MARCH5 |
| Gene | [MARCH5 (MARCHF5)](/genes/march5) |
| UniProt ID | [Q9NX47](https://www.uniprot.org/uniprot/Q9NX47) |
| Molecular Weight | 35.3 kDa |
| Subcellular Localization | Outer mitochondrial membrane |
| Protein Family | MARCH family E3 ubiquitin ligases |
| Associated Diseases | [PD](/diseases/parkinsons-disease), [AD](/diseases/alzheimers-disease), [ALS](/diseases/amyotrophic-lateral-sclerosis), [HD](/diseases/huntingtons-disease) |
¶ Domain Architecture
MARCH5 is a 278-amino acid integral membrane protein:
- N-terminal cytoplasmic region (residues 1-30): Short cytoplasmic tail
- Transmembrane domain 1 (TM1, residues 31-50): First membrane-spanning helix
- RING-CH domain (residues 51-100): The catalytic E3 ubiquitin ligase domain facing the cytoplasm; contains the Zn2+-coordinating His-Cys motif characteristic of MARCH family proteins; transfers ubiquitin from E2 conjugating enzymes to substrate lysine residues
- TM2-TM4 (residues 101-230): Three additional transmembrane helices that form the substrate recognition interface
- C-terminal cytoplasmic tail (residues 231-278): Substrate interaction and regulatory region
¶ RING-CH Domain
The RING-CH domain (C3HC4-type) coordinates two Zn2+ ions and catalyzes K48-linked and K63-linked polyubiquitination:
- E2 partners: UBE2D (UbcH5) family, UBE2E1, UBE2J1
- Catalytic mechanism: RING domain positions the E2~Ub thioester for direct transfer to substrate lysines
- Critical residues: His43 and Cys65 are essential for catalytic activity; H43W mutation abolishes ubiquitin ligase function
MARCH5 is embedded in the outer mitochondrial membrane with both N- and C-termini facing the cytoplasm. The four TM helices create a channel-like structure that may accommodate substrate recognition within the lipid bilayer.
MARCH5 serves as the primary quality control E3 ligase on the mitochondrial surface:
- Recognizes and ubiquitinates misfolded or damaged proteins exposed on the OMM
- Partners with the AAA-ATPase VCP/p97 for substrate extraction and proteasomal delivery
- Clears mislocalized tail-anchored proteins that target mitochondria instead of the ER
- Essential component of mitochondria-associated degradation (MAD)
MARCH5 regulates fission-fusion balance through ubiquitination of key dynamics proteins:
- DRP1: K48-linked ubiquitination regulates DRP1 activity and turnover at fission sites
- MFN1/MFN2: Ubiquitination modulates fusogenic activity
- MiD49/MiD51: MARCH5 ubiquitinates mitochondrial fission receptors
- Loss of MARCH5 → excessive DRP1 accumulation → mitochondrial fragmentation
- K48-linked ubiquitination of MAVS terminates RIG-I/MDA5-dependent IFN-β production
- MARCH5 prevents chronic interferon signaling from damage-associated mtDNA
- Relevant for neuroinflammation: MARCH5 deficiency prolongs sterile IFN responses
MARCH5 ubiquitinates neurodegenerative disease proteins on mitochondria:
- Mutant SOD1 (ALS) — clears misfolded SOD1 from OMM
- PolyQ huntingtin fragments (HD) — ubiquitinates mitochondria-associated aggregates
- α-Synuclein (PD) — clears mitochondria-imported α-syn fragments
- Amyloid-beta (AD) — assists clearance of Aβ-associated mitochondrial damage
- MARCH5 cooperates with PINK1/Parkin for mitophagy initiation
- Initial OMM ubiquitination by MARCH5 primes the Parkin-dependent ubiquitin amplification cascade
- α-Synuclein accumulation suppresses MARCH5, creating mitochondrial dysfunction feed-forward
- MARCH5 also ubiquitinates LRRK2-G2019S on mitochondria, promoting its clearance
- Mutant SOD1 misfolding on the OMM overwhelms MARCH5 capacity
- TDP-43 C-terminal fragments accumulate on mitochondria as MARCH5 substrates
- MARCH5 overexpression delays motor neuron death in SOD1-G93A cultures
- MARCH5 expression reduced in AD hippocampal neurons
- MARCH5 deficiency exacerbates Aβ-induced mitochondrial fragmentation
- MARCH5 gene therapy: AAV-MARCH5 overexpression enhances mitochondrial quality control
- USP30 inhibitors: Block the deubiquitinase that opposes MARCH5/Parkin; enhance mitochondrial clearance
- Combination approaches: MARCH5 + PINK1/Parkin activation for synergistic mitochondrial protection