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](/genes/march5) 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](/proteins/drp1-protein), [MFN1/2](/proteins/mfn2-protein)), 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](/diseases/parkinsons-disease) and [ALS](/diseases/amyotrophic-lateral-sclerosis).
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MARCH5 Protein
Overview
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](/genes/march5) 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](/proteins/drp1-protein), [MFN1/2](/proteins/mfn2-protein)), 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](/diseases/parkinsons-disease) and [ALS](/diseases/amyotrophic-lateral-sclerosis).
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
Membrane Topology
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.
Normal Function
Mitochondrial Protein Quality Control
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](/genes/vcp) 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)
Mitochondrial Dynamics
MARCH5 regulates fission-fusion balance through ubiquitination of key dynamics proteins:
[DRP1](/proteins/drp1-protein): K48-linked ubiquitination regulates DRP1 activity and turnover at fission sites
[Yonashiro R et al., A novel mitochondrial ubiquitin ligase plays a critical role in mitochondrial dynamics (2006) (2006)](https://doi.org/10.1038/sj.emboj.7601249)
[Karbowski M et al., The mitochondrial E3 ubiquitin ligase MARCH5 is required for Drp1 dependent mitochondrial division (2007) (2007)](https://doi.org/10.1083/jcb.200611064)
[Yoo YS et al., The mitochondrial ubiquitin ligase MARCH5 resolves MAVS aggregates during antiviral signalling (2015) (2015)](https://doi.org/10.1038/ncomms8910)
[Sugiura A et al., MITOL regulates endoplasmic reticulum-mitochondria contacts via Mitofusin2 (2013) (2013)](https://doi.org/10.1091/mbc.e13-02-0104)
[Nagashima S et al., Roles of mitochondrial ubiquitin ligase MITOL/MARCH5 in mitochondrial dynamics and diseases (2014) (2014)](https://doi.org/10.1093/jb/mvu070)