Cullin-3 — Protein <table class="infobox infobox-protein">
Overview ...
Cullin-3 — Protein <table class="infobox infobox-protein">
Overview Cullin-3 (CUL3) is the scaffold protein for Cullin-RING Ligase 3 (CRL3) complexes, the largest subfamily of E3 ubiquitin ligases in the human proteome. CUL3 bridges BTB-domain substrate adaptor proteins to the RING-finger protein RBX1, assembling multisubunit E3 ligases that ubiquitinate specific substrates for proteasomal degradation. With approximately 80 BTB-domain adaptor proteins in the human genome, CRL3 complexes regulate an enormous range of substrates.
The most neuroscience-relevant CRL3 complex is CRL3^KEAP1, which constitutively ubiquitinates [NRF2](/genes/nfe2l2), the master regulator of antioxidant gene expression. CUL3 haploinsufficiency causes autism spectrum disorder, highlighting its critical role in neurodevelopment and synaptic function.
Structure
Domain Architecture CUL3 is a 768-amino acid protein with an elongated architecture:
Cullin repeat domain (N-terminal, residues 1-384) : Three repeats of a five-helix bundle that form the curved, rod-like N-terminal region; binds BTB-domain adaptor proteins4-helix bundle (4HB, residues 385-455) : Connecting region between N- and C-terminal domainsCullin homology domain (CHD, residues 456-606) : Alpha/beta domain that binds RBX1 and is the site of neddylationWinged-helix B domain (WHB, residues 607-768) : C-terminal domain; the neddylation site (Lys712) resides hereCRL3 Assembly The complete CRL3 complex is assembled as:
BTB adaptor → CUL3 (scaffold) → RBX1 → E2~Ub
BTB adaptors (e.g., [KEAP1](/genes/keap1), SPOP, KLHL20) bind the N-terminal cullin repeat domain
RBX1 binds the C-terminal WHB domain and recruits charged E2 enzymes (UbcH5, CDC34)
NEDD8 conjugation at Lys712 activates the ligase by repositioning RBX1 for optimal ubiquitin transfer
Neddylation Cycle CRL3 activity is dynamically regulated by neddylation:
Activation : NAE (NEDD8-activating enzyme) → UBC12 (E2) → NEDD8 conjugation at CUL3 K712Active state : Neddylated CUL3-RBX1 adopts an open conformation enabling ubiquitin transferInactivation : CSN (COP9 signalosome) cleaves NEDD8 from CUL3 (deneddylation)Inhibition : CAND1 binds unneddylated CUL3, competing with BTB adaptors for exchange
Function
KEAP1-NRF2 Regulation The CRL3^KEAP1 complex is the primary negative regulator of [NRF2](/genes/nfe2l2):
[KEAP1](/genes/keap1) homodimer bridges NRF2 to CUL3 via its BTB and Kelch domains
Under basal conditions, CRL3^KEAP1 polyubiquitinates NRF2 with K48-linked chains
Ubiquitinated NRF2 is degraded by the 26S proteasome (half-life ~20 min)
Electrophilic/oxidative stress modifies KEAP1 cysteines, disrupting NRF2 presentation
NRF2 escapes ubiquitination, accumulates, and activates ARE-dependent genes
[BACH1](/proteins/bach1-protein) derepression further amplifies the antioxidant response
Synaptic Development (CRL3^KCTD13) CRL3^KCTD13 regulates synaptic morphogenesis:
KCTD13 adaptor recruits RhoA GTPase to CUL3 for ubiquitination
RhoA degradation permits Rac1-dependent actin polymerization and dendritic spine formation
CUL3 haploinsufficiency → elevated RhoA → impaired spine morphogenesis → ASD phenotype
Protein Quality Control Additional CRL3 complexes maintain neuronal proteostasis:
CRL3^KLHL20: Ubiquitinates DAPK1, regulating [autophagy](/entities/autophagy)
CRL3^SPOP: Broad substrate specificity in protein quality control
CRL3^BTBD6: Ubiquitinates PLZF, regulating neuronal differentiation
CRL3^KLHL12: Regulates COPII vesicle formation for ER-to-Golgi transport
Role in Neurodegenerative Diseases
Alzheimer's Disease CRL3 dysfunction in [AD](/diseases/alzheimers-disease):
Reduced CUL3 neddylation efficiency in aged brain impairs CRL3 activity globally
Impaired CRL3^KEAP1 complex paradoxically fails to enhance NRF2 activation in AD [neurons](/entities/neurons)
CRL3 substrates compete with [amyloid-beta](/proteins/amyloid-beta) for proteasomal capacity
CRL3 complexes regulate [tau](/proteins/tau) phosphorylation indirectly through kinase turnover
Parkinson's Disease In [PD](/diseases/parkinsons-disease):
CRL3^KEAP1 regulation of NRF2 is critical for dopaminergic neuron survival
CUL3 cooperates with [Parkin](/genes/prkn) (another E3 ligase) in mitochondrial quality control
[PINK1](/genes/pink1)-dependent events affect CRL3 substrate selection
CUL3 dysfunction contributes to [alpha-synuclein](/proteins/alpha-synuclein) accumulation
Autism Spectrum Disorder
De novo CUL3 loss-of-function mutations identified in ASD cohorts
CUL3+/- mice show social behavior deficits, repetitive behaviors, and altered cortical excitation/inhibition balance
Excess RhoA (due to impaired CRL3^KCTD13 degradation) disrupts dendritic spine development
See Also
[CUL3](/genes/cul3) — Encoding gene
[KEAP1](/genes/keap1) — Primary BTB adaptor for NRF2 regulation
[NFE2L2 (NRF2)](/genes/nfe2l2) — CRL3^KEAP1 substrate
[BACH1](/proteins/bach1-protein) — NRF2 competitor
[PRKN (Parkin)](/genes/prkn) — Cooperating E3 ligase
[Ubiquitin-Proteasome System](/mechanisms/ubiquitin-proteasome-system) — Proteostasis pathway
External Links
[UniProt: Q13618](https://www.uniprot.org/uniprot/Q13618)
[PDB: 4AP2](https://www.rcsb.org/structure/4AP2)
[GeneCards: CUL3](https://www.genecards.org/cgi-bin/carddisp.pl?gene=CUL3)
References
[Pintard et al., Cullin-based ubiquitin ligases: Cul3-BTB complexes join the family (2004) (2004)](https://doi.org/10.1093/emboj/cdg527)
[Furukawa & Bhatt et al., BTB protein KEAP1 targets antioxidant transcription factor Nrf2 for ubiquitination by the Cullin 3-Roc1 ligase (2005) (2005)](https://doi.org/10.1128/MCB.25.1.162-171.2005)
[Kong et al., Genetic variants in CUL3 contribute to autism susceptibility (2020) (2020)](https://doi.org/10.1038/s41380-019-0557-x)
[Lin et al., Loss of the haploinsufficient gene CUL3 in autism triggers cortical excitation/inhibition imbalance (2021) (2021)](https://doi.org/10.1016/j.celrep.2021.109813)
[Unknown, Baird & Bhatt, The cytoprotective role of the KEAP1-NRF2 pathway (2020) (2020)](https://doi.org/10.1016/j.abb.2019.108164) Show full description