| Structural highlights
Function
AMRA1_HUMAN Substrate-recognition component of a DCX (DDB1-CUL4-X-box) E3 ubiquitin-protein ligase complex involved in cell cycle control and autophagy (PubMed:20921139, PubMed:23524951, PubMed:24587252, PubMed:33854232, PubMed:33854235, PubMed:33854239, PubMed:32333458). The DCX(AMBRA1) complex specifically mediates the polyubiquitination of target proteins such as BECN1, CCND1, CCND2, CCND3, ELOC and ULK1 (PubMed:23524951, PubMed:33854232, PubMed:33854235, PubMed:33854239). Acts as an upstream master regulator of the transition from G1 to S cell phase: AMBRA1 specifically recognizes and binds phosphorylated cyclin-D (CCND1, CCND2 and CCND3), leading to cyclin-D ubiquitination by the DCX(AMBRA1) complex and subsequent degradation (PubMed:33854232, PubMed:33854235, PubMed:33854239). By controlling the transition from G1 to S phase and cyclin-D degradation, AMBRA1 acts as a tumor suppressor that promotes genomic integrity during DNA replication and counteracts developmental abnormalities and tumor growth (PubMed:33854232, PubMed:33854235, PubMed:33854239). AMBRA1 also regulates the cell cycle by promoting MYC dephosphorylation and degradation independently of the DCX(AMBRA1) complex: acts via interaction with the catalytic subunit of protein phosphatase 2A (PPP2CA), which enhances interaction between PPP2CA and MYC, leading to MYC dephosphorylation and degradation (PubMed:25803737, PubMed:25438055). Acts as a regulator of Cul5-RING (CRL5) E3 ubiquitin-protein ligase complexes by mediating ubiquitination and degradation of Elongin-C (ELOC) component of CRL5 complexes (PubMed:25499913, PubMed:30166453). Acts as a key regulator of autophagy by modulating the BECN1-PIK3C3 complex: controls protein turnover during neuronal development, and regulates normal cell survival and proliferation (PubMed:21358617). In normal conditions, AMBRA1 is tethered to the cytoskeleton via interaction with dyneins DYNLL1 and DYNLL2 (PubMed:20921139). Upon autophagy induction, AMBRA1 is released from the cytoskeletal docking site to induce autophagosome nucleation by mediating ubiquitination of proteins involved in autophagy (PubMed:20921139). The DCX(AMBRA1) complex mediates 'Lys-63'-linked ubiquitination of BECN1, increasing the association between BECN1 and PIK3C3 to promote PIK3C3 activity (By similarity). In collaboration with TRAF6, AMBRA1 mediates 'Lys-63'-linked ubiquitination of ULK1 following autophagy induction, promoting ULK1 stability and kinase activity (PubMed:23524951). Also activates ULK1 via interaction with TRIM32: TRIM32 stimulates ULK1 through unanchored 'Lys-63'-linked polyubiquitin chains (PubMed:31123703). Also acts as an activator of mitophagy via interaction with PRKN and LC3 proteins (MAP1LC3A, MAP1LC3B or MAP1LC3C); possibly by bringing damaged mitochondria onto autophagosomes (PubMed:21753002, PubMed:25215947). Also activates mitophagy by acting as a cofactor for HUWE1; acts by promoting HUWE1-mediated ubiquitination of MFN2 (PubMed:30217973). AMBRA1 is also involved in regulatory T-cells (Treg) differentiation by promoting FOXO3 dephosphorylation independently of the DCX(AMBRA1) complex: acts via interaction with PPP2CA, which enhances interaction between PPP2CA and FOXO3, leading to FOXO3 dephosphorylation and stabilization (PubMed:30513302). May act as a regulator of intracellular trafficking, regulating the localization of active PTK2/FAK and SRC (By similarity). Also involved in transcription regulation by acting as a scaffold for protein complexes at chromatin (By similarity).[UniProtKB:A2AH22][1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17]
Publication Abstract from PubMed
AMBRA1 is a tumor suppressor protein that functions as a substrate receptor of the ubiquitin conjugation system with roles in autophagy and the cell cycle regulatory network. The intrinsic disorder of AMBRA1 has thus far precluded its structural determination. To solve this problem, we analyzed the dynamics of AMBRA1 using hydrogen deuterium exchange mass spectrometry (HDX-MS). The HDX results indicated that AMBRA1 is a highly flexible protein and can be stabilized upon interaction with DDB1, the adaptor of the Cullin4A/B E3 ligase. Here, we present the cryo-EM structure of AMBRA1 in complex with DDB1 at 3.08 A resolution. The structure shows that parts of the N- and C-terminal structural regions in AMBRA1 fold together into the highly dynamic WD40 domain and reveals how DDB1 engages with AMBRA1 to create a binding scaffold for substrate recruitment. The N-terminal helix-loop-helix motif and WD40 domain of AMBRA1 associate with the double-propeller fold of DDB1. We also demonstrate that DDB1 binding-defective AMBRA1 mutants prevent ubiquitination of the substrate Cyclin D1 in vitro and increase cell cycle progression. Together, these results provide structural insights into the AMBRA1-ubiquitin ligase complex and suggest a mechanism by which AMBRA1 acts as a hub involved in various physiological processes.
Structure of the DDB1-AMBRA1 E3 ligase receptor complex linked to cell cycle regulation.,Liu M, Wang Y, Teng F, Mai X, Wang X, Su MY, Stjepanovic G Nat Commun. 2023 Nov 22;14(1):7631. doi: 10.1038/s41467-023-43174-6. PMID:37993427[18]
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.
References
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- ↑ Liu M, Wang Y, Teng F, Mai X, Wang X, Su MY, Stjepanovic G. Structure of the DDB1-AMBRA1 E3 ligase receptor complex linked to cell cycle regulation. Nat Commun. 2023 Nov 22;14(1):7631. PMID:37993427 doi:10.1038/s41467-023-43174-6
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