Biology subjects

Dikic, I.

Publications and source records attributed to Dikic, I..

At least 19 recordsLinked to original sources

bioRxiv2026

Structural basis for the ATP-dependence of omegasome biogenesis by DFCP1

Autophagosome formation begins at phosphatidylinositol 3-phosphate-enriched endoplasmic reticulum (ER) subdomains termed omegasomes. DFCP1/ZFYVE1 is recruited to omegasomes through its FYVE domains and has recently been shown to function as an ATPase involved in omegasome constriction and autophagosome biogenesis. However, the structural basis of DFCP1 ATPase activity and how nucleotide-dependent conformational states regulate omegasome dynamics remain unknown. Here, we determined the crystal structures of the DFCP1 ATPase domain in complex with either ADP or the non-hydrolyzable ATP analogue, AppNHp at near atomic resolution. We employed structure-guided mutagenesis to define residues required for DFCP1 function in cells. The structures reveal that the active site contains a trans-acting Arg271 finger coordinating the {psi}-phosphate and trans-acting His323 that stacks on the ATP adenine ring. ATP hydrolysis results in a conformational switch in the vicinity of Arg271, while contacts with His323 persist in the presence of ADP. Biochemical analyses of DFCP1 and its mutants show that DFCP1 forms ATP-dependent microdomains on membranes. Disruption of His323 and Arg271 uncouples nucleotide binding from ATP hydrolysis and alters the oligomeric state of the protein. Live-cell imaging of DFCP1 knockout cells reconstituted with wild-type or mutant DFCP1 further demonstrates that these biochemical defects translate into distinct omegasome phenotypes. Together, our data provides a structural-function framework for DFCP1 ATPase activity and reveals how distinct catalytic elements control omegasome dynamics in vivo. We propose that nucleotide-dependent assembly and hydrolysis-driven conformational changes enable DFCP1 to regulate omegasome formation and its progression toward autophagosome closure. Significance StatementDFCP1 organizes the ER subdomains known as omegasomes, which are sites of autophagosome biogenesis. DFCP1 is an ATPase whose catalytic activity is required for function, but the precise role of its ATPase activity is unknown. Crystal structures of the DFCP1 ATPase domain in the presence of a non-hydrolyzable ATP analogue and ADP reveal an Arg finger that operates in trans, such that dimerization is required for ATP hydrolysis, and ATP hydrolysis destabilizes dimers. Dimerization is also promoted by an adenine base-stacking interaction in trans with H323. These residues are important for DFCP1 clustering on membranes and omegasome constriction, clarifying that the role of ATP is to promote the dimerization of the ATPase domain and thereby control the organization of DFCP1 on membranes.

biochemistry↗

bioRxiv2026

Damage sensing recruitment of a lipid phosphatase couples lysosomal membrane repair to proteostatic adaptation

Restoration of organellar membrane integrity is critical for maintaining cellular homeostasis. Lysosomal membrane damage activates local repair machineries and global stress responses, but how signaling lipid metabolism is engaged by damage sensors to support and mechanistically link these processes remains poorly understood. Here we show that the phosphoinositide 3-phosphatase MTMR14 is recruited to damaged lysosomes through calcium-dependent binding to sphingomyelin. At these sites, MTMR14 promotes local PI(3)P hydrolysis and supports PI(4)P accumulation, thereby facilitating formation of ER-lysosome contact sites associated with membrane repair, without affecting ESCRT recruitment. MTMR14-dependent lipid remodelling causes reduced mTORC1 signalling and a decrease in global protein synthesis, consistent with an acute proteostatic adaptation to lysosomal injury. Cells lacking MTMR14 display impaired damage-induced lipid remodelling, altered repair-associated structures, sustained protein synthesis, and increased sensitivity to lysosomal injury, all of which can be mitigated by mTORC1/S6K inhibition. Our findings identify damage-sensing recruitment of MTMR14 and local PI(3)P turnover on damaged lysosomes as a phosphoinositide module that promotes lysosomal membrane integrity and homeostasis while functionally linking nutrient signalling to proteostasis under membrane stress.

cell biology↗

bioRxiv2026

TBK1 restricts IRGQ-mediated autophagy

The autophagy-lysosome system directs the degradation of a wide variety of cytoplasmic cargo such as damaged organelles, protein aggregates, and invading pathogens. The autophagy receptor IRGQ harbors two distinct LIR domains, with LIR1 exhibiting high selectivity for GABARAPL2. Proteomic, biochemical, and high-throughput microscopy studies revealed that the IRGQ-GABARAPL2 complex functions as a hub for the interaction between hATG8s and the autophagy initiation machinery, promoting their lipidation and overall autophagic flux. The interaction of IRGQ with GABARAPL2 is regulated via TBK1. Upon TBK1 activation, GABARAPL2 is phosphorylated on S10, which disrupts IRGQ-GABARAPL2 complexation and therefore its interaction with the autophagy initiation machinery, resulting in a reduction of the autophagic flux of GABARAPL2 and IRGQ-cargo, without affecting bulk autophagy. These findings broaden IRGQs role in autophagy, identifying it as an interaction hub for autophagy initiation that is negatively regulated by TBK1.

biochemistry↗

bioRxiv2026

ProxiCapture Reveals Context-Dependent CRBN Interactore Landscape of Molecular Glue Degraders

Molecular glue degraders represent a rapidly expanding class of small molecules that reprogram E3 ubiquitin ligases to ubiquitinate and degrade disease-relevant proteins. Despite their therapeutic potential, the rational design of molecular glues remains challenging, underscoring the need for unbiased discovery strategies to identify new chemical targets. To address this challenge, we developed ProxiCapture, an affinity-based proteomics workflow that models the systemic behavior of molecular glues by combining purified CRBN-{Delta}HBD protein with native cell or tissue lysates. Systematic application of ProxiCapture across eight cancer cell lines, three maturation states of immune cells, and paired primary healthy and tumor tissues, revealed a comprehensive atlas of pomalidomide interactors, including previously uncharacterized targets. These findings reveal that degrader-dependent interactors of CRBN are context-dependent, requiring broad, physiologically and systemically anchored sampling to uncover the full "glueable" proteome. Taken together, this study establishes a scalable platform that accelerates molecular glue discovery by capturing cell- and tissue-specific recruitment profiles and predicting system-wide degrader effects.

cancer biology↗

bioRxiv2025

Ferroptosis governs lymphatic vessel growth and regression

Whether, when, and how lymphatic vessels undergo cell death remains poorly understood. Here we identify ferroptosis as a physiological, cell-intrinsic regulator of the lymphatic endothelial cell survival during development and following injury, in stark contrast to the resilient organotypic blood endothelial cells. The lymphatic susceptibility to ferroptosis stems from tampered cystine/ hydropersulfide metabolism, alongside reduced glutathione availability triggered by an SH3RF3 E3 ligase mediated GPX4 degradation, and enhanced integration of polyunsaturated fatty acid enriched membrane phospholipids. Inducing ferroptosis genetically or pharmacologically elevated lymphatic lipid peroxidation, halted embryonic lymphangiogenesis and prevented post-injury lymphatic overgrowth while simultaneously shaped immune responses. Conversely, ferroptosis inhibition through saturated fatty acid supplementation led to pathological lymphatic hyperplasia. Targeting lymphatic ferroptotic mechanisms holds promise against pathological lymphatic growth in response to injury.

cell biology↗

bioRxiv2025

Ubiquitin-dependent signal amplification in lipid saturation sensing

Cellular membranes are dynamic platforms whose composition and biophysical properties are surveyed by sensor proteins to maintain homeostasis. Failure to preserve membrane homeostasis, however, results in cellular stress and organelle dysfunction. Using the prototypical lipid saturation sensor Mga2, we explored how weak physical cues that modulate rotational movements in the transmembrane region are converted into decisive biochemical outputs that ultimately control the production of unsaturated fatty acids. Quantitative in vitro ubiquitylation assays and kinetic modeling reveal vastly distinct rates of Mga2 ubiquitylation controlled by the membrane environment. Mga2 ubiquitylation dominates in tightly packed, saturated membranes, while loosely packed environments favor an inhibitory autoubiquitylation of the cognate E3 ligase Rsp5. This mechanism provides a means of signal amplification, which can function even in the absence of deubiquitylating enzymes. Our findings provide a mechanistic framework for how membrane property sensors convert weak, fluctuating physical cues into robust biochemical outcomes, and put a spotlight on the regulatory potential of E3 ligase autoubiquitylation in cellular surveillance.

biochemistry↗

bioRxiv2025

Vitamin B12 alleviates Verheij syndrome-like defects via phospholipid remodeling in a C. elegans PUF60 spliceosomopathy model

Verheij syndrome (VRJS) is a rare genetic disorder caused by mutations in the poly(U)-binding splicing factor 60 (PUF60), a core component of the spliceosomal complex. VRJS triggers multiple congenital anomalies, but the underlying pathomechanisms remain poorly understood. Mutation of the Caenorhabditis elegans PUF60 ortholog, rnp-6, recapitulates several hallmarks of VRJS, including growth delay and smaller body size. Here, we demonstrate that developmental defects in rnp-6 mutants are rescued by dietary K12-type Escherichia coli strains. Through complementary genetic screens and multi-omics analyses, we identify vitamin B12 (VB12) as a potent suppressor of these defects, acting via the methionine/S-adenosylmethionine/phosphatidylcholine metabolic axis. Mechanistically, rnp-6 mutation causes aberrant splicing with methionine and phospholipid metabolism-related genes, which cumulatively impair cellular methylation potential, dysregulate phosphatidylcholine metabolism, and induce integrated stress response. We identify intron retention of the nhr-114/HNF4 transcription factor as a primary driver of growth defects, and restoring its splicing robustly suppresses these phenotypes. VB12 supplementation bypasses the aberrant splicing, restores metabolic balance, and activates mTORC1 to rescue developmental phenotypes. Finally, we show that PUF60 deficiency induces aberrant splicing of methionine and phospholipid metabolism-related genes in a human cell line, and is associated with altered plasma methionine and phospholipid levels in VRJS patients. Our findings establish C. elegans as a tractable model for VRJS and uncover SAM/SAH/phospholipid dysregulation as a key mechanism underlying the spliceosomopathy, suggesting VB12 as a potential strategy to mitigate VRJS-related anomalies.

genetics↗

bioRxiv2025

TRIM28 regulates pre-mRNA splicing via phosphorylation and SUMOylation networks

Pre-mRNA splicing is a highly regulated process orchestrated by splicing factors, cis-acting elements, and interconnected cellular processes such as transcription and chromatin remodeling. Here, we identify a novel regulatory axis involving phosphorylation and SUMOylation that governs the function of Tripartite motif-containing 28 protein (TRIM28) and its role in pre-mRNA splicing. We demonstrate that TRIM28 interacts with the spliceosomal protein USP39 in a phosphorylation-dependent manner, with non-phosphorylated TRIM28 promoting USP39 SUMOylation at defined lysine residues. This post-translational modification enhances USP39s role within the U4/U6.U5 tri-snRNP complex. Functionally, TRIM28 knockdown induces widespread alterations in alternative splicing patterns, underscoring its importance in splicing regulation. Together, our findings uncover a mechanistic link between TRIM28-mediated post-translational modifications and the modulation of spliceosomal activity, offering new insights into how splicing decisions are integrated with cellular signaling pathways.

cell biology↗

bioRxiv2025

Phosphoribosyl ubiquitination of SNARE proteins regulate autophagy in Legionella infection

Legionella pneumophila is an intracellular pathogen that causes Legionnaires disease. The bacteria releases effector proteins some of which remodel the host autophagic-lysosomal pathways. One effector is RavZ, which delipidates ATG8 proteins, making Legionella-infected cells deficient in autophagy. Here we show that SidE effectors mediate the phosphoribosyl ubiquitination (PR-Ub) of autophagic SNARE proteins STX17 and SNAP29. STX17 modification induces recruitment of STX17+ membranes from the endoplasmic reticulum to Legionella-containing phagosomes to form replicative vacuoles. Using proximity labeling, biochemistry and Legionella infection studies, we have discovered a mechanism by which autophagy is hijacked by bacteria to recruit ER membranes to the bacterial vacuole which has autophagy markers but do not fuse with lysosomes. Mass spectrometric identification of PR-Ub sites and mutational studies show that PR-Ub modification of STX17 alters its interaction with ATG14L, which drives the recruitment of ER membranes to the bacterial vacuole in a PI3K dependent manner. On the other hand, PR-Ub of SNAP29 inhibits the formation of the autophagosomal SNARE complex (STX17-SNAP29-VAMP8) by steric hindrance, thereby preventing the fusion of bacterial vacuoles with lysosomes.

cell biology↗

bioRxiv2024

p53 isoforms have a high aggregation propensity, interact with chaperones and lack binding to p53 interaction partners

The p53 transcription factor family consists of the three members p53, p63 and p73. Both p63 and p73 exist in different isoforms that are well characterized. Isoforms have also been identified for p53 and it has been proposed that they are responsible for increased cancer metastasis. In contrast to the p63 and p73 isoforms, which do not contain truncations in folded domains, most of the p53 isoforms contain only parts of either the DNA binding domain or the oligomerization domain. To better understand the effect of p53 isoforms in cancer we provide here a comprehensive biochemical characterization. With the exception of the {Delta}40p53 isoform none of the other variants can bind to DNA with high affinity and none can upregulate transcription. Probing with antibodies, DARPins and other interaction partners confirmed that isoforms harboring deletions in the DNA binding domain cannot interact specifically with them, but instead are bound to chaperones and other factors known to interact with misfolded proteins. Expression of isoforms with deletions in the DNA binding domain results in upregulation of cellular chaperones. If the expression level surpasses a threshold, the chaperone system can no longer keep these isoforms soluble resulting in aggregation and co-aggregation with other factors.

biophysics↗

bioRxiv2024

Intracellular lipopolysaccharide regulates ER remodeling upon bacterial infection

Selective autophagy of the endoplasmic reticulum (ER), termed ERphagy or reticulophagy, plays a key role in organelle remodeling and cellular homeostasis. However, whether and how ERphagy is regulated during Gram-negative bacteria infection to influence host responses remains unclear. Here, we show that Salmonella enterica serovar Typhimurium releases lipopolysaccharide (LPS) that colocalizes with RETREG1/FAM134B, a reticulon-like ER-resident receptor for ERphagy. Cytosolic delivery of LPS, either during infection or via transfection, markedly increases RETREG1- and LC3B-decorated ER fragments. Mechanistically, affinity-isolation assays demonstrate that LPS directly binds RETREG1 through interactions between lipid A and positively charged residues within its amphipathic helices and C-terminal region. This interaction promotes RETREG1 oligomerization and drives ER membrane fragmentation, a process further amplified by the O-antigen moiety of LPS. The resulting ER fragments accumulate around LC3-positive Salmonella-containing vacuoles, facilitating bacterial clearance. Importantly, both intracellular and extracellular Salmonella exploit outer membrane vesicles (OMVs) to deliver LPS into the host cytosol, triggering RETREG1 activation and ER remodeling. Collectively, our findings reveal a previously unrecognized host response by which LPS of Gram-negative bacteria are sensed by the host ERphagy machinery to promote xenophagy and enhance antibacterial defense.

cell biology↗

bioRxiv2024

BRAT1 - a new therapeutic target for glioblastoma

Glioblastoma (GBM), the most malignant primary brain tumor in adults, has poor prognosis irrespective of therapeutic advances due to its radio-resistance and infiltrative growth into brain tissue. The present study assessed functions and putative druggability of protein breast cancer type 1 susceptibility protein (BRCA1)-associated Ataxia telangiectasia mutated (ATM)-activator 1 (BRAT1) as a crucial factor driving key aspects of GBM, including enhanced DNA damage response and tumor migration. By a stable depletion of BRAT1 in GBM and glioma stem-like (GSC) cell lines, we observed a delay in DNA double-strand break repair and increased sensitivity to radiation treatment, corroborated by in vitro and in vivo studies demonstrating impaired tumor growth and invasion. Proteomic analyses further emphasize the role of BRAT1s cell migration and invasion capacity, with a notable proportion of downregulated proteins associated with these processes. In line with the genetic manipulation, we found that treatment with the BRAT1 inhibitor Curcusone D (CurD) significantly reduced GSC migration and invasion in an ex vivo slice culture model, particularly when combined with irradiation, resulting a synergistic inhibition of tumor growth and infiltration. Our results reveal that BRAT1 contributes to GBM growth and invasion and suggest that therapeutic inhibition of BRAT1 with CurD or similar compounds might constitute a novel approach for anti-GBM directed treatments.

cancer biology↗

bioRxiv2024

Intrinsically disordered region amplifies membrane remodeling to augment selective ER-phagy

Intrinsically disordered regions (IDRs) play a pivotal role in organellar remodeling. They transduce signals across membranes, scaffold signaling complexes, and mediate vesicular traffic. Their functions are regulated by constraining conformational ensembles through specific intra- and inter-molecular interactions, physical tethering, and post-translational modifications. The ER-phagy receptor FAM134B/RETREG1, known for its Reticulon homology domain (RHD), includes a substantial C-terminal intrinsically disorder region (IDR) housing the LC3 interacting (LIR) motif. Beyond engaging the autophagic machinery, the function of the FAM134B-IDR is unclear. Here, we investigate the characteristics of the FAM134B-IDR by extensive modeling and molecular dynamics (MD) simulations. We present detailed structural models for the IDR, mapping its conformational landscape in solution and membrane-anchored configurations. Our analysis reveals that depending on the membrane anchor, the IDRs collapse onto the membrane and induce positive membrane curvature to varying degrees. The charge patterns underlying this Janus-like behavior are conserved across other ER-phagy receptors. We found that IDRs alone are sufficient to sense curvature. When combined with RHDs, they intensify membrane remodeling and drive efficient protein clustering, leading to faster budding, thereby amplifying RHD remodeling functions. Our simulations provide a new perspective on IDRs of FAM134B, their Janus-like membrane interactions, and the resulting modulatory functions during large-scale ER remodeling.

biophysics↗

bioRxiv2024

Long non-coding RNAs direct the SWI/SNF complex to cell-specific enhancers

The coordination of chromatin remodeling is essential for DNA accessibility and gene expression control1. The highly conserved and ubiquitously expressed SWItch/Sucrose Non-Fermentable (SWI/SNF) chromatin remodeling complex plays a central role in cell type- and context-dependent gene expression2. Despite the absence of a defined DNA recognition motif, SWI/SNF binds lineage specific enhancers genome-wide where it actively maintains open chromatin state2-5. It does so while retaining the ability to respond dynamically to cellular signals4. However, the mechanisms that guide SWI/SNF to specific genomic targets have remained elusive. Here we demonstrate that trans-acting long non-coding RNAs (lncRNAs) direct the SWI/SNF complex to cell type-specific enhancers. SWI/SNF preferentially binds lncRNAs and these predominantly bind DNA targets in trans. Together they localize to enhancers, many of which are cell type-specific. Knockdown of SWI/SNF- and enhancer-bound lncRNAs causes the genome-wide redistribution of SWI/SNF away from enhancers and a concomitant differential expression of spatially connected target genes. These lncRNA-SWI/SNF-enhancer networks support an enhancer hub model of SWI/SNF genomic targeting. Our findings reveal a competitive recruitment of SWI/SNF by lncRNAs which provide a specific and dynamic layer of control in chromatin accessibility and gene expression.

molecular biology↗

bioRxiv2024

Development of covalent probes to capture Legionella pneumophila effector enzymes

Upon infection of host cells, Legionella pneumophila releases a multitude of effector enzymes into the cells cytoplasm that hijack a plethora of cellular activities, including the hosts ubiquitination pathways. Effectors belonging to the SidE-family are involved in non-canonical serine phosphoribosyl ubiquitination of host substrate proteins contributing to the formation of a Legionella-containing vacuole that is crucial in the onset of Legionnaires disease. This dynamic process is reversed by effectors called Dups that hydrolyse the phosphodiester in the phosphoribosyl ubiquitinated protein. We installed reactive warheads on chemically prepared ribosylated ubiquitin to generate a set of probes targeting these Legionella enzymes. In vitro tests on recombinant DupA revealed that a vinyl sulfonate warhead was most efficient in covalent complex formation. Mutagenesis and x-ray crystallography approaches were used to identify the site of covalent crosslinking to be an allosteric cysteine residue. The subsequent application of this probe highlights the potential to selectively enrich the Dup enzymes from Legionella-infected cell lysates.

cell biology↗

bioRxiv2024

Engineering CRBN for rapid identification of next generation binders

The majority of clinical degrader candidates utilize an immunomodulatory imide drug (IMiD)-based derivative, that directs their target substrate to the E3 ligase receptor Cereblon (CRBN), however, concomitant neo-substrate degradation by IMiDs often results in severe off-target effects. Further biophysical screening is needed to discover CRBN binders that might overcome these safety concerns, but the previously reported CRBN protein constructs suffer significant limitations that reduce their applicability as tools for biophysical assays making large-scale screening efforts a costly endeavor. This is due to the requirement of CRBN co-expression with DDB1 in insect cells to produce soluble protein that contains all the reported structural features necessary for proper compound interaction. Here, a near full-length human CRBN construct was designed that retains these required features, but for the first time allows the generation of highly homogenous and cost-efficient expression in E.coli, eliminating the need for DDB1 co-expression. We have extensively profiled the new construct against the existing CRBN constructs in binary and ternary degrader complexes, showing it to be the "best of both worlds" in terms of binding characteristics and ease of protein production. We then designed the Enamine CRBN focused IMiD library of 4480-compounds and demonstrated applicability of the new construct to high throughput screening by identifying novel CRBN binders with high potency and ligand efficiency. The new methods described here should serve as valuable tools for the development of the next generation IMiD-based degraders.

biophysics↗

bioRxiv2023

Serine ubiquitination of p62 regulates Nrf2 dependent redox homeostasis

The KEAP1-Nrf2 axis is essential for the cellular response against metabolic and oxidative stress. KEAP1 is an adaptor protein of Cullin-3 ubiquitin ligase that controls the cellular levels of Nrf2, a critical transcription factor of several cytoprotective genes. Oxidative stress, defective autophagy and pathogenic infections activate Nrf2 signaling through phosphorylation of the adaptor protein p62, which competes with Nrf2 for binding to KEAP1. Here we show that phosphoribosyl-linked serine ubiquitination of p62 catalyzed by SidE effectors of Legionella pneumophila controls Nrf2 signaling and cell metabolism upon Legionella infection. Serine ubiquitination of p62 sterically blocks its binding to KEAP1, resulting in Nrf2 ubiquitination and degradation. This reduces Nrf2-dependent antioxidant synthesis in the early phase of infection. Levels of serine ubiquitinated p62 diminish in the later stage of infection allowing the expression of Nrf2-target genes; resulting in a differential regulation of the host metabolome and proteome in a Nrf2 dependent manner.

cell biology↗

bioRxiv2023

Mechanism and evolutionary origins of Alanine-tail C-degron recognition by E3 ligases Pirh2 and CRL2-KLHDC10

In Ribosome-associated Quality Control (RQC), nascent-polypeptides produced by interrupted translation are modified with C-terminal polyalanine tails ( Ala-tails) that function outside ribosomes to induce ubiquitylation by Pirh2 or CRL2-KLHDC10 E3 ligases. Here we investigate the molecular basis of Ala-tail function using biochemical and in silico approaches. We show that Pirh2 and KLHDC10 directly bind to Ala-tails, and structural predictions identify candidate Ala-tail binding sites, which we experimentally validate. The degron-binding pockets and specific pocket residues implicated in Ala-tail recognition are conserved among Pirh2 and KLHDC10 homologs, suggesting that an important function of these ligases across eukaryotes is in targeting Ala-tailed substrates. Moreover, we establish that the two Ala-tail binding pockets have convergently evolved, either from an ancient module of bacterial provenance (Pirh2) or via tinkering of a widespread C-degron recognition element (KLHDC10). These results shed light on the recognition of a simple degron sequence and the evolution of Ala-tail proteolytic signaling.

molecular biology↗