Biology subjects

Karagoz, G. E.

Publications and source records attributed to Karagoz, G. E..

5 recordsLinked to original sources

bioRxiv2025

Ancestral P-body proteins rewired for autophagic recyclingin the early land plant Marchantia polymorpha

Processing bodies (P-bodies) are conserved ribonucleoprotein (RNP) granules central to RNA metabolism across eukaryotes. Although the mechanisms underlying their assembly are well understood, the pathways governing their selective turnover remain unclear. Here, we identify the conserved decapping proteins EDC4 and DCP1 as a selective autophagy receptor pair responsible for P-body turnover in the early land plant Marchantia polymorpha. MpEDC4 engages ATG8 via a canonical AIM motif, while MpDCP1 contains a previously unrecognized reverse AIM within its intrinsically disordered region. Mutations disrupting these motifs impair autophagic degradation of P-bodies, demonstrating a cooperative receptor mechanism. Notably, this autophagic function is lineage-specific, as orthologs in Arabidopsis and humans lack ATG8-binding capacity. Strikingly, heterologous expression of MpEDC4 in human cells promotes degradation of -synuclein, a protein strongly linked to Parkinsons disease etiology. Our findings thus uncover an evolutionary innovation that links RNA metabolism to selective autophagy and opens avenues for cross-kingdom engineering of targeted protein degradation pathways.

plant biology↗

bioRxiv2025

Dual regulation of the unfolded protein response by IGF2BP3 during ER stress

Misfolded protein accumulation in the endoplasmic reticulum (ER) perturbs cellular homeostasis, causing pathological ER stress. The Unfolded Protein Response (UPR) is a highly conserved signaling cascade that restores ER homeostasis by countering ER protein overload. Transcriptional response is paramount for UPR signaling and negating ER stress. While multiple UPR-linked mRNAs are post-transcriptionally regulated, the mechanisms mediating this regulation are unclear. Here, we demonstrate that the highly conserved RNA-binding protein IGF2BP3 interacts with transcripts encoding a subset of UPR effectors. During ER stress, IGF2BP3 destabilized many of these target transcripts, including UPR targets. In contrast, IGF2BP3 stabilized mRNAs encoding transcriptional regulators and thereby upregulated expression of UPR target genes. This dual regulation allows IGF2BP3 to differentially upregulate stress response genes while tuning down the expression of other transcripts during ER stress, relieving protein folding load during this critical response. Our data reveal that posttranscriptional mechanisms control transcription, thus forming gene regulatory networks that robustly tune the UPR.

cell biology↗

bioRxiv2025

The coordinated action of UFMylation and ribosome-associated quality control pathway clears arrested nascent chains at the endoplasmic reticulum

Clearance of incomplete nascent polypeptides resulting from ribosomal stalling is essential for protein homeostasis. While ribosome-associated quality control (RQC) mechanisms that degrade these polypeptides are well-characterized in the cytosol, how stalled endoplasmic reticulum (ER)-bound ribosomes are cleared remains poorly understood. Stalled ER-bound ribosomes are marked by ubiquitin-fold modifier 1 (UFM1) on large ribosomal subunit protein RPL26, but the precise function and regulation of this process are unclear. Here, we demonstrate that canonical RQC factors associate with ribosomes stalled at the ER. Functional cellular assays using ER-targeted stalling reporters reveal that while ribosome splitting is a prerequisite for UFMylation of RPL26, the UFMylation persists without late RQC components that are involved in the clearance of arrested nascent chains (NEMF and LTN1). The UFM1 E3 ligase complex binds to and UFMylates the 60S-peptidyl-tRNA complex and, in concert with the canonical RQC pathway, facilitates the clearance of arrested polypeptides. Our findings reveal that UFMylation acts to maintain translational integrity at the ER.

cell biology↗

bioRxiv2023

IGF2BP1 phosphorylation regulates ribonucleoprotein condensate formation by impairing low-affinity protein and RNA interactions

The insulin-like growth factor 2 mRNA binding protein (IGF2BP1) is a conserved RNA-binding protein that regulates RNA stability, localization, and translation. IGF2BP1 is part of various ribonucleoprotein (RNP) condensates regulating RNA outputs. However, the mechanism that regulates its assembly into condensates remains unknown. Here we found, using proteomics, that IGF2BP1 phosphorylation at S181 in a disordered linker is regulated in a stress-dependent manner. Phosphomimetic mutations in two disordered linkers, S181E and Y396E, modulated RNP condensate formation by IGF2BP1 without impacting its binding affinity for RNA. Intriguingly, the S181E mutant, which lies in linker 1, impaired IGF2BP1 condensate formation in vitro and in cells, whereas a Y396E mutant in the second linker increased condensate size and dynamics. Structural approaches showed that the first linker binds RNAs nonspecifically through its RGG/RG motif, an interaction weakened in the S181E mutant. Notably, linker 2 interacts with IGF2BP1s folded domains and these interactions were partially impaired in the Y396E mutant. Our data reveal how phosphorylation modulates low affinity interaction networks in disordered linkers to regulate RNP condensate formation.

biochemistry↗

bioRxiv2023

Stress-induced clustering of the UPR sensor IRE1 is driven by disordered regions within its ER lumenal domain

Upon accumulation of unfolded proteins at the endoplasmic reticulum (ER), IRE1 activates the unfolded protein response (UPR) to restore protein-folding homeostasis. During ER stress, IRE1s ER lumenal domain (LD) drives its clustering on the ER membrane to initiate signaling. How IRE1s LD assembles into high-order oligomers remains largely unknown. By in vitro reconstitution experiments we show that human IRE1 LD forms dynamic biomolecular condensates. IRE1 LD condensates were stabilized when IRE1 LD was tethered to model membranes and upon binding of unfolded polypeptide ligands. Molecular dynamics simulations suggested that weak multivalent interactions are involved in IRE1 LD assemblies. Mutagenesis showed that disordered regions in IRE1 LD control its clustering in vitro and in cells. Importantly, dysregulated clustering led to defects in IRE1 signaling. Our results reveal that membranes and unfolded polypeptides act as scaffolds to assemble dynamic IRE1 condensates into stable, signaling competent clusters.

cell biology↗