Biology subjects

Tomko, R. J.

Publications and source records attributed to Tomko, R. J..

5 recordsLinked to original sources

bioRxiv2026

Dfm1 promotes Ste24-dependent translocon quality control

Proteins stalled during endoplasmic reticulum translocation clog Sec61 channels and require translocon quality control (TQC) mechanisms for clearance. Genetic screens implicated the derlin Dfm1 in TQC; however, its mechanistic role remained unclear. Using engineered and disease-relevant translocon-clogging substrates in Saccharomyces cerevisiae, we show Dfm1 functions in the Ste24-dependent branch of TQC, but not Hrd1- or Ltn1-dependent pathways. Loss of DFM1 increased accumulation and toxicity of translocon-clogging proteins. Increased dosage of wild type or catalytically inactive Hrd1 or Ste24 rescued toxicity, supporting a non-enzymatic buffering function for these factors in TQC. These findings identify Dfm1 as a key TQC factor whose critical role in clearing clogged translocons can be suppressed in multiple ways. Our results suggest enhancing TQC may protect cells from proteotoxic stress caused by disease-relevant translocon-clogging substrates, with potential implications for pancreatic {beta}-cell dysfunction in diabetes. Significance StatementO_LICells rely on translocon quality control (TQC) to clear proteins that clog the Sec61 translocon, but how the derlin Dfm1 contributes to this process has remained unclear. C_LIO_LIWe demonstrate that Dfm1 functions specifically in the Ste24-dependent TQC pathway and show that increased levels of the TQC factors Hrd1 or Ste24 rescues Dfm1 deficiency even without catalytic activity, revealing an unexpected non-enzymatic buffering function. C_LIO_LIThis work defines Dfm1s mechanistic role in TQC, provides new insight into how cells preserve endoplasmic reticulum function during translocation stress, and establishes a framework for investigating conserved pathways that protect against diseases associated with translocon clogging. C_LI

cell biology↗

bioRxiv2026

The vacuolar tauopathy-associated mutation D395G confers redox sensitivity to p97/VCP

The multifunctional AAA+ ATPase p97/VCP is a pivotal regulator of cellular proteostasis, extracting polyubiquitinated substrates from protein complexes or organelle membranes for proteasomal degradation. Mutations in p97 are linked to a broad spectrum of neurodegenerative disorders, including multisystem proteinopathy and amyotrophic lateral sclerosis. Here, we provide insights into the basis of dysfunction in p97D395G, implicated in vacuolar tauopathy, using an integrated structural approach. The mutation destabilizes the interaction network in the transient ADP.Pi state previously identified in p97WT and alters the dynamics of the linker between the tandem ATPase domains, resulting in decreased ATPase activity. We further demonstrate that the D395G mutation sensitizes p97 to oxidative stress by enhancing C522 oxidation, thereby perturbing nucleotide binding in D2, and define the functional basis of this oxidative inactivation of p97. These findings reveal redox control as a key regulatory layer of the p97 ATPase cycle and provide a mechanistic framework for how oxidative stress contributes to p97-associated neurodegeneration.

molecular biology↗

bioRxiv2025

A microsporidial deubiquitinase blocks ubiquitin transfer from adenylated E1 to human UBE2K ubiquitin conjugating enzyme

Intracellular pathogens frequently subjugate the ubiquitin system to evade host immune defenses and establish intracellular replication niches. Microsporidia are obligate intracellular animal parasites that typically cause self-limiting infections in humans, but can sometimes cause fatal disseminated disease. At present, the ubiquitin system of microsporidia is virtually unexplored. Here, we discover a likely effector deubiquitinase (DUB) of the otubain subgroup from the human pathogenic microsporidian Encephalitozoon hellem, which we designate ehOTUB1. We find that ehOTUB1 selectively binds the human ubiquitin conjugating (E2) enzyme UBE2K and inhibits its ubiquitin conjugation activity independent of ehOTUB1 DUB activity. We show that ehOTUB1 obstructs docking of UBE2K onto ubiquitin E1 enzyme via steric conflict with ubiquitin in the E1 adenylation site to prevent ubiquitin transfer to UBE2K. This unconventional mechanism of E2 inhibition expands the known repertoire by which pathogens manipulate ubiquitin signaling, and suggests that direct inhibition of E2 enzymes may be a broader function of otubain subfamily DUBs than originally appreciated.

biochemistry↗

bioRxiv2022

Sem1/DSS1 accelerates ATP-dependent substrate unfolding by the proteasome through a conformation-dependent intercomplex contact

The 26S proteasome is an [~]70 subunit ATP-dependent chambered protease that destroys proteins via multiple highly coordinated processing steps. The smallest and only intrinsically disordered proteasome subunit, Sem1 (DSS1 in metazoans), is critical for efficient substrate degradation despite lacking obvious enzymatic activities and being located far away from the proteasomes catalytic centers. Dissecting its role in proteolysis using cell-based approaches has been challenging because Sem1 also controls proteasome function indirectly via its role in proteasome biogenesis. To circumvent this challenge, we reconstituted Sem1-deficient proteasomes in vitro from purified components and systematically dissected its impact on distinct processing steps. Whereas most substrate processing steps are independent of Sem1, ATP-dependent unfolding is stimulated several-fold. Using structure-guided mutagenesis and engineered protein crosslinking, we demonstrate that Sem1 allosterically regulates ATP-dependent substrate unfolding via a distal conformation-dependent intersubunit contact. Together, this work reveals how a small, unstructured subunit comprising < 0.4% the total size of the proteasome can augment substrate processing from afar, and reveals a new allosteric pathway in controlling proteolysis.

biochemistry↗

bioRxiv2018

The anaphase-promoting complex regulates the degradation of the inner nuclear membrane protein Mps3 in budding yeast

The nucleus is enclosed by the inner nuclear membrane (INM) and the outer nuclear membrane (ONM). While the ONM is continuous with the endoplasmic reticulum (ER), the INM is independent and separates the nucleoplasm from the ER lumen. To maintain INM homeostasis, proteins mislocalized to the INM are degraded by the ER-associated protein degradation (ERAD) pathway. However, the mechanism for turnover of resident INM proteins is less clear. Here we show that the anaphase-promoting complex/cyclosome (APC/C), an E3 ubiquitin ligase, regulates the degradation of Mps3, a conserved integral protein of the INM. Turnover of Mps3 requires the ubiquitin-conjugating enzymes Ubc7 and Ubc6, but not the three known ERAD ubiquitin ligases, Doa10, Hrd1, and the Asi1-Asi3 complex. Using a genetic approach, we have found that Cdh1, a coactivator of APC/C, modulates Mps3 stability. APC/C controls Mps3 degradation through Mps3s N-terminus, which resides in the nucleoplasm and possesses two putative APC/C-dependent destruction motifs. Accumulation of Mps3 at the INM impairs nuclear morphological changes and cell division. Our findings therefore reveal an unexpected mechanism of APC/C-mediated protein quality control at the INM that coordinates nuclear morphogenesis and cell-cycle progression.

cell biology↗