Biology subjects

Sapmaz, A.

Publications and source records attributed to Sapmaz, A..

7 recordsLinked to original sources

bioRxiv2026

Salmonella exploits USP32 to coordinate Rab14 and Rab11 recycling pathways for intracellular survival

Many intracellular bacterial pathogens establish membrane-bound niches derived from host material to survive and replicate within host cells. These compartments are carved through subversion of host intracellular trafficking pathways to modulate the composition of the vacuolar membrane. Although recycling-associated small Rab GTPases are frequently observed at infection sites, their role in membrane remodeling and cargo sorting has remained poorly understood. Here, we leverage the extensive early membrane remodeling occurring during Salmonella infection to dissect this process. Using endogenously tagged cell lines, we characterize the dynamics of the recycling small GTPases Rab14 and Rab11 at Salmonella intracellular infection sites. We report that Rab14 recruits its effector Rufy1, which mediates sorting of CI-M6PR through recycling tubules. Subsequently, Rab11 disperses the newly formed recycling endosomes by interacting with its effector Fip3 for retrograde transport. This pathway is controlled by the deubiquitinating enzyme USP32, which targets both Rab14 and Rab11, enhancing their interactions with Rufy1 and Fip3, respectively. We further show that USP32 is recruited to the infection site via local enrichment of phosphatidylserine-positive membranes, a process triggered by the Salmonella effector proteins SopE/E2. Importantly, silencing USP32 significantly impairs intracellular bacterial survival. Our findings reveal a remarkable exploitation of host signaling and trafficking pathways by Salmonella to construct a replication-permissive niche. Targeting these pathways may offer new strategies for therapeutic intervention against intracellular bacterial infections.

cell biology↗

bioRxiv2025

Huib32: A Potent and Selective USP32 Inhibitor Modulating Endosomal Processes and Advancing Cell-Permeable USP32 Probes

Deubiquitinating enzymes (DUBs) are pivotal regulators of ubiquitination, a vital post-translational modification essential for cellular processes. Dysregulated DUB activity disrupts cellular homeostasis, driving diseases like cancer and neurodegeneration. Ubiquitin-specific protease 32 (USP32) has emerged as a promising therapeutic target due to its role in endosomal and autophagosomal dynamics and its association with breast, ovarian, and lung cancers. Here, we describe Huib32 (Human deUbiquitinase Inhibitor 32) as a USP32 inhibitor. Cyanimide-containing Huib32 potently and selectively inhibits USP32 by covalently binding to the active site Cys743 in vitro and in cells, enhancing substrate ubiquitination, altering endosomal morphology, and mimicking USP32 depletion. Additionally, we present two activity-based probes (ABPs), Huib32*1 and Huib32*2, which enable precise detection of USP32 activity and confirm probe selectivity via mass spectrometry. Together, Huib32 and its probes represent a unique approach for targeting USP32, offering new research tools and potential therapeutic avenues for cancer and disorders involving endocytic trafficking.

biochemistry↗

bioRxiv2025

High-Throughput Synthesis and Screening of a Cyanimide Library Identifies Selective Inhibitors of ISG15-specific Protease USP18

High-throughput screening (HTS) of (large) compound collections is a critical early step in many drug discovery programs, enabling the rapid identification of lead molecules with desirable biological activity. The success of HTS depends heavily on the quality of the compound libraries used, and as such, the development of targeted libraries has emerged as a promising approach to enhance the effectiveness of HTS efforts. However, the acquisition and synthesis of such libraries remain costly and labor-intensive, often yielding compound quantities far exceeding the small amounts required for screening. To address these challenges, we present a high-throughput synthesis-to-screening method for the efficient inplate generation and immediate HTS of a deubiquitinase (DUB)-focused compound library. Central to our approach is the use of an Echo acoustic liquid handler, which enables precise nanoliter-scale transfers of DMSO-based solutions, facilitating efficient and miniaturized synthesis directly in 1,536-well plates. Using this platform, we constructed a library of 7,536 compounds featuring a DUB-privileged cyanimide warhead and screened it against a panel of twelve DUBs and ubiquitin-like proteases. This identified two structurally related molecules with selective inhibitory activity against the interferon-stimulated gene 15 (ISG15) protease USP18, which we further developed into a first-in-class USP18 inhibitor with 35 nM potency. This compound, BB07CA902, demonstrated exceptional specificity for USP18 across a panel of 41 DUBs and effectively increased ISGylation levels in cells by inhibiting USP18 activity. With our technology, we enabled the efficient preparation of large DUB-targeted cyanimide-based libraries, which will accelerate future DUB inhibitor development.

biochemistry↗

bioRxiv2024

USP24 is an ISG15 cross-reactive deubiquitinasethat mediates IFN-I production by de-ISGylatingthe RNA helicase MOV10

The interferon-stimulated gene 15 (ISG15) is a ubiquitin-like modifier induced by type I Interferon (IFN-I) and plays a crucial role in the innate immune response against viral infections. ISG15 is conjugated to target proteins by an enzymatic cascade through a process called ISGylation. While ubiquitin-specific protease 18 (USP18) is a well-defined deISGylase counteracting ISG15 conjugation, ISG15 cross-reactive deubiquitylating enzymes (DUBs) have also been reported. Our study reports USP24 as a novel ISG15 cross-reactive DUB identified through activity-based protein profiling (ABPP). We demonstrate that recombinant USP24 processed pro-ISG15 and ISG15-linked synthetic substrates in vitro. Moreover, the depletion of USP24 significantly increased the accumulation of ISG15 conjugates upon IFN-{beta} stimulation. An extensive proteomic analysis of the USP24-dependent ISGylome, integrating total proteome, GG-peptidome, and ISG15 interactome data, identified the helicase Moloney leukemia virus 10 (MOV10) as a specific target of USP24 for deISGylation. Further validation in cells revealed that ISGylated MOV10 enhances IFN-{beta} production/secretion, whereas USP24 deISGylates MOV10 to negatively regulate the innate immune response. This study showcases USP24s novel roles in modulating ISGylation and modulation of the IFN-I-dependent immune responses, with potential therapeutic implications in infectious diseases, cancer, autoimmunity, and neuroinflammation.

biochemistry↗

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↗

bioRxiv2023

USP16 is an ISG15 cross-reactive deubiquitinase targeting a subset of metabolic pathway-related proteins

The ubiquitin-like modifier ISG15 can modulate host and viral proteins to restrict viral and microbial infections, and act as a cytokine. Its expression and conjugation are strongly up-regulated by type I interferons. Here we identify the deubiquitinating enzyme USP16 as an ISG15 cross-reactive protease. Ubiquitin-specific protease 16 (USP16) was found to react with an ISG15 activity-based probe in pull-down experiments using chronic myeloid leukaemia-derived human cells (HAP1). Supporting this finding, recombinant USP16 cleaved pro-ISG15 and ISG15 iso-peptide linked model substrates in vitro, as well as ISGylated substrates present in cell lysates. Moreover, the interferon-induced stimulation of ISGylation in human HAP1 cells was increased by knockdown or knockout of USP16. Depletion of USP16 did not affect interferon signaling, and interferon treatment did not affect USP16 expression or enzymatic activity either. A USP16-dependent ISG15 interactome was established by anti-ISG15 immunoprecipitation mass spectrometry (IP-MS), which indicated that the deISGylating function of USP16 may regulate metabolic pathways involving GOT1, ALDOA, SOD1 and MDH1, all of which were further confirmed to be deISGylated by USP16 in HEK293T cells. Together, our results indicate that USP16 may contribute to regulating the ISGylation status of a subset of proteins related to metabolism during type I interferon responses.

biochemistry↗

bioRxiv2019

A Small-Molecule Activity-Based Probe for Monitoring Ubiquitin C-terminal Hydrolase L1 (UCHL1) Activity in Live Cells and Zebrafish Embryos

Many reagents have been emerged to study the function of specific enzymes in vitro. On the other hand, target specific reagents are scarce or need improvement allowing investigations of the function of individual enzymes in a cellular context. We here report the development of a target-selective fluorescent small-molecule activity-based DUB probe that is active in live cells and whole animals. The probe labels active Ubiquitin Carboxy-terminal Hydrolase L1 (UCHL1), also known as neuron-specific protein PGP9.5 (PGP9.5) and parkinson disease 5 (PARK5), a DUB active in neurons that constitutes 1-2% of total brain protein. UCHL1 variants have been linked with the neurodegenerative disorders Parkinsons and Alzheimers disease. In addition, high levels of UCHL1 also correlate often with cancer and especially metastasis. The function of UCHL1 or its role in cancer and neurodegenerative disease is poorly understood and few UCHL1 specific research tools exist. We show that the reagents reported here are specific for UCHL1 over all other DUBs detectable by competitive activity-based protein profiling and by mass spectrometry. Our probe, which contains a cyanimide reactive moiety, binds to the active-site cysteine residue of UCHL1 irreversibly in an activity-dependent manner. Its use is demonstrated by labelling of UCHL1 both in vitro and in cells. We furthermore show that this probe can report UCHL1 activity during the development of zebrafish embryos.

biochemistry↗