Neuroprotective Properties of Quinone Reductase 2 Inhibitor M-11, a 2-Mercaptobenzimidazole Derivative

The ability of NQO2 to increase the production of free radicals under enhanced generation of quinone derivatives of catecholamines is considered to be a component of neurodegenerative disease pathogenesis. The present study aimed to investigate the neuroprotective mechanisms of original NQO2 inhibitor M-11 (2-[2-(3-oxomorpholin-4-il)-ethylthio]-5-ethoxybenzimidazole hydrochloride) in a cellular damage model using NQO2 endogenous substrate adrenochrome (125 µM) and co-substrate BNAH (100 µM). The effects of M-11 (10–100 µM) on the reactive oxygen species (ROS) generation, apoptosis and lesion of nuclear DNA were evaluated using flow cytometry and single-cell gel electrophoresis assay (comet assay). Results were compared with S29434, the reference inhibitor of NQO2. It was found that treatment of HT-22 cells with M-11 results in a decline of ROS production triggered by incubation of cells with NQO2 substrate and co-substrate. Pre-incubation of HT-22 cells with compounds M-11 or S29434 results in a decrease of DNA damage and late apoptotic cell percentage reduction. The obtained results provide a rationale for further development of the M-11 compound as a potential neuroprotective agent.

Multifaceted N-degron recognition and ubiquitylation by GID/CTLH E3 ligases

N-degron E3 ubiquitin ligases recognize specific residues at the N-termini of substrates. Although molecular details of N-degron recognition are known for several E3 ligases, the range of N-terminal motifs that can bind a given E3 substrate binding domain remains unclear. Here, studying the Gid4 and Gid10 substrate receptor subunits of yeast GID/human CTLH multiprotein E3 ligases, whose known substrates bear N-terminal prolines, we discovered capacity for high-affinity binding to diverse N-terminal sequences determined in part by context. Screening of phage displaying peptide libraries with exposed N-termini identified novel consensus motifs with non-Pro N-terminal residues distinctly binding Gid4 or Gid10 with high affinity. Structural data reveal that flexible loops in Gid4 and Gid10 conform to complementary folds of diverse interacting peptide sequences. Together with analysis of endogenous substrate degrons, the data show that degron identity, substrate domains harboring targeted lysines, and varying E3 ligase higher-order assemblies combinatorially determine efficiency of ubiquitylation and degradation.

EVI/WLS function is regulated by ubiquitination and linked to ER-associated degradation by ERLIN2

WNT signalling is important for development in all metazoan animals and is associated with various human diseases. The Ubiquitin-Proteasome System (UPS) and regulatory ER-associated degradation (ERAD) have been implicated in the production of WNT proteins. Here, we investigated how the WNT secretory factor EVI/WLS is ubiquitinated, recognised by ERAD components and subsequently removed from the secretory pathway. We performed a focused, immunoblot-based RNAi screen for factors that influence EVI/WLS protein stability. We identified the VCP-binding proteins FAF2 and UBXN4 as novel interaction partners of EVI/WLS and showed that ERLIN2 links EVI/WLS to the ubiquitination machinery. Interestingly, we found in addition that EVI/WLS is ubiquitinated and degraded in cells irrespective of their level of WNT production. This K11, K48, and K63-linked ubiquitination is mediated by the E2 ubiquitin conjugating enzymes UBE2J2, UBE2K, and UBE2N, but independent of the E3 ligases HRD1/SYVN or GP78/AMFR. Taken together, our study identified factors that link the UPS to the WNT secretory pathway and provides mechanistic details on the fate of an endogenous substrate of regulatory ERAD in mammalian cells.

Structures of ABCG2 under turnover conditions reveal a key step in the drug transport mechanism

ABCG2 is a multidrug transporter that affects drug pharmacokinetics and contributes to multidrug resistance of cancer cells. In previously reported structures, the reaction cycle was halted by the absence of substrates or ATP, mutation of catalytic residues, or the presence of small-molecule inhibitors or inhibitory antibodies. Here we present cryo-EM structures of ABCG2 under turnover conditions containing either the endogenous substrate estrone-3-sulfate or the exogenous substrate topotecan. We find two distinct conformational states in which both the transport substrates and ATP are bound. Whereas the state turnover-1 features more widely separated NBDs and an accessible substrate cavity between the TMDs, turnover-2 features semi-closed NBDs and an almost fully occluded substrate cavity. Substrate size appears to control which turnover state is mainly populated. The conformational changes between turnover-1 and turnover-2 states reveal how ATP binding is linked to the closing of the cytoplasmic side of the TMDs. The transition from turnover-1 to turnover-2 is the likely bottleneck or rate-limiting step of the reaction cycle, where the discrimination of substrates and inhibitors occurs.

Crambescin C1 Acts as A Possible Substrate of iNOS and eNOS Increasing Nitric Oxide Production and Inducing In Vivo Hypotensive Effect

Crambescins are guanidine alkaloids from the sponge Crambe crambe. Crambescin C1 (CC) induces metallothionein genes and nitric oxide (NO) is one of the triggers. We studied and compared the in vitro, in vivo, and in silico effects of some crambescine A and C analogs. HepG2 gene expression was analyzed using microarrays. Vasodilation was studied in rat aortic rings. In vivo hypotensive effect was directly measured in anesthetized rats. The targets of crambescines were studied in silico. CC and homo-crambescine C1 (HCC), but not crambescine A1 (CA), induced metallothioneins transcripts. CC increased NO production in HepG2 cells. In isolated rat aortic rings, CC and HCC induced an endothelium-dependent relaxation related to eNOS activation and an endothelium-independent relaxation related to iNOS activation, hence both compounds increase NO and reduce vascular tone. In silico analysis also points to eNOS and iNOS as targets of Crambescin C1 and source of NO increment. CC effect is mediated through crambescin binding to the active site of eNOS and iNOS. CC docking studies in iNOS and eNOS active site revealed hydrogen bonding of the hydroxylated chain with residues Glu377 and Glu361, involved in the substrate recognition, and explains its higher binding affinity than CA. The later interaction and the extra polar contacts with its pyrimidine moiety, absent in the endogenous substrate, explain its role as exogenous substrate of NOSs and NO production. Our results suggest that CC serve as a basis to develop new useful drugs when bioavailability of NO is perturbed.

Chaperones directly and efficiently disperse stress-triggered biomolecular condensates

Heat shock triggers formation of intracellular protein aggregates and induction of a molecular disaggregation system. Although this system (Hsp100/Hsp70/Hsp40 in most cellular life) can disperse aggregates of model misfolded proteins, its activity on these model substrates is puzzlingly weak, and its endogenous heat-induced substrates have largely eluded biochemical study. Recent work has revealed that several cases of apparent heat-induced aggregation instead reflect evolved, adaptive biomolecular condensation. In budding yeast Saccharomyces cerevisiae, the resulting condensates depend on molecular chaperones for timely dispersal in vivo, hinting that condensates may be major endogenous substrates of the disaggregation system. Here, we show that the yeast disaggregation system disperses heat-induced biomolecular condensates of poly(A)-binding protein (Pab1) orders of magnitude more rapidly than aggregates of the most commonly used model substrate, firefly luciferase. Pab1 condensate dispersal also differs from aggregate dispersal in its molecular requirements, showing no dependence on small heat-shock proteins and a strict requirement for type II Hsp40. Unlike luciferase, Pab1 is not fully threaded (and thus not fully unfolded) by the disaggregase Hsp104 during dispersal, which we show can contribute to the extreme differences in dispersal efficiency. The Hsp70-related disaggregase Hsp110 shows some Pab1 dispersal activity, a potentially important link to animal systems, which lack cytosolic Hsp104. Finally, we show that the long-observed dependence of the disaggregation system on excess Hsp70 stems from the precise mechanism of the disaggregation system, which depends on the presence of multiple, closely spaced Hsp70s for Hsp104 recruitment and activation. Our results establish heat-induced biomolecular condensates of Pab1 as a direct endogenous substrate of the disaggregation machinery which differs markedly from previously studied foreign substrates, opening a crucial new window into the native mechanistic behavior and biological roles of this ancient system.

Structures of ABCG2 under turnover conditions reveal a key step in drug transport mechanism

ABCG2 is a multidrug transporter expressed widely in the human body. Its physiological substrates include steroid derivatives and uric acid. In addition, it extrudes many structurally diverse cytotoxic drugs from various cells, thus affecting drug pharmacokinetics and contributing to multidrug resistance of cancer cells. Previous studies have revealed structures of ABCG2 bound to transport substrates, nucleotides, small-molecule inhibitors and inhibitory antibodies. However, the transport mechanism is not well-understood because all previous structures described trapped states, where the reaction cycle was halted by the absence of substrates or ATP, mutation of catalytic residues, or the presence of inhibitors. Here we present cryo-EM structures of nanodisc-reconstituted human ABCG2 under turnover conditions containing either the endogenous substrate estrone-3-sulfate or the exogenous substrate topotecan. We found two distinct conformational states in which both the transport substrates and ATP are bound. Whereas the state turnover-1 features more widely separated NBDs and an accessible cavity between the TMDs, turnover-2 features semi-closed NBDs and an almost fully occluded cavity between the TMDs. The transition from turnover-1 to turnover-2 includes conformational changes that link the binding of ATP by the NBDs to the closing of the cytoplasmic side of the TMDs. The size of the substrate appears to control which turnover state corresponds to the main state in the transport cycle. The transition from turnover-1 to turnover-2 is the likely bottleneck or rate-limiting step of the reaction cycle, where the discrimination of substrates and inhibitors occurs. Our results provide a structural basis of substrate specificity of ABCG2 and provide key insight to understand the transport cycle.

Using the CYP3A Activity Evaluation to Predict the Efficacy and Safety of Diazepam in Patients With Alcohol Withdrawal Syndrome

Background:Diazepam is one of the most commonly prescribed tranquilizers for the therapy of alcohol withdrawal syndrome (AWS). Despite its popularity, there is currently no precise information on the effect of genetic polymorphisms on the efficacy and safety of diazepam therapy.Objective:The objective of our study was to study the effect of CYP3A isoenzymes activity on the efficacy and safety of diazepam in patients with AWS.Methods:The study was conducted on 30 Russian male patients suffering from the AWS who received diazepam in injections at a dosage of 30.0 mg / day for 5 days. The efficacy and safety assessment was performed using psychometric scales and scales for assessing the severity of adverse drug reactions.Results:Based on the results of the study, we revealed the differences in the efficacy of therapy in patients with different CYP3A4 C>T intron 6 ( rs35599367) genotypes: ( CC) −9.0 [−13.0; −5.0], ( CT+TT) −13.5 [−15.0; −10.0], p = 0.014. The scores on the UKU scale, which was used to evaluate the safety of therapy, were also different: ( CC) 7.5 [6.0; 11.0], ( CT+TT) 11.0 [8.0; 12.0], p = 0.003.Conclusion:Possible relationship between the CYP3A activity, evaluated by the content of the urinary endogenous substrate of the given isoenzyme and its metabolite, the 6-beta-hydroxy cortisol (6-β-HC) / cortisol ratio, and the efficacy of diazepam was demonstrated. This possible relationship was also supported by the genotyping results. This should be taken into consideration when prescribing this drug to such patients in order to reduce the risk of pharmacoresistance.