GST Proteins Research Articles

Testing the Capability of Embedding-Based Alignments on the GST Superfamily Classification: The Role of Protein Length.

In order to shed light on the usage of protein language model-based alignment procedures, we attempted the classification of Glutathione S-transferases (GST; EC 2.5.1.18) and compared our results with the ARBA/UNI rule-based annotation in UniProt. GST is a protein superfamily involved in cellular detoxification from harmful xenobiotics and endobiotics, widely distributed in prokaryotes and eukaryotes. What is particularly interesting is that the superfamily is characterized by different classes, comprising proteins from different taxa that can act in different cell locations (cytosolic, mitochondrial and microsomal compartments) with different folds and different levels of sequence identity with remote homologs. For this reason, GST functional annotation in a specific class is problematic: unless a structure is released, the protein can be classified only on the basis of sequence similarity, which excludes the annotation of remote homologs. Here, we adopt an embedding-based alignment to classify 15,061 GST proteins automatically annotated by the UniProt-ARBA/UNI rules. Embedding is based on the Meta ESM2-15b protein language. The embedding-based alignment reaches more than a 99% rate of perfect matching with the UniProt automatic procedure. Data analysis indicates that 46% of the UniProt automatically classified proteins do not conserve the typical length of canonical GSTs, whose structure is known. Therefore, 46% of the classified proteins do not conserve the template/s structure required for their family classification. Our approach finds that 41% of 64,207 GST UniProt proteins not yet assigned to any class can be classified consistently with the structural template length.

Prostaglandin synthase activity of sigma- and mu-class glutathione transferases in a parasitic trematode, Clonorchis sinensis.

Sigma-class glutathione transferase (GST) proteins with dual GST and prostaglandin synthase (PGS) activities play a crucial role in the establishment of Clonorchis sinensis infection. Herein, we analyzed the structural and enzymatic properties of sigma-class GST (CsGST-σ) proteins to obtain insight into their antioxidant and immunomodulatory functions in comparison with mu-class GST (CsGST-μ) proteins. CsGST-σ proteins conserved characteristic structures, which had been described in mammalian hematopoietic prostaglandin D2 synthases. Recombinant forms of these CsGST-σ and CsGST-μ proteins expressed in Escherichia coli exhibited considerable degrees of GST and PGS activities with substantially different specific activities. All recombinant proteins displayed higher affinities toward prostaglandin H2 (PGS substrate; average Km of 30.7 and 3.0 μm for prostaglandin D2 [PGDS] and E2 synthase [PGES], respectively) than those toward CDNB (GST substrate; average Km of 1,205.1 μm). Furthermore, the catalytic efficiency (Kcat/Km) of the PGDS/PGES activity was higher than that of GST activity (average Kcat/Km of 3.1, 0.7, and 7.0×10-3 s-1μm-1 for PGDS, PGES, and GST, respectively). Our data strongly suggest that the C. sinensis sigma- and mu-class GST proteins are deeply involved in regulating host immune responses by generating PGD2 and PGE2 in addition to their roles in general detoxification.

Herbal cake-separated moxibustion relieves aspirin induced gastric mucosal injury by activating Nrf2/ARE/HO-1 signaling in rats

To investigate whether herbal cake-separated moxibustion can activate nuclear factor erythroid 2-related factor 2 （Nrf2） / antioxidant responsive element （ARE） /hemeoxygenase-1 （HO-1） signaling pathway to repair aspirin induced gastric mucosal injury （GMI） in rats. SD rats （half male and half female） were randomly divided into blank control, model, moxibustion, inhibitor of HO-1 （inhibitor）, model+inhibitor, moxibustion + inhibitor groups, with 20 rats in each group. The GMI model was established by gavage of aspirin 150 mg/kg（1 mL/100 g）. Herbal cake-separated moxibustion was alternatively applied to bilateral "Zusanli" （ST36） and "Zhongwan" （CV12） and bilateral "Pishu" （BL20） and "Weishu" （BL21） for 30 min, once daily for 8 days. The rats in the three inhibitor groups received intraperitoneal injection of HO-1 inhibitor zinc protoporphyrin （5 mg/kg）. The rats' behavior score, emotional response score, skin hair score, diet score and stool state score were given. The GMI index was calculated according to Guth's methods. Histopathological changes of gastric mucosa were observed by H.E. staining. The activity of superoxide dismutase （SOD） and the content of malondialdehyde （MDA） in the gastric mucosal tissue and serum were detected by ELISA. The levels of Nrf2/ARE/HO-1 signaling pathway-related factors Keap1, Nrf2, HO-1, CAT, GST, and NQO1 in the gastric mucosal tissue were detected by quantitative real-time PCR and Western blot, separately. Compared with the blank control group, the behavior score, emotional response score, skin hair score, diet score and stool state score, GMI index, MDA contents of gastric mucosal tissue and serum, expression le-vels of Keap1 mRNA and protein were significantly increased （P<0.01）, while the activity of gastric mucosal and serum SOD, the expression levels of Nrf2, HO-1, CAT, GST and NQO1 mRNAs and proteins were considerably decreased （P<0.01） in the model group. Compared with the model group, moxibustion obviously reversed the increase of emotional response score, skin hair score, stool state score, GMI index, MDA levels of gastric mucosal tissue and serum, and expression levels of Keap1 mRNA and protein （P<0.01, P<0.05）, and the decrease of activity of SOD of gastric mucosal and serum, and the expression levels of Nrf2, HO-1, CAT, GST and NQO1 mRNAs and proteins （P<0.01, P<0.05）. After administration of antagonist of HO-1, the effects of moxibustion were eliminated or weakened pronouncedly in reducing skin hair score, GMI index, contents of gastric mucosal and serum MDA, and expression of Keap1 mRNA and protein, and in up-regulating gastric mucosal and serum SOD, and expression of HO-1, CAT, GST and NQO1 mRNAs and proteins （P<0.01, P<0.05）. Herbal-cake separated moxibustion can improve the GMI in rats, which may be associated with its effects in reducing oxidative stress and activating Nrf2/ARE/HO-1 signaling pathway.

Herbal cake-separated moxibustion relieves aspirin induced gastric mucosal injury by activating Nrf2/ARE/HO-1 signaling in rats

To investigate whether herbal cake-separated moxibustion can activate nuclear factor erythroid 2-related factor 2 （Nrf2） / antioxidant responsive element （ARE） /hemeoxygenase-1 （HO-1） signaling pathway to repair aspirin induced gastric mucosal injury （GMI） in rats. SD rats （half male and half female） were randomly divided into blank control, model, moxibustion, inhibitor of HO-1 （inhibitor）, model+inhibitor, moxibustion + inhibitor groups, with 20 rats in each group. The GMI model was established by gavage of aspirin 150 mg/kg（1 mL/100 g）. Herbal cake-separated moxibustion was alternatively applied to bilateral "Zusanli" （ST36） and "Zhongwan" （CV12） and bilateral "Pishu" （BL20） and "Weishu" （BL21） for 30 min, once daily for 8 days. The rats in the three inhibitor groups received intraperitoneal injection of HO-1 inhibitor zinc protoporphyrin （5 mg/kg）. The rats' behavior score, emotional response score, skin hair score, diet score and stool state score were given. The GMI index was calculated according to Guth's methods. Histopathological changes of gastric mucosa were observed by H.E. staining. The activity of superoxide dismutase （SOD） and the content of malondialdehyde （MDA） in the gastric mucosal tissue and serum were detected by ELISA. The levels of Nrf2/ARE/HO-1 signaling pathway-related factors Keap1, Nrf2, HO-1, CAT, GST, and NQO1 in the gastric mucosal tissue were detected by quantitative real-time PCR and Western blot, separately. Compared with the blank control group, the behavior score, emotional response score, skin hair score, diet score and stool state score, GMI index, MDA contents of gastric mucosal tissue and serum, expression le-vels of Keap1 mRNA and protein were significantly increased （P<0.01）, while the activity of gastric mucosal and serum SOD, the expression levels of Nrf2, HO-1, CAT, GST and NQO1 mRNAs and proteins were considerably decreased （P<0.01） in the model group. Compared with the model group, moxibustion obviously reversed the increase of emotional response score, skin hair score, stool state score, GMI index, MDA levels of gastric mucosal tissue and serum, and expression levels of Keap1 mRNA and protein （P<0.01, P<0.05）, and the decrease of activity of SOD of gastric mucosal and serum, and the expression levels of Nrf2, HO-1, CAT, GST and NQO1 mRNAs and proteins （P<0.01, P<0.05）. After administration of antagonist of HO-1, the effects of moxibustion were eliminated or weakened pronouncedly in reducing skin hair score, GMI index, contents of gastric mucosal and serum MDA, and expression of Keap1 mRNA and protein, and in up-regulating gastric mucosal and serum SOD, and expression of HO-1, CAT, GST and NQO1 mRNAs and proteins （P<0.01, P<0.05）. Herbal-cake separated moxibustion can improve the GMI in rats, which may be associated with its effects in reducing oxidative stress and activating Nrf2/ARE/HO-1 signaling pathway.

Computational insights into diverse aspects of glutathione S-transferase gene family in Papaver somniferum.

Plant glutathione S-transferases are an ancient protein superfamily having antioxidant activity. These proteins are primarily involved in diverse plant functions such as plant growth and development, secondary metabolism, signaling pathways and defense against biotic and abiotic stresses. The current study aimed to comprehensively identify and characterize the GST gene family in the medicinally important crop Papaver somniferum. A total of 93 GST proteins were identified belonging to eight GST classes and found to be majorly localized in the cytoplasm. All GST genes were found on eleven opium chromosomes. Gene duplication analysis showed segmental duplication as a key factor for opium GST gene family expansion under strong purifying selection. Phylogenetic analysis with gymnosperm, angiosperm and bryophyte revealed the evolution of GSTs earlier than their division into separate groups and also prior to the divergence of monocot and dicot. The secondary structure prediction showed the dominance of α-helices indicative of PsomGSTs as structurally stable and elastic proteins. Gene architecture showed the conservation of number of exons across the classes. MEME analysis revealed only a few class specific and many across class conserved motifs. Ser was found to be the active site residue of tau, phi, theta and zeta class and Cys was catalytic residue of DHAR, lambda and GHR class. Promoter analyses identified many cis-acting regulatory elements related to hormonal, cellular, stress and light response functions. Ser was the key phosphorylation site. Only three glycosylation sites were found across the 93 PsomGSTs. 3D structure prediction was also performed and was validated. Interactome analyses revealed the correlation of PsomGSTs with glutathione metabolizing proteins. Gene enrichment analysis and KEGG pathway analyzed the involvement of PsomGSTs in three major pathways i.e. glutathione metabolism, tyrosine metabolism and ascorbate metabolism. The outcome revealed high model quality of PsomGSTs. The results of the current study will be of potential significance to understand the functional and structural importance of the GST gene family in opium, a medicinally important crop.

Congeners-Specific Intestinal Absorption Of Microcystins In An In Vitro 3D Human Intestinal Epithelium: The Role Of Influx/Efflux Transporters.

Microcystins constitute a group of over 200 variants and are increasingly considered as emerging toxins in food and feed safety, particularly with regards to sea-food and fish consumption. Toxicity of MCs is congener-specific, being characterised by different acute potencies, likely related to the differential activity of metabolic enzymes and transporters proteins involved in their cellular uptake. However, the active transport of MCs across intestinal membranes has not been fully elucidated. Our results, obtained using a fit for purpose 3D human reconstructed intestinal epithelium, provide new information on the complex mechanisms involved in the absorption of 5 MC variants’: it is indeed characterised by the equilibrium between uptake and extrusion, since the selected congeners are substrates of both influx and efflux proteins. In the range of tested nominal concentrations (10–40 µM) fully representative of relevant exposure scenarios, none of the active tested transporters were saturated. The comparison of permeability (Papp) values of MCs variants highlighted a dose independent relationship for MC-LR, -YR and -RR (Papp x 10–7 ranged from 2.95 to 3.54 cm/s), whereas -LW and–LF showed a dose dependent increase in permeability reaching Papp values which were similar to the other congeners at 40 µM. MC-RR, -LR, -YR show absorption values around 5% of the administered dose. Due to their lipophilicity, MC-LW and -LF were also detected within the cellular compartment. The intestinal uptake was only partially attributable to OATPs, suggesting the involvement of additional transporters. Regarding the efflux proteins, MCs are not P-gp substrates whereas MRP2 and to a lesser extent Breast cancer resistance protein are active in their extrusion. Despite the presence of GST proteins, as an indication of metabolic competence, in the intestinal tissue, MC-conjugates were never detected in our experimental settings.

GSTs, MRP and Apoptototic Markers in DLD-1 Human Colon Cancer Cell Line Before and After 5-FU Treatment

Multidrugresistance is an important factor limiting the effect of chemotherapy on cancer treatment. Disorders of drug transport and apoptosis, deterioration of redox homeostasis are among the main mechanisms that lead to multidrug resistance. The aim of this study was to determine the effect of 5-FU on GST isozymes, drug resistance proteins and apoptotic proteins before and after 5-Flourouracil application on DLD-1 colon cancer cell line. The cytotoxic effect of 5-FU was measured by WST-1test and, the efficiency of drug application was, also, proved by double staining via Hoechst 33342 with Propidium iodide. Next, the expression levels of GST isozymes, drug resistance proteins and apoptotic proteins were determined by immunocytochemistry. The cytotoxic effect of 5-FU at different doses on DLD-1 colon cancer cell line was determined by WST-1 method. MRP-2, 3, 6, 7 of drug resistance proteins; GSTA1, GSTM1, GSTT1, GSTZ1, GSTK1 and GSTO1 of GST proteins; bcl-2, caspase-3, p38, and p53, which are apoptotic proteins, have higher expression in the drug-treated DLD-1 cell line. GSTS1, MDR-1 and MRP-1expressions were not immunocytochemically different. It was determined that there is a direct correlation between the level of cytotoxicity and applied drug concentration. The cytotoxic effect of the drug increased with the increase in the dose of the drug. In this study, as first in the literature, the expression levels of some apoptotic markers, GST isozymes and drug resistance proteinswere evaluated togetherand except GSTS1, MDR-1 and MRP-1, they were all upregulated with respect to the control group after 5-FU administration.

Quantitative Proteomic Analysis for High- and Low-Aflatoxin-Yield Aspergillus flavus Strains Isolated From Natural Environments.

The molecular mechanisms underlying aflatoxin production have been well-studied in strains of the fungus Aspergillus flavus (A. flavus) under artificial conditions. However, aflatoxin biosynthesis has rarely been studied in A. flavus strains isolated from field conditions with different aflatoxin-producing ability. In the present study, tandem mass tag (TMT) labeling and high-performance liquid chromatography (HPLC) coupled with tandem-mass spectrometry analysis were used for proteomic quantification in natural isolates of high- and low-aflatoxin-yield A. flavus strains. Additionally, findings obtained using the TMT-labeling method were validated using the high-resolution multiple reaction monitoring (MRM-HR) method. In total, 4,363 proteins were quantified, among which 1,045 proteins were differentially expressed between the high- and low-aflatoxin-yield A. flavus strains. Bioinformatics analysis showed that the up-regulated proteins were significantly enriched in carbon-related metabolism and the biosynthesis of secondary metabolites, whereas the down-regulated proteins were enriched in oxidative phosphorylation. Moreover, GST proteins were found to be significantly down-regulated in high-yield A. flavus strains; this result contradicted previous findings obtained from A. flavus strains grown under artificial conditions. In summary, our study provides novel insights into aflatoxin regulation in A. flavus under field conditions and could facilitate the development of various strategies for the effective control of aflatoxin contamination in food crops.

Proteomic analysis of early-stage incompatible and compatible interactions between grapevine and P. viticola

Wild grapevines can show strong resistance to the downy mildew pathogen P. viticola, but the associated mechanisms are poorly described, especially at early stages of infection. Here, we performed comparative proteomic analyses of grapevine leaves from the resistant genotype V. davidii “LiuBa-8” (LB) and susceptible V. vinifera “Pinot Noir” (PN) 12 h after inoculation with P. viticola. By employing the iTRAQ technique, a total of 444 and 349 differentially expressed proteins (DEPs) were identified in LB and PN, respectively. The majority of these DEPs were related to photosynthesis, respiration, cell wall modification, protein metabolism, stress, and redox homeostasis. Compared with PN, LB showed fewer downregulated proteins associated with photosynthesis and more upregulated proteins associated with metabolism. At least a subset of PR proteins (PR10.2 and PR10.3) was upregulated upon inoculation in both genotypes, whereas HSP (HSP70.2 and HSP90.6) and cell wall-related XTH and BXL1 proteins were specifically upregulated in LB and PN, respectively. In the incompatible interaction, ROS signaling was evident by the accumulation of H2O2, and multiple APX and GST proteins were upregulated. These DEPs may play crucial roles in the grapevine response to downy mildew. Our results provide new insights into molecular events associated with downy mildew resistance in grapevine, which may be exploited to develop novel protection strategies against this disease.

1H, 13C and 15N NMR assignments of solubility tag protein Msyb of Escherichia coli.

Biochemical and structural characterizations of a protein are the prerequisite for the further understanding of its biological role and potential applications. The expression of recombinant protein is almost unavoidable to produce the amount of the protein required for these studies, especially at the industrial level. Escherichia coli is the single most used system for recombinant protein expression and the first choice for a trial expression. Besides the inherited defects of its prokaryotic origin, the E. coli system has problems like low protein solubility and formation of inclusion bodies. To improve the solubility while assisting correct folding of the target protein, fusing a tag protein prior to its N-terminus is one of the common approaches. GST, MBP, Trx and SUMO proteins are among the most used tags by providing different advantages during recombinant protein expression. Msyb, a small and acidic protein native to E. coli, is another example that could improve the solubility of the target protein. While the biophysical and biochemical properties of these common tag proteins have been studied to a great extent, Msyb protein remains largely uncharacterized. Here, using solution-state NMR, our near-complete resonance assignment of Msyb provides a basis for future structure determination which would help to expand its usage as a common tag protein.

An integrated approach to unravel a crucial structural property required for the function of the insect steroidogenic Halloween protein Noppera-bo

Ecdysteroids are the principal steroid hormones essential for insect development and physiology. In the last 18 years, several enzymes responsible for ecdysteroid biosynthesis encoded by Halloween genes were identified and genetically and biochemically characterized. However, the tertiary structures of these proteins have not yet been characterized. Here, we report the results of an integrated series of in silico, in vitro, and in vivo analyses of the Halloween GST protein Noppera-bo (Nobo). We determined crystal structures of Drosophila melanogaster Nobo (DmNobo) complexed with GSH and 17β-estradiol, a DmNobo inhibitor. 17β-Estradiol almost fully occupied the putative ligand-binding pocket and a prominent hydrogen bond formed between 17β-estradiol and Asp-113 of DmNobo. We found that Asp-113 is essential for 17β-estradiol–mediated inhibition of DmNobo enzymatic activity, as 17β-estradiol did not inhibit and physically interacted less with the D113A DmNobo variant. Asp-113 is highly conserved among Nobo proteins, but not among other GSTs, implying that this residue is important for endogenous Nobo function. Indeed, a homozygous nobo allele with the D113A substitution exhibited embryonic lethality and an undifferentiated cuticle structure, a phenocopy of complete loss-of-function nobo homozygotes. These results suggest that the nobo family of GST proteins has acquired a unique amino acid residue that appears to be essential for binding an endogenous sterol substrate to regulate ecdysteroid biosynthesis. To the best of our knowledge, ours is the first study describing the structural characteristics of insect steroidogenic Halloween proteins. Our findings provide insights relevant for applied entomology to develop insecticides that specifically inhibit ecdysteroid biosynthesis.

Interaction of organotin compounds with three major glutathione S-transferases in zebrafish

Glutathione S-transferases (GSTs) play an important role in cellular detoxification as enzymatic mediators of glutathione (GSH) conjugation with a wide range of deleterious compounds, enabling their easier extrusion out of the organism. GSTs are shown to interact with organotin compounds (OTCs), known environmental pollutants, either as substrates, serving as electrophilic targets to the nucleophilic attack of GSH, or as noncompetitive inhibitors by binding to GST active sites and disrupting their enzymatic functions. There is a wide range of deleterious biological effects caused by OTCs in low concentration range. Their environmental concentrations, further potentiated by bioaccumulation in aquatic organisms, correspond with inhibitory constants reported for Gsts in zebrafish, which implies their environmental significance. Therefore, our main goal in this study was to analyze interactions of three major zebrafish Gsts – Gstp1, Gstr1, and Gstt1a – with a series of ten environmentally relevant organotin compounds. Using previously developed Gst inhibition assay with recombinant Gst proteins and fluorescent monochlorobimane as a model substrate, we determined Gst inhibitory constants for all tested OCTs. Furthermore, in order to elucidate nature of Gst interactions with OTCs, we determined type of interactions between tested Gsts and the strongest OTC inhibitors. Our results showed that OTCs can interact with zebrafish Gsts as competitive, noncompetitive, or mixed-type inhibitors. Determined types of interactions were additionally confirmed in silico by molecular docking studies of tested OTCs with newly developed Gst models. In silico models were further used to reveal structures of tested Gsts in more detail and identify crucial amino acid residues which interact with OTCs within Gst active sites. Our results revealed more extensive involvement of Gstr1 and Gstp1 in detoxification of numerous tested OTCs, with low inhibitory constants in nanomolar to low micromolar range and different types of inhibition, whereas Gstt1a noncompetitively interacted with only two tested OTCs with significantly higher inhibitory constants.

Proteomic analysis of small intestinal epithelial cells in antibiotic-treated mice: Changes in drug transporters and metabolizing enzymes

Antibiotics act on bacterial flora originally present in the intestine, and changes in the intestinal flora have various effects on the host. This study investigated changes in the protein levels of drug transporters and metabolizing enzymes in the small intestines of antibiotic-treated mice by proteomic analysis. After the oral administration of non-absorbable antibiotics (vancomycin and polymyxin B) for 5 days, 15 drug transporter or metabolizing enzyme proteins had significantly changed levels among 1780 proteins identified in small intestinal epithelial cells. Of these, the levels of peptide transporter 1 (Pept1), multidrug resistance protein 1a (Mdr1a), and multidrug resistance-associated protein 2 (Mrp2) were increased approximately 2-fold. In addition, the levels of two Cyp4f proteins were decreased and those of Cyp4b1, Ces1d, and three glutathione S-transferase (Gst) proteins were increased. Our results indicate that the oral administration of antibiotics changes the levels of proteins related to the absorption and metabolism of drugs in the small intestine, and suggest that substrate drugs of these proteins have a risk for indirect drug interactions with antibacterial drugs via the intestinal flora.

Genome-wide analysis of the Tetrahymena thermophila glutathione S-transferase gene superfamily

The ciliate Tetrahymena thermophila has a rapid response to detoxify xenobiotics, which presents opportunity to study the diversification of Glutathione S-Transferase superfamily. In-silico identification of putative GST genes were resulted with 70 GST genes; 49 TtGSTmu, 7 TtGSTomega, 5 TtGSTtheta, 2 TtGSTzeta, 4 TtMAPEG and 3 TtEF1G. TtGST superfamily has short intron carrying or intronless genes. The most expressed mRNAs of TtGST are limited to 4 members at all life stages. TtGST genes are widely distributed to all five micronuclear chromosomes with the highest diversified members from different classes in chromosome 4. The clustering and the orientation of some TtGSTs in the T. thermophila genome give clues about the recent gene duplication. Analysis of GSH affinity-purified GST proteins with Western blot and activity assay showed GST activity carrying purified TtGST populations. In conclusion, the enhanced genome capacity of TtGST superfamily may have evolved through improved GST enzymatic activity.

GSTM3 and GSTP1: novel players driving tumor progression in cervical cancer.

The molecular processes and proteomic markers leading to tumor progression (TP) in cervical cancer (CC) are either unknown or only partially understood. TP affects metabolic and regulatory mechanisms that can be identified as proteomic changes. To identify which proteins are differentially expressed and to understand the mechanisms of cancer progression, we analyzed the dynamics of the tumor proteome in CC cell lines. This analysis revealed two proteins that are up-regulated during TP, GSTM3 and GSTP1. These proteins are involved in cell maintenance, cell survival and the cellular stress response via the NF-κB and MAP kinase pathways during TP. Furthermore, GSTM3 and GSTP1 knockdown showed that evasion of apoptosis was affected, and tumor proliferation was significantly reduced. Our data indicate the critical role of GST proteins in the regulation and progression of cervical cancer cells. Hence, we suggest GSTM3 and GSTP1 as novel biomarkers and potential therapeutic targets for treating cervical cancer.SignificanceCC is particularly hazardous in the advanced stages, and there are few therapeutic strategies specifically targeting these stages. We performed analyses on CC tumor proteome dynamics and identified GSTM3 and GSTP1 as novel potential therapeutic targets. Knockdown of these proteins showed that they are involved in cell survival, cell proliferation and cellular evasion of apoptosis.

Interaction of p190A RhoGAP with eIF3A and Other Translation Preinitiation Factors Suggests a Role in Protein Biosynthesis

The negative regulator of Rho family GTPases, p190A RhoGAP, is one of six mammalian proteins harboring so-called FF motifs. To explore the function of these and other p190A segments, we identified interacting proteins by tandem mass spectrometry. Here we report that endogenous human p190A, but not its 50% identical p190B paralog, associates with all 13 eIF3 subunits and several other translational preinitiation factors. The interaction involves the first FF motif of p190A and the winged helix/PCI domain of eIF3A, is enhanced by serum stimulation and reduced by phosphatase treatment. The p190A/eIF3A interaction is unaffected by mutating phosphorylated p190A-Tyr308, but disrupted by a S296A mutation, targeting the only other known phosphorylated residue in the first FF domain. The p190A-eIF3 complex is distinct from eIF3 complexes containing S6K1 or mammalian target of rapamycin (mTOR), and appears to represent an incomplete preinitiation complex lacking several subunits. Based on these findings we propose that p190A may affect protein translation by controlling the assembly of functional preinitiation complexes. Whether such a role helps to explain why, unique among the large family of RhoGAPs, p190A exhibits a significantly increased mutation rate in cancer remains to be determined.

Activation of Rac1 and RhoA Preserve Corneal Endothelial Barrier Function.

The corneal endothelium is responsible for the correct hydration of the corneal stroma. Corneal endothelial cells have a low proliferative capacity, so preserving their barrier function under suboptimal conditions that cause osmotic imbalance, such as those arising from corneal pathologies, age, cryopreservation, and transplantation, is essential for maintaining corneal transparency. We have investigated the signaling induced by hyperosmotic shock that reversibly disrupts corneal endothelial barriers in human endothelial cells and in murine corneas. Endothelial barrier properties were analyzed in vitro by electric cell substrate impedance sensing (ECIS) and confocal microscopy of the human endothelial cell line B4G12-HCEC, and, ex vivo, by confocal microscopy and stimulated emission-depletion (STED) super-resolution microscopy of murine corneas. Cell signaling in response to hyperosmotic stress, induced with an excess of sodium chloride, was investigated in B4G12-HCECs. Rho GTPase activity was detected by pulldown assays with recombinant GST proteins fused to the Rho binding domains of Rho effectors. Hyperosmotic stress increased actin polymerization and activated the Rho GTPases Rac1 and RhoA, but not Cdc42. Rac1- and RhoA-mediated pathway inhibition had a minor effect on barrier disruption but partially delayed barrier reformation after stress withdrawal. In contrast, Rac1 and RhoA activation enhanced constitutive endothelial barrier function and accelerated barrier repair. Our results indicate that Rac1 and RhoA activation do not mediate stress-induced cell contraction but are endothelial responses that act to restore and maintain barrier homeostasis. Therefore, pharmacological activation of these two GTPases could be a therapeutic strategy for preserving corneal endothelial barrier function.

NAT10 regulates p53 activation through acetylating p53 at K120 and ubiquitinating Mdm2.

As a genome guardian, p53 maintains genome stability by arresting cells for damage repair or inducing cell apoptosis to eliminate the damaged cells in stress response. Several nucleolar proteins stabilize p53 by interfering Mdm2–p53 interaction upon cellular stress, while other mechanisms by which nucleolar proteins activate p53 remain to be determined. Here, we identify NAT10 as a novel regulator for p53 activation. NAT10 acetylates p53 at K120 and stabilizes p53 by counteracting Mdm2 action. In addition, NAT10 promotes Mdm2 degradation with its intrinsic E3 ligase activity. After DNA damage, NAT10 translocates to nucleoplasm and activates p53‐mediated cell cycle control and apoptosis. Finally, NAT10 inhibits cell proliferation and expression of NAT10 decreases in human colorectal carcinomas. Thus, our data demonstrate that NAT10 plays a critical role in p53 activation via acetylating p53 and counteracting Mdm2 action, providing a novel pathway by which nucleolar protein activates p53 as a cellular stress sensor.

The Subproteome of mitoBKCa from Cardiomyocytes Reveals Novel Insights into BK Channel Function and Pathology

The mitochondrial large-conductance Ca2+ -activated K+ channel (mitoBKCa) of adult cardiomyocytes contains a C-terminal 50 amino acid insert (DEC) as essential for mitochondrial targeting. The activation of mitochondrial BK channels (mitoBKCa) protects the heart from ischemia and reperfusion injury, highlighting its significant role in cardiac function. Here, we characterized the subproteome of mitoBKCa in cardiomyocytes in the quest to better understand its physiological and pathological relevance in the heart. To this end, we used GST-DEC and GST proteins to pull down proteins interacting with DEC using cardiomyocyte lysates and mitochondrial lysates. We also used monoclonal BK antibody and IgG to immunoprecipitate proteins interacting with mitoBKCa using Percoll purified mitochondrial lysates from whole heart. In all, we identified 212 cellular proteins and 157 mitochondrial proteins interacting with DEC; and 60 mitochondrial proteins interacting with mitoBKCa. Gene oncology analysis revealed mitoBKCa potential contribution to multiple cellular functions. It could contribute to oxidative respiration through cytochrome c oxidase (5 subunits) and ADP/ATP translocase (AAC), including AAC1 (10 peptides, n=2) and AAC2 (13 peptides, n=2), and regulate mitochondrial metabolism through acetyl-Coenzyme transferase 2 (7 peptides, n=2). In addition, our data revealed that mitoBKCa has a broader impact. It might facilitate the pathological process of Parkinson's disease and multiple types of cancer by interacting with critical enzymes, such as NADH dehydrogenase (7 subunits, 3-7 peptides each) and integrin linked kinase (2 peptides, n =1). Excitingly, mitoBKCa interacted with 15 different subunits of the ATP synthase, which forms the permeability transition pore, underscoring a new mechanism for mitoBKCa to protect the heart. In summary, proteomic analysis identified a wide variety of cellular and mitochondrial proteins forming complex with mitoBKCa channel, revealing new paradigms for BK channel function.

Biochemical functions of the glutathione transferase supergene family of Larix kaempferi

Glutathione transferases (GSTs), which are ubiquitous in plants, play a major role in the detoxification of xenobiotics and oxidative stress metabolism. Due to their role in herbicide detoxification, previous studies of plant GSTs have mainly focused on agricultural plants. In contrast, functional information regarding gymnosperm GSTs is scarce. In this study, we cloned 27 full-length GST genes from the deciduous conifer Larix kaempferi, which is widely distributed across the cooler regions of the northern hemisphere. As with the angiosperm GST gene family, Larix GSTs are divided into eight classes, and tau class GSTs are the most numerous. Compared to the other seven classes of GSTs, Larix tau GST genes show substantially more variation in their expression patterns. The purified Larix GST proteins showed different substrate specificities, substrate activities, and kinetic characteristics. The pH and temperature profiles of purified Larix GST proteins showed broad optimum pH and temperature ranges for enzymatic activity, suggesting that Larix GSTs have evolutionary adaptations to various adverse environments. Taken together, this study provides comprehensive insight into the gymnosperm GST gene family.