Isomerase Function Research Articles

Modulation of Protein Disulfide Isomerase Functions by Localization: The Example of the Anterior Gradient Family.

Significance: Oxidative folding within the endoplasmic reticulum (ER) introduces disulfide bonds into nascent polypeptides, ensuring proteins' stability and proper functioning. Consequently, this process is critical for maintaining proteome integrity and overall health. The productive folding of thousands of secretory proteins requires stringent quality control measures, such as the unfolded protein response (UPR) and ER-Associated Degradation (ERAD), which contribute significantly to maintaining ER homeostasis. ER-localized protein disulfide isomerases (PDIs) play an essential role in each of these processes, thereby contributing to various aspects of ER homeostasis, including maintaining redox balance, proper protein folding, and signaling from the ER to the nucleus. Recent Advances: Over the years, there have been increasing reports of the (re)localization of PDI family members and other ER-localized proteins to various compartments. A prime example is the anterior gradient (AGR) family of PDI proteins, which have been reported to relocate to the cytosol or the extracellular environment, acquiring gain of functions that intersect with various cellular signaling pathways. Critical Issues: Here, we summarize the functions of PDIs and their gain or loss of functions in non-ER locations. We will focus on the activity, localization, and function of the AGR proteins: AGR1, AGR2, and AGR3. Future Directions: Targeting PDIs in general and AGRs in particular is a promising strategy in different human diseases. Thus, there is a need for innovative strategies and tools aimed at targeting PDIs; those strategies should integrate the specific localization and newly acquired functions of these PDIs rather than solely focusing on their canonical roles.

Proteomics and Metabolomics Analysis Reveal the Regulation Mechanism of Linoleate Isomerase Activity and Function in Propionibacterium acnes.

Conjugated linoleic acid (CLA) holds significant application prospects due to its anticancer, anti-atherosclerosis, lipid-lowering, weight-loss, and growth-promoting functions. The key to its efficient production lies in optimizing the biocatalytic performance of linoleic acid isomerase (LAI). Here, we constructed a Propionibacterium acnes mutant library and screened positive mutants with high linoleate isomerase activity. The proteomics and metabolomics were used to explore the mechanism in the regulation of linoleic acid isomerase activity. High-throughput proteomics revealed 104 differentially expressed proteins unique to positive mutant strains of linoleic acid isomerase of which 57 were upregulated and 47 were downregulated. These differentially expressed proteins were primarily involved in galactose metabolism, the phosphotransferase system, starch metabolism, and sucrose metabolism. Differential metabolic pathways were mainly enriched in amino acid biosynthesis, including glutamate metabolism, the Aminoacyl-tRNA biosynthesis pathway, and the ABC transporter pathway. The upregulated metabolites include dl-valine and Acetyl coA, while the downregulated metabolites include Glutamic acid and Phosphoenolpyruvate. Overall, the activity of linoleic acid isomerase in the mutant strain was increased by the regulation of key proteins involved in galactose metabolism, sucrose metabolism, and the phosphotransferase system. This study provides a theoretical basis for the development of high-yield CLA food.

Protein Disulfide-Isomerase A3 Is a Robust Prognostic Biomarker for Cancers and Predicts the Immunotherapy Response Effectively.

BackgroundProtein disulfide isomerase A3 (PDIA3) is a member of the protein disulfide isomerase (PDI) family that participates in protein folding through its protein disulfide isomerase function. It has been reported to regulate the progression of several cancers, but its function in cancer immunotherapy is unknown.MethodsThe RNA-seq data of cancer and normal tissues were downloaded from The Cancer Genome Atlas (TCGA) and the Genotype-Tissue Expression (GTEx) databases. The Cbioportal dataset was used to explore the genomic alteration information of PDIA3 in pan-cancer. Human Protein Atlas (HPA) and ComPPI websites were employed to mine the protein information of PDIA3, and western blot assay was performed to monitor the upregulated PDIA3 expression in clinical GBM samples. The univariate Cox regression and the Kaplan–Meier method were utilized to appraise the prognostic role of PDIA3 in pan-cancer. Gene Set Enrichment Analysis (GSEA) was applied to search the associated cancer hallmarks with PDIA3 expression. TIMER2.0 was the main platform to investigate the immune cell infiltrations related to PDIA3 in pan-cancer. The associations between PDIA3 and immunotherapy biomarkers were performed by Spearman correlation analysis. The immunoblot was used to quantify the PDIA3 expression levels, and the proliferative and invasive ability of glioma cells was determined by colony formation and transwell assays.FindingsPDIA3 is overexpressed in most cancer types and exhibits prognosis predictive ability in various cancers, and it is especially expressed in the malignant cells and monocytes/macrophages. In addition, PDIA3 is significantly correlated with immune-activated hallmarks, cancer immune cell infiltrations, and immunoregulators, and the most interesting finding is that PDIA3 could significantly predict anti-PDL1 therapy response. Besides, specific inhibitors that correlated with PDIA3 expression in different cancer types were also screened by using Connectivity Map (CMap). Finally, knockdown of PDIA3 significantly weakened the proliferative and invasive ability of glioma cells.InterpretationThe results revealed that PDIA3 acts as a robust tumor biomarker. Its function in protein disulfide linkage regulation could influence protein synthesis, degradation, and secretion, and then shapes the tumor microenvironment, which might be further applied to develop novel anticancer inhibitors.

Cyclophilin acts as a ribosome biogenesis factor by chaperoning the ribosomal protein (PlRPS15) in filamentous fungi.

The rapid transport of ribosomal proteins (RPs) into the nucleus and their efficient assembly into pre-ribosomal particles are prerequisites for ribosome biogenesis. Proteins that act as dedicated chaperones for RPs to maintain their stability and facilitate their assembly have not been identified in filamentous fungi. PlCYP5 is a nuclear cyclophilin in the nematophagous fungus Purpureocillium lilacinum, whose expression is up-regulated during abiotic stress and nematode egg-parasitism. Here, we found that PlCYP5 co-translationally interacted with the unassembled small ribosomal subunit protein, PlRPS15 (uS19). PlRPS15 contained an eukaryote-specific N-terminal extension that mediated the interaction with PlCYP5. PlCYP5 increased the solubility of PlRPS15 independent of its catalytic peptide-prolyl isomerase function and supported the integration of PlRPS15 into pre-ribosomes. Consistently, the phenotypes of the PlCYP5 loss-of-function mutant were similar to those of the PlRPS15 knockdown mutant (e.g. growth and ribosome biogenesis defects). PlCYP5 homologs in Arabidopsis thaliana, Homo sapiens, Schizosaccharomyces pombe, Sclerotinia sclerotiorum, Botrytis cinerea and Metarhizium anisopliae were identified. Notably, PlCYP5-PlRPS15 homologs from three filamentous fungi interacted with each other but not those from other species. In summary, our data disclosed a unique dedicated chaperone system for RPs by cyclophilin in filamentous fungi.

TM1385 from Thermotoga maritima functions as a phosphoglucose isomerase via cis-enediol-based mechanism with active site redundancy

Phosphoglucose isomerases (PGIs) belong to a class of enzymes that catalyze the reversible isomerization of glucose-6-phosphate to fructose-6-phosphate. PGIs are crucial in glycolysis and gluconeogenesis pathways and proposed as serving additional extracellular functions in eukaryotic organisms. The phosphoglucose isomerase function of TM1385, a previously uncharacterized protein from Thermotoga maritima, was hypothesized based on structural similarity to established PGI crystal structures and computational docking. Kinetic and colorimetric assays combined with 1H nuclear magnetic resonance (NMR) spectroscopy experimentally confirm that TM1385 is a phosphoglucose isomerase (TmPGI). Evidence of solvent exchange in 1H NMR spectra supports that TmPGI isomerization proceeds through a cis-enediol-based mechanism. To determine which amino acid residues are critical for TmPGI catalysis, putative active site residues were mutated with alanine and screened for activity. Results support that E281 is most important for TmPGI formation of the cis-enediol intermediate, and the presence of either H310 or K422 may be required for catalysis, similar to previous observations from homologous PGIs. However, only TmPGI E281A/Q415A and H310A/K422A double mutations abolished activity, suggesting that there are redundant catalytic residues, and Q415 may participate in sugar phosphate isomerization upon E281 mutation. Combined, we propose that TmPGI E281 participates directly in the cis-enediol intermediate step, and either H310 or K422 may facilitate sugar ring opening and closure.

Male-Specific Protein Disulphide Isomerase Function is Essential for Plasmodium Transmission and a Vulnerable Target for Intervention

Inhibiting transmission of Plasmodium is an essential strategy in malaria eradication, and the biological process of gamete fusion during fertilization is a proven target for this approach. Lack of knowledge of the mechanisms underlying fertilization have been a hindrance in the development of transmission-blocking interventions. Here we describe a protein disulphide isomerase essential for malarial transmission (PDI-Trans/PBANKA_0820300) to the mosquito. We show that PDI-Trans activity is male-specific, surface-expressed, essential for fertilization/transmission, and exhibits disulphide isomerase activity which is up-regulated post-gamete activation. We demonstrate that PDI-Trans is a viable anti-malarial drug and vaccine target blocking malarial transmission with the use of PDI inhibitor bacitracin (98.21%/92.48% reduction in intensity/prevalence), and anti-PDI-Trans antibodies (66.22%/33.16% reduction in intensity/prevalence). To our knowledge, these results provide the first evidence that PDI function is essential for malarial transmission, and emphasize the potential of anti-PDI agents to act as anti-malarials, facilitating the future development of novel transmission-blocking interventions.

Influences of cyclosporin A and non-immunosuppressive derivatives on cellular cyclophilins and viral nucleocapsid protein during human coronavirus 229E replication

The well-known immunosuppressive drug cyclosporin A inhibits replication of various viruses including coronaviruses by binding to cellular cyclophilins thus inactivating their cis-trans peptidyl-prolyl isomerase function. Viral nucleocapsid proteins are inevitable for genome encapsidation and replication. Here we demonstrate the interaction between the N protein of HCoV-229E and cyclophilin A, not cyclophilin B. Cyclophilin inhibitors abolish this interaction. Upon infection, cyclophilin A stays evenly distributed throughout the cell, whereas cyclophilin B concentrates at ER-bleb-like structures. We further show the inhibitory potential of non-immunosuppressive CsA derivatives Alisporivir, NIM811, compound 3 on HCoV-229E-GFP and -Luciferase replication in human Huh-7.5 hepatoma cells at 18 and 48 h time points post infection with EC50 s at low micromolar ranges. Thus, non-immunosuppressive CsA derivatives effectively inhibit HCoV-229E replication suggesting them as possible candidates for the treatment of HCoV infection. The interruption of interaction between CypA and N protein by CsA and its derivatives suggest a mechanism how CypA inhibitors suppress viral replication.

Protein disulfide isomerase regulation by nitric oxide maintains vascular quiescence and controls thrombus formation

Essentials Nitric oxide synthesis controls protein disulfide isomerase (PDI) function. Nitric oxide (NO) modulation of PDI controls endothelial thrombogenicity. S-nitrosylated PDI inhibits platelet function and thrombosis. Nitric oxide maintains vascular quiescence in part through inhibition of PDI. SUMMARY: Background Protein disulfide isomerase (PDI) plays an essential role in thrombus formation, and PDI inhibition is being evaluated clinically as a novel anticoagulant strategy. However, little is known about the regulation of PDI in the vasculature. Thiols within the catalytic motif of PDI are essential for its role in thrombosis. These same thiols bind nitric oxide (NO), which is a potent regulator of vessel function. To determine whether regulation of PDI represents a mechanism by which NO controls vascular quiescence, we evaluated the effect of NO on PDI function in endothelial cells and platelets, and thrombus formation in vivo. Aim To assess the effect of S-nitrosylation on the regulation of PDI and other thiol isomerases in the vasculature. Methods and results The role of endogenous NO in PDI activity was evaluated by incubating endothelium with an NO scavenger, which resulted in exposure of free thiols, increased thiol isomerase activity, and enhanced thrombin generation on the cell membrane. Conversely, exposure of endothelium to NO+ carriers or elevation of endogenous NO levels by induction of NO synthesis resulted in S-nitrosylation of PDI and decreased surface thiol reductase activity. S-nitrosylation of platelet PDI inhibited its reductase activity, and S-nitrosylated PDI interfered with platelet aggregation, α-granule release, and thrombin generation on platelets. S-nitrosylated PDI also blocked laser-induced thrombus formation when infused into mice. S-nitrosylated ERp5 and ERp57 were found to have similar inhibitory activity. Conclusions These studies identify NO as a critical regulator of vascular PDI, and show that regulation of PDI function is an important mechanism by which NO maintains vascular quiescence.

Greetings from the endoplasmic reticulum (ER): escaping ER thiol isomerases regulate thrombosis

Greetings from the endoplasmic reticulum (ER): escaping ER thiol isomerases regulate thrombosis

P4HB recurrent missense mutation causing Cole-Carpenter syndrome

BackgroundCole-Carpenter syndrome (CCS) is commonly classified as a rare Osteogenesis Imperfecta (OI) disorder. This was following the description of two unrelated patients with very similar phenotypes who were subsequently shown...

Maternal nicotine exposure leads to decreased cardiac protein disulfide isomerase and impaired mitochondrial function in male rat offspring.

Smoking throughout pregnancy can lead to complications during gestation, parturition and neonatal development. Thus, nicotine replacement therapies are a popular alternative thought to be safer than cigarettes. However, recent studies in rodents suggest that fetal and neonatal nicotine exposure alone results in cardiac dysfunction and high blood pressure. While it is well known that perinatal nicotine exposure causes increased congenital abnormalities, the mechanisms underlying longer-term deficits in cardiac function are not completely understood. Recently, our laboratory demonstrated that nicotine impairs placental protein disulfide isomerase (PDI) triggering an increase in endoplasmic reticulum stress, leading us to hypothesize that this may also occur in the heart. At 3months of age, nicotine-exposed offspring had 45% decreased PDI levels in the absence of endoplasmic reticulum stress. Given the association of PDI and superoxide dismutase enzymes, we further observed that antioxidant superoxide dismutase-2 levels were reduced by 32% in these offspring concomitant with a 26-49% decrease in mitochondrial complex proteins (I, II, IV and V) and tissue inhibitor of metalloproteinase-4, a critical matrix metalloprotease for cardiac contractility and health. Collectively, this study suggests that perinatal nicotine exposure decreases PDI, which can promote oxidative damage and mitochondrial damage, associated with a premature decline in cardiac function.

The integrin PSI domain has an endogenous thiol isomerase function and is a novel target for antiplatelet therapy

AbstractIntegrins are a large family of heterodimeric transmembrane receptors differentially expressed on almost all metazoan cells. Integrin β subunits contain a highly conserved plexin-semaphorin-integrin (PSI) domain. The CXXC motif, the active site of the protein-disulfide-isomerase (PDI) family, is expressed twice in this domain of all integrins across species. However, the role of the PSI domain in integrins and whether it contains thiol-isomerase activity have not been explored. Here, recombinant PSI domains of murine β3, and human β1 and β2 integrins were generated and their PDI-like activity was demonstrated by refolding of reduced/denatured RNase. We identified that both CXXC motifs of β3 integrin PSI domain are required to maintain its optimal PDI-like activity. Cysteine substitutions (C13A and C26A) of the CXXC motifs also significantly decreased the PDI-like activity of full-length human recombinant β3 subunit. We further developed mouse anti-mouse β3 PSI domain monoclonal antibodies (mAbs) that cross-react with human and other species. These mAbs inhibited αIIbβ3 PDI-like activity and its fibrinogen binding. Using single-molecular Biomembrane-Force-Probe assays, we demonstrated that inhibition of αIIbβ3 endogenous PDI-like activity reduced αIIbβ3-fibrinogen interaction, and these anti-PSI mAbs inhibited fibrinogen binding via different levels of both PDI-like activity-dependent and -independent mechanisms. Importantly, these mAbs inhibited murine/human platelet aggregation in vitro and ex vivo, and murine thrombus formation in vivo, without significantly affecting bleeding time or platelet count. Thus, the PSI domain is a potential regulator of integrin activation and a novel target for antithrombotic therapies. These findings may have broad implications for all integrin functions, and cell-cell and cell-matrix interactions.

Extracellular Thiol Isomerases and Their Role in Thrombus Formation.

The mammalian endoplasmic reticulum (ER) houses a large family of twenty thioredoxin-like proteins of which protein disulfide isomerase (PDI) is the archetypal member. Although the PDI family is best known for its role in oxidative protein folding of secretory proteins in the ER, these thioredoxin-like proteins fulfill ever-expanding roles, both within the secretory pathway and beyond. Secreted PDI family proteins have now been shown to serve a critical role in platelet thrombus formation and fibrin generation. Utilizing intravital microscopy to visualize thrombus formation in mice, we have demonstrated the presence of extracellular PDI antigen during thrombus formation following injury of the vascular wall. Inhibition of PDI abrogates thrombus formation in vivo (16, 26, 46, 55). These observations have been extended to other PDI family members, including ERp57 (39, 116, 118, 123) and ERp5 (77). The vascular thiol isomerases are those PDI family members secreted from platelets and/or endothelium (40): PDI, ERp57, ERp5, ERp72, ERp44, ERp29, and TMX3. We focus here on PDI (16, 46, 55), ERp57 (39, 116, 118, 123), and ERp5 (77), which have been implicated in thrombus formation in vivo. It would appear that a system of thiol isomerase redox catalysts has been hijacked from the ER to regulate thrombus formation in the vasculature. How this redox system is trafficked to and regulated at the cell surface, the identity of extracellular substrates, why so many thiol isomerases are required, and which thiol isomerase functions are necessary are critical unanswered questions in understanding the role of thiol isomerases in thrombus formation.

The DsbA2 disulfide‐bond oxidase/isomerase system from Legionella pneumophila is coupled to two membrane spanning DsbD proteins and two DsbB oxidases. Homodimeric DsbA2 is partially reduced (thereby providing both DsbA oxidase and DsbC‐like protein disulfide isomerase functions) and is required to manage disulfide bonding in DotG, a core component of the Dot/Icm secretion system. For details, see the article by Kpadeh

The DsbA2 disulfide‐bond oxidase/isomerase system from <i>Legionella pneumophila</i> is coupled to two membrane spanning DsbD proteins and two DsbB oxidases. Homodimeric DsbA2 is partially reduced (thereby providing both DsbA oxidase and DsbC‐like protein disulfide isomerase functions) and is required to manage disulfide bonding in DotG, a core component of the Dot/Icm secretion system. For details, see the article by Kpadeh

ML359, a Small Molecule Inhibitor of Protein Disulfide Isomerase That Prevents Thrombus Formation and Inhibits Oxidoreductase but Not Transnitrosylase Activity

Vascular thiol isomerases comprise a family of enzymes including protein disulfide isomerase (PDI), ERp5, and ERp57 that are important in the process of thrombus formation. PDI is secreted at sites of vascular injury, and antibody-mediated PDI inhibition prevents thrombus formation in a mouse laser injury model. Our group has previously reported on the discovery of the small molecule PDI inhibitors quercetin-3-rutinoside and ML359. Identified as part of a high-throughput screen, ML359 is a second-generation PDI inhibitor that selectively blocks PDI oxidoreductase activity with approximately ten-fold the potency of quercetin-3-rutinoside. To better understand the mechanism of allosteric modulation of PDI by small molecules, we evaluated the association of ML359 with isolated domains of PDI, determined the effects of ML359 on a variety of PDI functions, and compared the activity of ML359 to that of quercetin-3-rutinoside. PDI is composed of four thioredoxin-like domains and an x-linker region in the sequence a-b-b’-x-a’. Major substrate binding is thought to occur in the b-b’ region while the a and a’ domains contain catalytically active cysteine motifs (CGHC) that mediate the oxidoreducase, nitrosylase, and thiol isomerase functions of PDI. In order to identify potential binding sites of ML359 on PDI, we constructed and expressed the domain fragments a, ab, abb’, b’xa’, and a’. These fragments were tested in the presence of 10 µM ML359 using an insulin turbidometric assay that measures the oxidoreductase activity of PDI. ML359 demonstrated full inhibition of oxidoreductase activity when full-length PDI and the b’xa’ fragment were used whereas no inhibition was observed with the other fragments assayed. These results are consistent with docking studies showing that ML359 likely binds in a pocket formed at the b’x interface. In contrast, when the same experiment was performed in the presence of 30 µM of quercetin-3-rutinoside, inhibition was only noted with full-length PDI and the abb’ and b’xa’ fragments, suggesting that binding was dependent on the b’ and not the x-linker region. To determine if ML359 has differential effects on the oxidoreductase and nitrosylase functions of PDI, we utilized a platelet-based assay in which fluorescence intensity stemming from the NO-sensitive intracellular dye DAF-FM was measured as an indicator of PDI-mediated translocation of NO from the extracellular surface into the cytosol (transnitrosylation). While quercetin-3-rutinoside potently inhibited PDI-mediated transnitrosylation activity, ML359 had no effect. These results are consistent with the idea that the transnitrosylase and oxidoreducase functions of PDI are separable and inhibition of either is specific to the small molecule used. We evaluated the ability of ML359 to inhibit thrombosis in a mouse laser injury model. Intravital microscopy was used to follow thrombus formation in mouse cremaster arterioles after laser-induced vascular injury. Infusion of ML359 resulted in inhibition of thrombus formation, in contrast to thrombosis seen after infusion of vehicle alone. In summary, ML359 is a second generation small molecule inhibitor of PDI that likely binds at the b’x interface of the enzyme. Furthermore, ML359 is able to selectively inhibit PDI oxidoreductase activity without affecting transnitrosylase activity. ML359 may prove a useful molecular probe to better understand the different functions of PDI relative to thrombus formation in vivo. DisclosuresNo relevant conflicts of interest to declare.

Abstract 54: PSI Domain of ß3 Integrin Has Endogenous Thiol Isomerase Function and is a Novel Antithrombotic Therapeutic Target

Integrin αIIbβ3 plays a critical role in platelet aggregation and adhesion, key events in hemostasis and thrombosis. Integrin activation involves complex signalling events that lead to conformational changes exposing ligand-binding sites; however, mechanisms underlying integrin activation remain poorly understood. The β subunit contains a PSI domain that is highly conserved across integrins and species, though its function is unknown. Integrin β subunits are cysteine-rich and endogenous thiol isomerase activity in integrin β3 has been reported. The PSI domain contains two CXXC sequences, the active site motif of protein disulfide isomerase (PDI). Based on this observation and the location of this domain at the knee region of the integrin, we hypothesized that integrin PSI domain has endogenous thiol isomerase function, which plays a key regulatory role in integrin conformation and function. Targeting the PSI domain may have therapeutic potential. Using reduced, denatured RNase, a recombinant murine integrin β3 PSI domain demonstrated endogenous PDI-like activity. This PDI-like activity was dose-dependently inhibited by the PDI inhibitor, bacitracin. Mutation of either CXXC motif within the integrin β3 PSI domain reduced PDI-like activity, while removal of both CXXC motifs completely abolished this activity. We developed unique mouse anti-mouse/anti-human β3 PSI domain monoclonal antibodies (anti-PSI mAbs) that inhibited the PDI-like activity of both the murine recombinant integrin β3 PSI domain and purified human platelet β3 integrin, in a dose-dependent manner. Interestingly, the anti-PSI mAbs blocked fibrinogen to human platelet β3 integrin in a cell free system. Furthermore, anti-PSI mAbs inhibited murine and human platelet aggregation in vitro and ex vivo and inhibited murine thrombus formation in vivo without significantly changing bleeding time or platelet count. In conclusion, we identified that the PSI domain has PDI function, is a fundamental regulator of platelet β3 integrin activation, and is a potential novel target for anti-thrombotic therapies. Since PSI domain is conserved in all integrin β subunits, our discovery may have broad implications for the role of integrins in cell biology of many human diseases.

Contribution of two ζ-carotene desaturases to the poly-cis desaturation pathway in the cyanobacterium Nostoc PCC 7120

The presence of two completely unrelated ζ-carotene desaturases CrtQa and CrtQb in some Nostoc strains is unique. CrtQb is the ζ-carotene desaturase, which was acquired by almost all cyanobacteria. The additional CrtQa can be regarded as an evolutionary relict of the CrtI desaturase present in non-photosynthetic bacteria. By reconstruction of the carotene desaturation pathway, we showed that both enzymes from Nostoc PCC 7120 were active. However, they differed in their preferred utilization of ζ-carotene Z isomers. CrtQa converted ζ-carotene isomers that were poorly metabolized by CrtQb. In this respect, CrtQa complemented the reactions of CrtQb, which is an advantage avoiding dead ends in the poly-cis desaturation pathway. In addition to ζ-carotene desaturation, CrtQa still possesses the Z to E isomerase function of the ancestral desaturase CrtI. Biochemical characterization showed that CrtQb is an enzyme with one molecule of tightly bound FAD and acts as a dehydrogenase transferring hydrogen to oxidized plastoquinone.

Characterization of MIF family proteins: MIF and DDT from rock bream, Oplegnathus fasciatus

Macrophage migration inhibitory factor (MIF) is a pleiotropic molecule playing vital roles in various signaling cascades, including cell proliferation, and activation of immune responses against infections. It is well known as a pivotal regulator of innate immunity. In this study, we have rescued and characterized two members of the MIF family, macrophage migration inhibitory factor (OfMIF) and D-Dopachrome tautomerase (OfDDT) from rock bream, Oplegnathus fasciatus. The deduced OfMIF and OfDDT protein sequences revealed the presence of the catalytic oxidoreductase (CXXC), motif. They also possessed highly conserved proline (P2) and lysine residues (K33), responsible for their isomerase and tautomerase functions. Rock bream MIF and DDT homologues shared higher identity with fish homologues and also with mammals and occupied a distinct position in the phylogenetic tree, depicting their evolutionary conservation. The spatial expression analysis revealed the highest expression of both OfMIF and OfDDT in liver, while portraying constitutive expression in other tissues. The recombinant proteins purified using the Escherichia coli system revealed potent oxidoreductase activity against insulin with both dithiothreitol and glutathione as reducing agents. Stimulation of rock bream head kidney cells with recombinant OfMIF and OfDDT proteins induced the expression of proinflammatory cytokines like tumor necrosis factor alpha (TNF-α), interleukin-8 (IL-8) and interleukin-1β (IL-1β). These results together suggest their involvement in rock bream immune defense and this study on the novel MIF family member DDT from rock bream will pave the way for further studies of this homologue in other teleosts and delineate its multiple functions.

Correlation of Naturally Occurring HIV-1 Resistance to DEB025 with Capsid Amino Acid Polymorphisms

DEB025 (alisporivir) is a synthetic cyclosporine with inhibitory activity against human immunodeficiency virus type-1 (HIV-1) and hepatitis C virus (HCV). It binds to cyclophilin A (CypA) and blocks essential functions of CypA in the viral replication cycles of both viruses. DEB025 inhibits clinical HIV-1 isolates in vitro and decreases HIV-1 virus load in the majority of patients. HIV-1 isolates being naturally resistant to DEB025 have been detected in vitro and in nonresponder patients. By sequence analysis of their capsid protein (CA) region, two amino acid polymorphisms that correlated with DEB025 resistance were identified: H87Q and I91N, both located in the CypA-binding loop of the CA protein of HIV-1. The H87Q change was by far more abundant than I91N. Additional polymorphisms in the CypA-binding loop (positions 86, 91 and 96), as well as in the N-terminal loop of CA were detected in resistant isolates and are assumed to contribute to the degree of resistance. These amino acid changes may modulate the conformation of the CypA-binding loop of CA in such a way that binding and/or isomerase function of CypA are no longer necessary for virus replication. The resistant HIV-1 isolates thus are CypA-independent.

Dynamic control of the prolyl isomerase function of the dual-domain SlyD protein

Local dynamics on variable timescales are important to facilitate high catalytic efficiency in enzymes. In this study, we examined the dual-domain peptidyl-prolyl cis/trans-isomerase (PPIase) SlyD with regard to its catalytic cycle. Fluorescence- and NMR-based experiments were performed to understand the high catalytic efficiency of SlyD compared to single domain FKBP proteins. We probed local conformational changes for amino acids involved in substrate-binding (IF domain) and substrate-catalysis (FKBP domain) taking place on the timescale of substrate turnover. Binding of the PPIase activity inhibitors to the FKBP domain suppressed the conformational freedom of the remote IF domain. A single side-chain mutation in the active site strongly reduced the rate of substrate turnover and changed the conformational dynamics of all amino acids involved in catalysis. This dynamic interplay between substrate-binding domain and PPIase domain determines the high catalytic activity of SlyD and inhibitor-binding modulates the backbone plasticity required for enzyme activity.