Guanxining injection alleviates fibrosis in heart failure mice and regulates SLC7A11/GPX4 axis

ETHNOPHARMACOLOGICAL RELEVANCE

Radix et Rhizoma Salviae Miltiorrhizae (Salvia miltiorrhiza Bge., Lamiaceae, Danshen in Chinese) and Chuanxiong Rhizoma (rhizomes of Ligusticum chuanxiong Hort., Apiaceae, Chuanxiong in Chinese) both are important traditional Chinese medicine (TCM) for activating blood and eliminating stasis. Danshen-chuanxiong herb pair has been used for more than 600 years in China. Guanxinning injection (GXN) is a Chinese clinical prescription refined from aqueous extract of Danshen and Chuanxiong at the ratio of 1:1 (w/w). GXN has been mainly used in the clinical therapy of angina, heart failure (HF) and chronic kidney disease in China for almost twenty years.

AIM OF THE STUDY

This study aimed to explore the role of GXN on renal fibrosis in heart failure mice and the regulation of GXN on SLC7A11/GPX4 axis.

MATARIALS AND METHODS

The transverse aortic constriction model was used to mimic HF accompanied by kidney fibrosis model. GXN was administrated by tail vein injection in dose of 12.0, 6.0, 3.0 mL/kg, respectively. Telmisartan (6.1 mg/kg, gavage) was used as a positive control drug. Cardiac ultrasound indexes of ejection fraction (EF), cardiac output (CO), left ventricle volume (LV Vol), HF biomarker of pro-B type natriuretic peptide (Pro-BNP), kidney function index of serum creatinine (Scr), kidney fibrosis index of collagen volume fraction (CVF) and connective tissue growth factor (CTGF) were evaluated and contrasted. Metabolomic method was employed to analyze the endogenous metabolites changes in kidneys. Besides, contents of catalase (CAT), xanthine oxidase (XOD), nitricoxidesynthase (NOS), glutathione peroxidase 4 (GPX4), the x(c)(-) cysteine/glutamate antiporter (SLC7A11) and ferritin heavy chain (FTH1) in kidney were quantitatively analyzed. In addition, ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) was used to analyze the chemical composition of GXN and network pharmacology was used to predict possible mechanisms and the active ingredients of GXN.

RESULTS

The cardiac function indexes of EF, CO and LV Vol, kidney functional indicators of Scr, the degree of kidney fibrosis indicators CVF and CTGF were all relieved to different extent for the model mice treated with GXN. 21 differential metabolites involved in redox regulation, energy metabolism, organic acid metabolism, nucleotide metabolism, etc were identified. Aspartic acid, homocysteine, glycine, and serine, methionine, purine, phenylalanine and tyrosine metabolism were found to be the core redox metabolic pathways regulated by GXN. Furthermore, GXN were found to increase CAT content, upregulate GPX4, SLC7A11 and FTH1 expression in kidney significantly. Not only that, GXN also showed good effect in down-regulating XOD and NOS contents in kidney. Besides, 35 chemical constituents were initially identified in GXN. Active ingredients of GXN-targets-related enzymes/transporters-metabolites network was established to find out that GPX4 was a core protein for GXN and the top 10 active ingredients with the most relevant to renal protective effects of GXN were rosmarinic acid, caffeic acid, ferulic acid, senkyunolide E, protocatechualdehyde, protocatechuic acid, danshensu, L-Ile, vanillic acid, salvianolic acid A.

CONCLUSION

GXN could significantly maintain cardiac function and alleviate the progression of fibrosis in the kidney for HF mice, and the mechanisms of action were related to regulating redox metabolism of aspartate, glycine, serine, and cystine metabolism and SLC7A11/GPX4 axis in kidney. The cardio-renal protective effect of GXN may be attributed to multi-components like rosmarinic acid, caffeic acid, ferulic acid, senkyunolide E, protocatechualdehyde, protocatechuic acid, danshensu, L-Ile, vanillic acid, salvianolic acid A et al.

Recent advances of traditional Chinese medicine for the prevention and treatment of atherosclerosis

ETHNOPHARMACOLOGICAL RELEVANCE

Atherosclerosis (AS) is a common systemic disease with increasing morbidity and mortality worldwide. Traditional Chinese medicine (TCM) with characteristics of multiple pathways and targets, presents advantages in the diagnosis and treatment of atherosclerosis.

AIM OF THE STUDY

With the modernization of TCM, the active ingredients and molecular mechanisms of TCM for AS treatment have been gradually revealed. Therefore, it is necessary to examine the existing studies on TCM therapies aimed at regulating AS over the past two decades.

MATERIALS AND METHODS

Using "atherosclerosis" and "Traditional Chinese medicine" as keywords, all relevant TCM literature published in the last 10 years was collected from electronic databases (such as Elsevier, Springer, PubMed, CNKI, and Web of Science), books and papers until March 2022, and the critical information was statistically analyzed.

RESULTS

In this review, we highlighted extracts of 8 single herbs, a total of 41 single active ingredients, 20 TCM formulae, and 25 patented drugs, which were described with chemical structure, source, model, efficacy and potential mechanism.

CONCLUSION

We summarized the cytopathological basis for the development of atherosclerosis involving vascular endothelial cells, macrophages and vascular smooth muscle cells, and categorically elaborated the medicinal TCM used for AS, all of which provide the current evidence on the better management of atherosclerosis by TCM.

Oxysophocarpine inhibits airway inflammation and mucus hypersecretion through JNK/AP-1 pathway in vivo and in vitro

Asthma is a high-incidence disease in the world. Oxysophocarpine (OSC), a quinolizidine alkaloid displays various pharmacological functions including anti-inflammation, neuroprotective, anti-virus and antioxidant. Here, we established mice and cell asthmatic model to explore the effects of OSC for asthma treatment. Mice were sensitized and challenged with ovalbumin (OVA) and treated with OSC before challenge. Enzyme-linked immuno sorbent assay (ELISA), hematoxylin and eosin (H&E), periodic acid-schiff (PAS), tolonium chloride staining and immunohistochemical assay were performed. OSC treatment inhibited inflammatory cell infiltration and mucus secretion in the airway, reduced IgE level in mouse serum and decreased IL-4, IL-5 production in bronchoalveolar lavage fluid (BALF). OSC also reduced the spleen index to regulate immune function. Meanwhile, NCI-H292 cells were induced by lipopolysaccharide (LPS) to simulate airway epithelial injury. OSC pretreatment decreased the IL-6 and IL-8 cytokine levels, mucin 5 AC expression, and mucin 5 AC mRNA level in the cell model. Further, OSC suppressed the phosphorylation of c-Jun N-terminal kinase (JNK), and activator protein 1 (AP-1, Fos and Jun). These findings revealed that OSC alleviated bronchial asthma associated with JNK/AP-1 signaling pathway.

Proteome profiling reveals the efficacy and targets of sophocarpine against asthma

Sophocarpine (SPC) as a quinolizidine alkaloid displays powerful effects on inflammatory diseases through regulating multiple targets. Asthma is a complex heterogeneous and inflammatory disease with an increasing incidence worldwide. Here we established a mice asthma model and investigated the effect of SPC. Mice induced by ovalbumin (OVA) exhibits exacerbated Th1/Th2 immune imbalance and allergic lung inflammation. SPC treatment regulated Th1/Th2 cytokines production (IL-4, IL-5 and INF-γ) in BALF, reduced IgE level in serum, inhibited inflammatory cell infiltration, and improved the lung tissue pathology. Proteomic results showed that 5064 proteins in lung tissue were detected and among them 223 preliminary therapeutic targets of SPC were selected. Subsequently, excluding non-human genes, 109 targets with established crystal structures were harvested. Meanwhile, the molecular docking results showed that the binding energy of 87 targets with SPC was varied from -9.72 kcal/mol to 227.16 kcal/mol. Further, SPC suppressed arrb2, anxa1, myd88 and sphk1 expression and activated p-stat1. All of the five targets based on the screened results of proteomics and molecular docking are critical in allergic asthma. Thus, our data revealed that SPC alleviated bronchial asthma via targeting multi-targets.

Cinnamaldehyde attenuates atherosclerosis via targeting the IκB/NF-κB signaling pathway in high fat diet-induced ApoE−/− mice

Cinnamaldehyde is a flavor isolated from the bark of Cinnamomum cassia Presl and exerts anti-inflammation effects in various diseases.

Cinnamaldehyde protects VSMCs against ox-LDL-induced proliferation and migration through S arrest and inhibition of p38, JNK/MAPKs and NF-κB

Cinnamaldehyde (Cin), as a traditional flavor constituent isolated from the bark of Cinnamonum cassia Presl, has been commonly used for - digestive, cardiovascular and immune system diseases. The pathology of vascular smooth muscle cells (VSMCs) accelerated the progression of atherosclerosis. In our study, we found that cinnamaldehyde significantly suppressed ox-LDL-induced VSMCs proliferation, migration and inflammatory cytokine overproduction, as well as foam cell formation in VSMCs and macrophages. Moreover, cinnamaldehyde inhibited the phosphorylation of p38, JNK and p65 NF-κB and increased heme oxygenase-1 (HO-1) activity. In addition, cinnamaldehyde reduced monocyte chemotactic protein-1 (MCP-1), matrix metalloproteinase-2 (MMP-2) and lectin-like oxidized low density lipoprotein receptor-1 (LOX-1) expression. Furthermore, cinnamaldehyde arrested cell cycle in S phase. Thus, results indicated that cinnamaldehyde antagonized the ox-LDL-induced VSMCs proliferation, migration, inflammation and foam cell formation through regulation of HO-1, MMP-2, LOX-1 and blockage of cell cycle, and - suppression of p38, JNK/MAPK and NF-κB signaling pathways.

The gastroprotective effect of nobiletin against ethanol-induced acute gastric lesions in mice: impact on oxidative stress and inflammation

CONTEXT

Gastric ulcer is a common gastrointestinal disorder with increasing incidence and prevalence attributed to loss of balance between aggressive and protective factors. Nobiletin (NOB), a major component of polymethoxyflavones in citrus fruits, has a broad spectrum of health beneficial properties including anti-inflammatory and anti-tumor activities. Although NOB was originally shown to possess anti-inflammatory activity, its effects on gastric ulcer were rarely explored previously.

OBJECTIVE

The aim of the present study was to investigate the anti-ulcerogenic activity of NOB on ethanol-induced gastric ulcer in mice and to elucidate the underlying mechanisms.

METHODS

Seventy-two male Kunming mice administered with absolute ethanol (0.2 ml/animal) were pretreated with NOB (5, 10 or 20 mg/kg), cimetidine (100 mg/kg), or vehicles by intragastric administration in different experimental groups for three days, and animals were euthanized 3 h after ethanol ingestion. Gross and microscopic lesions, immunological and biochemical parameters were taken into consideration.

RESULTS

The results showed that ethanol induced gastric injury, increased malondialdehyde (MDA) levels, decreased glutathione (GSH) content, superoxide dismutase (SOD) activity, and prostaglandin E₂ (PGE₂) levels, increased pro-inflammatory cytokines tumor necrosis factor-alpha (TNF-α) and interleukin-6 (IL-6) levels and myeloperoxidase (MPO) activity, as well as the expression MAPK signaling pathway. Pretreatment with NOB significantly attenuated the gastric lesions as compared to the ethanol group.

CONCLUSIONS

These findings suggest that the gastroprotective activity is attribute to the improvement of antioxidant activities, the stimulation of PGE₂, and the reduction of pro-inflammatory cytokines through the MAPK pathway.

Atractylenolide I restores HO-1 expression and inhibits Ox-LDL-induced VSMCs proliferation, migration and inflammatory responses in vitro

Pathogenesis of atherosclerosis is characterized by the proliferation and migration of vascular smooth muscle cells (VSMCs) and inflammatory lesions. The aim of this study is to elucidate the effect of atractylenolide I (AO-I) on smooth muscle cell inflammation, proliferation and migration induced by oxidized modified low density lipoprotein (Ox-LDL). Here, We found that atractylenolide I inhibited Ox-LDL-induced VSMCs proliferation and migration in a dose-dependent manner, and decreased the production of inflammatory cytokines and the expression of monocyte chemoattractant protein-1 (MCP-1) in VSMCs. The study also identified that AO-I prominently inhibited p38-MAPK and NF-κB activation. More importantly, the specific heme oxygenase-1 (HO-1) inhibitor zinc protoporphyrin (ZnPP) IX partially abolished the beneficial effects of atractylenolide I on Ox-LDL-induced VSMCs. Furthermore, atractylenolide I blocked the foam cell formation in macrophages induced by Ox-LDL. In summary, inhibitory roles of AO-I in VSMCs proliferation and migration, lipid peroxidation and subsequent inflammatory responses might contribute to the anti-atherosclerotic property of AO-I.

Protective Effects of Nobiletin Against Endotoxic Shock in Mice Through Inhibiting TNF-α, IL-6, and HMGB1 and Regulating NF-κB Pathway

Nobiletin (NOB), the major bioactive component of polymethoxyflavones in citrus fruits, has been reported possessing significant biological properties. The purpose of the present study was to investigate the protective role of NOB on lipopolysaccharide (LPS)-induced endotoxic shock in mice. We found pretreatment with NOB increases the survival rate of mice after endotoxin injection. The present study clearly demonstrates that pretreatment with NOB decreases the production of early pro-inflammatory cytokines TNF-α, IL-6, and late-phase mediator HMGB1 in serum and tissues of kidney, lung, and liver. The histopathological study indicates that NOB administration significantly attenuate tissues injury induced by LPS. Moreover, NOB suppresses the activity of nuclear factor-kappa B (NF-κB). These results suggest that NOB protects mice against LPS-induced endotoxic shock through inhibiting the production of TNF-α, IL-6, and HMGB1 and the activation of NF-κB, which elucidate that NOB may be a promising drug candidate for the treatment of septic shock.

Esculin attenuates endotoxin shock induced by lipopolysaccharide in mouse and NO production in vitro through inhibition of NF-κB activation

Esculin, a coumarin compound derived from the traditional Chinese herbs such as Cortex Fraxini, has long been used for treating inflammatory and vascular diseases. In present study, we analyzed the role of esculin against macrophages and endotoxin shock induced by lipopolysaccharide (LPS) in mice. Here, we demonstrated that esculin suppressed inflammatory reactions in macrophages and protected mice from LPS-induced endotoxin shock. We found that esculin significantly inhibited the production of nitric oxide (NO) production via the inhibition of nuclear factor-κB (NF-κB) activation in macrophages. In animal model, esculin pretreatment significantly improved the survival rate of mice. LPS-induced increase of tumor necrosis factor alpha (TNF-α) and interleukin-6 (IL-6) in serum, lung, liver and kidney were markedly inhibited by esculin. IL-10, an anti-inflammatory cytokine, was up-regulated by esculin. Moreover, the histopathological analyses showed that esculin significantly attenuated the tissues injury of lung, liver, kidney in endotoxic mice. In addition, esculin significantly diminished the protein expression of NF-κB p65 in lung, liver, kidney, which resulted in lower levels of inflammatory mediators. These results suggest that esculin may be a potential drug for treatment of various inflammatory diseases.

Stromal cell-derived factor-1 promotes bone marrow-derived cells differentiation to cardiomyocyte phenotypes in vitro

OBJECTIVE

Recent studies have demonstrated the potential of bone marrow-derived cells (BMDC) to differentiate into cardiomyocytes. Up-regulation of stromal cell-derived factor-1 (SDF-1), a member of the chemokine CXC subfamily, mediating recruitment of BMDC has been documented in infarcted myocardium; however, it remains unknown whether SDF-1 plays a role in cardiomyogenesis of BMDC.

MATERIALS AND METHODS

Adherent BMDCs were cultured with SDF-1, or specific inhibitor for PI3K, CXCR4 or Akt with SDF-1, respectively. After 2 weeks, mRNAs and proteins from BMDCs were examined.

RESULTS

Two weeks after supplementation with SDF-1, either murine or human adherent BMDC cultured in vitro expressed cardiac specific mRNAs (NKX2.5, atrial natriuretic factor and heavy chain beta-myosin) and proteins (troponin I and heavy chain cardiac myosin), and expression levels were partly decreased by combined treatment of CXCR4, PI3K or Akt inhibitor, with SDF-1.

CONCLUSIONS

The novel findings suggest that beyond its role in mobilization and homing of BMDC, SDF-1 can promote BMDC to give rise to cardiomyocyte phenotypes in vitro, and the SDF-1/CXCR4/PI3K/Akt pathway may be one of the molecular mechanisms regulating cardiomyogenesis.

Modeling of branching structures of plants

Previous studies of branching structures generally focused on arteries. Four cost models minimizing total surface area, total volume, total drag and total power losses at a junction point have been proposed to study branching structures. In this paper, we highlight the branching structures of plants and examine which model fits data of branching structures of plants the best. Though the effect of light (e.g. phototropism) and other possible factors are not included in these cost models, a simple cost model with physiological significance, needs to be verified before further research on modeling of branching structures is conducted. Therefore, data are analysed in this paper to determine the best cost model. Branching structures of plants are studied by measuring branching angles and diameters of 234 junctions from four species of plants. The sample includes small junctions, large junctions, two- and three-dimensional junctions, junctions with three branches joining at a point and those with four branches joining at a point. First, junction exponents (x) were determined. Second, log-log plots indicate that model of volume minimization fits data better than other models. Third, one-sided t -tests were used to compare the fitness of four models. It is found that model of volume minimization fits data better than other cost models.

Accuracy in the determination of isoelectric points of some proteins and a peptide by capillary isoelectric focusing: utility of synthetic peptides as isoelectric point markers

To evaluate the accuracy ofisoelectric point determination by capillary isoelectric focusing, the pI values of nine proteins and a peptide, the pI values of which had been determined by other methods and ranging pI 3.55-9.60, were determined by capillary isoelectric focusing by cofocusing of recently developed peptide pI markers ranging 3.38-10.17, and the consistency of the pI values was examined. Isoelectric focusing was carried out in neutral polymer-coated capillaries, and the pH gradient was mobilized by pressure toward the cathode, to detect samples with absorption at 280 nm at a fixed detection point. Carrier ampholytes from two different suppliers and in different pH ranges were used. The sharp peaks of the highly pure peptide pI markers greatly facilitated the unambiguous identification of the peaks. When a carrier ampholyte ranging over the acidic side was used, the detection of acidic pI samples was anomalously delayed. This could be partly mitigated by reducing the viscosity of the anode solution in comparison with the pH gradient formed in the capillary. Since the detection times vs the pH relationships were not linear in most cases, the use of a linear calibration line over an entire pH gradient would be erroneous. Instead, the pI values of samples were calculated by assuming a linear relation for pH against detection time between two flanking marker peptides. Close agreement between the pI values, determined by capillary isoelectric focusing, and the reference values of the samples was observed within an average difference range of 0.04-0.08 pH unit with a sample consumption of 10-100 ng within 30-60 min. Some carrier ampholytes were preferentially more effective at either the acidic or the basic side of the pH gradient. For confirmation of the completion of focusing, the use of two different focusing times is recommended.

In vitro reconstitution of the 24-meric E2 inner core of bovine mitochondrial branched-chain alpha-keto acid dehydrogenase complex: requirement for chaperonins GroEL and GroES

We have investigated the in vitro reconstitution of the 24-meric inner core domain (E2c) of the transacylase (E2) component of bovine branched-chain alpha-keto acid dehydrogenase complex. The yield of recombinant E2c (amino acid residues 161-421 of bovine E2) expressed in Escherichia coli was markedly increased by fusing the bacterial maltose-binding protein (MBP) to the amino terminus of bovine E2c. Following factor Xa digestion to remove the MBP moiety, E2c was completely unfolded in 4.5 M guanidine HCl (Gdn.HCl). The denatured E2c monomers (apparent M(r) = 27,000) were diluted 100-fold at 25 degrees C into a refolding buffer containing 5 mM Mg-ATP and a 4-fold molar excess of chaperonins GroEL and GroES. Full E2 activity was recovered in 45 min. Omission of the chaperonins in the refolding buffer failed to recover any E2 activity. Recovery of E2 activity obeyed hyperbolic kinetics as a function of the chaperonin-to-E2c molar ratio and showed a requirement for hydrolysis of Mg-ATP. A stable GroEL-E2c complex was isolated which, in the presence of GroES and Mg-ATP, generated active E2c 24-mers. Dissociation of recombinant E2c 24-mers into active trimers was achieved by incubation in 1.5 M Gdn.HCl at 25 degrees C. The E2c trimers with an apparent M(r) of 84,000 were isolated by sucrose density gradient centrifugation in the presence of the chaotropic reagent. Removal of 1.5 M Gdn.HCl resulted in the spontaneous reassembly of trimers into the native 24-mer structure independent of chaperonins.(ABSTRACT TRUNCATED AT 250 WORDS)

Renaturation of citrate synthase: influence of denaturant and folding assistants

Citrate synthase (CS), which has been denatured in either guanidine hydrochloride (GdnHCl) or urea can be assisted in its renaturation in a variety of ways. The addition of each of the assistants--bovine serum albumin (BSA), oxaloacetate (OAA), and glycerol--promotes renaturation. In combination, the effect of these substances is additive with respect to the yield of folded CS. The report of Buchner et al. (Buchner, J., Schmidt, M., Fuchs, M., Jaenicke, R., Rudolph, R., Schmid, F.X., & Kiefhaber, T., 1991, Biochemistry 30, 1586-1591) that refolding of CS is facilitated by the GroE system (an Escherichia coli chaperonin [cpn] that is composed of GroEL [cpn60] and GroES [cpn10]) has been confirmed. However, we observed substantially higher yield of reactivated CS, 82%, and almost no reactivation in the absence of GroES, < 5%, whereas Buchner et al. reported 28% and 16%, respectively. In addition, we find that GroE-assisted refolding is more efficient for CS denatured in GdnHCl than for CS denatured in urea. This result is discussed in light of the known difference in the denatured states generated in GdnHCl and urea. Because GroEL inhibits the BSA/glycerol/OAA-assisted refolding, this system will be useful in future studies on the mechanism of GroE-facilitated refolding.

Increased systemic B- and T-lymphocyte responses in hereditary motor and sensory neuropathy (HMSN I)

Immune mechanisms of possible importance for the development and maintenance of peripheral nerve myelin breakdown in HMSN I were analysed by measuring B- and T-cell activation in blood, bone marrow and cerebrospinal fluid. Patients with polyneuropathies of other etiologies served as one control group and patients with tension headache as another. Flow cytometry of blood and bone marrow mononuclear cells revealed that an increased number of CD3+, CD4+ and CD4- CD8- T-cells expressed a late stage activation marker (Ta1). Analysis of T-cells primed for myelin antigens, by studies of IFN-gamma secretion in response to antigen in vitro, showed that both HMSN I and other polyneuropathy patients had low (but significant) numbers of T-cells recognizing whole PNS-myelin. Increased numbers of IgG- and IgM-producing cells were found in blood and bone marrow in the HMSN I patients. Patients with both HMSN I and the other polyneuropathies had few cells in peripheral blood and in bone marrow producing antibodies binding to P2, MAG and MBP in a solid phase immunospot assay. Many cells in the cerebrospinal fluid produced antibodies against MAG. Thus, there was a strong general activation of B- and T-cells in HMSN I while the immunity directed toward peripheral nerve was only slightly elevated. It is an open question if this immune activation is related to the primary gene defect or a secondary event to the nerve damage. The pathogenetic importance of the immune response in maintaining the nerve damage in HMSN I is unclear.

Conformational stability of pig citrate synthase and some active-site mutants

The conformational stabilities of native pig citrate synthase (PCS), a recombinant wild-type PCS, and six active-site mutant pig citrate synthases were studied in thermal denaturation experiments by circular dichroism and in urea denaturation experiments by using DTNB to measure the appearance of latent SH groups. His274 and Asp375 are conserved active-site residues in pig citrate synthase that bind to substrates and are implicated in the catalytic mechanism of the enzyme. By site-directed mutagenesis, His274 was replaced with Gly and Arg, while Asp375 was replaced with Gly, Asn, Glu, or Gln. These modifications were previously shown to result in 10(3)-10(4)-fold reductions in enzyme specific activities. The thermal unfolding of pig citrate synthase and the six mutants in the presence and absence of substrates showed large differences in the thermal stabilities of mutant proteins compared to the wild-type pig citrate synthase. The functions of His274 and Asp375 in ligand binding were measured by oxalacetate protection against urea denaturation. These data indicate that active-site mutations that decrease the specific activity of pig citrate synthase also cause an increase in the conformational stability of the protein. These results suggest that specific electrostatic interactions in the active site of citrate synthase are important in the catalytic mechanism in the chemical transformations as well as the conformational flexibility of the protein, both of which are important for the overall catalytic efficiency of the enzyme.

Immunological mapping of fine molecular surface structures of citrate synthase enzymes from different cell types

Citrate synthase (EC 4.1.3.7), which is present in all living organisms as a key enzyme in aerobic energy metabolism, is one of the most highly phylogenetically conserved enzymes known in terms of its primary and active site structure. However, in terms of other parameters such as in vitro stability, tolerance to changes in pH, degree of self-polymerization, etc., citrate synthases from different sources are markedly different. These divergences can be observed even between isoforms of the enzyme within the same species. Data documenting these diversities suggest that a high degree of difference in tertiary structures may occur. Therefore, the surface profiles of citrate synthase enzymes from yeast, pig, rat, tomato and Escherichia coli were investigated with immunological methods using monoclonal antibody families generated against either pig citrate synthase (alpha-PCS) or yeast citrate synthase-2 (alpha-YCS-2). A high degree of homology of enzyme epitopes was detected on the mitochondrial citrate synthases originating from yeast, tomato, pig and rat cells. Major differences were found between the hexameric citrate synthase originating from E. coli compared with those dimeric forms prepared from eukaryotic cells. Only modest similarities were detected between the highly homologous peroxisomal and mitochondrial yeast citrate synthases. Furthermore, a point mutation of one of the catalytic residues (H274R on recombinant pig and H313R on yeast enzyme) of mitochondrial citrate synthase (CS-1) resulted in a significant increase in immunological similarity with the peroxisomal isoenzyme (CS-2). These findings are discussed in terms of the possible mechanism of evolution of CS-2 in yeast.

Mutation of essential catalytic residues in pig citrate synthase

Two amino acid residues, His274 and Asp375, were replaced singly in the active site of pig citrate synthase (PCS) with Gly274, Arg274, Gly375, Asn375, Glu375, and Gln375. The nonmutant protein and the mutant proteins were expressed in and purified from Escherichia coli, and the effects of these amino acid substitutions on the overall reaction rate and conformation of the PCS protein were studied by initial velocity and full time course kinetic analysis, behavior during affinity column chromatography, and monoclonal antibody reactivity. Native and mutant proteins purified similarly had a subunit molecular weight of 50,000 and were homologous when examined with 10 independent a-PCS monoclonal IgGs or with a polyclonal anti-PHCS serum. No activity was detected for Asn375 or Gln375. The kcats of the other purified mutant proteins, however, were decreased by about 10(3) compared to the nonmutant enzyme activity. The Km for oxalacetate was decreased 10-fold in the Glu375 protein and was reduced by half in Gly274 and Arg274 PCSs, while the Km for acetyl-CoA was decreased 2-3-fold in Gly274, Arg274, and Gln375 PCSs. A mechanism is proposed that electrostatically links His274 and Asp375.