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1.
Human plasma paraoxonase (PON1) is calcium-dependent enzyme that hydrolyses esters, including organophosphates and lactones, and exhibits anti-atherogenic properties. Human phosphate binding protein (HPBP) was discovered as contaminant during crystallization trials of PON1. This observation and uncertainties for the real activities of PON1 led us to re-evaluate the purity of PON1 preparations. We developed a hydroxyapatite chromatography for the separation of both HDL-associated proteins. We confirmed that: (1) HPBP is strongly associated to PON1 in HDL, and generally both proteins are co-purified; (2) standard purification protocols of PON1 lead to impure enzyme; (3) hydroxyapatite chromatography allows the simultaneous purification of PON1 and HPBP.  相似文献   

2.
Paraoxonase1 (PON1), one of HDL-associated antioxidant proteins, is known to lose its activity in vivo systems under oxidative stress. Here, we examined the effect of various oxidants on lactonase activity of PON1, and tried to protect the lactonase activity from oxidative inactivation. Among the oxidative systems tested, the ascorbate/Cu2+ system was the most potent in inactivating the lactonase activity of purified PON1; in contrast to a limited role of Fe2+, Cu2+ (0.05–1.0 µM) remarkably enhanced the inactivation of PON1 in the presence of ascorbate (0.02–0.1 mM). Moreover, Cu2+ alone inhibited the lactonase activity at concentrations as low as 1 µM. The ascorbate/Cu2+-mediated inactivation of PON1 lactonase activity was prevented by catalase, but not general hydroxyl radical scavengers, suggesting the implication of Cu2+-bound hydroxyl radicals in the oxidative inactivation. Compared to arylesterase activity, lactonase activity appears to be more sensitive to Cu2+-catalyzed oxidation. Separately, ascorbate/Cu2+-mediated inactivation of lactonase activity was prevented by oleic acid as well as phoshatidylcholine. Taken together, our data demonstrate that Cu2+-catalyzed oxidation may be a primary factor to cause the decrease of PON1 lactonase activity under oxidative stress and that lactonase activity of PON1 is most susceptible to ascorbate/Cu2+ among PON1 activities. In addition, we have showed that radical-induced inactivation of lactonase activity is prevented by some lipids.  相似文献   

3.
Human serum paraoxonase (PON1) is a calcium-dependent organophosphatase. To identify residues essential for PON1 activity, we adopted complementary approaches based on chemical modification and site-directed mutagenesis. To detect 45Ca2+ binding to native and chemically modified PON1, we performed nondenaturating gel electrophoresis. The environment of calcium-binding sites was probed using the Ca2+ analogue, terbium. Tb3+ binds to calcium-binding sites as shown by displacement of 45Ca2+ by Tb3+. Binding of Tb3+ is accompanied by a complete loss of enzyme activity. PON1 chemical modification with the Trp-selective reagent, N-bromosuccinimide, and the Asp/Glu-selective, dicyclohexylcarbodiimide, established that Trp and Asp/Glu residues are components of the PON1 active center and calcium-binding sites. Additional evidence for the presence of a Trp residue in the PON1 calcium-binding sites was a characteristic fluorescence emission at 545 nm from the PON1-Tb3+ complex and abolishment of that fluorescence upon modification by N-bromosuccinimide. The importance of aromatic/hydrophobic character of the residue 280 was demonstrated by site-directed mutagenesis: the W280F mutant was fully active while the W280A and W280L mutants had markedly reduced activity. Twelve amino acids among conserved His and Asp/Glu residues were found essential for PON1 arylesterase and organophosphatase activities: H114, H133, H154, H242, H284, D53, D168, D182, D268, D278, E52, and E194. Finally, the cysteines constituting the PON1 disulfide bond (C41 and C352) were essential, but the glycan chains linked to Asn 252 and 323 were not essential for PON1 secretion and activity.  相似文献   

4.
Human serum paraoxonase 1 (PON1; EC 3.1.8.1) is a high-density lipoprotein associated, calcium-dependent enzyme that hydrolyses aromatic esters, organophosphates and lactones and can protect the low-density lipoprotein against oxidation. In this study, in vitro effect of some hydroxy and dihydroxy ionic coumarin derivatives (120) on purified PON1 activity was investigated. Among these compounds, derivatives 1120 are water soluble. In investigated compounds, compounds 6 and 13 were found the most active (IC50?=?35 and 34?µM) for PON1, respectively. The present study has demonstrated that PON1 activity is very highly sensitive to studied coumarin derivatives.  相似文献   

5.
Human plasma paraoxonase (HuPON1) is a high density lipoprotein (HDL)-bound enzyme exhibiting antiatherogenic properties. The molecular basis for the binding specificity of HuPON1 to HDL has not been established. Isolation of HuPON1 from HDL requires the use of detergents. We have determined the activity, dispersity, and oligomeric states of HuPON1 in solutions containing mild detergents using nondenaturing electrophoresis, size exclusion chromatography, and cross-linking. HuPON1 was active whatever its oligomeric state. In nonmicellar solutions, HuPON1 was polydisperse. In contrast, HuPON1 exhibited apparent homogeneity in micellar solutions, except with CHAPS. The enzyme apparent hydrodynamic radius varied with the type of detergent and protein concentration. In C(12)E(8) micellar solutions, from sedimentation velocity, equilibrium analytical ultracentrifugation, and radioactive detergent binding, HuPON1 was described as monomers and dimers in equilibrium. A decrease of the detergent concentration shifted this equilibrium toward the formation of dimers. About 100 detergent molecules were associated per monomer and dimer. The assembly of amphiphilic molecules, phospholipids in vivo, in sufficiently large aggregates could be a prerequisite for anchoring of HuPON1 and then allowing stabilization of the enzyme activity. Changes of HDL size and shape could strongly affect the binding affinity and stability of HuPON1 and result in reduced antioxidative capacity of the lipoprotein.  相似文献   

6.
Ornithine carbamoyltransferase (OTC; subunit, 36,000 Da) [EC 2.1.3.3] is initially synthesized as a precursor (pOTC) with a transient NH2-terminal presequence of 32 amino acid residues, then is imported posttranslationally nto the mitochondrial matrix. We expressed rat pOTC in Escherichia coli, purified it in a denatured form, and showed that could be transported into isolated mitochondria in the presence of rabbit reticulocyte lysate [Murakami et al. (1988) J. Biol. Chem. 263, 18437-18442]. In order to compare the properties of the precursor and mature form of OTC, the rat mature OTC was synthesized in E. coli and purified. The recombinant OTC represented about 5% of the total bacterial protein and was present in both the supernatant and precipitate of the disrupted bacteria. The OTC, extracted from the precipitate with 8 M urea or 6 M guanidine.HCl, was essentially homogeneous, as judged by SDS-PAGE. When guanidine.HCl-denatured mature OTC was diluted and incubated at 0 degrees C for 40-60 h, it was reactivated to a specific activity of 170 mumol/min/mg protein at 37 degrees C (18% of that of the purified mature enzyme). Guanidine.HCl-denatured pOTC was activated to a specific activity of 125 mumol/min/mg protein under similar conditions. The native and reactivated OTC sedimented with an s20.w value of 6.2S, whereas the activated pOTC sedimented with an s20.w of 5.2S. The activated pOTC was more unstable than the reactivated OTC at 50 degrees C. These observations indicate that the presequence does not prevent pOTC from folding into an enzymatically active trimeric form, although the pOTC trimer appears to be less compact than the mature trimer.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   

7.
Paraoxonase 1 (PON1), contained in plasma high-density lipoproteins, plays an important role in the protection of plasma lipoproteins and cell membranes from oxidative damage. Previous studies indicate that human PON1 is stimulated by high NaCl concentrations. The aim of this study was to characterize in more detail the effect of salts on serum PON1. Paraoxon-hydrolyzing activity of human serum was stimulated by 81.6% following the addition of 1 M NaCl. The effect of NaCl was dose-dependent between 0.5 and 2 M. PON1 activity toward phenyl acetate was reduced by 1 M NaCl by 55.2%. Both the paraoxon- and phenyl acetate-hydrolysing activity was slightly lower in heparinized plasma than in serum, but NaCl had similar stimulatory and inhibitory effects on these activities, respectively. In rat, rabbit, and mouse, NaCl reduced PON1 activity. KCl had a similar effect on human PON1 as NaCl. Sodium nitrite also stimulated human PON1 but much less effectively than chloride salts. In contrast, sucrose, sodium acetate and sodium lactate had no significant effect. NaBr was a less effective PON1 activator than NaCl, whereas the effect of NaJ was non-significant. The activity of human PON1 toward homogentisic acid lactone and gamma-decanolactone was unaltered by NaCl. These data indicate that: 1) high concentrations of chlorides stimulate human PON1 activity toward paraoxon but not other substrates, 2) PON1 is inhibited by Cl(-) in other mammalian species, 3) the potency of human PON1 activation by halogene salts increases with decreasing atomic mass of the halide anion.  相似文献   

8.
Low-density lipoproteins (LDLs), when modified by free radicals derived from artery wall cells, induce atherosclerosis. In contrast to oxidized LDL (ox-LDL), high-density lipoproteins (HDLs) are able to prevent atherosclerosis through a protein with antioxidant properties, paraoxonase 1 (PON1). The purpose of this study was to explore the association between the activity of HDL-associated PON1 and circulating ox-LDL as well as to investigate the relationship between ox-LDL and parameters of lipid profile in thirty Slovaks aged 21-73 years because recent studies have presented controversial results concerning PON1 and its role in LDL oxidation. For determination of circulating ox-LDL sandwich ELISA was used and other lipid parameters were determined by routine laboratory analyses. PON1 activities were assayed by two synthetic substrates - paraoxon and phenyl acetate. Lipid peroxides were determined spectrophotometrically. Of the lipid parameters examined, ox-LDL level correlated positively with total (P < 0.0001) and LDL-cholesterol (P < 0.001). Triacylglycerols (TAG) (P < 0.001), lipid peroxides (P < 0.01) and atherogenic index (AI = total cholesterol/HDL) (P < 0.0001) were also strongly correlated with ox-LDL. No inverse relationships were observed between ox-LDL and HDL-cholesterol or arylesterase/paraoxonase activities of PON1. Furthermore, it was found that ox-LDL (P < 0.01) and lipid peroxides (P < 0.05) were significantly higher in men than in women. PON1 arylesterase activity was marginally affected by sex. The results of this study suggest that the anti-atherogenic properties of HDLs are not directly related to their total concentration and that PON1 activity determined towards synthetic compounds (paraoxon and phenyl acetate) reflects no association with markers of oxidative stress. Furthermore, it follows from our results that men are more susceptible to developing atherosclerosis compared to women.  相似文献   

9.
Human serum paraoxonase (PON1), an HDL-associated esterase, protects lipoproteins against oxidation, probably by hydrolyzing specific lipid peroxides. As arterial macrophages play a key role in oxidative stress in early atherogenesis, the aim of the present study was to examine the effect of PON1 on macrophage oxidative stress. For this purpose we used mouse arterial and peritoneal macrophages (MPM) that were harvested from two populations of PON1 knockout (KO) mice: one on the genetic background of C57BL/6J (PON1(0)) and the other one on the genetic background of apolipoproteinE KO (PON1(0)/E(0)). Serum and LDL, but not HDL, lipids peroxidation was increased in PON1(0), compared to C57BL/6J mice, by 84% and by 220%, respectively. Increased oxidative stress was shown in peritoneal and in arterial macrophages derived from either PON1(0) or PON1(0)/E(0) mice, compared to their appropriate controls. Macrophage oxidative stress was expressed by increased lipid peroxides content in MPM from PON1(0) and from PON1(0)/E(0) mice by 48% and by 80%, respectively, and by decreased reduced glutathione (GSH) content, compared to the appropriate controls. Furthermore, increased capacity of MPM from PON1(0) and PON1(0)/E(0) mice to oxidize LDL (by 40% and by 19%, respectively) and to release superoxide anions was observed. In accordance with these results, PON1(0) mice MPM exhibited 130% increased translocation of the cytosolic p47phox component of NADPH-oxidase to the macrophage plasma membrane, suggesting increased activation of macrophage NADPH-oxidase in PON1(0) mice, compared to control mice MPM. The increase in oxidative stress in PON1-deficient mice was observed despite the presence of the two other members of the PON gene family. PON2 and PON3 activities and mRNA expression were both found to be present in PON1-deficient mice MPM. Upon incubation of PON1(0)/E(0) derived macrophages with human PON1 (7.5 arylesterase units/ml), cellular peroxides content was decreased by 18%, macrophage superoxide anion release was decreased by 33%, and macrophage-mediated oxidation of LDL was reduced by 22%. Finally, a 42% increase in the atherosclerotic lesion area was observed in PON1(0)/E(0) mice, in comparison to E(0) mice under regular chow diet. We thus concluded that PON1 can directly reduce oxidative stress in macrophages and in serum, and that PON1-deficiency results in increased oxidative stress not only in serum, but also in macrophages, a phenomenon that can contribute to the accelerated atherosclerosis shown in PON1-deficient mice.  相似文献   

10.
A common polymorphism at codon 192 in the human paraoxonase (PON) 1 gene has been shown to be associated with increased risk for coronary heart disease (CHD) in Caucasian populations. However, these findings have not been reported consistently in all Caucasian and non-Caucasian populations, suggesting that this is not a functional mutation but may mark a functional mutation present in either PON1 or a nearby gene. Recently, two other PON-like genes, designated "PON2" and "PON3," have been identified, and they are linked with the known PON1 gene on chromosome 7. Identification of additional polymorphisms in the PON-gene cluster may help to locate the functional polymorphism. In this report, we describe the existence of a common polymorphism at codon 311 (Cys-->Ser; PON2*S) in the PON2 gene, as well as its association with CHD alone and in combination with the PON1 codon 192 polymorphism in Asian Indians. The frequency of the PON2*S allele was significantly higher in cases than in controls (.71 vs. .61; P=.016). The age- and sex-adjusted odds ratio (OR) was 2.5 (95% confidence interval &sqbl0;95% CI&sqbr0;=1.8-3.1; P=.0090) for the PON2*S allele carriers. Further stratification of the PON2*S association, on the basis of the presence or absence of the PON1*B allele, showed that the CHD risk associated with the PON2*S allele was confined to PON1*B-allele carriers. Likewise, the PON1*B-allele risk was present only among PON2*S carriers. Age- and sex-adjusted ORs for the PON2*S and PON1*B were 3.6 (95% CI=2.6-4.6; P=.011) and 2.9 (95% CI=2.4-3.5; P=.0002) among the PON1*B and PON2*S carriers, respectively. Our data indicate that both polymorphisms synergistically contribute to the CHD risk in this sample and that this genetic risk is independent of the conventional plasma lipid profile.  相似文献   

11.
In a search for Polo-like kinase 1 (Plk1) interaction proteins, we have identified TRF1 (telomeric repeat binding factor 1) as a potential Plk1 target. In this communication we report further characterization of the interaction. We show that Plk1 associates with TRF1, and Plk1 phosphorylates TRF1 at Ser-435 in vivo. Moreover, Cdk1, serving as a priming kinase, phosphorylates TRF1 to generate a docking site for Plk1 toward TRF1. In the presence of nocodazole, ectopic expression of wild type TRF1 but not TRF1 with alanine mutation in the Plk1 phosphorylation site induces apoptosis in cells containing short telomeres but not in cells containing long telomeres. Unexpectedly, down-regulation of TRF1 by RNA interference affects cell proliferation and results in obvious apoptosis in cells with short telomeres but not in cells with long telomeres. Importantly, we observe that telomeric DNA binding ability of TRF1 is cell cycle-regulated and reaches a peak during mitosis. Upon phosphorylation by Plk1 in vivo and in vitro, the ability of TRF1 to bind telomeric DNA is dramatically increased. These results demonstrate that Plk1 interacts with and phosphorylates TRF1 and suggest that Plk1-mediated phosphorylation is involved in both TRF1 overexpression-induced apoptosis and its telomeric DNA binding ability.  相似文献   

12.
Fang DH  Fan CH  Ji Q  Qi BX  Li J  Wang L 《Molecular biology reports》2012,39(6):6801-6809
Paraoxonase is an HDL-associated enzyme that plays a preventive role against oxidative stress, which is thought to contribute to cancer development. PON1 activity varies widely among individuals, which is in part related to two common nonsynonymous polymorphisms in the PON1 gene (Q192R and L55M). The polymorphisms in PON1 have been implicated in cancer risk. However, results from the studies to date have been conflicting. To clarify the association, a meta-analysis was performed for 7,073 cases and 9,520 controls from 25 published case–control studies. Odds ratios (ORs) with 95% confidence intervals (CIs) were used to assess the strength of the association. Significant associations between PON1-L55M but not Q192R polymorphism and total cancer were observed from all the comparisons. In stratified analyses, PON1-55M allele was a risk factor for breast cancer. Similarly, increased risk was observed for prostate cancer (OR = 1.18, 95% CI: 1.01–1.36, P heterogeneity = 0.260) and Caucasian population (OR = 1.18, 95% CI: 1.02–1.38, P heterogeneity = 0.1) of the LM genotype, compared with the LL genotype. For PON1-Q192R polymorphism, PON1-192R allele was a decreased risk factor for cancer in the Asian group (RR vs QQ: OR = 0.61, 95% CI: 0.38–0.98, P heterogeneity = 0.268; QR vs QQ: OR = 0.71, 95% CI: 0.52–0.96, P heterogeneity = 0.130; RR + QR vs QQ: OR = 0.71, 95% CI: 0.53–0.95, P heterogeneity = 0.135). Although some modest bias could not be eliminated, this meta-analysis suggests that the PON1-55M allele is a risk factor for the development of cancer, in particular for breast cancer. Future studies with larger sample sizes are warranted to further evaluate these associations.  相似文献   

13.
W Y Tarn  C H Hsu  K T Huang  H R Chen  H Y Kao  K R Lee    S C Cheng 《The EMBO journal》1994,13(10):2421-2431
We have previously shown that the yeast PRP19 protein is a spliceosomal component, but is not tightly associated with small nuclear RNAs. It appears to associate with the spliceosome concomitant with or just after dissociation of the U4 small nuclear RNA during spliceosome assembly. We have found that PRP19 is associated with a protein complex in the splicing extract and that at least one of the associated components is essential for splicing. Taking advantage of the epitope tagging technique, we have isolated the PRP19-associated complex by affinity chromatography. The isolated complex is functional for complementation for the heat-inactivated prp19 mutant extract, and consists of at least seven polypeptides in addition to PRP19. At least three of these can interact directly with the PRP19 protein. We also show that the PRP19 protein itself is in an oligomeric form, which might be a prerequisite for its interaction with these proteins.  相似文献   

14.
Human serum paraoxonase 1 (PON1) is a HDL-associated enzyme that catalyzes the hydrolysis of a variety of aromatic carboxylic acid esters and several organophosphates. Recently it has been suggested that a physiological substrate of serum PON1 is homocysteine thiolactone which is a putative risk factor in atherosclerosis. In this study, human (192)Q and (192)R PON1 isoenzymes were purified from the respective phenotype human serum, using a protocol consisting of ammonium sulfate precipitation and four chromatography steps: gel filtration, ion-exchange, non-specific affinity, and a second ion-exchange. Using paraoxon as substrate, overall purification fold was found as 742 for (192)R PON1 and 590 for (192)Q PON1. The final purified enzymes were shown as single protein bands close to 45kDa on SDS-PAGE and confirmed by Western blot. Substrate kinetics were studied with phenyl acetate, paraoxon and homocysteine thiolactone. Both PON1 isoenzymes showed mixed type inhibition with phenyl acetate. K(m) values of (192)Q and (192)R PON1 for homocysteine thiolactone were 23.5mM and 22.6mM respectively. For (192)R PON1, the V(max) was 2.5-fold and k(cat)/K(m) was 2.6-fold higher than those for (192)Q PON1 when homocysteine thiolactone is used as substrate. The present data suggest that defining (192)Q and (192)R PON1 isoforms could be a good predictor and prognostic marker in the cardiovascular risk assessment.  相似文献   

15.
Liu D  Yin B  Wang Q  Ju W  Chen Y  Qiu H  Li J  Peng X  Lu C 《遗传学报》2012,39(8):369-374
Cytoplasmic poly(A) binding protein 4(PABPC4) is an RNA-processing protein that plays an important role in the regulation of gene expression.The aim of this study was to investigate the expression pattern and identify the potential clinical significance of PABPC4 in colorectal cancer.Immunohistochemical analysis revealed that 26.7%(27/101 patients) of primary colorectal tumors and 60.5%(23/38 patients) of corresponding adjacent,normal tissues showed high cytoplasmic expression of PABPC4,whereas expression was absent in 98%(43/44 patients) of distant,normal tissues.Using Kaplan-Meier analysis,we observed that the expression of PABPC4 was significantly correlated with disease-free survival and overall survival in patients with stageⅡand stageⅢcolorectal cancer(P = 0.022 and P = 0.020,respectively).PABPC4 expression was positively associated with survival outcome,and may have predictive value in the prognosis of patients with colorectal cancer.Taken together,our findings indicate that PABPC4 may play a role in the pathogenesis of colorectal cancer.  相似文献   

16.
Mammalian casein kinase 1delta (CK1delta) is a homologue of the S. cerevisiae Hrr25p protein kinase. Hrr25p is involved in regulating diverse events including vesicular trafficking, gene expression, DNA repair, and chromosome segregation. In contrast to Hrr25p, little is known about the function, regulation, or subcellular localization of CK1delta. In the present study, we show that CK1delta in mammalian cells is mainly cytoplasmic and enriched within the Golgi and/or ER-Golgi transport vesicles, consistent with a role in vesicular trafficking. Transient expression of green fluorescent protein (GFP)- or FLAG peptide-tagged CK1delta showed localization similar to that of the endogenous CK1delta. GFP-CK1delta was also enriched at the centrosomes in interphase cells. Strikingly, two inactive mutant CK1delta proteins (K38M and T176I) showed almost exclusive nuclear staining, suggesting that protein kinase activity is required for normal localization of CK1delta and prevention of nuclear accumulation. The nuclear export inhibitor leptomycin B promoted nuclear enrichment of CK1delta indicating that nuclear localization of CK1delta occurs physiologically. Both endogenous CK1delta and GFP-CK1delta are enriched on the spindle poles in mitotic cells, consistent with a role in regulating spindle formation. Localization is a property of the protein kinase domain and is independent of the C-terminal noncatalytic domain. These data are consistent with roles for CK1delta in mammalian cells analogous to those of its yeast counterparts.  相似文献   

17.
《Autophagy》2013,9(5):649-662
Macroautophagy is an intracellular, vesicle-mediated mechanism for the sequestration and ultimate lysosomal degradation of cytoplasmic proteins, organelles and macromolecules. The macroautophagy process and many of the autophagy specific (Atg) proteins are remarkably well conserved in higher eukaryotes. In yeast, the Atg1 kinase complex includes Atg1, Atg13, Atg17, and at least four other interacting proteins, some of which are phosphorylated in a TOR-dependent manner, placing the Atg1 signaling complex downstream of a major nutrient-sensing pathway. Atg1 orthologs, including mammalian unc-51-like kinase 1 (ULK1), have been identified in higher eukaryotes and have been functionally linked to autophagy. This suggests that other components of the Atg1 complex exist in higher eukaryotes. Recently, a putative human Atg13 ortholog, FLJ20698, was identified by gapped-BLAST analysis. We show here that FLJ20698 (Atg13) is a ULK1-interacting phosphoprotein that is essential for macroautophagy. Furthermore, we identify a novel, human Atg13-interacting protein, FLJ11773, which we have termed Atg101. Atg101 is essential for autophagy and interacts with ULK1 in an Atg13-dependent manner. Additionally, we present evidence that intracellular localization of the ULK1 complex is regulated by nutrient conditions. Finally, we demonstrate that Atg101 stabilizes the expression of Atg13 in the cell, suggesting that Atg101 contributes to Atg13 function by protecting Atg13 from proteasomal degradation. Therefore, the identification of the novel protein, Atg101, and the validation of Atg13 and Atg101 as ULK1-interacting proteins, suggests an Atg1 complex is involved in the induction of macroautophagy in mammalian cells.  相似文献   

18.
Escherichia coli clones expressing recombinant shiga toxin (Stx1) and its derivatives Stx1-A and Stx1-B subunits were established to release the proteins into periplasmic space. The expression was examined by SDS-PAGE to visualize the subunits. The secreted assembled subunits were extracted with polymyxin B and assessed for biological activity. The results showed that the presence of N-terminus leader sequence of the gene is essential for assembly of the subunits to yield biologically active holotoxin (AB5). The absence of the leader sequence did not affect the expression of the subunits but did disrupt the holotoxin assembly.  相似文献   

19.
APOBEC3G (APO3G), a cytidine deaminase with two zinc finger domains, inhibits human immunodeficiency virus type 1 replication in the absence of Vif. Here, we provide a comprehensive molecular analysis of the deaminase and nucleic acid binding activities of human APO3G using a pure system containing only one protein component, i.e., highly purified, catalytically active enzyme expressed in a baculovirus system. We demonstrate that APO3G deaminates cytosines in single-stranded DNA (ssDNA) only, whereas it binds efficiently to ssDNA and ssRNA, about half as well to a DNA/RNA hybrid, and poorly to double-stranded DNA and RNA. In addition, the base specificities for deamination and binding of ssDNA are not correlated. The minimum length required for detection of APO3G binding to an ssDNA oligonucleotide in an electrophoretic mobility shift assay is 16 nucleotides. Interestingly, if nucleocapsid protein and APO3G are present in the same reaction, we find that they do not interfere with each other's binding to RNA and a complex containing the RNA and both proteins is formed. Finally, we also identify the functional activities of each zinc finger domain. Thus, although both zinc finger domains have the ability to bind nucleic acids, the first zinc finger contributes more to binding and APO3G encapsidation into virions than finger two. In contrast, deamination is associated exclusively with the second zinc finger. Moreover, zinc finger two is more important than finger one for the antiviral effect, demonstrating a correlation between deaminase and antiviral activities.  相似文献   

20.
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