bluuebunny/crossref_metadata_2025 huggingface dataset:
Electron donation to the flavoprotein NifL, a redox-sensing transcriptional regulator
Authors: MACHEROUX Peter , HILL Susan , AUSTIN Sara , EYDMANN Trevor , JONES Tamera , KIM Sung-Oog , POOLE Robert , DIXON Ray
Published: August 2015

Transcriptional control of the nitrogen fixation (nif) genes in response to oxygen in Azotobacter vinelandii is mediated by nitrogen fixation regulatory protein L (NifL), a regulatory flavoprotein that modulates the activity of the transcriptional activator nitrogen fixation regulatory protein A (NifA). CD spectra of purified NifL indicate that FAD is bound to NifL in an asymmetric environment and the protein is predominantly α-helical. The redox potential of NifL is -226 mV at pH 8 as determined by the enzymic reduction of NifL by xanthine oxidase/xanthine in the presence of appropriate mediators. The reduction of NifL by xanthine oxidase prevented NifL from acting as an inhibitor of NifA. In the absence of electron mediators NifL could also be reduced by Escherichia coli flavohaemoprotein (Hmp) with NADH as reductant. Hmp contains a globin-like domain with haem B as prosthetic group and an FAD-containing oxidoreductase module. The carboxyferrohaem form of Hmp was competent to reduce NifL, suggesting that electron donation to NifL originates from the flavin in Hmp rather than by direct electron transfer from the haem. Spinach ferredoxin:NAD(P) oxidoreductase, which adopts a folding similar to the FAD- and NAD-binding domains of Hmp, also reduced NifL with NADH as reductant. Re-oxidation of NifL occurs rapidly in the presence of air, raising the possibility that NifL might sense intracellular oxygen. We propose a physiological redox cycle in which the oxidation of NifL by oxygen and hence the activation of its inhibitory properties occurs rapidly, in contrast with the switch from the active to the reduced form of NifL, which occurs more slowly.
Inhibition of etoposide-induced apoptosis with peptide aldehyde inhibitors of proteasome
Authors: STEFANELLI Claudio , BONAVITA Francesca , STANIC Ivana , PIGNATTI Carla , FARRUGGIA Giovanna , MASOTTI Lanfranco , GUARNIERI Carlo , CALDARERA Claudio M.
Published: August 2015

Recent investigations have indicated the involvement of proteasome in programmed cell death. The present studies show that although peptide aldehyde inhibitors of proteasome are by themselves weak inducers of apoptosis, they inhibit the apoptotic effect of the anticancer drug etoposide in rat thymocytes. Acetyl-Leu-Leu-norvalinal (LLnV-al) and other related peptide aldehydes inhibited the increase in caspase activity and DNA fragmentation that followed treatment with etoposide and their effect was related to their potency as proteasome inhibitors. To inhibit etoposide-induced apoptosis, LLnV-al must be present within 3 h of treatment with etoposide, in the same way as the inhibitor of protein synthesis cycloheximide must be. Etoposide caused a rapid accumulation of p53 protein that was not inhibited by LLnV-al, which was also a strong inducer of p53. Peptide aldehydes were also weak activators of caspase activity, suggesting that the same mechanism, i.e. the blocking of proteasome function, both triggers apoptosis and inhibits the effect of etoposide. These results are consistent with a model in which proteasome is selectively involved in the pathway used by etoposide to induce cell suicide.
Molecular cloning and expression of a cDNA encoding an apoptotic endonuclease DNase γ
Authors: SHIOKAWA Daisuke , TANUMA Sei-ichi
Published: August 2015

An endonuclease named DNase γ has been purified from the nuclei of apoptotic rat thymocytes [Shiokawa, Ohyama, Yamada and Tanuma (1997) Biochem. J. 326, 675–681]. Here we report the molecular cloning of a cDNA encoding a 35 kDa precursor protein for rat DNase γ. A 1.6 kb mRNA coding for the DNase γ precursor is detected at high levels in spleen, lymph nodes, thymus and liver. By using reverse transcriptase-mediated PCR, expression of DNase γ mRNA is observed in kidney and testis but not in brain or heart. Analysis of recombinant DNase γ reveals that full-length DNase γ, including the N-terminal precursor, is an inactive proenzyme. The mature form of recombinant DNase γ, from which the N-terminal precursor has been removed, has the same properties as purified DNase γ: requirement for divalent cations, dependence on pH, sensitivity to Zn2+, and cleavage of chromosome DNA to nucleosomal units. In HeLa S3 cells stably transfected with the DNase γ cDNA, exogenously introduced DNase γ is activated by apoptotic stimuli; enhancement of DNA fragmentation, chromatin condensation and nuclear collapse are observed. These findings provide evidence for the involvement of DNase γ in DNA fragmentation and nuclear structural changes during apoptosis.
Cytotoxic effect of HIV-1 coat glycoprotein gp120 on human neuroblastoma CHP100 cells involves activation of the arachidonate cascade
Authors: MACCARRONE Mauro , NAVARRA Michele , CORASANITI M. Tiziana , NISTICÒ Giuseppe , FINAZZI AGRÒ Alessandro
Published: August 2015

HIV type-1 (HIV-1) coat glycoprotein gp120 causes necrotic death in human neuroblastoma CHP100 cells. Here, we investigated the possible role of the arachidonate cascade and membrane peroxidation in gp120-induced cell necrosis. It is shown that gp120 increases the intracellular concentrations of prostaglandin E2 and leukotriene B4 by up-regulating the activity and expression of the arachidonate-metabolizing enzymes prostaglandin H synthase and 5-lipoxygenase respectively. Consistent with this observation, selective inhibitors of prostaglandin H synthase (i.e. indomethacin) and 5-lipoxygenase (i.e. MK886 and caffeic acid) protected CHP100 cells against gp120-induced necrosis. Treatment with gp120 also enhanced membrane lipid peroxidation and this may be implicated in the execution of cell damage. Interestingly, incubation with exogenous nitric oxide (NO) mimicked the effects of gp120 on necrotic death of CHP100 cells and activation of prostaglandin H synthase and 5-lipoxygenase. This suggests that NO might participate in the mechanism by which gp120 activates the arachidonate cascade.
Different Sp1 family members differentially affect transcription from the human elongation factor 1 A-1 gene promoter
Authors: NIELSEN S⊘ren J. , PRÆSTEGAARD Morten , ØRGENSEN Helle F. J. , CLARK Brian F. C.
Published: August 2015

The GC box is an important transcriptional regulatory element present in the promoters of many mammalian genes. In the present study we examine the effect of known GC-box-binding proteins on the promoter of the human elongation factor 1 A-1 (hEF1A-1) gene in human HeLa cells and Drosophila SL2 cells. In HeLa cells co-transfection with the GC-box-binding protein BTEB resulted in a 4–10-fold increase in hEF1A-1 promoter activity. This stimulation was dependent on a single GC box located between positions -69 and -50 of the promoter. Little or no effect was observed of other GC-box-binding proteins including Sp1, Sp3, Sp4 and BTEB2. In SL2 cells stimulation by Sp1 and Sp3 through the single GC box of the proximal promoter led to 13-fold and 21-fold increases respectively in promoter activity. Inclusion of further upstream sequences resulted in high levels of expression when Sp1 or Sp3 was co-transfected with the reporter plasmid. In this setting Sp1 stimulated transcription by 750-fold, whereas Sp3 was even more potent, yielding a 1150-fold stimulation. Mobility-shift assays performed with the promoter-proximal GC box demonstrated the binding of Sp1, Sp3 and Sp4 to this sequence. To our knowledge, the present study represents the first comparison of all known GC-box-binding proteins on a natural promoter.
Microvesicle release is associated with extensive protein tyrosine dephosphorylation in platelets stimulated by A23187 or a mixture of thrombin and collagen
Authors: PASQUET Jean-Max , DACHARY-PRIGENT Jeanne , NURDEN Alan T.
Published: August 2015

Phosphatidylserine exposure and microvesicle release give rise to procoagulant activity during platelet activation. We have previously shown that whereas the Ca2+ ionophore A23187 and 2,5-di-(t-butyl)-1,4-benzohydroquinone, a Ca2+-ATPase inhibitor, induce phosphatidylserine exposure, only the former triggers microvesicle release. We now report that microvesicle formation with ionophore A23187 is specifically associated with µ-calpain activation, increased protein tyrosine phosphatase (PTP) activity and decreased tyrosine phosphorylation. The degree to which calpain and individual PTPs were activated in response to A23187 depended on the extent of bivalent cation chelation in the external medium. EGTA (2 mM) blocked or severely retarded their activation, and addition of extracellular Ca2+ in excess (2 mM) resulted in virtually immediate tyrosine dephosphorylation. Dephosphorylation was correlated with an increase in total PTP activity in platelet lysates. In platelets stimulated by a combination of thrombin and collagen, only the subpopulation undergoing microvesicle release and isolated by their binding to annexin-V-coated magnetic beads exhibited protein tyrosine dephosphorylation. Detection of PTP activity in an ‘in-gel ’ assay showed the Ca2+-dependent appearance of active low-molecular-mass bands at 38, 36 and 27 kDa. Individual PTPs varied in their protease sensitivity to changes in intracellular Ca2+ levels. For example, PTP1B was a more sensitive substrate than SH2-domain-containing tyrosine phosphatase-1 for µ-calpain cleavage. Incubation of platelets with the PTP inhibitors, phenylarsine oxide and benzylphosphonic acid acetoxymethyl ester, led to increased tyrosine phosphorylation and the surface expression of aminophospholipids but little microvesicle formation. Furthermore, microvesicle release in response to ionophore A23187 was inhibited. We conclude that platelet microvesicle formation is associated with extensive protein tyrosine dephosphorylation.
Identification of endoplasmic reticulum proteins involved in glycan assembly: synthesis and characterization of P3-(4-azidoanilido)uridine 5′-triphosphate, a membrane-topological photoaffinity probe for uridine diphosphate-sugar binding proteins
Authors: RANCOUR David M. , MENON Anant K.
Published: August 2015

Much of the enzymic machinery required for the assembly of cell surface carbohydrates is located in the endoplasmic reticulum (ER) of eukaryotic cells. Structural information on these proteins is limited and the identity of the active polypeptide(s) is generally unknown. This paper describes the synthesis and characteristics of a photoaffinity reagent that can be used to identify and analyse members of the ER glycan assembly apparatus, specifically those glycosyltransferases, nucleotide phosphatases and nucleotide–sugar transporters that recognize uridine nucleotides or UDP-sugars. The photoaffinity reagent, P3-(4-azidoanilido)uridine 5´-triphosphate (AAUTP), was synthesized easily from commercially available precursors. AAUTP inhibited the activity of ER glycosyltransferases that utilize UDP-GlcNAc and UDP-Glc, indicating that it is recognized by UDP-sugar-binding proteins. In preliminary tests AAUTP[α-32P] labelled bovine milk galactosyltransferase, a model UDP-sugar-utilizing enzyme, in a UV-light-dependent, competitive and saturable manner. When incubated with rat liver ER vesicles, AAUTP[α-32P] labelled a discrete subset of ER proteins; labelling was light-dependent and metal ion-specific. Photolabelling of intact ER vesicles with AAUTP[α-32P] caused selective incorporation of radioactivity into proteins with cytoplasmically disposed binding sites; UDP-Glc:glycoprotein glucosyltransferase, a lumenal protein, was labelled only when the vesicle membrane was disrupted. These data indicate that AAUTP is a membrane topological probe of catalytic sites in target proteins. Strategies for using AAUTP to identify and study novel ER proteins involved in glycan assembly are discussed.
Purification and characterization of catechol 1,2-dioxygenase from Rhodococcus rhodochrous NCIMB 13259 and cloning and sequencing of its catA gene
Authors: STRACHAN Philip D. , FREER Andrew A. , FEWSON Charles A.
Published: August 2015

A method was developed for the purification of catechol 1,2-dioxygenase from Rhodococcus rhodochrous NCIMB 13259 that had been grown in the presence of benzyl alcohol. The enzyme has very similar apparent Km (1–2 µM) and Vmax (13–19 units/mg of protein) values for the intradiol cleavage of catechol, 3-methylcatechol and 4-methylcatechol and it is optimally active at pH 9. Cross-linking studies indicate that the enzyme is a homodimer. It contains 0.6 atoms of Fe per subunit. The enzyme was crystallized with 15% (w/v) poly(ethylene glycol) 4000/0.33 M CaCl2/25 mM Tris (pH 7.5) by using a microseeding technique. Preliminary X-ray characterization showed that the crystals are in space group C2 with unit-cell dimensions a = 111.9 Å, b = 78.1 Å, c = 134.6 Å, β = 100 °. An oligonucleotide probe, made by hemi-nested PCR, was used to clone the gene encoding catechol 1,2-dioxygenase (catA). The deduced 282-residue sequence corresponds to a protein of molecular mass 31539 Da, close to the molecular mass of 31558 Da obtained by electrospray MS of the purified enzyme. catA was subcloned into the expression vector pTB361, allowing the production of catechol 1,2-dioxygenase to approx. 40% of the total cellular protein. The deduced amino acid sequence of the enzyme has 56% and 75% identity with the catechol 1,2-dioxygenases of Arthrobacter mA3 and Rhodococcus erythropolis AN-13 respectively, but less than 35% identity with intradiol catechol and chlorocatechol dioxygenases of Gram-negative bacteria.

The nucleotide sequence data reported will appear in DDBJ, EMBL and GenBank Nucleotide Sequence Databases under the accession number AF043741.
Expression, characterization and engineered specificity of rat epididymal retinoic acid-binding protein
Authors: SUNDARAM Manickavasagam , SIVAPRASADARAO Asipu , AALTEN Daan M. F. van , FINDLAY John B. C.
Published: August 2015

Epididymal retinoic acid-binding protein (ERABP) is the major androgen-dependent protein present in the lumen of the epididymis and is thought to be involved in sperm maturation. It displays a high degree of three-dimensional structural similarity to serum retinol-binding protein (RBP). Although both proteins interact with retinoids, RBP exhibits a broad specificity, binding retinol, retinoic acid and retinaldehyde with roughly equal affinities, whereas ERABP is specific for all-trans- and 9-cis-retinoic acids. Consistent with this, the binding pockets of the two proteins are different: in RBP it is predominantly hydrophobic, whereas that for ERABP is amphipathic, with a network of charged residues at the open end of the binding pocket. In order to investigate the roles of these charged residues, Arg-80 and Glu-63 have been mutated to isoleucine. The resultant double mutant, Glu-63 → Ile/Arg-80 → Ile, as well as the wild-type protein, were subsequently expressed in Escherichia coli as fusion proteins, with the streptavidin recognition sequence (Strep) tagged to their C-termini. The expressed proteins were purified in a single step by streptavidin-affinity chromatography and their ligand-binding properties were examined using fluorimetric titrations. Whereas the wild-type ERABP binds only retinoic acid, the double mutant is capable of binding retinol, retinoic acid and retinaldehyde with similar affinities. These observations provide experimental support for the proposition that the charged residues near the open end of the binding pocket are responsible for restricting the specificity of ERABP for retinoic acid. These studies demonstrate that changes in specificity can be engineered into lipocalins.
Expression of novel isoforms of carnitine palmitoyltransferase I (CPT-1) generated by alternative splicing of the CPT-Iβ gene
Authors: YU Geng-Sheng , LU Yi-Chun , GULICK Tod
Published: August 2015

Carnitine palmitoyltransferase I (CPT-I) catalyses the rate-determining step in mitochondrial fatty acid β-oxidation. The enzyme has two cognate structural genes that are preferentially expressed in liver (α) or fat and muscle (β). We hypothesized the existence of additional isoforms in heart to account for unique kinetic characteristics of enzyme activity in this tissue. Hybridization and PCR screening of a human cardiac cDNA library revealed the expression of two novel CPT-I isoforms generated by alternative splicing of the CPT-Iβ transcript, in addition to the β and α cDNA species previously described. Ribonuclease protection and reverse transcriptase-mediated PCR assays confirmed the presence of mRNA species of each splicing variant in heart, skeletal muscle and liver, with differing relative concentrations in the tissues. The novel splicing variants omit exons or utilize a cryptic splice donor site within an exon. Deduced polypeptide sequences of the novel enzymes include omissions in the region of putative membrane-spanning and malonyl-CoA regulatory domains compared with the previously described CPT-Is, implying that the encoded enzymes will exhibit unique features with respect to outer mitochondrial membrane topology and response to physiological and pharmacological inhibitors.
Secondary structure of oleosins in oil bodies isolated from seeds of safflower (Carthamus tinctorius L.) and sunflower (Helianthus annuus L.)
Authors: LACEY Dominic J. , WELLNER Nikolaus , BEAUDOIN Frederic , NAPIER Johnathan A. , SHEWRY Peter R.
Published: August 2015

Oil bodies were isolated from mature seeds of sunflower (Helianthus annuus L.) and safflower (Carthamus tinctorius L.). Oil body preparations containing only oleosin proteins could be obtained from safflower seeds by salt-washing followed by centrifugation on discontinuous sucrose density gradients. However, it was necessary to treat sunflower oil bodies with urea to obtain preparations of similar purity. Incubation of the oil bodies with proteinases gave two fragments with molecular masses of 6 and 8 kDa which were protected from digestion. These fragments represented the hydrophobic domain of the oleosins, as determined by N-terminal sequencing. Intact and proteinase-treated oil bodies of both species were analysed by Fourier-transform infrared spectroscopy, as dry films and in aqueous medium, the spectra being compared with those obtained for pure oil samples in order to identify the bands resulting from the oleosin proteins and protected peptides. This investigation showed that the hydrophobic domain of the oleosins in intact oil bodies is predominantly α-helical in structure and that the conformation was not greatly affected by washing the oil bodies with urea during preparation.
Species barrier in prion diseases: a kinetic interpretation based on the conformational adaptation of the prion protein
Authors: KELLERSHOHN Nicolas , LAURENT Michel
Published: August 2015

Prion diseases are thought to result from the conformational change of the normal cellular prion protein to a pathogenic protease-resistant isoform. However, brain extracts not containing the protease-resistant isoform of the prion protein can be infectious following interspecies transmission. The ‘protein-only ’ hypothesis of pathogenesis is extended to provide possible explanations which could be interpreted in terms of a different infectious agent. It is proposed that normal cellular protein (PrPC) may be transformed into a form (PrP*) that is conformationally distinct from the host-specific abnormal isoform (PrPSc). In infection from a heterologous donor, the dimeric forms of heterologous PrPSc, which may catalyse the formation of host PrP* from PrPC, host PrP* and host PrPSc are all considered to be capable of catalysing, to some extent, the conversion of PrPC into PrPSc. However, depending on the species involved, PrP* may, or may not, be pathogenic, and may, or may not, be sensitive to proteolysis. It is shown, by numerical integration of the differential rate equations derived from this model, that a strain may be stabilized after two or three passages through a different species and that transmission might occur in the absence of detectable protease-resistant prion protein. The natural transmission of scrapie to cattle is discussed in relation to the model.
Isolation and identification of metallothionein isoforms (MT-1 and MT-2) in the rat testis
Authors: SUZUKI Junko S. , KODAMA Naomi , MOLOTKOV Andrei , AOKI Etsuko , TOHYAMA Chiharu
Published: August 2015

It has been a long-lasting controversial issue as to whether or not the male genital organs, such as the testis and prostate, contain metallothioneins (MTs), a group of cysteine-rich heavy-metal-binding proteins that play a role in detoxifying heavy metals such as cadmium (Cd). Earlier studies reported that the rodent testis lacks MTs and concluded that this is why the testis is very susceptible to Cd, although other indirect experimental evidence suggests that MTs are present in this organ. A deficiency of MTs in the testis was originally suspected on the basis of amino acid composition analysis, since MT-like proteins isolated as Cd-binding proteins did not have a characteristic MT structure. In the present study, we demonstrate that the rat testis indeed expresses Cd-binding proteins with sequences identical to those previously described for MT-1 and MT-2, the major isoforms. To confirm that MT-1 and MT-2 are present in the rat testis, we purified and isolated Cd-binding proteins by homogenization using Cd-containing buffer, followed by sequential purification using Sephadex G-75 gel filtration chromatography and anion HPLC column chromatography, which yielded Cd-binding protein-1 (Cd-BP-1) and -2 (Cd-BP-2). After pyridylethylation, Cd-BP-1 and Cd-BP-2 were subjected to specific protein fragmentation by acids and endopeptidases, which revealed that these Cd-binding proteins have the same primary structures as MT-1 and MT-2 respectively. Thus we believe that the present results clearly resolve the long-standing debate about the presence of MTs in the testis, at least in the rodent.
Sulphoxidation reaction catalysed by myeloperoxidase from human leucocytes
Authors: CAPEILLÈRE-BLANDIN Chantal , MARTIN Christelle , GAGGERO Nicoletta , PASTA Piero , CARREA Giacomo , COLONNA Stefano
Published: August 2015

The oxidation of alkyl aryl sulphides by myeloperoxidase (MPO) at the expense of hydrogen peroxide was investigated under steady-state conditions. The sulphide concentration effect was studied under saturating H2O2 concentrations at pH 5.0 and 20 °C. The kinetic constants, kcat and Km, of the different substrates were determined and the values were in the 1–10 s-1 range and around 43±26 µM respectively, whatever the sulphide considered. In the case of p-substituted thioanisoles, the oxidation rate was dependent upon the substituent effect. The correlation of log(kcat) with the substituent constants (δ+ values) (Hammett equation) could be explained by a reaction mechanism involving the enzyme compound II and a sulphenium radical cation. This conclusion was also supported by spectrophotometric analysis of catalytic intermediates of the enzyme, showing the accumulation of compound II. Moreover, chiral HPLC analyses showed that MPO oxidation of alkyl aryl sulphides produced the corresponding (R)-sulphoxides with a low enantioselectivity (4–8%). Chloride ion effects on the MPO-catalysed oxygenation of sulphides were also studied. Chloride acted as a substrate for MPO and as an activator in MPO-catalysed sulphoxidation. Inhibition occurred at chloride concentrations above 120 mM, whereas below 120 mM, chloride increased the reaction rate when using p-tolyl methyl sulphide as the substrate. In the presence of 100 mM chloride the catalytic efficiency (kcat/Km) of MPO increased 3–4-fold, whatever the sulphide considered, but racemic products were obtained. These data have been interpreted in the light of known structural information on the accessibility of the distal haem cavity.
Cobalamin (vitamin B12) biosynthesis: functional characterization of the Bacillus megaterium cbi genes required to convert uroporphyrinogen III into cobyrinic acid a,c-diamide
Authors: RAUX Evelyne , LANOIS Anne , RAMBACH Alain , WARREN Martin J. , THERMES Claude
Published: August 2015

The function of individual genes of the Bacillus megaterium cobI operon genes in cobalamin (vitamin B12) biosynthesis was investigated by their ability to complement defined Salmonella typhimurium cob mutants. This strategy confirmed the role of cbiA, -D, -F, -J, -L and cysGA. Furthermore the operon as a whole was used to restore corrin biosynthesis in Escherichia coli, which, although closely related to S. typhimurium, does not possess the CobI pathway. When the B. megaterium cob operon was cloned into a plasmid and transformed into an E. coli strain containing the S. typhimurium cbiP, it conferred upon the host strain the ability to make the cobyric acid de novo. However, cobyric acid synthesis was observed only when the strain was grown anaerobically. Derivatives of the corrin-producing E. coli strain were constructed in which genes of the B. megaterium cob operon had been inactivated. These strains were used to demonstrate that, whereas B. megaterium cbiD, -G and -X are essential for cobyric acid synthesis, the cbiW and -Y genes could be deleted without detriment to cobyric acid production in E. coli.
Secondary structure analysis of the putative membrane-associated domains of the inward rectifier K+ channel ROMK1
Authors: BRAZIER Stephen P. , RAMESH Bala. , HARIS Parvez I. , LEE David C. , SRAI Surjit K. S.
Published: August 2015

The inward rectifier K+ channels contain two putative membrane-spanning domains per subunit (M1, M2) and a ‘pore ’ (P) region, which is similar to the H5 domain of voltage-gated K+ channels. Here we have used Fourier transform infrared (FTIR) and CD spectroscopy to analyse the secondary structures of synthetic peptides corresponding to the M1, M2 and P regions of ROMK1 in aqueous solution, in organic solvents and in phospholipid membranes. A previous CD study was unable to provide any structural data on a similar P peptide [Ben-Efraim and Shai (1997) Biophys. J. 72, 85–96]. However, our FTIR and CD spectroscopic analyses indicate that this peptide adopts an α-helical structure when reconstituted into dimyristoyl phosphatidylcholine vesicles and lysophosphatidyl choline (LPC) micelles as well as in trifluoroethanol (TFE) solvent. This result is in good agreement with a previous study on a peptide corresponding to the pore domain of a voltage-gated K+ channel [Haris, Ramesh, Sansom, Kerr, Srai and Chapman (1994) Protein Eng. 7, 255–262]. FTIR spectra of the M1 peptide in LPC micelles displayed a strong absorbance characteristic of an intermolecular β-sheet structure, suggesting aggregation of the M1 peptide. Sucrose gradient centrifugation was used to separate aggregated peptide from peptide incorporated into micelles in an unaggregated manner; subsequent analysis by FTIR suggested that the M1 peptide adopted an α-helical structure when incorporated into phospholipid membranes. FTIR and CD spectra of the M2 peptide in phospholipids and high concentrations of TFE suggest that this peptide adopts an α-helical structure. The structural data obtained in these experiments have been used to propose a model for the structure of the membrane-associated core (M1-P-M2) of the inward rectifier K+ channel protein.
Cytosolic deglycosylation process of newly synthesized glycoproteins generates oligomannosides possessing one GlcNAc residue at the reducing end
Authors: DUVET Sandrine , LABIAU Odette , MIR Anne-Marie , KMIÉCIK Daniel , KRAG Sharon S. , VERBERT André , CACAN René
Published: August 2015

Recent studies on the mechanism of degradation of newly synthesized glycoproteins suggest the involvement of a retrotranslocation of the glycoprotein from the lumen of the rough endoplasmic reticulum into the cytosol, where a deglycosylation process takes place. In the studies reported here, we used a glycosylation mutant of Chinese hamster ovary cells that does not synthesize mannosylphosphoryldolichol and has an increased level of soluble oligomannosides originating from glycoprotein degradation. In the presence of anisomycin, an inhibitor of protein synthesis, we observed an accumulation of glucosylated oligosaccharide-lipid donors (Glc3Man5GlcNAc2-PP-Dol), which are the precursors of the soluble neutral oligosaccharide material. Inhibition of rough endoplasmic reticulum glucosidase(s) by castanospermine led to the formation of Glc3Man5GlcNAc2(OSGn2) (in which OSGn2 is an oligomannoside possessing two GlcNAc residues at its reducing end), which was then retained in the lumen of intracellular vesicles. Thus they were protected during an 8 h chase period from the action of cytosolic chitobiase, which is responsible for the conversion of OSGn2 to oligomannosides possessing one GlcNAc residue at the reducing end (OSGn1). In contrast, when protein synthesis was maintained in the presence of castanospermine, glucosylated oligomannosides (Glc1–3Man5GlcNAc1) were recovered in cytosol. Except for monoglucosylated Man5 species, which are potential substrates for luminal calnexin and calreticulin, the pattern of oligomannosides was similar to that observed on glycoproteins. The occurrence in the cytosol of glucosylated species with one GlcNAc residue at the reducing end implies that the deglycosylation process that generates glucosylated OSGn1 from glycoproteins occurs in the cytosol.
Stimulation of the Ca2+-mediated egr-1 and c-fos expression in murine erythroleukaemia cells by cyclosporin A
Authors: SCHAEFER András , MAGÓCSI Mária , FANDRICH Anette , MARQUARDT Hans
Published: August 2015

The Ca2+-induced expression of the primary response genes egr-1 and c-fos was investigated in the murine erythroleukaemia cell line ELM-I-1. Exposure of the cells to the Ca2+-ionophore A23187 led to a rapid transient rise in egr-1 and c-fos mRNA production followed by an increase in Egr-1 and c-Fos protein levels as well as an increase in Egr-1 and activator protein 1 (AP-1) DNA-binding activity. Preincubation of the cells with KN-62, a specific inhibitor of Ca2+/calmodulin-dependent protein kinases, strongly decreased the Ca2+-mediated expression of egr-1 and c-fos. In contrast, treatment with cyclosporin A, which inhibits the Ca2+/calmodulin-dependent protein phosphatase 2B or calcineurin, increased both egr-1 and c-fosmRNA production and the DNA-binding activity of the Egr-1 and AP-1 transcription factors in response to the intracellular Ca+ concentration ([Ca2+]i)-increasing agents A23187 or cyclopiazonic acid. Enhancement of the Ca2+-induced c-fos and egr-1 expression by cyclosporin A was correlated with the capability of this agent to inhibit calcineurin phosphatase activity in ELM-I-1 cells. Studies on the phosphorylation state and DNA-binding activity of the cAMP response element-binding protein (CREB) did not demonstrate an early Ca2+-dependent activation of this transcription factor, suggesting that the regulation of c-fos and egr-1 expression by Ca2+ is not linked to CREB in the haematopoietic ELM-I-1 cells. The results indicate that calcineurin exerts negative regulatory effects on both egr-1 and c-fos expression in murine erythroleukaemia cells, in addition to the calcineurin-mediated down-regulation of c-myb expression observed previously in this cell system. This study therefore emphasizes the important role of calcineurin as a negative modulator of gene expression in certain cell types.
Sterol carrier protein 2 participates in hypersecretion of biliary cholesterol during gallstone formation in genetically gallstone-susceptible mice
Authors: FUCHS Michael , LAMMERT Frank , WANG David Q.-H. , PAIGEN Beverly , CAREY Martin C. , COHEN David E.
Published: August 2015

In inbred mice, susceptibility to cholesterol gallstone disease is conferred by Lith genes, which in part promote hypersecretion of cholesterol into bile in response to a high-fat/cholesterol/cholic acid (lithogenic) diet. Because cytosolic sterol carrier protein 2 (SCP2) is believed to participate in cellular cholesterol trafficking and is elevated in the liver cytosol of cholesterol gallstone patients, we defined the hepatic expression of SCP2 during cholesterol gallstone formation in gallstone-susceptible C57L and gallstone-resistant AKR mice fed the lithogenic diet. Steady-state cytosolic SCP2 levels in C57L, but not AKR mice increased as a function of time and were correlated positively with biliary cholesterol hypersecretion, cholesterol saturation indices of gall-bladder biles and the appearance of liquid and solid cholesterol crystals leading to gallstone formation. Steady-state mRNA levels increased co-ordinately, consistent with regulation of SCP2 expression at the transcriptional level. Our results suggest that overexpression of SCP2 contributes to biliary cholesterol hypersecretion and the pathogenesis of gallstones in genetically susceptible mice. Because of the different chromosomal localizations of the Lith and Scp2 genes, we postulate that Lith genes control SCP2 expression indirectly.
Cholesterol regulates oxysterol binding protein (OSBP) phosphorylation and Golgi localization in Chinese hamster ovary cells: correlation with stimulation of sphingomyelin synthesis by 25-hydroxycholesterol
Authors: STOREY Margo K. , BYERS David M. , COOK Harold W. , RIDGWAY Neale D.
Published: August 2015

Sphingomyelin (SM) and cholesterol content is positively correlated in cellular membranes, and in several pathological and experimental conditions there is evidence for coregulation. The potential role of oxysterols and oxysterol binding protein (OSBP) in mediating the coregulation of cholesterol and SM was examined using Chinese hamster ovary (CHO) and cholesterol auxotrophic, sterol regulatory defective (SRD) 6 cells. SRD 6 cells grown in the presence or absence of cholesterol for 24 h displayed a 30–50% reduction in SM synthesis compared with control CHO 7 cells. SM synthesis in CHO 7 and cholesterol-supplemented SRD 6 cells was stimulated 2-fold by 25-hydroxycholesterol, but cholesterol-starved SRD 6 cells were unresponsive. Basal and 25-hydroxycholesterol-stimulated SM synthesis was also inhibited in lovastatin-treated wild-type CHO-K1 cells. Lack of 25-hydroxycholesterol activation of SM synthesis in cholesterol-starved SRD 6 and lovastatin-treated CHO-K1 cells was correlated with dephosphorylation of OSBP. In SRD 6 cells, this was evident after 12 h of cholesterol depletion, it occurred equally at all phosphorylation sites and was exacerbated by 25-hydroxycholesterol. Unlike CHO 7 cells, where OSBP was observed in small vesicles and the cytoplasm, OSBP in cholesterol-starved SRD 6 cells was constitutively localized in the Golgi apparatus. Supplementation with non-lipoprotein cholesterol promoted redistribution to vesicles and the cytoplasm. Similarly, OSBP in CHO-K1 cells grown in delipidated serum was predominantly in the Golgi apparatus. Low-density lipoprotein (LDL) supplementation of CHO-K1 cells caused the redistribution of OSBP to the cytoplasm and small vesicles, and this effect was blocked by pharmacological agents {3-β-[2-(diethylamino)ethoxy]androst-5-en-17-one and progesterone}, which inhibited LDL cholesterol efflux from lysosomes. The results showed that localization of OSBP between the Golgi apparatus and a cytoplasmic/vesicular compartment was responsive to changes in cholesterol content and trafficking. In cholesterol depleted SRD 6 cells, this was accompanied by dephosphorylation of OSBP and attenuation of 25-hydroxycholesterol activation of SM synthesis.
Roles of the C-terminal domains of human dihydrodiol dehydrogenase isoforms in the binding of substrates and modulators: probing with chimaeric enzymes
Authors: MATSUURA Kazuya , HARA Akira , DEYASHIKI Yoshihiro , IWASA Harunori , KUME Toshiyuki , ISHIKURA Syuhei , SHIRAISHI Hiroaki , KATAGIRI Yoshihiro
Published: August 2015

Human liver dihydrodiol dehydrogenase (DD; EC 1.3.1.20) exists in isoforms (DD1, DD2 and DD4) composed of 323 amino acids. DD1 and DD2 share 98% amino acid sequence identity, but show lower identities (approx. 83%) with DD4, in which a marked difference is seen in the C-terminal ten amino acids. DD4 exhibits unique catalytic properties, such as the ability to oxidize both (R)- and (S)-alicyclic alcohols equally, high dehydrogenase activity for bile acids, potent inhibition by steroidal anti-inflammatory drugs and activation by sulphobromophthalein and clofibric acid derivatives. In this study, we have prepared chimaeric enzymes, in which we exchanged the C-terminal 39 residues between the two enzymes. Compared with DD1, CDD1-4 (DD1 with the C-terminal sequence of DD4) had increased kcat/Km values for 3α-hydroxy-5β-androstanes and bile acids of 3–9-fold and decreased values for the other substrates by 5–100-fold. It also became highly sensitive to DD4 inhibitors such as phenolphthalein and hexoestrol. Another chimaeric enzyme, CDD4-1 (DD4 with the C-terminal sequence of DD1), showed the same (S)-stereospecificity for the alicyclic alcohols as DD1, had decreased kcat/Km values for bile acids with 7β- or 12α-hydroxy groups by more than 120-fold and was resistant to inhibition by betamethasone. In addition, the activation effects of sulphobromophthalein and bezafibrate decreased or disappeared for CDD4-1. The recombinant DD4 with the His314 → Pro (the corresponding residue of DD1) mutation showed intermediate changes in the properties between those of wild-type DD4 and CDD4-1. The results indicate that the binding of substrates, inhibitors and activators to the enzymes is controlled by residues in their C-terminal domains; multiple residues co-ordinately act as determinants for substrate specificity and inhibitor sensitivity.
Genomic organization, 5′-flanking region and chromosomal localization of the human glutathione transferase A4 gene
Authors: DESMOTS Fabienne , RAUCH Claudine , HENRY Catherine , GUILLOUZO André , MOREL Fabrice
Published: August 2015

We have isolated and characterized a human glutathione transferase A4 (hGSTA4) subunit gene from a yeast artificial chromosome containing several other glutathione transferase alpha genes and pseudogenes. The homodimeric protein hGSTA4-4, is involved in the detoxification of 4-hydroxynonenal and other reactive electrophiles produced by oxidative metabolism, and may have a significant role in protecting intracellular components from oxidative damage. The hGSTA4 gene spans nearly 18 kb, contains seven exons, maps onto chromosome 6p12, and lies in close proximity to the 7SK small nuclear RNA gene in a head-to-tail orientation. The intron/exon borders conform to the standard rules, an open reading frame is present beginning at position 154 in exon 2, and the stop codon is at position 822 in exon 7. The transcription initiation site has been determined by primer extension analysis and is located 135 bp upstream of intron 1. Isolation and sequencing of the hGSTA4 gene 5´-flanking region revealed it to be devoid of TATA or CCAAT boxes but it does contain an initiator element overlapping the transcription start site, a GC box and putative binding sites for transcription factors AP1, STAT, GATA1 and NF-κB. Reverse transcription-PCR analysis revealed that hGSTA4 mRNA was present in all the tissues tested, although in low amounts, suggesting that this subunit may be ubiquitously expressed.
Monocyte–macrophage ferric reductase activity is inhibited by iron and stimulated by cellular differentiation
Authors: PARTRIDGE Jason , WALLACE Daniel F. , RAJA Kishor B. , DOOLEY James S. , WALKER Ann P.
Published: August 2015

The enzyme ferric reductase catalyses the reduction of Fe(III) as a prerequisite to its transportation across the cell membrane. Duodenal mucosal biopsies from iron overloaded patients with genetic haemochromatosis (GH) have increased ferric reductase activity and iron absorption compared with controls, yet the GH mucosa is iron deficient. A similar GH-related iron deficiency is also seen in macrophages. The aim of this study was to investigate whether macrophage ferric reductase activity is altered in GH, and to determine ferric reductase activity in monocytes and differentiated macrophages. The erythroleukaemic K562 cell line was studied as a clonal reference cell line. The basal K562 ferric reductase activity is characteristic of a membrane bound enzyme, being both temperature and protease sensitive. Ferric reductase activity was also demonstrated in human leucocyte, monocyte and macrophage preparations. Assays of K562 and macrophage cell supernatants confirmed that the ferric reductase activity was not due to a secreted factor. Assay of ferric reductase in normalized-iron and iron-enriched (100 µM ferric citrate) conditions showed no significant difference between Cys282Tyr (Cys282 → Tyr) homozygous GH macrophages and Cys282-Tyr negative control activities (P> 0.05). However, a 900% increase in ferric reductase activity was observed during monocyte to macrophage differentiation (P< 0.05), possibly reflecting the co-ordinate up-regulation of iron metabolism in these cells. The demonstration of approx. 25% activity after macrophage differentiation at high free-iron concentrations compared with ‘normalized ’ iron is consistent with repression of human ferric reductase activity by iron. The identification of the human ferric reductase gene and its protein will ultimately provide insight into its regulation and role in mammalian iron metabolism.
Identification of an important cysteine residue in human glutamate–cysteine ligase catalytic subunit by site-directed mutagenesis
Authors: TU Zhongheng , ANDERS M. W.
Published: August 2015

Glutamate–cysteine ligase (GLCL) catalyses the rate-limiting step in glutathione biosynthesis. To identify cysteine residues in GLCL that are involved in its activity, eight conserved cysteine residues in human GLCL catalytic subunit (hGLCLC) were replaced with glycine residues by PCR-based site-directed mutagenesis. Both recombinant hGLCLC and hGLCL holoenzyme were expressed and purified with a baculovirus expression system. The activity of purified hGLCL holoenzyme with the mutant hGLCLC-C553G was 110±12 µmol/h per mg of protein compared with 370±20 µmol/h per mg of protein for the wild-type. Holoenzymes with hGLCLC-C52G, -C248G, -C249G, -C295G, -C491G, -C501G or -C605G showed activities similar to the wild type. The Km values of hGLCL containing hGLCLC-C553G were slightly lower than those of the wild type, indicating that the replacement of cysteine-553 with Gly in hGLCLC did not significantly affect substrate binding by the enzyme. hGLCLC-C553G was more easily dissociated from hGLCLR than the wild-type hGLCLC. GLCL activity increased by 11% after hGLCLC-C553G was incubated with an equimolar amount of purified hGLCL regulatory subunit (hGLCLR) at room temperature for 30 min, but increased by 110% after wild-type hGLCLC was incubated with hGLCLR for 10 min. These results indicate that cysteine-553 in hGLCLC is involved in heterodimer formation between hGLCLC and hGLCLR.
Cathepsin-6, a novel cysteine proteinase showing homology with and co-localized expression with cathepsin J/P in the labyrinthine layer of mouse placenta
Authors: NAKAJIMA Akinori , KATAOKA Ken , TAKATA Yoshimi , HUH Nam-ho
Published: August 2015

A novel cysteine proteinase, cathepsin-6, was isolated by RNA differential display from mouse placenta. Cathepsin-6 showed the highest homology with cathepsin J (same as P) and L. The structural features including the catalytic triad of the C1 proteinase family were well conserved in cathepsin-6. The expression of cathepsin-6 and cathepsin J/P was restricted in labyrinthine trophoblasts of the placenta.
Chicken ovalbumin upstream-promoter transcription factor and E-box-binding proteins enhance thyroid-hormone responsiveness of the malic enzyme gene in avian hepatocytes
Authors: WANG Yutong , ZHANG Yanqiao , HILLGARTNER F. Bradley
Published: August 2015

In chick embryo hepatocytes (CEH), stimulation of malic enzyme transcription by 3,3′,5-tri-iodothyronine (T3) is mediated by a liver-specific and T3-inducible DNase I hypersensitive region (−3910 to −3640bp) in the malic enzyme gene. Previous studies have shown that this region contains a cluster of five T3 response elements (T3REs), referred to as a T3 response unit (T3RU), plus three accessory elements that enhance T3 responsiveness conferred by the T3RU. Here we report the identification of two additional accessory elements within the −3910 to −3640bp region. Each element augments T3 regulation of malic enzyme transcription in CEH. One element, designated region G (−3681/−3666bp), contains a single nuclear-hormone-receptor half-site that binds the orphan receptor chicken ovalbumin upstream-promoter transcription factor. The other element, designated region H (−3655/−3646bp), contains an E-box motif that binds proteins of unknown identity. Stimulation of T3RE function by region G or region H does not require the presence of additional malic enzyme sequences. In contrast with the stimulatory effects of regions G and H on T3 responsiveness in CEH, neither of these elements is effective in modulating T3 responsiveness in chick embryo fibroblasts (CEF). Instead, region H functions as a T3-insensitive repressor of transcription in CEF. These results indicate that chicken ovalbumin upstream-promoter transcription factor and E-box-binding proteins interact with nuclear T3 receptors to enhance T3 regulation of malic enzyme transcription in CEH and that alterations in region G and region H activities contribute to diminished T3 regulation of malic enzyme transcription in CEF relative to CEH. As the pattern of protein binding to regions G and H varies substantially between CEH and CEF, the mechanism for cell-type-dependent differences in region G and region H activity may involve alterations in protein binding to these T3 accessory elements.
Cloning and characterization of hELD/OSA1, a novel BRG1 interacting protein
Authors: HURLSTONE Adam F.L. , OLAVE Ivan A. , BARKER Nick , van NOORT Mascha , CLEVERS Hans
Published: August 2015

A highly conserved multisubunit enzymic complex, SWI/SNF, participates in the regulation of eukaryote gene expression through its ability to remodel chromatin. While a single component of SWI/SNF, Swi2 or a related protein, can perform this function in vitro, the other components appear to modulate the activity and specificity of the complex in vivo. Here we describe the cloning of hELD/OSA1, a 189KDa human homologue of Drosophila Eld/Osa protein, a constituent of Drosophila SWI/SNF. By comparing conserved peptide sequences in Eld/Osa homologues we define three domains common to all family members. A putative DNA binding domain, or ARID (AT-rich DNA-interacting domain), may function in targetting SWI/SNF to chromatin. Two other domains unique to Eld/Osa proteins, EHD1 and EHD2, map to the C-teminus. We show that EHD2 mediates binding to Brahma-related gene 1 (BRG1), a human homologue of yeast Swi2. EHD1 and EHD2 also appear capable of interacting with each other. Using an antibody raised against EHD2 of hELD/OSA1, we detected Eld/Osa1 in endogenous SWI/SNF complexes derived from mouse brain.
Inhibition of peptidases in the control of blood pressure
Authors: Kubota Eiji , Dean Rachel G , Balding Leanne C , Burrell Louise M
Published: August 2015

The natriuretic peptide and renin-angiotensin systems are physiological counterparts with opposite roles in the regulation of electrolyte balance and blood pressure. In both systems, membrane-bound, zinc-dependent peptidases play an important role in the inactivation or activation of the system. Angiotensin-converting enzyme (ACE) converts angiotensin I into angiotensin II, and neutral endopeptidase (NEP) degrades the natriuretic peptides. Simultaneous inhibition NEP and ACE by a single molecule (a vasopeptidase inhibitor) is a new therapeutic approach in hypertension. Wider applications for vasopeptidase inhibitors being studied include their role as cardioprotective agents in heart failure, as renoprotective agents in chronic renal failure and diabetic nephropathy, and as vasculoprotective agents in endothelial dysfunction and athersclerosis.