bluuebunny/crossref_metadata_2025 huggingface dataset:
Positional importance of Pro53 adjacent to the Arg49-Gly50-Asp51 sequence of rhodostomin in binding to integrin αIIbβ3
Authors: CHANG Chih-Pei , CHANG Jui-Chin , CHANG Hsin-Hou , TSAI Wei-Jern , LO Szecheng J.
Published: August 2015

Rhodostomin (RHO), a disintegrin isolated from snake venom, has been demonstrated to inhibit platelet aggregation through interaction with integrin αIIbβ3, but there is a lack of direct evidence for RHO–integrin αIIbβ3 binding. In addition, no study on the length of Arg49-Gly50-Asp51 (RGD) loop of RHO influencing on its binding to integrin αIIbβ3 has been reported. In the present study we have developed a highly sensitive dot-blot and glutathione S-transferase–RHO pull-down assays; the latter was coupled with a biotin–avidin–horseradish peroxidase enhanced-chemiluminescence detection system. These were able to demonstrate the direct binding of RHO to integrin αIIbβ3. The pull-down assay further showed that four alanine-insertion mutants upstream of the RGD motif and three insertions downstream of the RGD were able to decrease integrin αIIbβ3 binding activity to only a limited extent. By contrast, two insertions immediately next to RGD and one insertion in front of the Cys57 caused almost complete loss of binding activity to αIIbβ3. The results of the platelet-aggregation-inhibition assay and platelet-adhesion assay for the insertion mutants were consistent with results of the pull-down assay. It is thus concluded that, although an insertion of a single alanine residue in many positions of the RGD loop has only minor effects on RHO binding to integrin αIIbβ3, the specific position of Pro53 residue adjacent to the RGD sequence is important for RHO binding to platelet integrin αIIbβ3.
Roles of triosephosphate isomerase and aerobic metabolism in Trypanosoma brucei
Authors: HELFERT Sandra , ESTÉVEZ Antonio M. , BAKKER Barbara , MICHELS Paul , CLAYTON Christine
Published: August 2015

Kinetoplastid protozoa compartmentalize the first seven enzymes of glycolysis and two enzymes of glycerol metabolism in a microbody, the glycosome. While in its mammalian host, Trypanosoma brucei depends entirely on glucose for ATP generation. Under aerobic conditions, most of the glucose is metabolized to pyruvate. Aerobic metabolism depends on the activities of glycosomal triosephosphate isomerase and a mitochondrial glycerophosphate oxidase, and on glycerophosphate ↔ dihydroxyacetone phosphate exchange across the glycosomal membrane. Using a combination of genetics and computer modelling, we show that triosephosphate isomerase is probably essential for bloodstream trypanosome survival, but not for the insect-dwelling procyclics, which preferentially use amino acids as an energy source. When the enzyme level decreased to about 15% of that of the wild-type, the growth rate was halved. Below this level, a lethal rise in dihydroxyacetone phosphate was predicted. Expression of cytosolic triosephosphate isomerase inhibited cell growth. Attempts to knockout the trypanosome alternative oxidase genes (which are needed for glycerophosphate oxidase activity) were unsuccessful, but when we lowered the level of the corresponding mRNA by expressing a homologous double-stranded RNA, oxygen consumption was reduced fourfold and the rate of trypanosome growth was halved.
Molecular cloning and characterization of chemokine-like factor 1 (CKLF1), a novel human cytokine with unique structure and potential chemotactic activity
Authors: HAN Wenling , LOU Yaxin , TANG Junmin , ZHANG Yingmei , CHEN Yingyu , LI Ying , GU Weifeng , HUANG Jiaqiang , GUI Liming , TANG Yan , LI Feng , SONG Quansheng , DI Chunhui , WANG Lu , SHI Qun , SUN Ronghua , XIA Donglan , RUI Min , TANG Jian , MA Dalong
Published: August 2015

Cytokines are small proteins that have an essential role in the immune and inflammatory responses. The repertoire of cytokines is becoming diverse and expanding. Here we report the identification and characterization of a novel cytokine designated as chemokine-like factor 1 (CKLF1). The full-length cDNA of CKLF1 is 530bp long and a single open reading frame encoding 99 amino acid residues. CKLF1 bears no significant similarity to any other known cytokine in its amino acid sequence. Expression of CKLF1 can be partly inhibited by interleukin 10 in PHA-stimulated U937 cells. Recombinant CKLF1 is a potent chemoattractant for neutrophils, monocytes and lymphocytes; moreover, it can stimulate the proliferation of murine skeletal muscle cells. These results suggest that CKLF1 might have important roles in inflammation and in the regeneration of skeletal muscle.
Active-site mutations impairing the catalytic function of the catalytic subunit of human protein phosphatase 2A permit baculovirus-mediated overexpression in insect cells
Authors: MYLES Timothy , SCHMIDT Karsten , EVANS David R. H. , CRON Peter , HEMMINGS Brian A.
Published: August 2015

Members of the phosphoprotein phosphatase (PPP) family of protein serine/threonine phosphatases, including protein phosphatase (PP)1, PP2A and PP2B, share invariant active-site residues that are critical for catalytic function [Zhuo, Clemens, Stone and Dixon (1994) J. Biol. Chem. 269, 26234–26238]. Mutation of the active-site residues Asp88 or His118 within the human PP2A catalytic subunit (PP2Ac)α impaired catalytic activity in vitro; the D88N and H118N substitutions caused a 9- and 23-fold reduction in specific activity respectively, when compared with wild-type recombinant PP2Ac, indicating an important role for these residues in catalysis. Consistent with this, the D88N and H118N substituted forms failed to provide PP2A function in vivo, because, unlike wild-type human PP2Acα, neither substituted for the endogenous PP2Ac enzyme of budding yeast. Relative to wild-type PP2Ac, the active-site mutants were dramatically overexpressed in High Five® insect cells using the baculovirus system. Milligram quantities of PP2Ac were purified from 1×109 High Five cells and the kinetic constants for dephosphorylation of the peptide RRA(pT)VA (single-letter amino-acid notation) by PP2Ac (Km = 337.5μM; kcat = 170s−1) and D88N (Km = 58.4μM; kcat = 2s−1) were determined. The results show that the substitution impairs catalysis severely without a significant effect on substrate binding, consistent with the PPP catalytic mechanism. Combination of the baculovirus and yeast systems provides a strategy whereby the structure–function of PP2Ac may be fully explored, a goal which has previously proven difficult, owing to the stringent auto-regulatory control of PP2Ac protein levels in vivo.
Glucose regulates protein catabolism in ras-transformed fibroblasts through a lysosomal-dependent proteolytic pathway
Authors: TOURNU Cécile , OBLED Alain , ROUX Marie-Paule , FERRARA Marc , OMURA Satoshi , BÉCHET Daniel M.
Published: August 2015

Transformed cells are exposed to heterogeneous microenvironments, including low d-glucose (Glc) concentrations inside tumours. The regulation of protein turnover is commonly impaired in many types of transformed cells, but the role of Glc in this regulation is unknown. In the present study we demonstrate that Glc controls protein turnover in ras-transformed fibroblasts (KBALB). The regulation by Glc of protein breakdown was correlated with modifications in the levels of lysosomal cathepsins B, L and D, while autophagic sequestration and non-lysosomal proteolytic systems (m- and μ-calpains and the zeta-subunit of the proteasome) remained unaffected. Lactacystin, a selective inhibitor of the proteasome, depressed proteolysis, but did not prevent its regulation by Glc. The sole inhibition of the cysteine endopeptidases (cathepsins B and L, and calpains) by E-64d [(2S,3S)-trans-epoxysuccinyl-l-leucylamido-3-methylbutane ethyl ester] was also not sufficient to alter the effect of Glc on proteolysis. The Glc-dependent increase in proteolysis was, however, prevented after optimal inhibition of lysosomal cysteine and aspartic endopeptidases by methylamine. We conclude that, in transformed cells, Glc plays a critical role in the regulation of protein turnover and that the lysosomal proteolytic capacity is mainly responsible for the control of intracellular proteolysis by Glc.
Neuroendocrine secretory protein 7B2: structure, expression and functions
Authors: MBIKAY Majambu , SEIDAH Nabil G. , CHRÉTIEN Michel
Published: August 2015

7B2 is an acidic protein residing in the secretory granules of neuroendocrine cells. Its sequence has been elucidated in many phyla and species. It shows high similarity among mammals. A Pro-Pro-Asn-Pro-Cys-Pro polyproline motif is its most conserved feature, being carried by both vertebrate and invertebrate sequences. It is biosynthesized as a precursor protein that is cleaved into an N-terminal fragment and a C-terminal peptide. In neuroendocrine cells, 7B2 functions as a specific chaperone for the proprotein convertase (PC) 2. Through the sequence around its Pro-Pro-Asn-Pro-Cys-Pro motif, it binds to an inactive proPC2 and facilitates its transport from the endoplasmic reticulum to later compartments of the secretory pathway where the zymogen is proteolytically matured and activated. Its C-terminal peptide can inhibit PC2 in vitro and may contribute to keep the enzyme transiently inactive in vivo. The PC2–7B2 model defines a new neuroendocrine paradigm whereby proteolytic activation of prohormones and proneuropeptides in the secretory pathway is spatially and temporally regulated by the dynamics of interactions between converting enzymes and their binding proteins. Interestingly, unlike PC2-null mice, which are viable, 7B2-null mutants die early in life from Cushing's disease due to corticotropin (‘ACTH’) hypersecretion by the neurointermediate lobe, suggesting a possible involvement of 7B2 in secretory granule formation and in secretion regulation. The mechanism of this regulation is yet to be elucidated. 7B2has been shown to be a good marker of several neuroendocrine cell dysfunctions in humans. The possibility that anomalies in its structure and expression could be aetiological causes of some of these dysfunctions warrants investigation.
Variation in aspects of cysteine proteinase catalytic mechanism deduced by spectroscopic observation of dithioester intermediates, kinetic analysis and molecular dynamics simulations
Authors: REID James D. , HUSSAIN Syeed , SREEDHARAN Suneal K. , BAILEY Tamara S. F. , PINITGLANG Surapong , THOMAS Emrys W. , VERMA Chandra S. , BROCKLEHURST Keith
Published: August 2015

The possibility of a slow post-acylation conformational change during catalysis by cysteine proteinases was investigated by using a new chromogenic substrate, N-acetyl-Phe-Gly methyl thionoester, four natural variants (papain, caricain, actinidin and ficin), and stopped-flow spectral analysis to monitor the pre-steady state formation of the dithioacylenzyme intermediates and their steady state hydrolysis. The predicted reversibility of acylation was demonstrated kinetically for actinidin and ficin, but not for papain or caricain. This difference between actinidin and papain was investigated by modelling using QUANTA and CHARMM. The weaker binding of hydrophobic substrates, including the new thionoester, by actinidin than by papain may not be due to the well-known difference in their S2-subsites, whereby that of actinidin in the free enzyme is shorter due to the presence of Met211. Molecular dynamics simulation suggests that during substrate binding the sidechain of Met211 moves to allow full access of a Phe sidechain to the S2-subsite. The highly anionic surface of actinidin may contribute to the specificity difference between papain and actinidin. During subsequent molecular dynamics simulations the P1 product, methanol, diffuses rapidly (over < 8ps) out of papain and caricain but ‘lingers’ around the active centre of actinidin. Uniquely in actinidin, an Asp142–Lys145 salt bridge allows formation of a cavity which appears to constrain diffusion of the methanol away from the catalytic site. The cavity then undergoes large scale movements (over 4.8 Å) in a highly correlated manner, thus controlling the motions of the methanol molecule. The changes in this cavity that release the methanol might be those deduced kinetically.
Phosphorylation of human plasma α2-Heremans–Schmid glycoprotein (human fetuin) in vivo
Authors: HAGLUND Åsa C. , EK Bo , EK Pia
Published: August 2015

A fraction of α2-Heremans–Schmid (α2-HS) glycoprotein (human fetuin) isolated from plasma was phosphorylated at serine-120 and serine-312 as shown by MS and peptide fragment sequencing after tryptic digestion. Serine-312-containing peptides were phosphorylated to 77% as determined from relative peak heights in the mass spectrum, which together with the phosphorylation of serine-120 implies a molar degree of phosphorylation of at least 1. Approximately 20% of the circulating fetuin plasma pool was phosphorylated to approx. 1mol of phosphate/mol of protein. The remainder did not contain phosphate, resulting in an average phosphorylation degree for the protein in plasma of approx. 0.2 mol/mol. The isolated α2-HS glycoprotein was a heterodimer in which the entire C-terminal part of the connecting peptide including threonine-321 was present, but traces of C-terminally trimmed connecting peptide fragments were also found. The short B-chain was O-glycosylated to approx. 40%, whereas the N-glycosylation of asparagine-138 and asparagine-158 seemed to be 100%. This finding, for the first time, that circulating human plasma fetuin is partly phosphorylated, implies that the effects of phosphorylated α2-HS glycoprotein on insulin signal transduction seen in different cell systems could be relevant to its physiological function in vivo.
Protein-binding elements in the proximal parotid secretory protein gene enhancer essential for salivary-gland-specific expression
Authors: SVENDSEN Pia , KRISTIANSEN Karsten , HJORTH J. Peter
Published: August 2015

The murine parotid secretory protein (PSP) gene is expressed at high levels in the parotid gland and at lower levels in the sublingual gland. A proximal enhancer core necessary for tissue-specific expression was identified previously, and it was demonstrated that one element, parotid gland element I (PGE I), exhibited specific binding of parotid gland nuclear proteins. In the present study, we demonstrate that a related adjacent element, PGE II, which binds nuclear proteins in a much less tissue-restricted manner, is able to compete with PGE I for binding of parotid-gland-specific factors. The functional significance of PGE I and PGE II was examined in transgenic mice. Deletion of PGE II reduced transgene expression only in the parotid gland, whereas deletion of PGE I appeared to reduce expression in both of the PSP-expressing salivary glands. Combined deletion of PGE I and PGE II reduced expression below the limit of detection. Thus PGE I and PGE II are functionally important salivary-gland-specific binding elements that are necessary for the salivary-gland-specific expression of a PSP minigene in transgenic mice.
Autocatalytic tyrosine-phosphorylation of protein kinase CK2 α and α′ subunits: implication of Tyr182
Authors: DONELLA-DEANA Arianna , CESARO Luca , SARNO Stefania , BRUNATI Anna Maria , RUZZENE Maria , PINNA Lorenzo A.
Published: August 2015

CK2 is a pleiotropic and constitutively active serine/threonine protein kinase composed of two catalytic (α and/or α′) and two regulatory β-subunits, whose mechanism of modulation is still obscure. Here we show that CK2 α/α′ subunits undergo intermolecular (trans) tyrosine-autophosphorylation, which is dependent on intrinsic catalytic activity and is suppressed by the individual mutation of Tyr182, a crucial residue of the activation loop, to phenylalanine. At variance with serine-autophosphorylation, tyrosine-autophosphorylation of CK2α is reversed by ADP and GDP and is counteracted by the β-subunit and by a peptide reproducing the activation loop of CK2α/α′ (amino acids 175–201). These results disclose new perspectives about the mode of regulation of CK2 catalytic subunits.
Identification of PEX5p-related novel peroxisome-targeting signal 1 (PTS1)-binding proteins in mammals
Authors: AMERY Leen , SANO Hideki , MANNAERTS Guy P. , SNIDER Jamie , van LOOY Jeroen , FRANSEN Marc , van VELDHOVEN Paul P.
Published: August 2015

Based on peroxin protein 5 (Pex5p) homology searches in the expressed sequence tag database and sequencing of large full-length cDNA inserts, three novel and related human cDNAs were identified. The brain-derived cDNAs coded for two related proteins that differ only slightly at their N-terminus, and exhibit 39.8% identity to human PEX5p. The shorter liver-derived cDNA coded for the C-terminal tetratricopeptide repeat-containing domain of the brain cDNA-encoded proteins. Since these three proteins specifically bind to various C-terminal peroxisome-targeting signals in a manner indistinguishable from Pex5p and effectively compete with Pex5p in an in vitro peroxisome-targeting signal 1 (PTS1)-binding assay, we refer to them as ‘Pex5p-related proteins’ (Pex5Rp). In contrast to Pex5p, however, human PEX5Rp did not bind to Pex14p or to the RING finger motif of Pex12p, and could not restore PTS1 protein import in Pex5−/− mouse fibroblasts. Immunofluorescence analysis of epitope-tagged PEX5Rp in Chinese hamster ovary cells suggested an exclusively cytosolic localization. Northern-blot analysis showed that the PEX5R gene, which is localized to chromosome 3q26.2–3q27, is expressed preferentially in brain. Mouse PEX5Rp was also delineated. In addition, experimental evidence established that the closest-related yeast homologue, YMR018wp, did not bind PTS1. Based on its subcellular localization and binding properties, Pex5Rp may function as a regulator in an early step of the PTS1 protein import process.
Folding of βpep-4 β-sheet sandwich dimers and tetramers is influenced by aliphatic hydrophobic residues at the intersubunit interface
Authors: COX Andrew , ARROYO Monica M. , MAYO Kevin H.
Published: August 2015

For the designed peptide 33mer, βpep-4, formation of β-sheet structure [Ilyina, Roongta and Mayo (1997) Biochemistry 36, 5245–5250] is thermodynamically linked to self-association. Dimers and tetramers are stabilized by interactions between hydrophobic residues lying on the hydrophobic faces of the amphipathic monomer subunits. The present study investigates the effects on folding and self-association of the substitution of two key hydrophobic residues (Ile20 and Val22) at the β-sheet sandwich interface of βpep-4. Single-site (I20L, I20V, I20A, V22L, V22I and V22A; where I20L corresponds to the substitution of Ile20 with leucine etc.) and double-site (I20L/V22L and I20V/V22I) variants have been investigated. Like parent βpep-4, all variants can form dimers and tetramers. NOESY data indicate that the overall β-sheet fold and intersubunit β-strand alignments are the same in all variant tetramers. CD data for all variants indicate mostly β-sheet character in dimers and random coil character in monomers. Only for the V22I variant is the β-sheet fold stabilized in the monomer state. Pulse-field gradient NMR-derived diffusion coefficients, measured as a function of peptide concentration, provide a means for deriving the distribution of monomer, dimer and tetramer states and, therefore, equilibrium association constants. Relative thermodynamic stabilities, which vary no more than approx. 0.5kcal/mol (where 1kcal≡4.184kJ) from peptide to peptide, are I20V/V22I>I20V>I20L/V22L = βpep-4 (ΔGD of 7.5kcal/mol) = I20L = I20A>V22I>V22L>V22A for dimer formation and I20V>I20L/V22L>I20L>βpep-4 (ΔGT of 6kcal/mol)>V22I>I20V/V22I>V22L>I20A>V22A for tetramer formation. For the most part, dimer and/or tetramer stabilities are enhanced by the presence of valine and leucine and are attenuated by the presence of isoleucine and alanine.
Effect of angiotensin II and ethanol on the expression of connexin 43 in WB rat liver epithelial cells
Authors: BOKKALA Shaila , REIS Helena M. , RUBIN Emanuel , JOSEPH Suresh K.
Published: August 2015

The turnover of connexin 43 (Cx43) is very rapid in many cells and involves both the lysosomal and proteasomal protease pathways. Here we show that Ca2+-mobilizing agonists such as angiotensin II (Ang II) can up-regulate the expression of Cx43 in WB rat liver epithelial cells. Vasopressin had the same effect in A7R5 smooth-muscle cells. The effect of Ang II was not prevented by pretreatment with proteasomal or lysosomal inhibitors and was associated with an enhanced biosynthesis of Cx43 as measured by metabolic labelling experiments. The accumulation of Cx43 occurred in intracellular compartments and at the cell surface, as determined by confocal immunofluorescence studies and by immunoblotting of fractions soluble and insoluble in Triton X-100. Chronic treatment of WB cells with ethanol inhibited Cx43 expression; this was associated with decreased biosynthesis of Cx43. Neither treatment with Ang II nor treatment with ethanol altered the levels of Cx43 mRNA. Incubation of WB cells with Ang II did not alter gap-junctional communication as judged by a dye-coupling assay. However, treatment with ethanol markedly decreased gap-junctional communication and this effect was diminished in Ang-II-treated cells, demonstrating that gap-junctional communication is linked to the level of Cx43 expression. We conclude that Cx43 biosynthesis is regulated by Ca2+-mobilizing agonists and ethanol in WB cells. The changes in Cx43 expression might have a role in modifying the conduction of metabolites and second messengers between cells.
Continuous affinity-based selection: rapid screening and simultaneous amplification of bacterial surface-display libraries
Authors: PATEL Dipak , VITOVSKI Srdjan , SENIOR H. Jennifer , EDGE Michael D. , HOCKNEY Robert C. , DEMPSEY Michael J. , SAYERS Jon R.
Published: August 2015

A new method for continuous biopanning has been developed. We have combined the power of affinity chromatography with the fecundity of bacteria in a unique process that mimics clonal selection. Mixed populations of bacteria were applied to a fermenter containing the immobilized ligand of interest. Bacteria retained in this affinity fermenter were allowed to grow under continuous washout conditions, such that weakly bound organisms were selectively lost. Those initially rare founder bacteria expressing a receptor for the immobilized ligand (R+ve) were thus enriched and amplified simultaneously. From an initial culture containing 1×1010 R-ve cells spiked with fewer than 30 R+ve bacteria (< 1 in 108), final ratios of R+ve/R-ve bacteria as high as 1 in 12 were observed, representing an enrichment factor of 55 million-fold. This technology has considerable potential for rapid screening of bacterial surface-display libraries and in facilitating directed-evolution studies.
Constitutive shedding of the amyloid precursor protein ectodomain is up-regulated by tumour necrosis factor-α converting enzyme
Authors: SLACK Barbara E. , MA Leona K. , SEAH Ching Ching
Published: August 2015

The amyloid precursor protein (APP) of Alzheimer's disease is a transmembrane protein that is cleaved within its extracellular domain, liberating a soluble N-terminal fragment (sAPPα). Putative mediators of this process include three members of the ADAM (a disintegrin and metalloprotease) family, ADAM9, ADAM10 and ADAM17/TACE (tumour necrosis factor-α converting enzyme). Tumour necrosis factor-α protease inhibitor (TAPI-1), an inhibitor of ADAMs, reduced constitutive and muscarinic receptor-stimulated sAPPα release in HEK-293 cells stably expressing M3 muscarinic receptors. However, the former was less sensitive to TAPI-1 (IC50 = 8.09μM) than the latter (IC50 = 3.61μM), suggesting that these processes may be mediated by different metalloproteases. Constitutive sAPPα release was increased several-fold in cells transiently transfected with TACE, and this increase was proportional to TACE expression. In contrast, muscarinic-receptor-activated sAPPα release was not altered in TACE transfectants. TACE-dependent constitutive release of co-transfected APP695 was inhibited by TAPI-1 with an IC50 of 0.92μM, a value significantly lower than the IC50s for inhibition of either constitutive or receptor-regulated sAPPα shedding mediated by endogenous secretases. The results indicate that TACE is capable of catalysing constitutive α-secretory cleavage of APP, but it is likely that additional members of the ADAM family mediate endogenous constitutive and receptor-coupled release of sAPPα in HEK-293cells.
Effect of chemical modification of recombinant human acetylcholinesterase by polyethylene glycol on its circulatory longevity
Authors: COHEN Ofer , KRONMAN Chanoch , CHITLARU Theodor , ORDENTLICH Arie , VELAN Baruch , SHAFFERMAN Avigdor
Published: August 2015

Post-translational modifications were recently shown to be responsible for the short circulatory mean residence time (MRT) of recombinant human acetylcholinesterase (rHuAChE) [Kronman, Velan, Marcus, Ordentlich, Reuveny and Shafferman (1995) Biochem. J. 311, 959–967; Chitlaru, Kronman, Zeevi, Kam, Harel, Ordentlich, Velan and Shafferman (1998) Biochem. J. 336, 647–658; Chitlaru, Kronman, Velan and Shafferman (2001) Biochem. J. 354, 613–625], which is one of the major obstacles to the fulfilment of its therapeutic potential as a bioscavenger. In the present study we demonstrate that the MRT of rHuAChE can be significantly increased by the controlled attachment of polyethylene glycol (PEG) side chains to lysine residues. Attachment of as many as four PEG molecules to monomeric rHuAChE had minimal effects, if any, on either the catalytic activity (Km = 0.09mM and kcat = 3.9×105min−1) or the reactivity of the modified enzyme towards active-centre inhibitors, such as edrophonium and di-isopropyl fluorophosphate, or to peripheral-site ligands, such as propidium, BW284C51 and even the bulky snake-venom toxin fasciculin-II. The increase in MRT of the PEG-modified monomeric enzyme is linearly dependent, in the tested range, on the number of attached PEG molecules, as well as on their size. It appears that even low level PEG-conjugation can overcome the deleterious effect of under-sialylation on the pharmacokinetic performance of rHuAChE. At the highest tested ratio of attached PEG-20000/rHuAChE (4:1), an MRT of over 2100min was attained, a value unmatched by any other known form of recombinant or native serum-derived AChE reported to date.
Localization, purification and specificity of the full-length membrane-bound form of human recombinant α1,3/4-fucosyltransferase from BHK-21B cells
Authors: SOUSA Vítor L. , COSTA Maria Teresa , PALMA Angelina S. , ENGUITA Francisco , COSTA Júlia
Published: August 2015

Fucosyltransferase III [galactoside 3(4)-l-fucosyltransferase; EC 2.4.1.65] (FT3) is a Golgi type II membrane protein that catalyses the synthesis of fucosylated Lewis motifs that are associated with cell-adhesion events and are differentially expressed during cell differentiation. In the present work, the full-length membrane bound form of FT3 has been expressed in baby hamster kidney cells. The enzyme has been found in the trans-Golgi and trans-Golgi network (TGN) of the transfected cells, where it appeared as monomers and dimers, but not as oligomers with high molecular masses. Therefore oligomerization is not the basis for correct localization of FT3 in the Golgi. The enzyme has been purified, with a final yield of 2% and a total purification of 2900-fold, by DEAE-Sepharose, SP-Sepharose, GDP-Fractogel and Superdex 200 chromatography. The purified enzyme showed a clear preference for the Galβ3GlcNAc motif in oligosaccharides conjugated with the hydrophobic tail (CH2)3-NHCO-(CH2)5-NH-biotin. Substitution of galactose with α2-linked fucose or α2,3-linked N-acetylneuraminic acid yielded a 1.9-fold increase or a 43% decrease in activity respectively. The enzyme showed no activity towards asialofetuin, a glycoprotein containing the Galβ3GlcNAc acceptor motif. Therefore it has been concluded that the membrane-bound form of FT3 is present in the Golgi and the TGN in an equilibrium of monomers ↔ dimers, which might fucosylate glycans from glycolipids, but not from glycoproteins.
Phorbol ester-induced activation of mitogen-activated protein kinase/extracellular-signal-regulated kinase kinase and extracellular-signal-regulated protein kinase decreases glucose-6-phosphatase gene expression
Authors: SCHMOLL Dieter , GREMPLER Rolf , BARTHEL Andreas , JOOST Hans-Georg , WALTHER Reinhard
Published: August 2015

Glucose-6-phosphatase (G6Pase) plays a central role in blood glucose homoeostasis, and insulin suppresses G6Pase gene expression by the activation of phosphoinositide 3-kinase (PI 3-kinase). Here, we show that the phorbol ester PMA decreases both basal and dexamethasone/cAMP-induced expression of a luciferase gene under the control of the G6Pase promoter in transiently transfected H4IIE hepatoma cells. This regulation was suppressed by the inhibitors of the mitogen-activated protein kinase/extracellular-signal-regulated kinase kinase (MEK), PD98059 and U0126, but not by the inhibitor of PI 3-kinase, LY294002. The co-expression of a constitutively active mutant of MEK mimicked the regulation of G6Pase promoter activity by PMA. The effect of PMA on both basal and induced G6Pase gene transcription was impaired by the overexpression of a dominant negative MEK construct, as well as by the expression of mitogen-activated protein kinase phosphatase-1. The mutation of the forkhead-binding sites within the insulin-response unit of the G6Pase promoter, which decreases the effect of insulin on G6Pase gene expression, did not alter the regulation of gene expression by PMA. The data show that PMA decreases G6Pase gene expression by the activation of MEK and extracellular-signal regulated protein kinase. With that, PMA mimics the effect of insulin on G6Pase gene expression by a different signalling pathway.
Cartilage oligomeric matrix protein (COMP) and collagen IX are sensitive markers for the differentiation state of articular primary chondrocytes
Authors: ZAUCKE Frank , DINSER Robert , MAURER Patrik , PAULSSON Mats
Published: August 2015

Primary chondrocytes dedifferentiate in serial monolayer with respect to their morphological and biosynthetic phenotype. They change from a round to a flattened fibroblast-like shape, and collagen I is secreted instead of the cartilage-specific collagen II. We analysed in detail the time course of dedifferentiation of mature bovine articular chondrocytes in monolayer for up to 32 weeks. Assessment of RNA expression by reverse transcription-PCR led to the identification of two novel phenotypical markers, the cartilage oligomeric matrix protein (COMP) and collagen IX, which are down-regulated faster than the widely accepted marker, collagen II. The different kinetics of COMP and collagen expression suggest differential regulation at the level of transcription. Immunostaining and metabolic labelling experiments confirmed the switch in the collagen expression pattern and the rapid down-regulation of de novo synthesis of COMP and collagen IX. Culture of chondrocytes in a three-dimensional matrix is known to stabilize the chondrocytic phenotype. We maintained cells for up to 28 weeks in an alginate bead system, which prevented dedifferentiation and led to a stabilization of collagen and COMP expression. Immunohistochemical analysis of the alginate beads revealed a similar distribution of matrix proteins to that found in vivo. Chondrocytes were transferred after a variable length of monolayer culture into the alginate matrix and the potential for redifferentiation was investigated. The re-expression of COMP and collagen IX was differentially regulated. The expression of COMP was re-induced within days after transfer into the three-dimensional matrix, while the expression of collagen IX was irreversibly down-regulated. In summary, these results demonstrate that the potential for redifferentiation decreases with increasing length of monolayer culture and show that the alginate bead system represents an attractive in vitro model to study the chondrocyte de- and re-differentiation processes, as well as extracellular matrix assembly.
Targeted overexpression of ornithine decarboxylase enhances β-adrenergic agonist-induced cardiac hypertrophy
Authors: SHANTZ Lisa M. , FEITH David J. , PEGG Anthony E.
Published: August 2015

These studies were designed to determine the consequences of constitutive overexpression of ornithine decarboxylase (ODC) in the heart. Induction of ODC is known to occur in response to agents that induce cardiac hypertrophy. However, it is not known whether high ODC levels are sufficient for the development of a hypertrophic phenotype. Transgenic mice were generated with cardiac-specific expression of a stable ODC protein using the α-myosin heavy-chain promoter. Founder lines with > 1000-fold overexpression of ODC in the heart were established, resulting in a 50-fold overaccumulation of putrescine, 4-fold elevation in spermidine, a slight increase in spermine and accumulation of large amounts of cadaverine compared with littermate controls. Despite these significant alterations in polyamines, myocardial hypertrophy, as measured by ratio of heart to body weight, did not develop, although atrial natriuretic factor RNA was slightly elevated in transgenic ventricles. However, stimulation of β-adrenergic signalling by isoproterenol resulted in severe hypertrophy and even death in ODC-overexpressing mice without further altering polyamine levels, compared with only a mild hypertrophy in littermates. When β1-adrenergic stimulation was blocked by simultaneous treatment with isoproterenol and the β1 antagonist atenolol, a significant, although reduced, hypertrophy was still present in the hearts of transgenic mice, suggesting that both β1 and β2 adrenergic receptors contribute to the hypertrophic phenotype. Therefore these mice provide a model to study the in vivo co-operativity between high ODC activity and activation of other pathways leading to hypertrophy in the heart.
Overexpression of matrix metalloproteinase-2 mediates phenotypic transformation of lens epithelial cells
Authors: SEOMUN Young , KIM Jeong-a , LEE Eunjoo H. , JOO Choun-Ki
Published: August 2015

Transforming growth factor-β (TGF-β) is known to be a causative factor in pathological fibrosis and the metastasis of cancer cells, through effects on molecules of the extracellular matrix (ECM). We evaluated the influence of TGF-β1 on the gene expression of matrix metalloproteinase-2 (MMP-2) in lens epithelial cells (LECs). The results showed that TGF-β1 induced the expression of mRNA for MMP-2 in LECs. Subsequently, in order to examine the role of MMP-2, we overexpressed MMP-2 in LECs by stable transfection. The MMP-2-overexpressing LECs showed typical indicators of a myofibroblast-like cell phenotype, such as multiple layers of cells, elongated morphology, and expression of α-smooth muscle actin. We also showed that an MMP inhibitor blocked the TGF-β1-induced morphological change in LECs. These results demonstrate that MMP-2 plays a role in the transformation of LECs, which has implications for the pathological fibrosis of these cells.
Regulation of pyruvate dehydrogenase activity through phosphorylation at multiple sites
Authors: KOLOBOVA Elena , TUGANOVA Alina , BOULATNIKOV Igor , POPOV Kirill M.
Published: August 2015

The enzymic activity of the mammalian pyruvate dehydrogenase complex is regulated by the phosphorylation of three serine residues (sites 1, 2 and 3) located on the E1 component of the complex. Here we report that the four isoenzymes of protein kinase responsible for the phosphorylation and inactivation of pyruvate dehydrogenase (PDK1, PDK2, PDK3 and PDK4) differ in their abilities to phosphorylate the enzyme. PDK1 can phosphorylate all three sites, whereas PDK2, PDK3 and PDK4 each phosphorylate only site 1 and site 2. Although PDK2 phosphorylates site 1 and 2, it incorporates less phosphate in site 2 than PDK3 or PDK4. As a result, the amount of phosphate incorporated by each isoenzyme decreases in the order PDK1>PDK3PDK4>PDK2. Significantly, binding of the coenzyme thiamin pyrophosphate to pyruvate dehydrogenase alters the rates and stoichiometries of phosphorylation of the individual sites. First, the rate of phosphorylation of site 1 by all isoenzymes of kinase is decreased. Secondly, thiamin pyrophosphate markedly decreases the amount of phosphate that PDK1 incorporates in sites 2 and 3 and that PDK2 incorporates in site 2. In contrast, the coenzyme does not significantly affect the total amount of phosphate incorporated in site 2 by PDK3 and PDK4, but instead decreases the rate of phosphorylation of this site. Furthermore, pyruvate dehydrogenase complex phosphorylated by the individual isoenzymes of kinase is reactivated at different rates by pyruvate dehydrogenase phosphatase. Both isoenzymes of phosphatase (PDP1 and PDP2) readily reactivate the complex phosphorylated by PDK2. When pyruvate dehydrogenase is phosphorylated by other isoenzymes, the rates of reactivation decrease in the order PDK4PDK3> PDK1. Taken together, results reported here strongly suggest that the major determinants of the activity state of pyruvate dehydrogenase in mammalian tissues include the phosphorylation site specificity of isoenzymes of kinase in addition to the absolute amounts of kinase and phosphatase protein expressed in mitochondria.
Apolipoprotein A-I stimulates the transport of intracellular cholesterol to cell-surface cholesterol-rich domains (caveolae)
Authors: SVIRIDOV Dmitri , FIDGE Noel , BEAUMIER-GALLON Gabrielle , FIELDING Christopher
Published: August 2015

We have studied the effect of lipid-free human plasma apolipoprotein A-I (apoA-I) on the transport of newly synthesized cholesterol to cell-surface cholesterol-rich domains, which in human skin fibroblasts are mainly represented by caveolae. Changes in transport of newly synthesized cholesterol were assessed after labelling cells with [14C]acetate at 15°C and warming cells to permit the transfer of cholesterol, followed by the selective oxidation of cholesterol in cholesterol-rich domains (caveolae) in the plasma membrane before their partial purification. ApoA-I, but not BSA added in an equimolar concentration, enhanced the transport of cholesterol to the caveolae up to 5-fold in a dose- and time-dependent manner. The effect of apoA-I on cholesterol transport exceeded its effect on cholesterol efflux, resulting in an accumulation of intracellular cholesterol in caveolae. Methyl-β-cyclodextrin, added at a concentration promoting cholesterol efflux to the same extent as apoA-I, also stimulated cholesterol trafficking, but was 3-fold less effective than apoA-I. Progesterone inhibited the transport of newly synthesized cholesterol to the caveolae. Treatment of cells with apoA-I stimulated the expression of caveolin, increasing the amount of caveolin protein and mRNA by approx. 2-fold. We conclude that apoA-I induces the transport of intracellular cholesterol to cell-surface caveolae, possibly in part through the stimulation of caveolin expression.
Spot 14 protein interacts and co-operates with chicken ovalbumin upstream promoter-transcription factor 1 in the transcription of the L-type pyruvate kinase gene through a specificity protein 1 (Sp1) binding site
Authors: COMPE Emmanuel , de SOUSA Georges , FRANCÇOIS Kamel , ROCHE Régis , RAHMANI Roger , TORRESANI Janine , RAYMONDJEAN Michel , PLANELLS Richard
Published: August 2015

In hepatocytes, the amount of the Spot 14 (S14) protein is closely related to the full expression of enzymes involved in the glycolytic and lipogenic pathways. In the present study we address the role played by this protein in the control of transcription of the L-type pyruvate kinase (L-PK) gene in primary hepatocytes. We show that human S14, which by itself does not bind to the L-PK promoter, physically interacts with the human chicken ovalbumin upstream promoter-transcription factor 1 (COUP-TF1) and induces the switch of this factor from a repressor to an activator. However, the enhancing activity of S14 and COUP-TF1 depends on the presence of a proximal GC-rich box (the L0 element) that specifically binds nuclear proteins from the livers of rats fed a glucose-rich diet. Moreover, the L0 element, which strongly binds dephosphorylated specificity protein 1 (Sp1), loses all affinity when this factor is phosphorylated by cAMP-dependent protein kinase. Mutations that affect binding of Sp1 and nuclear proteins to the L0 box also decrease basal transcription and impair glucose responsiveness of the promoter. These results therefore shed light on the mechanism by which the S14 protein, whose concentration rapidly rises after glucose intake, contributes to the full activity of the L-PK promoter.
Crystal structure of the phosphatidylinositol 3,4-bisphosphate-binding pleckstrin homology (PH) domain of tandem PH-domain-containing protein 1 (TAPP1): molecular basis of lipid specificity
Authors: THOMAS Christine C. , DOWLER Simon , DEAK Maria , ALESSI Dario R. , van AALTEN Daan M.F.
Published: August 2015

Phosphatidylinositol 3,4,5-trisphosphate [PtdIns(3,4,5)P3] and its immediate breakdown product PtdIns(3,4)P2 function as second messengers in growth factor- and insulin-induced signalling pathways. One of the ways that these 3-phosphoinositides are known to regulate downstream signalling events is by attracting proteins that possess specific PtdIns-binding pleckstrin homology (PH) domains to the plasma membrane. Many of these proteins, such as protein kinase B, phosphoinositide-dependent kinase 1 and the dual adaptor for phosphotyrosine and 3-phosphoinositides (DAPP1) interact with both PtdIns(3,4,5)P3 and PtdIns(3,4)P2 with similar affinity. Recently, a new PH-domain-containing protein, termed tandem PH-domain-containing protein (TAPP) 1, was described which is the first protein reported to bind PtdIns(3,4)P2 specifically. Here we describe the crystal structure of the PtdIns(3,4)P2-binding PH domain of TAPP1 at 1.4 Å (1 Å = 0.1 nm) resolution in complex with an ordered citrate molecule. The structure is similar to the known structure of the PH domain of DAPP1 around the D-3 and D-4 inositol-phosphate-binding sites. However, a glycine residue adjacent to the D-5 inositol-phosphate-binding site in DAPP1 is substituted for a larger alanine residue in TAPP1, which also induces a conformational change in the neighbouring residues. We show that mutation of this glycine to alanine in DAPP1 converts DAPP1 into a TAPP1-like PH domain that only interacts with PtdIns(3,4)P2, whereas the alanine to glycine mutation in TAPP1 permits the TAPP1 PH domain to interact with PtdIns(3,4,5)P3.
Adenine nucleotide translocator isoforms 1 and 2 are differently distributed in the mitochondrial inner membrane and have distinct affinities to cyclophilin D
Authors: VYSSOKIKH Mikhail Yu , KATZ Annette , RUECK Alexander , WUENSCH Christine , DÖRNER Andrea , ZOROV Dmitry B. , BRDICZKA Dieter
Published: August 2015

Different isoforms of the adenine nucleotide translocase (ANT) are expressed in a tissue-specific manner. It was assumed that ANT-1 and ANT-2 co-exist in every single mitochondrion and might be differently distributed within the membrane structures that constitute the peripheral inner membrane or the crista membrane. To discriminate between ANT originating from peripheral or from cristal inner membranes we made use of the fact that complexes between porin, the outer-membrane pore protein, and the ANT can be generated. Such complexes between porin and the ANT in the peripheral inner membrane were induced in rat heart mitochondria and isolated from rat brain and kidney. Using ANT-isotype-specific antibodies and sequence analysis of the N-terminal end, it was discovered that the peripheral inner membrane contained ANT-1 and ANT-2, whereas the cristal membrane contained exclusively ANT-2. Cyclophilin was co-purified with the porin–ANT complexes, whereas it was absent in the crista-derived ANT. This suggested that ANT-1 might have a higher affinity for cyclophilin. This specific intra-mitochondrial distribution of the two ANT isotypes and cyclophilin D suggests specific functions of the peripheral and crista-forming parts of the inner membrane and the two ANT isotypes therein.
Evidence for a novel natriuretic peptide receptor that prefers brain natriuretic peptide over atrial natriuretic peptide
Authors: GOY Michael F. , OLIVER Paula M. , PURDY Kit E. , KNOWLES Joshua W. , FOX Jennifer E. , MOHLER Peter J. , QIAN Xun , SMITHIES Oliver , MAEDA Nobuyo
Published: August 2015

Atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) exert their physiological actions by binding to natriuretic peptide receptor A (NPRA), a receptor guanylate cyclase (rGC) that synthesizes cGMP in response to both ligands. The family of rGCs is rapidly expanding, and it is plausible that there might be additional, as yet undiscovered, rGCs whose function is to provide alternative signalling pathways for one or both of these peptides, particularly given the low affinity of NPRA for BNP. We have investigated this hypothesis, using a genetically modified (knockout) mouse in which the gene encoding NPRA has been disrupted. Enzyme assays and NPRA-specific Western blots performed on tissues from wild-type mice demonstrate that ANP-activated cGMP synthesis provides a good index of NPRA protein expression, which ranges from maximal in adrenal gland, lung, kidney, and testis to minimal in heart and colon. In contrast, immunoreactive NPRA is not detectable in tissues isolated from NPRA knockout animals and ANP- and BNP-stimulatable GC activities are markedly reduced in all mutant tissues. However, testis and adrenal gland retain statistically significant, high-affinity responses to BNP. This residual response to BNP cannot be accounted for by natriuretic peptide receptor B, or any other known mammalian rGC, suggesting the presence of a novel receptor in these tissues that prefers BNP over ANP.
Independent and synergistic interaction of retinal G-protein subunits with bovine rhodopsin measured by surface plasmon resonance
Authors: CLARK William A. , JIAN Xiaoying , CHEN Loren , NORTHUP John K.
Published: August 2015

We have used surface plasmon resonance (SPR) measurements for the kinetic analysis of G-protein-receptor interaction monitored in real time. Functionally active rhodopsin was immobilized on an SPR surface, with full retention of biochemical specific activity for catalysis of nucleotide exchange on the retinal G-protein α subunit, via binding to immobilized concanavalin A. The binding interactions of bovine retinal αt and β1γ1 subunits with rhodopsin measured by SPR were profoundly synergistic. Synergistic binding of the retinal G-protein subunits to rhodopsin was not observed for guanosine 5′-[γ-thio]triphosphate-bound Gαt, nor was binding observed with squid retinal Gαq, which is not activated by bovine rhodopsin. The binding affinity (336±171nM; mean value±S.D.) of retinal βγ for rhodopsin in the presence of retinal α subunit measured by SPR confirmed the apparent affinity of 254nM determined previously by nucleotide exchange assays. Binding of β1γ1, β1γ2, and β1γ8-olf dimers to rhodopsin, independently of the α subunit, was readily observable by SPR. Further, these dimers, differing only in their γ subunit compositions, displayed markedly distinct binding affinities and kinetics. The β1γ2 dimer bound with a kinetically determined Kd of 13±3nM, a value nearly identical with the biochemically determined K1/2 of 10nM. The physiologically appropriate β1γ1 displayed rapid association and dissociation kinetics, whereas the other β1γ dimers dissociated at a rate less than 1/100 as fast. Thus rhodopsin interaction with its native signalling partners is both rapid and transient, whereas the interaction of rhodopsin with heterologous Gβγ dimers is markedly prolonged. These results suggest that the duration of a G-protein-coupled receptor signalling event is an intrinsic property of the G-protein coupling partners; in particular, the βγ dimer.