Effect of distal sugar and interglycosidic linkage of disaccharides on the activity of proline rich antimicrobial glycopeptides

The effect of glycosylation on protein structure and function depends on a variety of intrinsic factors including glycan chain length. We have analyzed the effect of distal sugar and interglycosidic linkage of disaccharides on the properties of proline‐rich antimicrobial glycopeptides, formaecin I and drosocin. Their glycosylated analogs‐bearing lactose, maltose and cellobiose, as a glycan side chain on their conserved threonine residue, were synthesized where these disaccharides possess identical proximal sugar and vary in the nature of distal sugar and/or interglycosidic linkage. The structural and functional properties of these disaccharide‐containing formaecin I and drosocin analogs were compared with their corresponding monoglycosylated forms, β‐d ‐glucosyl‐formaecin I and β‐d ‐glucosyl‐drosocin, respectively. We observed neither major secondary structural alterations studied by circular dichroism nor substantial differences in the toxicity with mammalian cells among all of these analogs. The comparative analyses of antibacterial activities of these analogs of formaecin I and drosocin displayed that β‐d ‐maltosyl‐formaecin I and β‐d ‐maltosyl‐drosocin were more potent than that of respective β‐d ‐Glc‐analog, β‐d ‐cellobiosyl‐analog and β‐d ‐lactosyl‐analog. Despite the differences in their antibacterial activity, all the analogs exhibited comparable binding affinity to DnaK that has been reported as one of the targets for proline‐rich class of antibacterial peptides. The comparative–quantitative internalization studies of differentially active analogs revealed the differences in their uptake into bacterial cells. Our results exhibit that the sugar chain length as well as interglycosidic linkage of disaccharide may influence the antibacterial activity of glycosylated analogs of proline‐rich antimicrobial peptides and the magnitude of variation in antibacterial activity depends on the peptide sequence. Copyright © 2015 European Peptide Society and John Wiley & Sons, Ltd.     

Secreted expression of an active human interferon‐beta (HuIFNβ) in Kluyveromyces lactis

Interferon‐beta (IFNβ) is a cytokine involved in the antiviral, anti‐proliferative and immunomodulatory responses of cells, and a potent drug for multiple sclerosis. Human interferon beta (HuIFNβ) gene fused with the glucoamylase signal sequence in the N‐terminus and 6 His Tag in the C‐terminus was cloned into pKlac1 vector and introduced in Kluyveromyces lactis to allow secreted expression and one‐step purification of the protein. Recombinant yeast transformant with the highest level of HuIFNβ production was identified, and this secreted up to 1 mg/L of the cytokine after 72 h of incubation. Glycosylated and non‐glycosylated forms of the cytokine were elaborated by the yeast, the latter in higher quantities. His tag of the protein allowed easy one‐step purification by nickel‐nitriloacetic acid affinity chromatography, yielding close to 100% purity. SDS‐PAGE, western blot and MALDI‐TOF‐TOF confirmed the identity of the protein. The biological activity of the recombinant HuIFNβ was confirmed by its anti cell proliferative activity on HeLa cells. Expression of HuIFNβ in K. lactis is advantageous since it is a very safe organism to produce proteins for therapeutic applications, allows glycosylation and offers a cost effective method for large scale production as it can be grown in cheap carbon sources.     

Identification of Glycosylated Subtypes of Interferon-α Produced by Human Leukocytes

We found that interferon-α produced by human leukocytes contained four subtypes that were glycosylated by N-linkages according to the results of lectin blot analysis. These glycosylated subtypes were type H or type ω and thei sugar moieties had no relation to their biological activities.     

Synthesis,oxygen radical absorbance capacity,and tyrosinase inhibitory activity of glycosides of resveratrol,pterostilbene, and pinostilbene

The stilbene compound resveratrol was glycosylated to give its 4′-O-β-D-glucoside as the major product in addition to its 3-O-β-D-glucoside by a plant glucosyltransferase from Phytolacca americana expressed in recombinant Escherichia coli. This enzyme transformed pterostilbene to its 4′-O-β-D-glucoside, and converted pinostilbene to its 4′-O-β-D-glucoside as a major product and its 3-O-β-D-glucoside as a minor product. An analysis of antioxidant capacity showed that the above stilbene glycosides had lower oxygen radical absorbance capacity (ORAC) values than those of the corresponding stilbene aglycones. The 3-O-β-D-glucoside of resveratrol showed the highest ORAC value among the stilbene glycosides tested, and pinostilbene had the highest value among the stilbene compounds. The tyrosinase inhibitory activities of the stilbene aglycones were improved by glycosylation; the stilbene glycosides had higher activities than the stilbene aglycones. Resveratrol 3-O-β-D-glucoside had the highest tyrosinase inhibitory activity among the stilbene compounds tested.     

The Recombinant Amyloid-β Peptide Aβ1-42 Aggregates Faster and Is More Neurotoxic than Synthetic Aβ1-42

Aggregation of the amyloid-β (Aβ) peptide is considered a central event in the pathogenesis of Alzheimer's disease (AD). In order to bypass methodological bias related to a variety of impurities commonly present in typical preparations of synthetic Aβ, we developed a simple, generally applicable method for recombinant production of human Aβ and Aβ variants in Escherichia coli that provides milligram quantities of Aβ in very high purity and yield. Amyloid fibril formation in vitro by human Aβ1-42, the key amyloidogenic Aβ species in AD, was completed threefold faster with recombinant Aβ1-42 compared to synthetic preparations. In addition, recombinant Aβ1-42 was significantly more toxic to cultured rat primary cortical neurons, and it was more toxic in vivo, as shown by strongly increased induction of abnormal phosphorylation of tau and tau aggregation into neurofibrillary tangles in brains of P301L tau transgenic mice. We conclude that even small amounts of impurities in synthetic Aβ—including a significant fraction of racemized peptides that cannot be avoided due to the technical limitations of peptide synthesis—prevent or slow Aβ incorporation into the regular quaternary structure of growing β-amyloid fibrils. The results validate the use of recombinant Aβ1-42 for both in vitro and in vivo studies addressing the mechanisms underlying Aβ aggregation and its related biological consequences for the pathophysiology, therapy, and prevention of AD.     

Asn-linked sugar chain structures of recombinant human thrombopoietin produced in Chinese hamster ovary cells

Human thrombopoietin (TPO) that regulates the numbers of megakaryocytes and platelets is a heavily N- and O-glycosylated glycoprotein hormone with partial homology to human erythropoietin (EPO). We prepared recombinant human TPO produced in Chinese hamster ovary (CHO) cells and analyzed the sugar chain structures quantitatively using 2-aminobenzamide labeling, sequential glycosidase digestion and matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF/MS).We found bi-, tri- and tetraantennary complex-type sugar chains with one or two N-acetyllactosamine repeats, which are common to recombinant human EPO produced in CHO cells. On the other hand, there were triantennary sugar chains with one or two N-acetyllactosamine repeats that were specific to the recombinant human TPO, and their distributions of branch structures were also different. These results suggested that proximal protein structure should determine the branch structure of Asn-linked sugar chains in addition to the glycosyltransferases subset.     

Promoting α‐secretase cleavage of beta‐amyloid with engineered proteolytic antibody fragments

Deposition of beta‐amyloid (Aβ) is considered as an important early event in the pathogenesis of Alzheimer's Disease (AD), and reduction of Aβ levels by various therapeutic approaches is actively being pursued. A potentially non‐inflammatory approach to facilitate clearance and reduce toxicity is to hydrolyze Aβ at its α‐secretase site. We have previously identified a light chain fragment, mk18, with α‐secretase‐like catalytic activity, producing the 1–16 and 17–40 amino acid fragments of Aβ40 as primary products, although hydrolysis is also observed following other lysine and arginine residues. To improve the specific activity of the recombinant antibody by affinity maturation, we constructed a single chain variable fragment (scFv) library containing a randomized CDR3 heavy chain region. A biotinylated covalently reactive analog mimicking α‐secretase site cleavage was synthesized, immobilized on streptavidin beads, and used to select yeast surface expressed scFvs with increased specificity for Aβ. After two rounds of selection against the analog, yeast cells were individually screened for proteolytic activity towards an internally quenched fluorogenic substrate that contains the α‐secretase site of Aβ. From 750 clones screened, the two clones with the highest increase in proteolytic activity compared to the parent mk18 were selected for further study. Kinetic analyses using purified soluble scFvs showed a 3‐ and 6‐fold increase in catalytic activity (k_cat/K_M) toward the synthetic Aβ substrate compared to the original scFv primarily due to an expected decrease in K_M rather than an increase in k_cat. This affinity maturation strategy can be used to select for scFvs with increased catalytic specificity for Aβ. These proteolytic scFvs have potential therapeutic applications for AD by decreasing soluble Aβ levels in vivo. © 2009 American Institute of Chemical Engineers. Biotechnol. Prog., 2009     

人TANK结合激酶1的基因克隆、表达及生物活性鉴定

目的:克隆人TANK结合激酶1(TBK1)基因,构建其真核表达载体,检测该基因在293细胞中的表达,并利用萤光素酶报告基因实验检测其生物活性。方法:应用RT-PCR方法,以HeLa细胞RNA为模板,扩增获得TBK1基因,定向克隆到pcDNA3-Flag载体中,以LipofectAMINE2000转染试剂转染pcDNA-Flag-TBK1至293细胞中进行瞬时表达,并利用萤光素酶报告基因实验检测诱导β干扰素(IFN-β)转录的情况。结果:测序结果表明,从人HeLa细胞总RNA中克隆到正确的TBK1基因全长编码序列,利用Western印迹检测其在293细胞中获得有效表达,利用萤光素酶报告基因实验检测TBK1可以诱导IFN-β转录激活。结论:真核表达的人TBK1具有相应的生物学活性,为研究其功能奠定了基础。     

Upregulation of interferon-induced indoleamine 2,3-dioxygenase in human macrophage cultures by lipopolysaccharide, muramyl tripeptide, and interleukin-1

The tryptophan decyclizing enzyme indoleamine 2,3-dioxygenase (IDO) was induced in human monocyte-derived macrophages (MDM) treated with human recombinant interferon-β (IFN-β) or interferon-γ (IFN-γ). Treated cells exhibited dose-dependent increases in IDO when assayed 48 hr after treatment. Cells exposed to IFN-γ were observed to exhibit consistently higher peak levels of IDO when compared with cells incubated in the presence of IFN-β. When IFN-β-treated cells were incubated in the presence of specified amounts of bacterial lipopolysaccharide (LPS) or liposome-encapsulated muramyl tripeptide (MTP), peak IDO activity increased such that enzyme activity was comparable to maximal activity observed with IFN-γ-treated cells. LPS and MTP also upregulated IFN-γ-mediated IDO activity when suboptimal amounts of IFN-γ were used. When macrophages were costimulated with various concentrations of human recombinant interleukin 1α (IL-1α), along with either maximum-stimulating amounts of IFN-β or suboptimal amounts of IFN-γ, IDO activity was upregulated in a manner similar to results obtained using the microbial products as stimuli. While neither IL-1α or IL-1β was detected in culture supernatants from macrophages treated with either LPS or MTP (alone or in combination with IFN), IL-1α was detected in cell lysates of macrophages treated with these upregulators. Although neutralizing antibody to IL-1α abolished the upregulatory effect of exogenous IL-1α, it had no effect on upregulation by LPS or MTP. This suggests that although LPS and MTP may induce production of cell-associated IL-1α, upregulation of IDO activity by these agents is independent of IL-1α production and may be mediated through distinct pathways.     

Citrullination of TNF-α by peptidylarginine deiminases reduces its capacity to stimulate the production of inflammatory chemokines

Citrullination, a posttranslational modification (PTM) recently discovered on inflammatory chemokines such as interleukin-8 (IL-8/CXCL8) and interferon-γ-inducible protein-10 (IP-10/CXCL10), seriously influences their biological activity. Citrullination or the deimination of arginine to citrulline is dependent on peptidylarginine deiminases (PADs) and has been linked to autoimmune diseases such as multiple sclerosis (MS) and rheumatoid arthritis (RA). Chemokines are to date the first identified PAD substrates with receptor-mediated biological activity. We investigated whether cytokines that play a crucial role in RA, like interleukin-1β (IL-1β) and tumor necrosis factor-alpha (TNF-α), may be citrullinated by PAD and whether such a PTM influences the biological activity of these cytokines. IL-1β and TNF-α were first incubated with PAD in vitro and the occurrence of citrullination was examined by Edman degradation and a recently developed detection method for citrullinated proteins. Both techniques confirmed that human TNF-α, but not IL-1β, was citrullinated by PAD. Citrullination of TNF-α reduced its potency to stimulate chemokine production in vitro on human primary fibroblasts. Concentrations of the inflammatory chemokines CXCL8, CXCL10 and monocyte chemotactic protein-1 (MCP-1/CCL2) were significantly lower in supernatants of fibroblasts induced with citrullinated TNF-α compared to unmodified TNF-α. However, upon citrullination TNF-α retained its capacity to induce apoptosis/necrosis of mononuclear cells, its binding potency to Infliximab and its ability to recruit neutrophils to the peritoneal cavity of mice.     

Conformational energy calculations on glycosylated turns in glycoproteins

Analysis of the amino acid sequence of glycoproteins has suggested the β-turn as a likely site of glycosylation in glycoproteins. According to this model, the peptide chain traverses the interior of a globular protein, reversing its direction at the protein surface, a likely point for the attachment of hydrophilic carbohydrate residues. In order to search for plausible conformations of glycosylated β-turns in asparagine-linked glycoproteins, we have adapted the conformational energy calculation method of Scheraga and coworkers for use in carbohydrates. The parameters for nonbonded and hydrogen-bonded interactions have been published, and electrostatic parameters are derived from a CNDO calculation on a model glycopeptide. Our results indicate that the orientation of the glycosyl amide bond having the amide proton nearly trans to the anomeric proton of the sugar has the lowest energy. Although CD and nmr experiments in our laboratory have consistently found this conformation, our calculations show the conformation having these two protons in a cis relationship to lie very close in energy. Calculations on the glycopeptide linkage model, α-N-acetyl, δ-N(2-acetamido-1,2-dideoxy-β-D -glucopyranosyl)-N′-methyl-L -asparaginyl amide show that several distinct geometries are allowed for glycosylated β-turns. For a type I β-turn, three conformations of the glycosylated side chain are found within 4 kcal of the minimum, while two conformations of the glycosylated side chain are allowed for a type II turn. The hydrogen-bonded C7 conformation is also allowed. Stereoviews of the low-energy conformations reveal no major hydrogen-bonding interaction between the peptide and sugar.     

Analysis of the interaction between the bacterial superantigen streptococcal pyrogenic exotoxin A (SpeA) and the human T-cell receptor

Streptococcus pyogenes that produces the bacterial superantigen streptococcal pyrogenic exotoxin A (SpeA) is associated with outbreaks of streptococcal toxic shock syndrome (STSS) in the United States and Europe. SpeA stimulates Vβ2.1, 12.2, 14.1, and 15.1-positive T cells, and the lymphokine production from the activated T cells is believed to result in the symptoms associated with STSS. The T-cell receptor (TCR)–SpeA interaction is crucial for superantigenic activity, and studies were undertaken to determine regions of both SpeA and the TCR involved in the formation of MHC/SpeA/TCR complexes. Previously, recombinant toxins encoded by speA alleles 1, 2, and 3 as well as toxins resulting from 19 distinct point mutations in speA1 were generated. Here, these 22 toxin forms were incubated with human peripheral blood mono- nuclear cells (PBMCs), and the percentages of T-cell blasts bearing Vβ chains 2.1, 12.2, and 14.1 were quantified by flow cytometry. The analysis indicates that the residues of SpeA needed for a productive TCR interaction differ for each Vβ chain examined. An amino acid substitution at only one site significantly affected the toxin’s ability to stimulate Vβ2.1-expressing T cells, three individual amino acid substitutions resulted in significant loss of ability to stimulate Vβ12.2-expressing T cells, and substitution at 13 individual sites significantly affected the ability to stimulate Vβ14.1-expressing T cells. To elucidate the regions of the Vβ chains that interacted with SpeA, synthetic peptides representative of the human Vβ12.2 complementary-determining regions (CDRs) 1, 2, and 4 were used to block the SpeA-mediated proliferation of human PBMCs. The CDR1, CDR2 and CDR4 peptides were each able to block proliferation, with the activity of CDR1 > CDR2 > CDR4. Combinations of CDR1 peptide with CDR2 or CDR4 peptides allosterically enhanced the ability of each to block proliferation, suggesting SpeA has distinct binding sites for the CDR loops.     

Properties of Recombinant Staphylococcus haemolyticus Cystathionine β‐Lyase (metC) and Its Potential Role in the Generation of Volatile Thiols in Axillary Malodor

Enzymes implicated in cysteine and methionine metabolism such as cystathionine β‐lyase (CBL; EC 4.4.1.8), a pyridoxal‐5′‐phosphate (PLP)‐dependent carbon–sulfur lyase, have been shown to play a central role in the generation of sulfur compounds. This work describes the unprecedented cloning and characterization of the metC‐cystathionine β‐lyase from the axillary‐isolated strain Staphylococcus haemolyticus AX3, in order to determine its activity and its involvement in amino acid biosynthesis, and in the generation of sulfur compounds in human sweat. The gene contains a cysteine/methionine metabolism enzyme pattern, and also a sequence capable to effect β‐elimination. The recombinant enzyme was shown to cleave cystathionine into homocysteine and to convert methionine into methanethiol at low levels. No odor was generated after incubation of the recombinant enzyme with sterile human axillary secretions; sweat components were found to have an inhibitory effect. These results suggest that the generation of sulfur compounds by Staphylococci and the β‐lyase activity in human sweat are mediated by enzymes other than the metC gene or by the concerted activities of more than one enzyme.     

Rat testicular germ cells and sertoli cells release different types of bioactive transforming growth factor beta in vitro

Several in vivo studies have reported the presence of immunoreactive transforming growth factor-β's (TGF-β's) in testicular cells at defined stages of their differentiation. The most pronounced changes in TGF-β₁ and TGF-β₂ immunoreactivity occurred during spermatogenesis. In the present study we have investigated whether germ cells and Sertoli cells are able to secrete bioactive TGF-β's in vitro, using the CCl64 mink lung epithelial cell line as bioassay for the measurement of TGF-β. In cellular lysates, TGF-β bioactivity was only observed following heat-treatment, indicating that within these cells TGF-β is present in a latent form. To our surprise, active TGF-β could be detected in the culture supernatant of germ cells and Sertoli cells without prior heat-treatment. This suggests that these cells not only produce and release TGF-β in a latent form, but that they also release a factor which can convert latent TGF-β into its active form. Following heat-activation of these culture supernatant's, total TGF-β bioactivity increased 6- to 9-fold. Spermatocytes are the cell type that releases most bioactive TGF-β during a 24 h culture period, although round and elongated spermatids and Sertoli cells also secrete significant amounts of TGF-β. The biological activity of TGF-β could be inhibited by neutralizing antibodies against TGF-β₁ (spermatocytes and round spermatids) and TGF-β₂ (round and elongating spermatids). TGF-β activity in the Sertoli cell culture supernatant was inhibited slightly by either the TGF-β₁ and TGF-β₂ neutralizing antibody.These in vitro data suggest that germ cells and Sertoli cells release latent TGF-β's. Following secretion, the TGF-β's are converted to a biological active form that can interact with specific TGF-β receptors. These results strengthen the hypothesis that TGF-β's may play a physiological role in germ cell proliferation/differentiation and Sertoli cell function.     

Synthesis and Biological Activity of Methyl 3-Demethyl-Abscisate and Its Related Analogs

To elucidate the role of the methyl substituent on the side chain of abscisic acid (ABA), we synthesized (2Z,4E)-3-demethyl-α-ionylideneacetic acid (4) and its related analogs, methyl (2Z)-3-demethyl-β-ionylideneacetate 1′,2′-epoxide (9) and methyl (2Z) and (2E)-3-demethyl-abscisate (12) and (13). The biological assay of these compounds suggested that the 3-methyl group on the side chain of ABA was indispensable to biological activity.     

Continuous production of homopolynucleotides by immobilized polynucleotide phosphorylase

A polynucleotide phosphorylase was immobilized with glutaraldehyde, via an aminopropyl spacer, on porous glass. The specific activity of the immobilized enzyme was effectively increased by the addition of an appropriate ribonucleoside diphosphate on immobilization.A homopolynucleotide could be synthesized continuously by passing a nucleoside diphosphate solution through the immobilized enzyme column. The chain length of the product depended upon the temperature and the flow rate. Polyinosinic acid, poly(I), was continuously synthesized with the immobilized enzyme for about one month without appreciable loss of activity.Polyinosinic acid-polycytidylic acid, poly(I)·poly(C), prepared from poly(I) and poly(C) synthesized with the immobilized polynucleotide phosphorylase, induced interferon-β (IFN-β) in human cultured cells as effectively as that prepared from homopolynucleotides synthesized with the free enzyme.     

Silencing and re-expression of retinoic acid receptor beta2 in human melanoma

Many melanoma cells are resistant to the anti-proliferative effect of all trans retinoic acid (ATRA). Retinoic Acid Receptor-β2 (RAR-β2) mediates the ATRA growth inhibition. We found a correlation between the anti-proliferative activity of ATRA and expression of RAR-β2. There was not a strict correlation between DNA methylation of RAR-β gene and its expression. There was no difference in global and RARβ specific nucleosome repeat length (NRL) in melanoma and melanocytes or between control and ATRA treated cells. Pan-acetylation of H3 and H4 within the RAR-β gene promoter was higher in cells expressing RAR-β2. All trans retinoic acid treatment of responsive cells did not change pan-acetylation of H3/H4, but addition of ATRA to non-responsive cells increased H4 pan-acetylation. Phytochemicals or the histone deacetylase inhibitor Trichostatin A did not restore expression of RAR-β2. Treatment of WM1366 melanoma cells with 5-aza 2′-deoxycytidine reactivated RAR-β2 gene expression and restored the ability of ATRA to further induce the expression of this gene. Therefore, promoter methylation is responsible for silencing of RAR-β2 in some melanoma cells and pan-acetylation of H3 likely plays a permissive role in expression of RAR-β2.