Deglycosylation of glycoproteins by trifluoromethanesulfonic acid

Fungal chitin-binding glycoprotein induces Dectin-2-mediated allergic airway inflammation synergistically with chitin

Although chitin in fungal cell walls is associated with allergic airway inflammation, the precise mechanism underlying this association has yet to be elucidated. Here, we investigated the involvement of fungal chitin-binding protein and chitin in allergic airway inflammation. Recombinant Aspergillus fumigatus LdpA (rLdpA) expressed in Pichia pastoris was shown to be an O-linked glycoprotein containing terminal α-mannose residues recognized by the host C-type lectin receptor, Dectin-2. Chitin particles were shown to induce acute neutrophilic airway inflammation mediated release of interleukin-1α (IL-1α) associated with cell death. Furthermore, rLdpA-Dectin-2 interaction was shown to promote phagocytosis of rLdpA-chitin complex and activation of mouse bone marrow-derived dendritic cells (BMDCs). Moreover, we showed that rLdpA potently induced T helper 2 (Th2)-driven allergic airway inflammation synergistically with chitin, and Dectin-2 deficiency attenuated the rLdpA-chitin complex-induced immune response in vivo. In addition, we showed that serum LdpA-specific immunoglobulin levels were elevated in patients with pulmonary aspergillosis.

Glycan-selective in-situ growth of thermoresponsive polymers for thermoprecipitation and enrichment of N-glycoprotein/glycopeptides

In view of the biological significance and micro-heterogeneity of protein glycosylation for human health, specific enrichment of N-glycosylated proteins/peptides from complex biological samples is a prerequisite for the discovery of disease biomarkers and clinical diagnosis. In this work, we propose a "grafting-from" N-glycoprotein enriching method based on the in-situ growth of thermoresponsive polymer brushes from the N-glycosylated site of proteins. The initiator was first attached to the pre-oxidized glycan moieties by hydrazide chemistry, from which the thermoresponsive polymers can be grown to form giant protein-polymer conjugates (PPC). The thermosensitive PPC can be precipitated and separated by raising the temperature to above its lower critical solubility temperature (LCST). Mass spectrometry verified 210 N-glycopeptides corresponding to 136 N-glycoproteins in the rabbit serum. These results demonstrate the capability of the tandem thermoprecipitation strategy to enrich and separate N-glycoprotein/glycopeptide. Due to its simplicity and efficiency specifically, this method holds the potential for identifying biomarkers from biological samples in N-glycoproteome analysis.

Two Typical Glycosylated Metabolites of Tetrabromobisphenol A Formed in Plants: Excretion and Deglycosylation in Plant Root Zones

The glycosylation process was investigated for the common brominated flame retardant tetrabromobisphenol A (TBBPA) in hydroponic exposure systems with pumpkin seedlings. Two typical glycosylation metabolites of TBBPA formed in pumpkin seedlings, TBBPA mono-β-d-glucopyranoside (TBBPA MG) and TBBPA di-β-d-glucopyranoside (TBBPA DG), increasing their mass early in the exposure (reaching maximum masses of 608 ± 53 and 3806 ± 1570 pmol at 12 h, respectively) and then falling throughout exposure. These two metabolites were released from roots to rhizosphere solutions, where they also exhibited initial increases followed by decreasing trends (reaching maximum masses of 595 ± 272 pmol at 3 h and 77.1 ± 36.0 pmol at 6 h, respectively). However, a (pseudo)zero-order deglycosylation of TBBPA MG and TBBPA DG (during the first 1.5 h) back to TBBPA was unexpectedly detected in the hydroponic solutions containing pumpkin exudates and microorganisms. The function of microorganisms in the solutions was further investigated, revealing that the microorganisms were main contributors to deglycosylation. Plant detoxification through glycosylation and excretion, followed by deglycosylation of metabolites back to the toxic parent compound (TBBPA) in hydroponic solutions, provides new insight into the uptake, transformation, and environmental fate of TBBPA and its glycosylated metabolites in plant/microbial systems.

Glycoprotein G-protein Coupled Receptors in Disease: Luteinizing Hormone Receptors and Follicle Stimulating Hormone Receptors

Signal transduction by luteinizing hormone receptors (LHRs) and follicle-stimulating hormone receptors (FSHRs) is essential for the successful reproduction of human beings. Both receptors and the thyroid-stimulating hormone receptor are members of a subset of G-protein coupled receptors (GPCRs) described as the glycoprotein hormone receptors. Their ligands, follicle-stimulating hormone (FSH) and luteinizing hormone (LH) and a structurally related hormone produced in pregnancy, human chorionic gonadotropin (hCG), are large protein hormones that are extensively glycosylated. Although the primary physiologic functions of these receptors are in ovarian function and maintenance of pregnancy in human females and spermatogenesis in males, there are reports of LHRs or FSHRs involvement in disease processes both in the reproductive system and elsewhere. In this review, we evaluate the aggregation state of the structure of actively signaling LHRs or FSHRs, their functions in reproduction as well as summarizing disease processes related to receptor mutations affecting receptor function or expression in reproductive and non-reproductive tissues. We will also present novel strategies for either increasing or reducing the activity of LHRs signaling. Such approaches to modify signaling by glycoprotein receptors may prove advantageous in treating diseases relating to LHRs or FSHRs function in addition to furthering the identification of new strategies for modulating GPCR signaling.

Reactivities of an anti-CEA peptide monoclonal antibody

Synthetic peptides representing different areas of the CEA molecule were used as immunogens for the development of anti-CEA antibodies. Both polyclonal and monoclonal antibodies were generated using peptides composed of CEA amino acid positions 99–128 and 585–613, respectively. One MAb, designated CP4, generated using the CEA peptide 99–128, was chosen for a more detailed analysis of reactivity. MAb CP4 reacts in solid phase RIAs with CEA peptide 99–128 immunogen and purified native CEA. CP4 did not react with purified non- specific cross reacting antigen (NCA), even though there were two single amino acid differences between NCA and CEA in the 29 amino acid peptide. The affinity constants of CP4 for the CEA peptide 99–128 and native CEA are 4.07 × 109M−1and 5.75 × 108M−1, respectively. When CP4 was reacted with purified CEA in Western blotting experiments, the Mr 180,000 glycoprotein characteristic of CEA was detected, but CP4 reacted to various size entities in tumor cell extracts. The results of liquid competition RIAs showed that the epitope that MAb CP4 recognized on native CEA is not available for binding when CEA is in solution. Physical (adsorption to a solid matrix) or chemical (deglycosylation or formalin-fixation) alteration of CEA is required for binding of CP4 to CEA. MAb CP4 reacted approximately 1,000-fold greater to deglycosylated CEA than native CEA. Immunohistochemical studies using formalin-fixed paraffin-embedded tissue sections demonstrated that, among carcinomas, CP4 reacts selectively with colorectal carcinomas, while normal colon is negative. Although stomach carcinoma is negative, dysplastic lesions and areas of intestinal metaplasia are reactive. Two of 7 normal stomach tissues showed focal cytoplasmic reactivity of the surface epithelium. CP4, therefore, appears to react with an epitope with highly restricted expression in colorectal carcinoma. These studies demonstrate the complexities in dealing with an anti-peptide MAb with reactivity to an epitope which is accessible only under certain conditions.

Isolation and Characterization of a Novel Sialoglycopeptide Promoting Osteogenesis from Gadus morhua Eggs

Gadus morhua eggs contain several nutrients, including polyunsaturated fatty acids, lecithin and glycoproteins. A novel sialoglycopeptide from the eggs of G. morhua (Gm-SGPP) was extracted with 90% phenol and purified by Q Sepharose Fast Flow (QFF) ion exchange chromatography, followed by S-300 gel filtration chromatography. Gm-SGPP contained 63.7% carbohydrate, 16.2% protein and 18.6% N-acetylneuraminic acid. High-performance size exclusion chromatography and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) demonstrated that Gm-SGPP is a 7000-Da pure sialoglycopeptide. β-elimination reaction suggested that Gm-SGPP contained N-glycan units. Amino acid N-terminal sequence analysis indicated the presence of Ala-Ser-Asn-Gly-Thr-Gln-Ala-Pro amino acid sequence. Moreover, N-glycan was connected at the third Asn location of the peptide chain through GlcNAc. Gm-SGPP was composed of D-mannose, D-glucuronic acid and D-galactose. Fourier transform-infrared spectroscopy (FT-IR), ¹H-nuclear magnetic resonance spectroscopy (¹H-NMR) and methylation analysis were performed to reveal the structure profile of Gm-SGPP. In vitro results showed that the proliferation activity of MC3T3-E1 cells was significantly promoted by Gm-SGPP. In vivo data revealed that Gm-SGPP increased the calcium and phosphorus content of tibias and promoted longitudinal bone growth in adolescent rats.

Global and site-specific analysis of protein glycosylation in complex biological systems with Mass Spectrometry

Protein glycosylation is ubiquitous in biological systems and plays essential roles in many cellular events. Global and site-specific analysis of glycoproteins in complex biological samples can advance our understanding of glycoprotein functions and cellular activities. However, it is extraordinarily challenging because of the low abundance of many glycoproteins and the heterogeneity of glycan structures. The emergence of mass spectrometry (MS)-based proteomics has provided us an excellent opportunity to comprehensively study proteins and their modifications, including glycosylation. In this review, we first summarize major methods for glycopeptide/glycoprotein enrichment, followed by the chemical and enzymatic methods to generate a mass tag for glycosylation site identification. We next discuss the systematic and quantitative analysis of glycoprotein dynamics. Reversible protein glycosylation is dynamic, and systematic study of glycoprotein dynamics helps us gain insight into glycoprotein functions. The last part of this review focuses on the applications of MS-based proteomics to study glycoproteins in different biological systems, including yeasts, plants, mice, human cells, and clinical samples. Intact glycopeptide analysis is also included in this section. Because of the importance of glycoproteins in complex biological systems, the field of glycoproteomics will continue to grow in the next decade. Innovative and effective MS-based methods will exponentially advance glycoscience, and enable us to identify glycoproteins as effective biomarkers for disease detection and drug targets for disease treatment. © 2019 Wiley Periodicals, Inc. Mass Spec Rev 9999: XX-XX, 2019.

Isolation and characterization of an aspartic protease able to hydrolyze and decolorize heme proteins from Aspergillus glaucus

BACKGROUND

The xerophilic Aspergillus molds, Aspergillus glaucus and Aspergillus repens, have been used in the ripening and fermentation of dried tuna bonito (katsuobushi). These molds, and especially their extracellular hydrolytic enzymes, may also be of wider industrial value.

RESULTS

Aspergillus glaucus strain MA0196 produces different types of hydrolytic enzymes, including amylase, serine protease, aspartic protease, lipase and cellulase, depending on the composition of the medium. We characterized several of these enzymes, focusing on a glycosylated aspartic protease. The results showed that the lower the d-glucose concentration in the medium, the higher the degree of protease glycosylation, with excess glycosylation tending to decrease protease activity. The molecular mass of the glycosylated protease as determined by gel filtration and sodium dodecyl sulphate-polyacrylamide gel electrophoresis was 243 and 253 kDa, respectively. The chemically deglycosylated protease had a molecular mass of only 46 kDa. The amount of myoglobin-decolorizing activity was similar to that of a previously reported aspartic protease from A. repens strain MK82. However, the strain MA0196 protease more broadly hydrolyzed myoglobin and hemoglobins than did the strain MK82 protease.

CONCLUSION

The results of the present study demonstrate the potential utility of Aspergillus molds as a functionally new microbial resource for industrial applications such as the bleaching of heme proteins. © 2018 Society of Chemical Industry.

Collagen glycosylation

Despite the ubiquity of collagens in the animal kingdom, little is known about the biology of the disaccharide Glc(α1-2)Gal(β1-O) bound to hydroxylysine across collagens from sponges to mammals. The extent of collagen glycosylation varies by the types of collagen, with basement membrane collagen type IV being more glycosylated than fibrillar collagens. Beyond true collagens, proteins including collagen domains such as the complement protein 1Q and the hormone adiponectin also feature glycosylated hydroxylysine. Collagen glycosylation is initiated in the endoplasmic reticulum by the galactosyltransferases COLGALT1 and COLGALT2. Mutations in the COLGALT1 gene cause cerebral small vessel abnormality and porencephaly, which are common in collagen type IV deficiency. Beyond the strongly conserved Glc(α1-2)Gal(β1-O) glycan, additional forms of collagen glycosylation have been described in the deep-sea worm Riftia pachyptila and in the giant virus Mimivirus, thereby suggesting that further forms of collagen glycosylation are likely to be identified in the future.

Triflic Acid Treatment Enables LC-MS/MS Analysis of Insoluble Bacterial Biomass

The lysis and extraction of soluble bacterial proteins from cells is a common practice for proteomics analyses, but insoluble bacterial biomasses are often left behind. Here, we show that with triflic acid treatment, the insoluble bacterial biomass of Gram^- and Gram⁺ bacteria can be rendered soluble. We use LC-MS/MS shotgun proteomics to show that bacterial proteins in the soluble and insoluble postlysis fractions differ significantly. Additionally, in the case of Gram^- Pseudomonas aeruginosa, triflic acid treatment enables the enrichment of cell-envelope-associated proteins. Finally, we apply triflic acid to a human microbiome sample to show that this treatment is robust and enables the identification of a new, complementary subset of proteins from a complex microbial mixture.

Characterizing bacterial glycoproteins with LC-MS

INTRODUCTION

Though eukaryotic glycoproteins have been studied since their discovery in the 1930s, the first bacterial glycoprotein was not identified until the 1970s. As a result, their role in bacterial pathogenesis is still not well understood and they remain an understudied component of bacterial virulence. In recent years, mass spectrometry has emerged as a leading technology for the study of bacterial glycoproteins, largely due to its sensitivity and versatility. Areas covered: Identification and comprehensive characterization of bacterial glycoproteins usually requires multiple complementary mass spectrometry approaches, including intact protein analysis, top-down analysis, and bottom-up methods used in combination with specialized liquid chromatography. This review provides an overview of liquid chromatography separation technologies, as well as current and emerging mass spectrometry approaches used specifically for bacterial glycoprotein identification and characterization. Expert commentary: Bacterial glycoproteins may have significant clinical utility as a result of their unique structures and exposure on the surface of the cells. Better understanding of these glycoconjugates is an essential first step towards that goal. These often unique structures, and by extension the key enzymes involved in their synthesis, represent promising targets for novel antimicrobials, while unique carbohydrate structures may be used as antigens in vaccines or as biomarkers.

High-yield secretion of recombinant proteins from the microalga Chlamydomonas reinhardtii

Microalga-based biomanufacturing of recombinant proteins is attracting growing attention due to its advantages in safety, metabolic diversity, scalability and sustainability. Secretion of recombinant proteins can accelerate the use of microalgal platforms by allowing post-translational modifications and easy recovery of products from the culture media. However, currently, the yields of secreted recombinant proteins are low, which hampers the commercial application of this strategy. This study aimed at expanding the genetic tools for enhancing secretion of recombinant proteins in Chlamydomonas reinhardtii, a widely used green microalga as a model organism and a potential industrial biotechnology platform. We demonstrated that the putative signal sequence from C. reinhardtii gametolysin can assist the secretion of the yellow fluorescent protein Venus into the culture media. To increase the secretion yields, Venus was C-terminally fused with synthetic glycomodules comprised of tandem serine (Ser) and proline (Pro) repeats of 10 and 20 units [hereafter (SP)_n , wherein n = 10 or 20]. The yields of the (SP)_n -fused Venus were higher than Venus without the glycomodule by up to 12-fold, with the maximum yield of 15 mg/L. Moreover, the presence of the glycomodules conferred an enhanced proteolytic protein stability. The Venus-(SP)_n proteins were shown to be glycosylated, and a treatment of the cells with brefeldin A led to a suggestion that glycosylation of the (SP)_n glycomodules starts in the endoplasmic reticulum (ER). Taken together, the results demonstrate the utility of the gametolysin signal sequence and (SP)_n glycomodule to promote a more efficient biomanufacturing of microalgae-based recombinant proteins.

Chemical Glycoproteomics

Chemical tools have accelerated progress in glycoscience, reducing experimental barriers to studying protein glycosylation, the most widespread and complex form of posttranslational modification. For example, chemical glycoproteomics technologies have enabled the identification of specific glycosylation sites and glycan structures that modulate protein function in a number of biological processes. This field is now entering a stage of logarithmic growth, during which chemical innovations combined with mass spectrometry advances could make it possible to fully characterize the human glycoproteome. In this review, we describe the important role that chemical glycoproteomics methods are playing in such efforts. We summarize developments in four key areas: enrichment of glycoproteins and glycopeptides from complex mixtures, emphasizing methods that exploit unique chemical properties of glycans or introduce unnatural functional groups through metabolic labeling and chemoenzymatic tagging; identification of sites of protein glycosylation; targeted glycoproteomics; and functional glycoproteomics, with a focus on probing interactions between glycoproteins and glycan-binding proteins. Our goal with this survey is to provide a foundation on which continued technological advancements can be made to promote further explorations of protein glycosylation.

Halogenated methanesulfonic acids: A new class of organic micropollutants in the water cycle

Mobile and persistent organic micropollutants may impact raw and drinking waters and are thus of concern for human health. To identify such possible substances of concern nineteen water samples from five European countries (France, Switzerland, The Netherlands, Spain and Germany) and different compartments of the water cycle (urban effluent, surface water, ground water and drinking water) were enriched with mixed-mode solid phase extraction. Hydrophilic interaction liquid chromatography - high resolution mass spectrometry non-target screening of these samples led to the detection and structural elucidation of seven novel organic micropollutants. One structure could already be confirmed by a reference standard (trifluoromethanesulfonic acid) and six were tentatively identified based on experimental evidence (chloromethanesulfonic acid, dichloromethanesulfonic acid, trichloromethanesulfonic acid, bromomethanesulfonic acid, dibromomethanesulfonic acid and bromochloromethanesulfonic acid). Approximated concentrations for these substances show that trifluoromethanesulfonic acid, a chemical registered under the European Union regulation REACH with a production volume of more than 100 t/a, is able to spread along the water cycle and may be present in concentrations up to the μg/L range. Chlorinated and brominated methanesulfonic acids were predominantly detected together which indicates a common source and first experimental evidence points towards water disinfection as a potential origin. Halogenated methanesulfonic acids were detected in drinking waters and thus may be new substances of concern.

Proteome-Based Analysis of Colloidal Instability Enables the Detection of Haze-Active Proteins in Beer

Colloidal haze is a serious quality defect of bright beers that considerably reduces their shelf life and is thought to be triggered by hordeins, a class of proline-rich barley proteins. In this work, the proteomes of fresh and old beers were investigated in bottled pilsners and compared to the protein inventory of haze to identify specific haze-active proteins. Haze isolates dissolved in rehydration buffer contained high concentrations of proteins and sugars but provided protein gels with weak spot signals. Consequently, a treatment for the chemical deglycation with trifluoromethanesulfonic acid was applied, which resulted in the identification of protein Z4, LTP1, CMb, CMe, pUP13, 3a, and Bwiph as constituents of the haze proteome. Because only one hordein was detectable and the proline content in haze hydrolysates was lower than those of barley prolamins, our results suggest that this class of proteins is of minor importance for haze development.

Proteomic analysis of the venom and venom sac of the woodwasp, Sirex noctilio - Towards understanding its biological impact

The European horntail woodwasp, Sirex noctilio, is an invasive insect that attacks conifer hosts, particularly Pinus species. Venom injected by female S. noctilio, together with its symbiotic fungus, damages the normal physiology of Pinus, leading to death of the tree. To identify the proteinaceous components in the venom and uncover the interplay between venom proteins and tree proteins, clarification of the overall profile of proteins produced in the venom gland apparatus was carried out in this work. The venom sac proteome utilised in-solution digested in either a natural or deglycosylated state, prior to nanoHPLC LTQ-Orbitrap under CID/ETD mode. Here, we report the identification of 1454 and 1225 proteins in venom and sac, respectively, with 410 mutual proteins. Approximately 90 proteins were predicted to be secretory, of which 8 have features characteristic of toxins. Chemosensory binding proteins were also identified. Gene ontology and KEGG pathway analysis were employed to predict the protein functions and biological pathways in venom and sac. Protein-protein interaction (PPI) analysis suggested that one-step responses represent the majority of the Sirex-Pinus PPIs, and the proteins representing network hub nodes could be of importance for the development of pest management strategies.

SIGNIFICANCE

The woodwasp Sirex noctilio is an invasive species in many parts of the world, including Australia and North America, where it is considered within the top 10 most serious forest insects. Where they have been introduced, the female woodwasps attack living pine trees, causing significant economic losses. Central to this destruction is the woodwasp's life cycle requirement to bore a hole to deposit eggs and a toxic mucus that disables the tree's network for transporting water and nutrients, yet aids in larval survival. Here we specifically examine the mucus gland apparatus and its contents, revealing the protein components that together with 'noctilisin' facilitate this complex association. The identification of chemosensory binding proteins further supports a role for the woodwasp ovipositor as an instrument for early stages of host tree selection. These findings could provide important clues towards the development of novel control tools against this pest.

Identification of Novel N-Glycosylation Sites at Noncanonical Protein Consensus Motifs

N-glycosylation of proteins is well known to occur at asparagine residues that fall within the canonical consensus sequence N-X-S/T but has also been identified at a small number of asparagine residues within N-X-C motifs, including the N491 residue of human serotransferrin. Here we report novel glycosylation sites within noncanonical consensus motifs, in the conformation N-X-C, based on mass spectrometry analysis of partially deglycosylated glycopeptide targets. Alpha-1-acid glycoprotein (A1AG) and serotransferrin (Tf) were observed for the first time to be N-glycosylated on asparagine residues within a total of six unique noncanonical motifs. N-glycosylation was initially predicted in silico based on the evolutionary conservation of the N-X-C motif among related mammalian species and demonstrated experimentally in A1AG from porcine, canine, and feline sources and in human serotransferrin. High-resolution liquid chromatography-tandem mass spectrometry was employed to collect fragmentation data of predicted GlcNAcylated peptides and to assign modification sites within N-X-C motifs. A combination of targeted analytical techniques that includes complementary mass spectrometry platforms, enzymatic digestions, and partial-deglycosylation procedures was developed to confirm the novel observations. Additionally, we found that A1AG in porcine and canine sources is highly N-glycosylated at a noncanonical motif (N-Q-C) based on semiquantitative multiple reaction monitoring analysis-the first report of an N-X-C motif exhibiting substantial N-glycosylation. Although reports of N-X-C motif N-glycosylation are relatively uncommon in the literature, this work adds to a growing list of glycoproteins reported with glycosylation at various forms of noncanonical motifs.

Novel proline-hydroxyproline glycopeptides from the dandelion (Taraxacum officinale Wigg.) flowers: de novo sequencing and biological activity

Two novel homologous peptides named ToHyp1 and ToHyp2 that show no similarity to any known proteins were isolated from Taraxacum officinale Wigg. flowers by multidimensional liquid chromatography. Amino acid and mass spectrometry analyses demonstrated that the peptides have unusual structure: they are cysteine-free, proline-hydroxyproline-rich and post-translationally glycosylated by pentoses, with 5 carbohydrates in ToHyp2 and 10 in ToHyp1. The ToHyp2 peptide with a monoisotopic molecular mass of 4350.3Da was completely sequenced by a combination of Edman degradation and de novo sequencing via top down multistage collision induced dissociation (CID) and higher energy dissociation (HCD) tandem mass spectrometry (MS(n)). ToHyp2 consists of 35 amino acids, contains eighteen proline residues, of which 8 prolines are hydroxylated. The peptide displays antifungal activity and inhibits growth of Gram-positive and Gram-negative bacteria. We further showed that carbohydrate moieties have no significant impact on the peptide structure, but are important for antifungal activity although not absolutely necessary. The deglycosylated ToHyp2 peptide was less active against the susceptible fungus Bipolaris sorokiniana than the native peptide. Unique structural features of the ToHyp2 peptide place it into a new family of plant defense peptides. The discovery of ToHyp peptides in T. officinale flowers expands the repertoire of molecules of plant origin with practical applications.

Immuno-affinity purification of PglPGIP1, a polygalacturonase-inhibitor protein from pearl millet: studies on its inhibition of fungal polygalacturonases and role in resistance against the downy mildew pathogen

Polygalacturonase-inhibitor proteins (PGIPs) are important plant defense proteins which modulate the activity of microbial polygalacturonases (PGs) leading to elicitor accumulation. Very few studies have been carried out towards understanding the role of PGIPs in monocot host defense. Hence, present study was taken up to characterize a native PGIP from pearl millet and understand its role in resistance against downy mildew. A native glycosylated PGIP (PglPGIP1) of ~43 kDa and pI 5.9 was immunopurified from pearl millet. Comparative inhibition studies involving PglPGIP1 and its non-glycosylated form (rPglPGIP1; recombinant pearl millet PGIP produced in Escherichia coli) against two PGs, PG-II isoform from Aspergillus niger (AnPGII) and PG-III isoform from Fusarium moniliforme, showed both PGIPs to inhibit only AnPGII. The protein glycosylation was found to impact only the pH and temperature stability of PGIP, with the native form showing relatively higher stability to pH and temperature changes. Temporal accumulation of both PglPGIP1 protein (western blot and ELISA) and transcripts (real time PCR) in resistant and susceptible pearl millet cultivars showed significant Sclerospora graminicola-induced accumulation only in the incompatible interaction. Further, confocal PGIP immunolocalization results showed a very intense immuno-decoration with highest fluorescent intensities observed at the outer epidermal layer and vascular bundles in resistant cultivar only. This is the first native PGIP isolated from millets and the results indicate a role for PglPGIP1 in host defense. This could further be exploited in devising pearl millet cultivars with better pathogen resistance.

Identification of the flagellin glycosylation system in Burkholderia cenocepacia and the contribution of glycosylated flagellin to evasion of human innate immune responses

Burkholderia cenocepacia is an opportunistic pathogen threatening patients with cystic fibrosis. Flagella are required for biofilm formation, as well as adhesion to and invasion of epithelial cells. Recognition of flagellin via the Toll-like receptor 5 (TLR5) contributes to exacerbate B. cenocepacia-induced lung epithelial inflammatory responses. In this study, we report that B. cenocepacia flagellin is glycosylated on at least 10 different sites with a single sugar, 4,6-dideoxy-4-(3-hydroxybutanoylamino)-D-glucose. We have identified key genes that are required for flagellin glycosylation, including a predicted glycosyltransferase gene that is linked to the flagellin biosynthesis cluster and a putative acetyltransferase gene located within the O-antigen lipopolysaccharide cluster. Another O-antigen cluster gene, rmlB, which is required for flagellin glycan and O-antigen biosynthesis, was essential for bacterial viability, uncovering a novel target against Burkholderia infections. Using glycosylated and nonglycosylated purified flagellin and a cell reporter system to assess TLR5-mediated responses, we also show that the presence of glycan in flagellin significantly impairs the inflammatory response of epithelial cells. We therefore suggest that flagellin glycosylation reduces recognition of flagellin by host TLR5, providing an evasive strategy to infecting bacteria.

Characterization of alpha-2-macroglobulin from groupers

Alpha-2-macroglobulin (α-2-M) is a protease inhibitor broadly present in the plasma of vertebrates and invertebrates, and is an important non-specific humoral factor in defence system of the animals. This study conducted the immuno-analysis and mass spectrometric analysis methods to investigate the characteristics of the protease inhibitor, α-2-M, among groupers and related species. Rabbit antiserum to the purified α-2-M of Epinephelus coioides was used in different immunological methods to determine the immune cross-reactions of the α-2-M in samples. Plasma of Epinephelus bruneus, Epinephelus fuscoguttatus, Epinephelus lanceolatus, and Epinephelus quoyanus exhibited high protease inhibitory activities by BAPNA-trypsin assay. To purify the α-2-M protein, plasma protein of grouper E. coioides was first precipitated by using PEG 6000, then Blue Sepharose 6 Fast Flow, DEAE Sephacel, Con A Separose 4B and Phenyl Sepharose High Performance columns were used on FPLC system for purification. The molecular mass of grouper plasma α-2-M was determined as a 180 kDa protein on non-reduced SDS-PAGE. In addition, it was determined as 97 and 80 kDa protein on reduced SDS-PAGE. Enzymatic and chemical deglycosylation of glycogen revealed that the contents of glycogen in 97 and 80 kDa subunits were 12.4% and 15%, respectively, and were all belonging to N-linked type. Only one precipitation arc was visualized in all plasma of Epinephelus spp. using the rabbit antiserum to the purified α-2-M of E. coioides, on crossed immunoelectrophoresis (CIE) gels. The plasma of Epinephelus spp. and seawater fish species showed stronger responses than freshwater fish species while that of other animal species showed no response by dot-blot assay. One single band was detected on Native PAGE-Western blotting assay, one single 180 kDa band was detected on non-reduced SDS-PAGE-Western blotting, and four bands (80, 97, 160, 250 kDa) were detected on reduced SDS-PAGE when various grouper plasma was performed respectivity. However, no band was detected using plasma from the freshwater fish species and other animal species. Thus, further indicates that the protein structure of α-2-M of Epinephelus spp. was closely related among seawater fish species. In addition the identity of the two subunits was identified using LC/MS/MS which was similar to α-2-M of grass carp (Ctenopharyngodon idella) and bluegill sunfish (Lepomis macrochirus) on the protein hit.

One single basic amino acid at the ω-1 or ω-2 site is a signal that retains glycosylphosphatidylinositol-anchored protein in the plasma membrane of Aspergillus fumigatus

Although the plasma membrane is the terminal destination for glycosylphosphatidylinositol (GPI) proteins in higher eukaryotes, cell wall-attached GPI proteins (GPI-CWPs) are found in many fungal species. In yeast, some of the cis-requirements directing localization of GPI proteins to the plasma membrane or cell wall are now understood. However, it remains to be determined how Aspergillus fumigatus, an opportunistic fungal pathogen, signals, and sorts GPI proteins to either the plasma membrane or the cell wall. In this study, chimeric green fluorescent proteins (GFPs) were constructed as fusions with putative C-terminal GPI signal sequences from A. fumigatus Mp1p, Gel1p, and Ecm33p, as well as site-directed mutations thereof. By analyzing cellular localization of chimeric GFPs using Western blotting, electron microscopy, and fluorescence microscopy, we showed that, in contrast to yeast, a single Lys residue at the ω-1 or ω-2 site alone could retain GPI-anchored GFP in the plasma membrane. Although the signal for cell wall distribution has not been identified yet, it appeared that the threonine/serine-rich region at the C-terminal half of AfMp1 was not required for cell wall distribution. Based on our results, the cis-requirements directing localization of GPI proteins in A. fumigatus are different from those in yeast.

Pathogen-Related Yeast (PRY) proteins and members of the CAP superfamily are secreted sterol-binding proteins

Sterols and related membrane-perturbing agents are subject to a quality control cycle. Compounds that fail to pass this control are acetylated and secreted into the culture media, whereas lipids that pass the cycle are deacetylated and retained within the cell. Here we describe the identification of a family of conserved proteins, the Pathogen-Related Yeast (PRY) proteins, as a class of sterol-binding proteins. Saccharomyces cerevisiae has three members of this family, two of which, Pry1 and Pry2, are secreted, whereas Pry3 is a cell wall-associated protein. Cells lacking both PRY1 and PRY2 have a complete block in secretion of the acetylated lipid and Pry1 and Pry2 proteins bind free cholesterol and cholesteryl acetate in vitro. PRY proteins belong to a large protein superfamily of unknown mode of action, the CAP protein superfamily [i.e. cysteine-rich secretory proteins (CRISP), antigen 5, and pathogenesis related 1 proteins]. The conserved CAP domain of Pry1 is necessary and sufficient for lipid export and sterol binding. Expression of a human CAP superfamily member, the cysteine-rich secretory protein 2 (CRISP2), rescues the phenotype of yeast mutants lacking Pry function and purified CRISP2 binds cholesterol in vitro, indicating that lipid binding is a conserved function of the CAP superfamily proteins.

Barley γ3-hordein: glycosylation at an atypical site, disulfide bridge analysis, and reactivity with IgE from patients allergic to wheat

Post translational modifications of a seed storage protein, barley γ3-hordein, were determined using immunochemical and mass spectrometry methods. IgE reactivity towards this protein was measured using sera from patients diagnosed with allergies to wheat. N-glycosylation was found at an atypical Asn-Leu-Cys site. The observed glycan contains xylose. This indicates that at least some γ3-hordein molecules trafficked through the Golgi apparatus. Disulfide bridges in native γ3-hordein were almost the same as those found in wheat γ46-gliadin, except the bridge involving the cysteine included in the glycosylation site. IgE reacted more strongly towards the recombinant than the natural γ3-hordein protein. IgE binding to γ3-hordein increased when the protein sample was reduced. Glycosylation and disulfide bridges therefore decrease epitope accessibility. Thus the IgE from patients sensitized to wheat cross-react with γ3-hordein due to sequence homology with wheat allergens rather than through shared carbohydrate determinants.

Proteoglycans from Boswellia serrata Roxb. and B. carteri Birdw. and identification of a proteolytic plant basic secretory protein

Water-soluble high molecular weight compounds were isolated in yields of 21-22% from the oleogum of Boswellia serrata and B. carteri. Using anion exchange chromatography and gel permeation chromatography, different proteoglycans were purified and characterized, leading to four principally different groups: (i) Hyp-/Ser-rich extensins with O-glycosidic attached arabinan side chains; (ii) Modified extensins, with arabinogalactosylated side chains containing GlA and 4-O-Me-GlcA; (iii) Glycoproteins with N-glycosidic side chains containing higher amounts of Fuc, Man and GluNH(2,) featuring a 200 kD metalloproteinase that has been de novo sequenced and is described for the first time; (iv) Type II arabinogalactans-proteins. Significant differences between the gums from the two species were observed in the protein content (6% vs 22%), offering the possibility of a quick differentiation of gums from both species for analytical quality control. The data also offer an insight into the plant response towards wound-closing by the formation of extensin and AGP-containing gum.

A Tn antigen binding lectin from Myrsine coriacea displays toxicity in human cancer cell lines

The Tn antigen (GalNAc-O-Ser/Thr) is one of the most specific human cancer-associated structures. In the present study we characterize the biochemical and functional properties of the Myrsine coriacea lectin (McL). We show that McL is an unusual high molecular weight highly glycosylated protein, which displays a strong Tn binding activity. The lectin exhibits in vitro inhibition of proliferation in the six cancer cell lines evaluated, in a dose-dependent manner (the strongest activity being against HT-29 and HeLa cells), whereas it does not exhibit toxicity against normal lymphocytes. McL could be exploited in the design of potential new tools for the diagnosis or treatment of cancer.

Purification and characterization of α-galactosidase from white chickpea (Cicer arietinum)

Glycosylated α-galactosidase (melibiase) has been purified from white chickpea ( Cicer arietinum ) to 340-fold with a specific activity of 61 units/mg. Cicer α-galactosidase showed a M(r) of 45 kDa on SDS-PAGE and by MALDI-TOF. The optimum pH and temperature with pNPGal were 4.5 and 50 °C, respectively. The K(m) for hydrolysis of pNPGal was 0.70 mM. Besides hydrolyzing the pNPGal, Cicer α-galactosidase also hydrolyzed natural substrates such as melibiose, raffinose, and stachyose very effectively; hence, it can be exploited commercially for improving the nutritional value of soy milk. Galactose was found to be a competitive inhibitor. The property of this enzyme to cleave the terminal galactose residues can be utilized for converting the group B erythrocytes to group O erythrocytes.

Up-regulation of MUC2 and IL-1β expression in human colonic epithelial cells by Shigella and its interaction with mucins

BACKGROUND

The entire gastrointestinal tract is protected by a mucous layer, which contains complex glycoproteins called mucins. MUC2 is one such mucin that protects the colonic mucosa from invading microbes. The initial interaction between microbes and mucins is an important step for microbial pathogenesis. Hence, it was of interest to investigate the relationship between host (mucin) and pathogen interaction, including Shigella induced expression of MUC2 and IL-1β during shigellosis.

METHODS

The mucin-Shigella interaction was revealed by an in vitro mucin-binding assay. Invasion of Shigella dysenteriae into HT-29 cells was analyzed by Transmission electron microscopy. Shigella induced mucin and IL-1β expression were analyzed by RT-PCR and Immunofluorescence.

RESULTS

The clinical isolates of Shigella were found to be virulent by a congo-red binding assay. The in vitro mucin-binding assay revealed both Shigella dysenteriae and Shigella flexneri have binding affinity in the increasing order of: guinea pig small intestinal mucin

CONCLUSIONS

Our study concludes that the Shigella species specifically binds to guinea pig colonic mucin, but not to guinea pig small intestinal mucin. The guinea pig colonic mucin showed a greater binding parameter (R), and more saturable binding, suggesting the presence of a finite number of receptor binding sites in the colonic mucin of the host. In addition, modification of mucins with TFMS and sodium metaperiodate significantly reduced mucin-bacterial binding; suggesting that the mucin-Shigella interaction occurs through carbohydrate epitopes on the mucin backbones. Overproduction of MUC2 may alter adherence and invasion of Shigella dysenteriae into human colonic epithelial cells.

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MESH Headings

• Animals
• Base Sequence
• Cell Line
• Colon/cytology
• Colon/metabolism
• DNA Primers
• Enzyme-Linked Immunosorbent Assay
• Epithelial Cells/metabolism
• Guinea Pigs
• Humans
• Interleukin-1beta/metabolism
• Microscopy, Electron, Transmission
• Mucin-2/metabolism
• Reverse Transcriptase Polymerase Chain Reaction
• Shigella dysenteriae/pathogenicity
• Shigella dysenteriae/physiology
• Up-Regulation
• Virulence

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Affiliation(s)

Radhakrishnan Prakash Department of Biochemistry, University of Madras, Guindy Campus, Chennai, Tamilnadu, India
Subramaniya Bharathi Raja Department of Biochemistry, University of Madras, Guindy Campus, Chennai, Tamilnadu, India
Halagowder Devaraj Unit of Biochemistry, Department of Zoology, University of Madras, Guindy Campus, Chennai, Tamilnadu, India
Sivasitambaram Niranjali Devaraj Department of Biochemistry, University of Madras, Guindy Campus, Chennai, Tamilnadu, India

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Monitoring the glycosylation status of proteins using Raman spectroscopy

Protein-based biopharmaceuticals are becoming increasingly widely used as therapeutic agents, and the characterization of these biopharmaceuticals poses a significant analytical challenge. In particular, monitoring posttranslational modifications (PTMs), such as glycosylation, is an important aspect of this characterization because these glycans can strongly affect the stability, immunogenicity, and pharmacokinetics of these biotherapeutic drugs. Raman spectroscopy is a powerful tool, with many emerging applications in the bioprocessing arena. Although the technique has a relatively rich history in protein science, only recently has Raman spectroscopy been investigated for assessing posttranslational modifications, including phosphorylation, acetylation, trimethylation, and ubiquitination. In this investigation, we develop for the first time Raman spectroscopy combined with multivariate data analyses, including principal components analysis and partial least-squares regression, for the determination of the glycosylation status of proteins and quantifying the relative concentrations of the native ribonuclease (RNase) A protein and RNase B glycoprotein within mixtures.

Restricted lateral diffusion of luteinizing hormone receptors in membrane microdomains

Single particle tracking was used to evaluate lateral motions of individual FLAG-tagged human luteinizing hormone (LH) receptors expressed on CHO cells and native LH receptors on both KGN human granulosa-derived tumor cells and M17 human neuroblastoma cells before and after exposure to human chorionic gonadotropin (hCG). Compared with LH receptors on untreated cells, LH receptors on cells treated with 100 nm hCG exhibit restricted lateral diffusion and are confined in small, nanometer-scale, membrane compartments. Similar to LH receptors labeled with Au-hCG, LH receptors labeled with gold-deglycosylated hCG, an hCG antagonist, also exhibit restricted lateral diffusion and are confined in nanoscale membrane compartments on KGN cells treated with 100 nm hCG. LH receptor point mutants lacking potential palmitoylation sites remain in large compartments despite treatment with 100 nm hCG as do LH receptors on cells treated with cytochalasin D. Finally, both polarization homotransfer fluorescence resonance energy transfer imaging and photon counting histogram analysis indicate that treatment with hCG induces aggregation of YFP-coupled LH receptors stably expressed on CHO cells. Taken together, our results demonstrate that binding of hCG induces aggregation of LH receptors within nanoscale, cell surface membrane compartments, that hCG binding also affects the lateral motions of antagonist binding LH receptors, and that receptor surface densities must be considered in evaluating the extent of hormone-dependent receptor aggregation.

Nautilin-63, a novel acidic glycoprotein from the shell nacre of Nautilus macromphalus

In molluscs, and more generally in metazoan organisms, the production of a calcified skeleton is a complex molecular process that is regulated by the secretion of an extracellular organic matrix. This matrix constitutes a cohesive and functional macromolecular assemblage, containing mainly proteins, glycoproteins and polysaccharides that, together, control the biomineral formation. These macromolecules interact with the extruded precursor mineral ions, mainly calcium and bicarbonate, to form complex organo-mineral composites of well-defined microstructures. For several reasons related to its remarkable mechanical properties and to its high value in jewelry, nacre is by far the most studied molluscan shell microstructure and constitutes a key model in biomineralization research. To understand the molecular mechanism that controls the formation of the shell nacreous layer, we have investigated the biochemistry of Nautilin-63, one of the main nacre matrix proteins of the cephalopod Nautilus macromphalus. After purification of Nautilin-63 by preparative electrophoresis, we demonstrate that this soluble protein is glycine-aspartate-rich, that it is highly glycosylated, that its sugar moieties are acidic, and that it is able to bind chitin in vitro. Interestingly, Nautilin-63 strongly interacts with the morphology of CaCO(3) crystals precipitated in vitro but, unexpectedly, it exhibits an extremely weak ability to inhibit in vitro the precipitation of CaCO(3) . The partial resolution of its amino acid sequence by de novo sequencing of its tryptic peptides indicates that Nautilin-63 exhibits short collagenous-like domains. Owing to specific polyclonal antibodies raised against the purified protein, Nautilin-63 was immunolocalized mainly in the intertabular nacre matrix. In conclusion, Nautilin-63 exhibits 'hybrid' biochemical properties that are found both in the soluble and insoluble proteins, rendering it difficult to classify according to the standard view on nacre proteins.

DATABASE

The protein sequences of N63 appear on the UniProt Knowledgebase under accession number P86702.

The membrane mucin Msb2 regulates invasive growth and plant infection in Fusarium oxysporum

Fungal pathogenicity in plants requires a conserved mitogen-activated protein kinase (MAPK) cascade homologous to the yeast filamentous growth pathway. How this signaling cascade is activated during infection remains poorly understood. In the soil-borne vascular wilt fungus Fusarium oxysporum, the orthologous MAPK Fmk1 (Fusarium MAPK1) is essential for root penetration and pathogenicity in tomato (Solanum lycopersicum) plants. Here, we show that Msb2, a highly glycosylated transmembrane protein, is required for surface-induced phosphorylation of Fmk1 and contributes to a subset of Fmk1-regulated functions related to invasive growth and virulence. Mutants lacking Msb2 share characteristic phenotypes with the Δfmk1 mutant, including defects in cellophane invasion, penetration of the root surface, and induction of vascular wilt symptoms in tomato plants. In contrast with Δfmk1, Δmsb2 mutants were hypersensitive to cell wall targeting compounds, a phenotype that was exacerbated in a Δmsb2 Δfmk1 double mutant. These results suggest that the membrane mucin Msb2 promotes invasive growth and plant infection upstream of Fmk1 while contributing to cell integrity through a distinct pathway.

Diversity in protein glycosylation among insect species

BACKGROUND

A very common protein modification in multicellular organisms is protein glycosylation or the addition of carbohydrate structures to the peptide backbone. Although the Class of the Insecta is the largest animal taxon on Earth, almost all information concerning glycosylation in insects is derived from studies with only one species, namely the fruit fly Drosophila melanogaster.

METHODOLOGY/PRINCIPAL FINDINGS

In this report, the differences in glycoproteomes between insects belonging to several economically important insect orders were studied. Using GNA (Galanthus nivalis agglutinin) affinity chromatography, different sets of glycoproteins with mannosyl-containing glycan structures were purified from the flour beetle (Tribolium castaneum), the silkworm (Bombyx mori), the honeybee (Apis mellifera), the fruit fly (D. melanogaster) and the pea aphid (Acyrthosiphon pisum). To identify and characterize the purified glycoproteins, LC-MS/MS analysis was performed. For all insect species, it was demonstrated that glycoproteins were related to a broad range of biological processes and molecular functions. Moreover, the majority of glycoproteins retained on the GNA column were unique to one particular insect species and only a few glycoproteins were present in the five different glycoprotein sets. Furthermore, these data support the hypothesis that insect glycoproteins can be decorated with mannosylated O-glycans.

CONCLUSIONS/SIGNIFICANCE

The results presented here demonstrate that oligomannose N-glycosylation events are highly specific depending on the insect species. In addition, we also demonstrated that protein O-mannosylation in insect species may occur more frequently than currently believed.

The role of the proteinase inhibitor ovorubin in apple snail eggs resembles plant embryo defense against predation

BACKGROUND

Fieldwork has thoroughly established that most eggs are intensely predated. Among the few exceptions are the aerial egg clutches from the aquatic snail Pomacea canaliculata which have virtually no predators. Its defenses are advertised by the pigmented ovorubin perivitellin providing a conspicuous reddish coloration. The nature of the defense however, was not clear, except for a screening for defenses that identified a neurotoxic perivitellin with lethal effect on rodents. Ovorubin is a proteinase inhibitor (PI) whose role to protect against pathogens was taken for granted, according to the prevailing assumption. Through biochemical, biophysical and feeding experiments we studied the proteinase inhibitor function of ovorubin in egg defenses.

METHODOLOGY/PRINCIPAL FINDINGS

Mass spectrometry sequencing indicated ovorubin belongs to the Kunitz-type serine proteinase inhibitor family. It specifically binds trypsin as determined by small angle X-ray scattering (SAXS) and cross-linking studies but, in contrast to the classical assumption, it does not prevent bacterial growth. Ovorubin was found extremely resistant to in vitro gastrointestinal proteolysis. Moreover feeding studies showed that ovorubin ingestion diminishes growth rate in rats indicating that this highly stable PI is capable of surviving passage through the gastrointestinal tract in a biologically active form.

CONCLUSIONS

To our knowledge, this is the first direct evidence of the interaction of an egg PI with a digestive protease of potential predators, limiting predator's ability to digest egg nutrients. This role has not been reported in the animal kingdom but it is similar to plant defenses against herbivory. Further, this would be the only defense model with no trade-offs between conspicuousness and noxiousness by encoding into the same molecule both the aposematic warning signal and an antinutritive/antidigestive defense. These defenses, combined with a neurotoxin and probably unpalatable factors would explain the near absence of predators, opening new perspectives in the study of the evolution and ecology of egg defensive strategies.