Asparagine-linked Glycosylation Sites Research Articles

26P Structurally constrained tumor-specific epitope within the largest extracellular domain of sodium-dependent phosphate transporter NaPi2b

The search for tumor-specific targets among membrane proteins is important for the development for new effective anticancer drugs because membrane proteins represent 60% of drug targets. Transmembrane proteins in cancer cells exhibit an altered pattern of post-translational modifications and generally contain a large extracellular domains with multiple glycosylation and sulfhydryl sites with unknown function. We analyze the features of membrane protein which are required for recognition by monoclonal antibodies using the sodium-dependent phosphate transporter NaPi2b, containing a large extracellular domain 4 (EMD4, 250-360 a.a.) with 4 cysteines and 6 potential asparagine-linked glycosylation sites which can potentially contribute to foldability of conformationally exposed epitope corresponding to this domain.

N-glycosylation of the human \u03b21,4-galactosyltransferase 4 is crucial for its activity and Golgi localization

β1,4-galactosyltransferase 4 (B4GalT4) is one of seven B4GalTs that belong to CAZy glycosyltransferase family 7 and transfer galactose to growing sugar moieties of proteins, glycolipids, glycosaminoglycans as well as single sugar for lactose synthesis. Herein, we identify two asparagine-linked glycosylation sites in B4GalT4. We found that mutation of one site (Asn220) had greater impact on enzymatic activity while another (Asn335) on Golgi localization and presence of N-glycans at both sites is required for production of stable and enzymatically active protein and its secretion. Additionally, we confirm B4GalT4 involvement in synthesis of keratan sulfate (KS) by generating A375 B4GalT4 knock-out cell lines that show drastic decrease in the amount of KS proteoglycans and no significant structural changes in N- and O-glycans. We show that KS decrease in A375 cells deficient in B4GalT4 activity can be rescued by overproduction of either partially or fully glycosylated B4GalT4 but not with N-glycan-depleted B4GalT4 version.

Quantitative assessment of mAb Fc glycosylation of CQA importance by capillary electrophoresis

The attached carbohydrates at the highly conserved asparagine-linked glycosylation site in the CH 2 domain of the fragment crystallizable (Fc) region of monoclonal antibody therapeutics can play an essential role in their mechanism of action, including ADCC, CDC, anti-inflammatory functions, and serum half-life. Thus, this particular glycosylation represents one of the important critical quality attributes (CQA) of therapeutic monoclonal antibodies, which should be closely monitored and controlled during all stages of biopharmaceutical manufacturing. To study Fc glycosylation related quantitative critical quality attributes, the N-glycan pool of adalimumab (Humira® ) was spiked with increasing amounts of mannose-5 oligosaccharide, a glycan with high CQA importance. The method enabled precise quantitative CQA assessment with high detection sensitivity.

Abstract P206: Structural Analysis of Glycosyl Chain at 14th Amino Acid Of Human Angiotensinogen in Plasma

The Renin angiotensin system (RAS) is a major regulator of body fluid balance and control of blood pressure. The protease enzyme renin secreted from kidneys cleaves speci[[Unable to Display Character: fi]]cally angiotensinogen (Aogen) circulating in the blood to produce angiotensin I (Ang I). Human Aogen is a heterogeneous glycoprotein constitutively secreted by the liver. In addition, human Aogen contains four putative asparagine-linked glycosylation sites (Asn 14, 137, 271, 295) and contains four cysteines (Cys 18, 138, 232, 308), with Cys18 and Cys138 linked by a disulfide bridge. The glycosyl chains and cysteines position are very important for binding of the renin. Big angiotensin-25 (Bang-25) is a consisting of 25 amino acids with glycosyl chain (14th amino asid) and added cysteine (18th amino acid), which we recently isolated from human urine. To compare glycosyl chain of Bang-25 and Aogen, we analyzed of structure glycosyl chain at position 14th amino acid of human Aogen in plasma. To determine of glycosyl chain at position 14th amino acid, we performed lysyl endopeptidase digestion and reduction on human plasma Aogen. Then, Aogen after digest was purified by reverse-phase high-performance liquid chromatograpy (RP-HPLC), and glycosyl chain structure analyzed by the two-/three-dimensional HPLC mapping method. We show that plasma Aogen has three types of glycosyl chain at position 14th amino acid. One glycosyl chain structure is identical to Bang-25 in urine. N-linked glycosylation on 14th amino acid of Aogen plays an important role about renin reaction. In addition, Bang-25 is rapidly cleaved by chymase to Ang II, but is resistant to cleave by renin. These results suggest that the structure of the glycosyl chain at position 14th amino acid of the human Aogen may be involved in the substrate specificity for renin or chymase.

Altered trafficking and unfolded protein response induction as a result of M3 muscarinic receptor impaired N-glycosylation

The human M(3) muscarinic acetylcholine receptor is present in both the central and peripheral nervous system, and it is involved in the pathophysiology of several neurodegenerative and autoimmune diseases. We suggested a possible N-glycosylation map for the M(3) muscarinic receptor expressed in COS-7 cells. Here, we examined the role that N-linked glycans play in the folding and in the cell surface trafficking of this receptor. The five potential asparagine-linked glycosylation sites in the muscarinic receptor were mutated and transiently expressed in COS-7 cells. The elimination of N-glycan attachment sites did not affect the cellular expression levels of the receptor. However, proper receptor localization to the plasma membrane was affected as suggested by reduced [(3)H]-N-methylscopolamine binding. Confocal microscopy confirmed this observation and showed that the nonglycosylated receptor was primarily localized in the intracellular compartments. The mutant variant showed an increase in phosphorylation of the α-subunit of eukaryote initiation factor 2, and other well-known endoplasmic reticulum stress markers of the unfolded protein response pathway, which further supports the proposal of the improper intracellular accumulation of the nonglycosylated receptor. The receptor devoid of glycans showed more susceptibility to events that culminate in apoptosis reducing cell viability. Our findings suggest up-regulation of pro-apoptotic Bax protein, down-regulation of anti-apoptotic Bcl-2, and cleavage of caspase-3 effectors. Collectively, our data provide experimental evidence of the critical role that N-glycan chains play in determining muscarinic receptor distribution, localization, as well as cell integrity.

Loss of Asparagine-Linked Glycosylation Sites in Variable Region 5 of Human Immunodeficiency Virus Type 1 Envelope Is Associated with Resistance to CD4 Antibody Ibalizumab

Ibalizumab (formerly TNX-355) is a first-in-class, monoclonal antibody inhibitor of CD4-mediated human immunodeficiency type 1 (HIV-1) entry. Multiple clinical trials with HIV-infected patients have demonstrated the antiviral activity, safety, and tolerability of ibalizumab treatment. A 9-week phase Ib study adding ibalizumab monotherapy to failing drug regimens led to transient reductions in HIV viral loads and the evolution of HIV-1 variants with reduced susceptibility to ibalizumab. This report characterizes these variants by comparing the phenotypic susceptibilities and envelope (env) sequences of (i) paired baseline and on-treatment virus populations, (ii) individual env clones from selected paired samples, and (iii) env clones containing site-directed mutations. Viruses with reduced susceptibility to ibalizumab were found to exhibit reduced susceptibility to the anti-CD4 antibody RPA-T4. Conversely, susceptibility to soluble CD4, which targets the HIV-1 gp120 envelope protein, was enhanced. No changes in susceptibility to the fusion inhibitor enfuvirtide or the CCR5 antagonist maraviroc were observed. Functionally, viruses with reduced ibalizumab susceptibility also displayed high levels of infectivity relative to those of paired baseline viruses. Individual env clones exhibiting reduced ibalizumab susceptibility contained multiple amino acid changes in different regions relative to the paired baseline clones. In particular, clones with reduced susceptibility to ibalizumab contained fewer potential asparagine-linked glycosylation sites (PNGSs) in variable region 5 (V5) than did paired ibalizumab-susceptible clones. The reduction in ibalizumab susceptibility due to the loss of V5 PNGSs was confirmed by site-directed mutagenesis. Taken together, these findings provide important insights into resistance to this new class of antiretroviral drug.

Crystallographic Complexes of Surfactant Protein A and Carbohydrates Reveal Ligand-induced Conformational Change

Surfactant protein A (SP-A), a C-type lectin, plays an important role in innate lung host defense against inhaled pathogens. Crystallographic SP-A·ligand complexes have not been reported to date, limiting available molecular information about SP-A interactions with microbial surface components. This study describes crystal structures of calcium-dependent complexes of the C-terminal neck and carbohydrate recognition domain of SP-A with d-mannose, D-α-methylmannose, and glycerol, which represent subdomains of glycans on pathogen surfaces. Comparison of these complexes with the unliganded SP-A neck and carbohydrate recognition domain revealed an unexpected ligand-associated conformational change in the loop region surrounding the lectin site, one not previously reported for the lectin homologs SP-D and mannan-binding lectin. The net result of the conformational change is that the SP-A lectin site and the surrounding loop region become more compact. The Glu-202 side chain of unliganded SP-A extends out into the solvent and away from the calcium ion; however, in the complexes, the Glu-202 side chain translocates 12.8 Å to bind the calcium. The availability of Glu-202, together with positional changes involving water molecules, creates a more favorable hydrogen bonding environment for carbohydrate ligands. The Lys-203 side chain reorients as well, extending outward into the solvent in the complexes, thereby opening up a small cation-friendly cavity occupied by a sodium ion. Binding of this cation brings the large loop, which forms one wall of the lectin site, and the adjacent small loop closer together. The ability to undergo conformational changes may help SP-A adapt to different ligand classes, including microbial glycolipids and surfactant lipids.

Analysis of the Fusion Protein Gene of Newcastle Disease Viruses Isolated in Japan

The complete nucleotide sequences of the fusion (F) protein gene of Newcastle disease viruses (NDV) isolated in Japan from 1930 to 2007 (45 strains total) were determined and genetically analyzed. In the deduced amino acid sequences of fusion protein, the 5 potential asparagine-linked glycosylation sites and 10 cysteine residues were all conserved in the NDV examined in this study. The major epitopes involved in virus neutralization are conserved in most of the NDV strains isolated in Japan except a few strains. By virus neutralization test, no major antigenic differences were observed among representative strains of each genotype in Japan. All chickens vaccinated with the B1 strain survived without clinical signs after challenge with 2 NDV strains isolated in Japan (velogenic strains, JP/Ibaraki/2000 and JP/Kagoshima/91), which possess amino acids substitutions involved in virus neutralization in the F protein gene.

A Single Asparagine-Linked Glycosylation Site of the Severe Acute Respiratory Syndrome Coronavirus Spike Glycoprotein Facilitates Inhibition by Mannose-Binding Lectin through Multiple Mechanisms

Mannose-binding lectin (MBL) is a serum protein that plays an important role in host defenses as an opsonin and through activation of the complement system. The objective of this study was to assess the interactions between MBL and severe acute respiratory syndrome-coronavirus (SARS-CoV) spike (S) glycoprotein (SARS-S). MBL was found to selectively bind to retroviral particles pseudotyped with SARS-S. Unlike several other viral envelopes to which MBL can bind, both recombinant and plasma-derived human MBL directly inhibited SARS-S-mediated viral infection. Moreover, the interaction between MBL and SARS-S blocked viral binding to the C-type lectin, DC-SIGN. Mutagenesis indicated that a single N-linked glycosylation site, N330, was critical for the specific interactions between MBL and SARS-S. Despite the proximity of N330 to the receptor-binding motif of SARS-S, MBL did not affect interactions with the ACE2 receptor or cathepsin L-mediated activation of SARS-S-driven membrane fusion. Thus, binding of MBL to SARS-S may interfere with other early pre- or postreceptor-binding events necessary for efficient viral entry.

Synthesis, purification and characterization of recombinant glycosylated human prolactin (G-hPRL) secreted by cycloheximide-treated CHO cells

Human prolactin (hPRL) is a 199 aminoacid protein hormone with a wide spectrum of biological activities which is best known for its stimulation of lactation and development of mammary gland. This protein contains only one potential asparagine-linked glycosylation site, which is partially (10–30%) occupied when the protein is synthesized in eukaryotic cells. Although the biological activity of glycosylated hPRL (G-hPRL) has been found to be ∼4-fold lower than that of hPRL, its physiological function is not yet well defined. In order to better characterize and study this hormone variant, we carried out its laboratory scale purification from conditioned medium of genetically modified CHO cells that had been supplemented with cycloheximide. Addition of cycloheximide increased the absolute concentration of G-hPRL ∼4-fold and the glycosylated versus non-glycosylated hPRL concentration ratio by ∼7-fold. G-hPRL purification was carried out via a two-step process based on a cationic exchanger and a size-exclusion HPLC (HPSEC) column. Characterization was carried out by HPSEC, Western blotting, MALDI-TOF-MS and in vitro bioassay based on Nb2 and Ba/F3-LLP cells, the biological activity being of the same order (11–15 IU mg −1) in the two assays. Our results show that addition of cycloheximide can be an important strategy for increasing glycosylated protein production, facilitating the purification and characterization of these isoforms.

The role of asparagine-linked glycosylation site on the catalytic domain of matriptase in its zymogen activation

Matriptase is a type II transmembrane serine protease containing one potential site for asparagine-linked glycosylation (N-glycosylation) on the catalytic domain (Asn772). It has been found that the activation of matriptase zymogen occurs via a mechanism requiring its own activity and that the N-glycosylation site is critical for the activation. The present study aimed to determine the underlying reasons for the site requirement using Madin–Darby canine kidney cells stably expressing recombinant variants of rat matriptase. A full-length variant with glutamine substitution at Asn772 appeared to be unable to undergo activation because of its catalytic incompetence (i.e., decreased availability of the soluble catalytic domain and/or of the correctly folded domain). This was evidenced by the observations that (i) a recombinant catalytic domain of matriptase with glutamine substitution at the site corresponding to matriptase Asn772 [N772Q-CD-Myc(His)6] was not detected in the medium conditioned by transfected cells but was on the cell surface and (ii) purified N772Q-CD-Myc(His)6 exhibited markedly reduced activity toward a peptide substrate. It is concluded that N-glycosylation site at Asn772 of matriptase is required for the zymogen activation because it plays an important role in rendering this protease catalytically competent in the cellular environment.

Reduction of Inhibitory Anti-FVIII Antibody Titer by Using a B Domain Variant FVIII/N6 cDNA for Nonviral Gene Therapy in Hemophilia a Mice

Due to the large size of FVIII, a B-domain deleted FVIII (BDD-FVIII) cDNA is usually used for developing gene therapy protocols for treating hemophilia A. Inefficient transcription of wild- type FVIII cDNA can be overcome by deletion of the heavily glycosylated B-domain encoding portion of the gene. BDD-FVIII is as clinically efficacious and not more immunogenic than full-length recombinant FVIII. More recently, it was demonstrated that a partial deletion of the B-domain leaving an N-terminal 226 amino acid stretch containing 6 putative asparagine-linked glycosylation sites intact (FVIII/N6) was able to increase in vitro and in vivo secretion of FVIII by 10–15 fold. We have inserted this B domain variant FVIII/N6 cDNA into our liver-specific gene expression vector. The resulting construct, FVIII/N6 plasmid was delivered into the hemophilia A mouse liver by the hydrodynamic method. In control mice treated with BDD-FVIII plasmid (n=5/group), FVIII expression dropped to undetectable levels at 2 weeks post injection and high-titer anti-FVIII antibodies were generated in all the plasmid-treated mice. However, in mice treated with FVIII/N6 plasmid (n=5/group), one out of five mice never developed inhibitory antibodies and still had some FVIII gene expression (~10%) at 8 weeks post gene transfer. Three FVIII/N6 plasmid-treated mice developed anti-FVIII antibodies with significantly reduced inhibitor titer and only one mouse developed high-titer inhibitory antibodies. The CD4+ T cells isolated from the spleen of mice injected with FVIII/N6 constructs proliferated less in response to FVIII stimulation than those from mice injected with BDD-FVIII. These results indicate that FVIII/N6 protein is less immunogenic than BDD-FVIII. Interestingly, both BDD-FVIII and FVIII/N6 constructs produced similar levels of FVIII gene expression (100–300%) initially following nonviral gene transfer. However this could be due to saturation of the ER to Golgi transport apparatus for FVIII by the initial high-level gene expression. Gene expression levels produced by using reduced dosages of BDD-FVIII and FVIII/N6 plasmids are currently being evaluated and compared. These findings suggest that use of a FVIII/N6 construct decreases transgene-specific immune responses following nonviral gene transfer and facilitates long-term gene expression.

Pharmacological Characterization of Membrane-Expressed Human Trace Amine-Associated Receptor 1 (TAAR1) by a Bioluminescence Resonance Energy Transfer cAMP Biosensor

Trace amines are neurotransmitters whose role in regulating invertebrate physiology has been appreciated for many decades. Recent studies indicate that trace amines may also play a role in mammalian physiology by binding to a novel family of G protein-coupled receptors (GPCRs) that are found throughout the central nervous system. A major obstacle impeding the careful pharmacological characterization of trace amine associated receptors (TAARs) is their extremely poor membrane expression in model cell systems, and a molecular basis for this phenomenon has not been determined. In the present study, we show that the addition of an asparagine-linked glycosylation site to the N terminus of the human trace amine associated receptor 1 (TAAR1) is sufficient to enable its plasma membrane expression, and thus its pharmacological characterization with a novel cAMP EPAC (exchange protein directly activated by cAMP) protein based bioluminescence resonance energy transfer (BRET) biosensor. We applied this novel cAMP BRET biosensor to evaluate the activity of putative TAAR1 ligands. This study represents the first comprehensive investigation of the membrane-expressed human TAAR1 pharmacology. Our strategy to express TAARs and to identify their ligands using a cAMP BRET assay could provide a foundation for characterizing the functional role of trace amines in vivo and suggests a strategy to apply to groups of poorly expressing GPCRs that have remained difficult to investigate in model systems.

Quail Sulf1 Function Requires Asparagine-linked Glycosylation

The heparan sulfate endosulfatases Sulf1 and Sulf2 are cell-surface enzymes that control growth factor signaling through regulation of the 6-O-sulfation states of cell-surface and matrix heparan sulfate proteoglycans. Here, we report that quail Sulf1 (QSulf1) is an asparagine-linked glycosylated protein. Domain mapping studies in combination with a protein glycosylation prediction program identified multiple asparagine-linked glycosylation sites in the enzymatic and C-terminal domains. Glycosylation inhibitor studies revealed that glycosylation of QSulf1 is essential for its enzymatic activity, membrane targeting, and secretion. Furthermore, N-glycanase cleavage of asparagine-linked sites in native QSulf1 provided direct evidence that these N-linked glycosylation sites are specifically required for QSulf1 heparin binding and its 6-O-desulfation activity, revealing that N-linked glycosylation has a key role in the control of sulfatase enzymatic function.

Specific Asparagine-Linked Glycosylation Sites Are Critical for DC-SIGN- and L-SIGN-Mediated Severe Acute Respiratory Syndrome Coronavirus Entry

Severe acute respiratory syndrome (SARS) is caused by a newly emerged coronavirus (CoV) designated SARS-CoV. The virus utilizes angiotensin-converting enzyme 2 (ACE2) as the primary receptor. Although the idea is less clear and somewhat controversial, SARS-CoV is thought to use C-type lectins DC-SIGN and/or L-SIGN (collectively referred to as DC/L-SIGN) as alternative receptors or as enhancer factors that facilitate ACE2-mediated virus infection. In this study, the function of DC/L-SIGN in SARS-CoV infection was examined in detail. The results of our study clearly demonstrate that both proteins serve as receptors independently of ACE2 and that there is a minimal level of synergy between DC/L-SIGN and ACE2. As expected, glycans on spike (S) glycoprotein are important for DC/L-SIGN-mediated virus infection. Site-directed mutagenesis analyses have identified seven glycosylation sites on the S protein critical for DC/L-SIGN-mediated virus entry. They include asparagine residues at amino acid positions 109, 118, 119, 158, 227, 589, and 699, which are distinct from residues of the ACE2-binding domain (amino acids 318 to 510). Amino acid sequence analyses of S proteins encoded by viruses isolated from animals and humans suggest that glycosylation sites N227 and N699 have facilitated zoonotic transmission.

Biochemical characterization and molecular cloning of a plasminogen activator proteinase (LV-PA) from bushmaster snake venom

The protein (LV-PA) from bushmaster ( Lachesis muta muta) venom is a serine proteinase which specifically activates the inactive proenzyme plasminogen. LV-PA is a single chain glycoprotein with an apparent molecular mass of 33 kDa that fell to 28 kDa after treatment with N-Glycosidase F (PNGase F). Approximately 93% of its protein sequence was determined by automated Edman degradation of various fragments derived from a digestion with trypsin. A cDNA library of L. m. muta was constructed to generate expressed sequence tags (ESTs) and the plasminogen activator precursor cDNA was sequenced. The complete amino acid sequence of the enzyme was deduced from the cDNA sequence. LV-PA is composed of 234 residues and contains a single asparagine-linked glycosylation site, Asn-X-Ser, bearing sugars that account for ∼ 10% of the enzyme's total molecular mass of 33 kDa. The sequence of LV-PA is highly similar to the plasminogen activators (PAs) TSV-PA from Trimeresurus stejnegeri venom and Haly-PA from Agkistrodon halys. Furthermore, the mature protein sequence of LV-PA exhibits significant similarity with other viperidae venom serine proteinases which affect many steps of hemostasis, ranging from the blood coagulation cascade to platelet function. The Michaelis constant (Km) and the catalytic rate constant (kcat) of LV-PA on four chromogenic substrates were obtained from Lineweaver–Burk plots. In addition, we used an indirect enzyme-linked immunoabsorbent assay (ELISA) to explore the phylogenetic range of immunological cross-reactivity (using antibodies raised against LV-PA) with analogous serine proteinases from two viperidae venoms and mammals.

Thematic review series: Lipid Posttranslational Modifications. Lysosomal metabolism of lipid-modified proteins

Much is now understood concerning the synthesis of prenylated and palmitoylated proteins, but what is known of their metabolic fate? This review details metabolic pathways for the lysosomal degradation of S-fatty acylated and prenylated proteins. Central to these pathways are two lysosomal enzymes, palmitoyl-protein thioesterase (PPT1) and prenylcysteine lyase (PCL). PPT1 is a soluble lipase that cleaves fatty acids from cysteine residues in proteins during lysosomal protein degradation. Notably, deficiency in the enzyme causes a neurodegenerative lysosomal storage disorder, infantile neuronal ceroid lipofuscinosis. PCL is a membrane-associated flavin-containing lysosomal monooxygenase that metabolizes prenylcysteine to prenyl aldehyde through a completely novel mechanism. The eventual metabolic fates of other lipidated proteins (such as glycosylphosphatidylinositol-anchored and N-myristoylated proteins) are poorly understood, suggesting directions for future research.

Molecular cloning and sequence analysis of a cDNA encoding pituitary thyroid stimulating hormone β-subunit of the Chinese soft-shell turtle Pelodiscus sinensis and regulation of its gene expression

A cDNA encoding thyroid stimulating hormone β-subunit (TSHβ) was cloned from pituitary of the Chinese soft-shell turtle, Pelodiscus sinensis, and its regulation of mRNA expression was investigated for the first time in reptile. The Chinese soft-shell turtle TSHβ cDNA was cloned from pituitary RNA by reverse transcription and polymerase chain reaction (RT-PCR), and rapid amplification cDNA end (RACE) methods. The Chinese soft-shell turtle TSHβ cDNA consists of 580-bp nucleotides, including 67-bp nucleotides of 5′-untranslated region (UTR), 402-bp of the open reading frame, and 97-bp of 3′-UTR followed by a 14 poly (A) trait. It encodes a precursor protein molecule of 133 amino acids with a putative signal peptide of 19 amino acids and a putative mature protein of 114 amino acids. The number and position of 12 cysteine residues, presumably forming six disulfide bonds, one putative asparagine-linked glycosylation site, and six proline residues that are found at positions for changing the backbone direction of the protein have been conserved in the turtle as in other vertebrate groups. The deduced amino acid sequence of the Chinese soft-shell turtle TSHβ mature protein shares identities of 82–83% with birds, 71–72% with mammals, 49–57% with amphibians, and 44–61% with fish. The Chinese soft-shell turtle pituitaries were incubated in vitro with synthetic TRH (TSH-releasing hormone), thyroxine and triiodothyronine at doses of 10 −10 and 10 −8 M. TRH stimulated, while thyroid hormones suppressed, TSHβ mRNA levels in dose-related manner. The sequences of cDNA and its deduced peptide of TSHβ as well as the regulation of its mRNA level were reported for the first time in reptile.

Elucidation of N-Glycosylation Sites on Human Platelet Proteins

Among known platelet proteins, a prominent and functionally important group is represented by glycoprotein isoforms. They account e.g. for secretory proteins and plasma membrane receptors including integrins and glycoprotein VI as well as intracellular components of cytosol and organelles including storage proteins (multimerin 1 etc.). Although many of those proteins have been studied for some time with regard to their function, little attention has been paid with respect to their glycosylation sites. Here we report the analysis of N-glycosylation sites of human platelet proteins. For the enrichment of glycopeptides, lectin affinity chromatography as well as chemical trapping of protein bound oligosaccharides was used. Therefore, concanavalin A was used for specific interaction with carbohydrate species along with periodic acid oxidation and hydrazide bead trapping of glycosylated proteins. Derivatization by peptide:N-glycosidase F yielded deglycosylated peptides, which provided the basis for the elucidation of proteins and their sites of modification. Using both methods in combination with nano-LC-ESI-MS/MS analysis 70 different glycosylation sites within 41 different proteins were identified. Comparison with the Swiss-Prot database established that the majority of these 70 sites have not been specifically determined by previous research projects. With this approach including hydrazide bead affinity trapping, the immunoglobulin receptor G6f, which is known to couple to the Ras-mitogen-activated protein kinase pathway in the immune system, was shown here for the first time to be present in human platelets.

Expression of Nox genes in rat organs, mouse oocytes, and sea urchin eggs

Degenerate primers were designed to isolate new homologs of Nox family genes in rat organs and sea urchin eggs. The primers were capable of amplifying Nox1, Nox2, Nox3, Nox4, Duox1 and Duox2 but not Nox5, and failed to isolate novel homologs in rat. However, a novel homolog (named as Nox-U1) was identified in sea urchin eggs. In the most conserved region (amino acid 336--417 in human Nox2) Nox-U1 has the highest identity with Nox2, which appears to be abundant in mouse oocytes. However, phylogenetic analysis of the entire sequence has revealed that Nox-U1 is closer to Nox4 or Nox5 than Nox2 or Nox3. Histidine residues assumed to be responsible for heme ligation, motifs for FAD- and NADPH-binding, and two asparagine-linked glycosylation sites are conserved.