Aberrant Protein Glycosylation Research Articles

Glycomic Analysis Using Glycoprotein Immobilization for Glycan Extraction

Glycosylation is one of the most common protein modifications and is involved in many functions of glycoproteins. Investigating aberrant protein glycosylation associated with diseases is useful in improving disease diagnostics. Due to the nontemplate nature of glycan biosynthesis, the glycans attached to glycoproteins are enormously complex; thus, a method for comprehensive analysis of glycans from biological or clinical samples is needed. Here, we describe a novel method for glycomic analysis using glycoprotein immobilization for glycan extraction (GIG). Proteins or peptides from complex samples were first immobilized on solid support, and other nonconjugated molecules were removed. Glycans were enzymatically or chemically modified on solid phase before releasing from glycoproteins/glycopeptides for mass spectrometry analysis. The method was applied to the glycomic analysis of both N- and O-glycans.

Aberrant glycosylation of plasma proteins in HIV-infected patients (P6361)

Abstract Background: Glycosylation is one of the most abundant post-translational modifications, and is involved in protein structure formation and protein-protein interactions. Aberrant glycosylation profiles are often observed on plasma proteins from patients with inflammatory diseases. Increased levels of non-galactosylated glycans have been reported on serum IgGs of HIV-infected patients. We investigated the effects of HIV infection on protein glycosylation by N-glycomic profiling of plasma and plasma IgG. Methods: We obtained plasma samples of 22 HIV infected patients (11 therapy-naïve, 11 receiving anti-retroviral therapy) and 11 HIV-negative controls. First, a nano-LC-TOF-MS strategy was employed for the evaluation of plasma N-glycan profiles in each of the samples. Then, a UPLC-QQQ-MS method was used to evaluate the IgG specific glycosylation patterns. N-glycan peak integrals were used for biostatistical analysis. Results and conclusion: Several neutral, fucosylated and sialylated glycan compositions as well as high mannose type glycans in plasma samples were significantly altered in therapy-naïve HIV infected patients compared to controls. Moreover, galactose-deficient glycans were increased on the IgG in these patients, independent of IgG subclass. Interestingly, these effects were largely reduced in HIV infected patients receiving therapy. These results suggest an important role for protein glycosylation in immune dysfunction that is driven by active HIV infection.

Quantitative analysis of aberrant protein glycosylation in liver cancer plasma by AAL-enrichment and MRM mass spectrometry

A lectin-coupled mass spectrometry (MS) approach was employed to quantitatively monitor aberrant protein glycosylation in liver cancer plasma. To do this, we compared the difference in the total protein abundance of a target glycoprotein between hepatocellular carcinoma (HCC) plasmas and hepatitis B virus (HBV) plasmas, as well as the difference in lectin-specific protein glycoform abundance of the target glycoprotein. Capturing the lectin-specific protein glycoforms from a plasma sample was accomplished by using a fucose-specific aleuria aurantia lectin (AAL) immobilized onto magnetic beads via a biotin-streptavidin conjugate. Following tryptic digestion of both the total plasma and its AAL-captured fraction of each HCC and HBV sample, targeted proteomic mass spectrometry was conducted quantitatively by a multiple reaction monitoring (MRM) technique. From the MRM-based analysis of the total plasmas and AAL-captured fractions, differences between HCC and HBV plasma groups in fucosylated glycoform levels of target glycoproteins were confirmed to arise from both the change in the total protein abundance of the target proteins and the change incurred by aberrant fucosylation on target glycoproteins in HCC plasma, even when no significant change occurs in the total protein abundance level. Combining the MRM-based analysis method with the lectin-capturing technique proved to be a successful means of quantitatively investigating aberrant protein glycosylation in cancer plasma samples. Additionally, it was elucidated that the differences between HCC and control groups in fucosylated biomarker candidates A1AT and FETUA mainly originated from an increase in fucosylation levels on these target glycoproteins, rather than an increase in the total protein abundance of the target glycoproteins.

Glycoproteomics on the rise: Established methods, advanced techniques, sophisticated biological applications

Glycosylation is the most complex form of protein PTMs. Affected proteins may carry dozens of glycosylation sites with tens to hundreds of glycan residues attached to every site. Glycosylated proteins have many important functions in biology, from cellular to organismal levels, being involved in cell-cell signaling, cell adhesion, immune response, host-pathogen interactions, and development and growth. Glycosylation, however, expands the biological functional diversity of proteins at the expense of a tremendous increase in structural heterogeneity. Aberrant glycosylation of cell surface proteins, as well as their detectable fingerprint in plasma samples, has been associated with cancer, inflammatory and degenerative diseases, and congenital disorders of glycosylation. Therefore, there are on-going efforts directed toward developing new technologies and approaches for glycan sequencing and high-throughput analysis of glycosylated proteins in complex samples with simultaneous characterization of both the protein and glycan moieties. This work is aimed primarily at pinpointing the challenges associated with the large-scale analysis of glycoproteins and the latest developments in glycoproteomic research, with focus on recent advancements (2011-2012) in microcolumn separations and MS detection.

Tumor-associated glycans and their role in gynecological cancers: accelerating translational research by novel high-throughput approaches.

Glycans are important partners in many biological processes, including carcinogenesis. The rapidly developing field of functional glycomics becomes one of the frontiers of biology and biomedicine. Aberrant glycosylation of proteins and lipids occurs commonly during malignant transformation and leads to the expression of specific tumor-associated glycans. The appearance of aberrant glycans on carcinoma cells is typically associated with grade, invasion, metastasis and overall poor prognosis. Cancer-associated carbohydrates are mostly located on the surface of cancer cells and are therefore potential diagnostic biomarkers. Currently, there is increasing interest in cancer-associated aberrant glycosylation, with growing numbers of characteristic cancer targets being detected every day. Breast and ovarian cancer are the most common and lethal malignancies in women, respectively, and potential glycan biomarkers hold promise for early detection and targeted therapies. However, the acceleration of research and comprehensive multi-target investigation of cancer-specific glycans could only be successfully achieved with the help of a combination of novel high-throughput glycomic approaches.

AtAPY1 and AtAPY2 Function as Golgi-Localized Nucleoside Diphosphatases in Arabidopsis thaliana

Nucleoside triphosphate diphosphohydrolases (NTPDases; apyrases) (EC 3.6.1.5) hydrolyze di- and triphosphate nucleotides, but not monophosphate nucleotides. They are categorized as E-type ATPases, have a broad divalent cation (Mg(2+), Ca(2+)) requirement for activation and are insensitive to inhibitors of F-type, P-type and V-type ATPases. Among the seven NTPDases identified in Arabidopsis, only APYRASE 1 (AtAPY1) and APYRASE 2 (AtAPY2) have been previously characterized. In this work, either AtAPY1 or AtAPY2 tagged with C-terminal green fluorescent protein (GFP) driven by their respective native promoter can rescue the apy1 apy2 double knockout (apy1 apy2 dKO) successfully, and confocal microscopy reveals that these two Arabidopsis apyrases reside in the Golgi apparatus. In Saccharomyces cerevisiae, both AtAPY1 and AtAPY2 can complement the Golgi-localized GDA1 mutant, rescuing its aberrant protein glycosylation phenotype. In Arabidopsis, microsomes of the wild type show higher substrate preferences toward UDP compared with other NDP substrates. Loss-of-function Arabidopsis AtAPY1 mutants exhibit reduced microsomal UDPase activity, and this activity is even more significantly reduced in the loss-of-function AtAPY2 mutant and in the AtAPY1/AtAPY2 RNA interference (RNAi) technology repressor lines. Microsomes from wild-type plants also have detectable GDPase activity, which is significantly reduced in apy2 but not apy1 mutants. The GFP-tagged AtAPY1 or AtAPY2 constructs in the apy1 apy2 dKO plants can restore microsomal UDP/GDPase activity, confirming that they both also have functional competency. The cell walls of apy1, apy2 and the RNAi-silenced lines all have an increased composition of galactose, but the transport efficiency of UDP-galactose across microsomal membranes was not altered. Taken together, these results reveal that AtAPY1 and AtAPY2 are Golgi-localized nucleotide diphosphatases and are likely to have roles in regulating UDP/GDP concentrations in the Golgi lumen.

Using lectins to harvest the plasma/serum glycoproteome

Aberrant protein glycosylation has been shown to be associated with disease processes and identification of disease-specific glycoproteins and glycosylation changes may serve as potential diagnostic and therapeutic biomarkers. However despite recent advances in proteomic-based biomarker discovery, this knowledge has not yet translated into an extensive mining of the glycoproteome for potential biomarkers. The major challenge for a comprehensive glycoproteomics analysis arises primarily from the enormous complexity and the large dynamic range in protein constituent in biological samples. Methods that specifically target glycoproteins are therefore necessary to facilitate their selective enrichment prior to their identification by MS-based analysis. The use of lectins, with selective affinities for specific carbohydrate epitopes, to enrich glycoprotein fractions coupled with modern MS, have greatly enhanced the identification of the glycoproteome. On account of their ability to specifically bind cell surface carbohydrates lectins have, during the recent past, found extensive applications in elucidation of the architecture and dynamics of cell surface carbohydrates, glycoconjugate purification, and structural characterization. Combined with complementary depletion and MS technologies, lectin affinity chromatography is becoming the most widely employed method of choice for biomarker discovery in cancer and other diseases.

A lectin-coupled, multiple reaction monitoring based quantitative analysis of human plasma glycoproteins by mass spectrometry

Aberrant protein glycosylation may be closely associated with cancer pathology. To measure the abundance of protein glycoforms with a specific glycan structure in plasma samples, we developed a lectin-coupled multiple reaction monitoring (MRM)-based mass spectrometric method. It was confirmed that the method could provide reproducible results with precision sufficient to distinguish differences in the abundance of protein glycoforms between individuals. Plasma samples prepared from hepatocellular carcinoma (HCC) patients without immuno-depletion of highly abundant plasma proteins were fractionated by use of fucose-specific aleuria aurantia lectin (AAL) immobilized on magnetic beads by use of a biotin-streptavidin conjugate. The lectin-captured fractions were digested by trypsin and profiled by tandem mass spectrometry. From the proteomic profiling data, target glycoproteins were selected and analyzed quantitatively by MRM-based analysis. The reproducibility of MRM-based quantification of the selected target proteins was reliable, with precision (CV; ≤14% for batch-to-batch replicates and ≤19% for replicates over three days) sufficient to distinguish differences in the abundance of AAL-captured glycoforms between individual plasma samples. This lectin-coupled, MRM-based method, measuring only lectin-captured glycoforms of a target protein rather than total target protein, is a tool for monitoring differences between individuals by measuring the abundance of aberrant glycoforms of a target protein related to a disease. This method may be further applied to rapid verification of biomarker candidates involved in aberrant protein glycosylation in human plasma.

Glycosylation of the Sodium Channel β4 Subunit is Developmentally Regulated and Involves in Neuritic Degeneration

Aberrant protein glycosylation plays major roles in neurodegenerative diseases, including Parkinson's disease (PD). Glycoproteomics showed that the glycosylation of sodium channel β4 was significantly increased in human brain tissue. β4-specific antibodies reacted in immunoblot assays with the 35- and 38-kDa bands from the membrane fractions isolated from neonatal PD transgenic mice but only with the 35-kDa band of the neonatal wild-type mice. The size of the 38-kDa immunoreactive protein is in close agreement with previously reported, suggesting heavy glycosylation of this protein in adult wild-type and neonatal PD transgenic brain tissues. However, the neonatal wild-type mice membrane fractions only contained the 35-kDa immunoreactive protein, and the additional 38-kDa band was not shown until postnatal day 7. Enzymatic deglycosylation of the membrane preparations only converted the 38-kDa band into a faster migrating protein, which was consistent with heavy glycosylation of this protein. The glycosylated state of β4 was developmentally regulated and was altered in disease state. Neurite outgrowth assay demonstrated that overexpression of deglycosylated mutant β4-MUT accelerated neurite extension and increased the number of filopodia-like protrusions, when compared with β4-WT and the vector. These results suggest that extensive glycosylation of β4 subunit play roles in morphological changes, and the altered glycosylation may be involved in the pathogenesis of PD.

Development of a combined chemical and enzymatic approach for the mass spectrometric identification and quantification of aberrant N-glycosylation

Direct mass spectrometric analysis of aberrant protein glycosylation is a challenge to the current analytical techniques. Except lectin affinity chromatography, no other glycosylation enrichment techniques are available for analysis of aberrant glycosylation. In this study, we developed a combined chemical and enzymatic strategy as an alternative for the mass spectrometric analysis of aberrant glycosylation. Sialylated glycopeptides were enriched with reverse glycoblotting, cleaved by endoglycosidase F3 and analyzed by mass spectrometry with both neutral loss triggered MS(3) in collision induced dissociation (CID) and electron transfer dissociation (ETD). Interestingly, a great part of resulted glycopeptides were found with fucose attached to the N-acetylglucosamine (N-GlcNAc), which indicated that the aberrant glycosylation that is carrying both terminal sialylation and core fucosylation was identified. Totally, 69 aberrant N-glycosylation sites were identified in sera samples from hepatocellular carcinoma (HCC) patients. Following the identification, quantification of the level of this aberrant glycosylation was also carried out using stable isotope dimethyl labeling and pooled sera sample from liver cirrhosis and HCC was compared. Six glycosylation sites demonstrated elevated level of aberrancy, which demonstrated that our developed strategy was effective in both qualitative and quantitative studies of aberrant glycosylation.

Microheterogeneity of some serum glycoproteins in neurodegenerative diseases

BackgroundParticipation of protein polymorphism is often considered in the pathogenesis of various diseases. Aberrant protein glycosylation has been recognized to play major roles in human disorders, including neurodegenerative diseases. ObjectiveThe aim of the study was to examine possible involvement of protein genetic variants and degree of glycosylation of some serum glycoproteins in the manifestation of neurodegenerative disorders in a Czech population sample. MethodsApolipoprotein (Apo) E and three main serum markers of glycosylation defects (transferrin, Tf, alpha1-antitrypsin, aAT and ApoCIII) in patients with Alzheimer's dementia (AD), Parkinson's disease (PD) and vascular dementia (n=62, 139 and 44, respectively) were analyzed by isoelectric focusing. Children with serious neurological symptoms (n=55) and three age-matched control groups (n=45, 45 and 42) were examined for comparison. ResultsOf the supposedly pathognomonic protein variants Tf C2, aAT ZM and ApoE e4 only the latter was detected with higher frequency in AD patients; significant synergy of the C2/e4 allelic combination was not confirmed. The most prominent finding among PD adults was an increased appearance of Tf C2 allele and significant mean hypoglycosylation of ApoCIII, besides a C2/e4 positive correlation in PD seniors. Laboratory signs of Tf hypoglycosylation and a pattern of Tf/ApoCIII hyperglycosylation have been occasionally found.

Enhanced sensitivity of LC‐MS analysis of permethylated N‐glycans through online purification

Aberrant glycosylation of proteins and lipids has been implicated in many human diseases, thus prompting the need for reliable analytical methods that permit dependable quantification of glycans originating from biological specimens. MS of permethylated glycans is currently employed to monitor disease-related aberrant glycosylation of proteins and lipids. However, enhancing the sensitivity of this type of analysis is still needed. Here, analysis of permethylated glycans at enhanced sensitivity is attained through miniaturized solid-phase permethylation and online solid-phase purification. Solid-phase permethylation method was miniaturized by reducing the amount of sodium hydroxide beads (one-third the original amount) packed in microspin columns. The efficiency of glycan permethylation was not adversely affected by this reduction. Online solid-phase purification of permethylated N-glycans derived from model glycoproteins, such as fetuin, α-1 acid glycoprotein and ribonuclease B, offered more sensitive and reproducible results than offline liquid-liquid and solid-phase extractions. Online solid-phase purification method described here permitted a 75% increase in signal intensities of permethylated glycans relative to offline purification methods. This is mainly due to the minimized sample handling associated with an online cleaning procedure. The efficiency and utility of online solid-phase purification was also demonstrated here for N-glycans derived from human blood serum. Online solid-phase purification permitted the detection of 73 N-glycan structures, while only 63 glycan structures were detected in the case of samples purified through liquid-liquid extraction. The intensities of the 63 structures that were detected in both cases were 75% higher for samples that were purified through the online method.

Glycoproteomics-Based Identification of Cancer Biomarkers

Protein glycosylation is one of the most common posttranslational modifications in mammalian cells. It is involved in many biological pathways and molecular functions and is well suited for proteomics-based disease investigations. Aberrant protein glycosylation may be associated with disease processes. Specific glycoforms of glycoproteins may serve as potential biomarkers for the early detection of disease or as biomarkers for the evaluation of therapeutic efficacy for treatment of cancer, diabetes, and other diseases. Recent technological developments, including lectin affinity chromatography and mass spectrometry, have provided researchers the ability to obtain detailed information concerning protein glycosylation. These in-depth investigations, including profiling and quantifying glycoprotein expression, as well as comprehensive glycan structural analyses may provide important information leading to the development of disease-related biomarkers. This paper describes methodologies for the detection of cancer-related glycoprotein and glycan structural alterations and briefly summarizes several current cancer-related findings.

Simultaneous analysis of glycosylated and sialylated prostate-specific antigen revealing differential distribution of glycosylated prostate-specific antigen isoforms in prostate cancer tissues.

Aberrant protein glycosylation has been shown to be associated with disease progression and can be potentially useful as a biomarker if disease-specific glycosylation can be identified. However, high-throughput quantitative analysis of protein glycosylation derived from clinical specimens presents technical challenges due to the typically high complexity of biological samples. In this study, a mass spectrometry-based analytical method was developed to measure different glycosylated forms of glycoproteins from complex biological samples by coupling glycopeptide extraction strategy for specific glycosylation with selected reaction monitoring (SRM). Using this method, we monitored glycosylated and sialylated prostate-specific antigen (PSA) in prostate cancer and noncancer tissues. Results of this study demonstrated that the relative abundance of glycosylated PSA isoforms were not correlated with total PSA protein levels measured in the same prostate cancer tissue samples by clinical immunoassay. Furthermore, the sialylated PSA was differentially distributed in cancer and noncancer tissues. These data suggest that differently glycosylated isoforms of glycoproteins can be quantitatively analyzed and may provide unique information for clinically relevant studies.

Inhibition of N-linked glycosylation by tunicamycin induces E-cadherin-mediated cell–cell adhesion and inhibits cell proliferation in undifferentiated human colon cancer cells

Aberrant protein glycosylation and disassembly of E-cadherin-mediated cell-cell adhesion are characteristics of epithelial cancer. However, the relationship between these two events in colorectal cancer remains to be defined. In this study, we analyzed whether N-glycan expression is crucial for the loss of E-cadherin-mediated cell-cell adhesion in human colorectal cancer cells. Differentiated Caco-2 and undifferentiated HCT-116 colon cancer cells were used as models of stable and unstable adherens junctions (AJs), respectively. Complex-type N-glycans were detected using the lectins E-PHA (Phaseolus vulgaris E.) and L-PHA (Phaseolus vulgaris L.). To study E-cadherin-mediated AJ assembly, we examined the effects of swainsonine, an inhibitor of α-mannosidase II, and tunicamycin, a drug that inhibits the biosynthesis of N-glycans, via western blot, immunofluorescence, differential extraction in Triton X-100, and electron microscopy. Cell proliferation and apoptosis were examined by crystal violet staining and flow cytometry, respectively. We observed positive labeling for E-PHA and L-PHA lectins in both cell lines; however, HCT-116 cells had increased E-cadherin-linked complex-type N-glycans. Interestingly, tunicamycin, but not swainsonine, was able to induce functional E-cadherin-mediated cell-cell adhesion in undifferentiated HCT-116 cells, as shown by the increased association of E-cadherin with the actin cytoskeleton. Moreover, in HCT-116 cells, tunicamycin also induced the formation of tight cell-cell contacts, and it inhibited cell proliferation without triggering apoptosis. Collectively, our results demonstrate for the first time that altered N-glycan expression plays an important role in the loss of AJ stability in undifferentiated colorectal cancer cells and that this loss may be associated with the progression of colorectal cancer.

Abstract 2720: Glycosylation of Mucins Expressed in Pancreatic Adenocarcinoma

Abstract Glycosylation of mucins expressed by pancreatic adenocarcinoma There were an estimated 42,470 new cases and 35,240 deaths due to pancreatic adenocarcinoma (PA) for 2009, ranking PA as the third leading cause of cancer related death. Virtually all long term survivors are diagnosed early but only 7% are detected in the early stages of disease thus highlighting the need for an early diagnostic test. CA19-9, the only current clinical serum-based assay used to monitor PA, detects an oligosaccharide blood group antigen Sialyl Lewisa (sLeA) with the structure (Neu5Acα2-3Galβ1-3[Fucα1-4]GlcNAc), which can be present on glycolipids or as an O-linked oligosaccharide on glycoproteins, and is expressed at relatively low levels on the surfaces of normal epithelial cells. The full spectrum of proteins on which the CA19-9 epitope is expressed has never been defined. CA19-9 is differentially expressed on mucins, which are extensively glycosylated. The CA19-9 test lacks high specificity for PA, as CA19-9 is commonly elevated in patients with benign chronic pancreatitis and other malignant diseases. Different epithelial tissues and cell types produce distinct combinations of mucin-type core proteins, and the expression patterns of these are generally altered during different disease processes including malignant transformation. Mucin expression is deregulated in cancer, which results in aberrant expression and glycosylation of mucin core proteins. We employed immunohistochemistry and immunofluorescence to show the unique mucin and glycosylation patterns seen in tissue specimens from patients diagnosed with PA. Deglycosylation of samples immunoprecipitated from cancer cell lines and pancreatic cancer patient tissue specimens was used to enable detection of mucin core proteins. Immunoaffinity chromatography was used to isolate CA19-9 from patient ascites and serum samples and mass spectrometry was used to analyze the core proteins. Results show that pancreatic cancers expressing the mucin core proteins MUC1, MUC4 and MUC5AC carry the CA19-9 epitope. Preliminary results suggest that a strategy to detect the CA19-9 tumor antigen and its cognate mucin core protein(s) will improve the performance characteristics of this assay. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2720.

Glycoproteomics and glycomics investigation of membrane N‐glycosylproteins from human colon carcinoma cells

Aberrant glycosylation of proteins is known to profoundly affect cellular adhesion or motility of tumoral cells. In this study, we used HT-29 human colon epithelial cancer cells as a cellular model of cancer progression, as they can either proliferate or differentiate into enterocyte phenotype. A glycoproteomic approach based on Con A lectin-affinity chromatography, SDS-PAGE and MS analysis, allowed the identification of membrane N-glycoproteins from Triton X-100-solubilized proteins from membrane preparation. Among them, 65% were membrane proteins, and 45% were known to be N-glycosylated, such as alpha chains integrin and dipeptidyl isomerase IV. By lectin-blot analysis, significant changes of alpha-2,3- and alpha-2,6-sialylation of membrane glycoproteins were observed between proliferating and differentiated HT-29 cells. From these results, nano-LC-MS/MS analysis of the tryptic digests of the corresponding bands was performed and led to the identification of several transmembrane glycoproteins, like members of the solute carrier family and adhesion proteins. Finally, we compared N-glycans profiles and monosaccharide composition of proliferating and enterocyte-like HT-29 cells using MALDI-MS and GC-MS analyses of permethylated derivatives. This glycomic approach allowed to underscore significant changes in N-glycans structure, in particular the expression of atypical N-acetylglucosamine (GlcNAc)-ended N-glycans in enterocyte-like HT-29 cells.

Finding of O‐Mannosyl Glycan in Mammals and Congenital Muscular Dystrophies due to Glycosylation Defects

AbstractFor Abstract see ChemInform Abstract in Full Text.

Finding of O-mannosyl glycan in mammals and congenital muscular dystrophies due to glycosylation defects

Most proteins within living organisms contain glycans. Glycan structures can modulate the biological properties and function of glycoproteins. Developments in glycobiology have revealed a new type of glycosidic linkage to the peptide portion, the O-mannosyl linkage in mammals, although heretofore it had been thought to be specific to yeast. One of the best known O-mannosyl-modified glycoproteins is dystroglycan, which is a central component of dystrophinglycoprotein complex isolated from skeletal muscle membranes. We identify and characterize a glycosyltransferase, UDP-N-acetylglucosamine: protein O-mannose beta 1,2-N-acetylglucosaminyltransferase (POMGnT1), involved in the biosynthesis of mammalian type O-mannosyl glycans. Finally, we find that the POMGnT1 gene is responsible for muscle-eye-brain disease (MEB). MEB is an autosomal recessive disorder characterized by congenital muscular dystrophy, ocular abnormalities and brain malformation (type II lissencephaly). Like MEB, recent data suggest that the aberrant protein glycosylation of a specific glycoprotein, alpha-dystroglycan, is the primary cause of some forms of congenital muscular dystrophy. Here I review the new insight into glycobiology of muscular dystrophy and neuronal migration disorder.

Glycosylation in congenital muscular dystrophies.

Mammalian cells produce many glycoproteins, i.e., proteins with covalently attached sugar chains. Recent advances in glycobiology have revealed the importance of sugar chains as biosignals for multi-cellular organisms including cell-cell communication, intracellular signaling, protein folding, and targeting of proteins within cells. The O-mannosyl linkage, which used to be considered specific to yeast, has recently been found in mammals. One of the best known O-mannosyl-modified glycoproteins is alpha-dystroglycan, which is a central component of the dystrophin-glycoprotein complex isolated from skeletal muscle membranes. We have identified and characterized a glycosyltransferase, UDP-N-acetylglucosamine: protein O-mannose beta1,2-N-acetylglucosaminyltransferase (POMGnT1), involved in the biosynthesis of O-mannosyl glycans. We subsequently found that loss of function of the POMGnT1 gene is responsible for muscle-eye-brain disease (MEB). MEB is an autosomal recessive disorder characterized by congenital muscular dystrophy, ocular abnormalities and brain malformation (type II lissencephaly). Moreover, recent data suggest that aberrant protein glycosylation of alpha-dystroglycan is the primary cause of some forms of congenital muscular dystrophy. Here we review new insights into the glycobiology of muscular dystrophy and neuronal migration disorder.