Multiorgan MRI findings after hospitalisation with COVID-19 in the UK (C-MORE): a prospective, multicentre, observational cohort study

INTRODUCTION

The multiorgan impact of moderate to severe coronavirus infections in the post-acute phase is still poorly understood. We aimed to evaluate the excess burden of multiorgan abnormalities after hospitalisation with COVID-19, evaluate their determinants, and explore associations with patient-related outcome measures.

METHODS

In a prospective, UK-wide, multicentre MRI follow-up study (C-MORE), adults (aged ≥18 years) discharged from hospital following COVID-19 who were included in Tier 2 of the Post-hospitalisation COVID-19 study (PHOSP-COVID) and contemporary controls with no evidence of previous COVID-19 (SARS-CoV-2 nucleocapsid antibody negative) underwent multiorgan MRI (lungs, heart, brain, liver, and kidneys) with quantitative and qualitative assessment of images and clinical adjudication when relevant. Individuals with end-stage renal failure or contraindications to MRI were excluded. Participants also underwent detailed recording of symptoms, and physiological and biochemical tests. The primary outcome was the excess burden of multiorgan abnormalities (two or more organs) relative to controls, with further adjustments for potential confounders. The C-MORE study is ongoing and is registered with ClinicalTrials.gov, NCT04510025.

FINDINGS

Of 2710 participants in Tier 2 of PHOSP-COVID, 531 were recruited across 13 UK-wide C-MORE sites. After exclusions, 259 C-MORE patients (mean age 57 years [SD 12]; 158 [61%] male and 101 [39%] female) who were discharged from hospital with PCR-confirmed or clinically diagnosed COVID-19 between March 1, 2020, and Nov 1, 2021, and 52 non-COVID-19 controls from the community (mean age 49 years [SD 14]; 30 [58%] male and 22 [42%] female) were included in the analysis. Patients were assessed at a median of 5·0 months (IQR 4·2-6·3) after hospital discharge. Compared with non-COVID-19 controls, patients were older, living with more obesity, and had more comorbidities. Multiorgan abnormalities on MRI were more frequent in patients than in controls (157 [61%] of 259 vs 14 [27%] of 52; p<0·0001) and independently associated with COVID-19 status (odds ratio [OR] 2·9 [95% CI 1·5-5·8]; padjusted=0·0023) after adjusting for relevant confounders. Compared with controls, patients were more likely to have MRI evidence of lung abnormalities (p=0·0001; parenchymal abnormalities), brain abnormalities (p<0·0001; more white matter hyperintensities and regional brain volume reduction), and kidney abnormalities (p=0·014; lower medullary T1 and loss of corticomedullary differentiation), whereas cardiac and liver MRI abnormalities were similar between patients and controls. Patients with multiorgan abnormalities were older (difference in mean age 7 years [95% CI 4-10]; mean age of 59·8 years [SD 11·7] with multiorgan abnormalities vs mean age of 52·8 years [11·9] without multiorgan abnormalities; p<0·0001), more likely to have three or more comorbidities (OR 2·47 [1·32-4·82]; padjusted=0·0059), and more likely to have a more severe acute infection (acute CRP >5mg/L, OR 3·55 [1·23-11·88]; padjusted=0·025) than those without multiorgan abnormalities. Presence of lung MRI abnormalities was associated with a two-fold higher risk of chest tightness, and multiorgan MRI abnormalities were associated with severe and very severe persistent physical and mental health impairment (PHOSP-COVID symptom clusters) after hospitalisation.

INTERPRETATION

After hospitalisation for COVID-19, people are at risk of multiorgan abnormalities in the medium term. Our findings emphasise the need for proactive multidisciplinary care pathways, with the potential for imaging to guide surveillance frequency and therapeutic stratification.

FUNDING

UK Research and Innovation and National Institute for Health Research.

Low frequency attenuation of acoustic waves in a perforated pipe

This paper presents new experimental and numerical evidence that perforations in a pipe wall result in a low-frequency bandgap within which sound waves rapidly attenuate. These perforations are modelled as an acoustically soft boundary condition on the pipe wall and show that a low frequency bandgap is created from 0 Hz. The upper bound of this bandgap is determined by the dimensions and separation of the perforations. An analytical model based on the transfer matrix method is proposed. This model is validated against numerical predictions for the pipe with varying perforation geometries. A numerical study is undertaken to model the effect of perforations with ideal acoustically soft boundary conditions and surrounded with an air gap. Close agreement is found between the numerical and analytical models. Experimental evidence shows that the width of the bandgap is accurately predicted with the numerical and analytical models.

Clinical characteristics with inflammation profiling of long COVID and association with 1-year recovery following hospitalisation in the UK: a prospective observational study

BACKGROUND

No effective pharmacological or non-pharmacological interventions exist for patients with long COVID. We aimed to describe recovery 1 year after hospital discharge for COVID-19, identify factors associated with patient-perceived recovery, and identify potential therapeutic targets by describing the underlying inflammatory profiles of the previously described recovery clusters at 5 months after hospital discharge.

METHODS

The Post-hospitalisation COVID-19 study (PHOSP-COVID) is a prospective, longitudinal cohort study recruiting adults (aged ≥18 years) discharged from hospital with COVID-19 across the UK. Recovery was assessed using patient-reported outcome measures, physical performance, and organ function at 5 months and 1 year after hospital discharge, and stratified by both patient-perceived recovery and recovery cluster. Hierarchical logistic regression modelling was performed for patient-perceived recovery at 1 year. Cluster analysis was done using the clustering large applications k-medoids approach using clinical outcomes at 5 months. Inflammatory protein profiling was analysed from plasma at the 5-month visit. This study is registered on the ISRCTN Registry, ISRCTN10980107, and recruitment is ongoing.

FINDINGS

2320 participants discharged from hospital between March 7, 2020, and April 18, 2021, were assessed at 5 months after discharge and 807 (32·7%) participants completed both the 5-month and 1-year visits. 279 (35·6%) of these 807 patients were women and 505 (64·4%) were men, with a mean age of 58·7 (SD 12·5) years, and 224 (27·8%) had received invasive mechanical ventilation (WHO class 7-9). The proportion of patients reporting full recovery was unchanged between 5 months (501 [25·5%] of 1965) and 1 year (232 [28·9%] of 804). Factors associated with being less likely to report full recovery at 1 year were female sex (odds ratio 0·68 [95% CI 0·46-0·99]), obesity (0·50 [0·34-0·74]) and invasive mechanical ventilation (0·42 [0·23-0·76]). Cluster analysis (n=1636) corroborated the previously reported four clusters: very severe, severe, moderate with cognitive impairment, and mild, relating to the severity of physical health, mental health, and cognitive impairment at 5 months. We found increased inflammatory mediators of tissue damage and repair in both the very severe and the moderate with cognitive impairment clusters compared with the mild cluster, including IL-6 concentration, which was increased in both comparisons (n=626 participants). We found a substantial deficit in median EQ-5D-5L utility index from before COVID-19 (retrospective assessment; 0·88 [IQR 0·74-1·00]), at 5 months (0·74 [0·64-0·88]) to 1 year (0·75 [0·62-0·88]), with minimal improvements across all outcome measures at 1 year after discharge in the whole cohort and within each of the four clusters.

INTERPRETATION

The sequelae of a hospital admission with COVID-19 were substantial 1 year after discharge across a range of health domains, with the minority in our cohort feeling fully recovered. Patient-perceived health-related quality of life was reduced at 1 year compared with before hospital admission. Systematic inflammation and obesity are potential treatable traits that warrant further investigation in clinical trials.

FUNDING

UK Research and Innovation and National Institute for Health Research.

Effects of oral anticoagulation for atrial fibrillation after spontaneous intracranial haemorrhage in the UK: a randomised, open-label, assessor-masked, pilot-phase, non-inferiority trial

BACKGROUND

Oral anticoagulation reduces the rate of systemic embolism for patients with atrial fibrillation by two-thirds, but its benefits for patients with previous intracranial haemorrhage are uncertain. In the Start or STop Anticoagulants Randomised Trial (SoSTART), we aimed to establish whether starting is non-inferior to avoiding oral anticoagulation for survivors of intracranial haemorrhage who have atrial fibrillation.

METHODS

SoSTART was a prospective, randomised, open-label, assessor-masked, parallel-group, pilot phase trial done at 67 hospitals in the UK. We recruited adults (aged ≥18 years) who had survived at least 24 h after symptomatic spontaneous intracranial haemorrhage, had atrial fibrillation, and had a CHA2DS2-VASc score of at least 2. Web-based computerised randomisation incorporating a minimisation algorithm allocated participants (1:1) to start or avoid long-term (≥1 year) full treatment dose open-label oral anticoagulation. The participants assigned to start oral anticoagulation received either a direct oral anticoagulant or vitamin K antagonist, and the group assigned to avoid oral anticoagulation received standard clinical practice (antiplatelet agent or no antithrombotic agent). The primary outcome was recurrent symptomatic spontaneous intracranial haemorrhage, and was adjudicated by an individual masked to treatment allocation. All outcomes were ascertained for at least 1 year after randomisation and assessed in the intention-to-treat population of all randomly assigned participants, using Cox proportional hazards regression adjusted for minimisation covariates. We planned a sample size of 190 participants (one-sided p=0·025, power 90%, allowing for non-adherence) based on a non-inferiority margin of 12% (or adjusted hazard ratio [HR] of 3·2). This trial is registered with ClinicalTrials.gov (NCT03153150) and is complete.

FINDINGS

Between March 29, 2018, and Feb 27, 2020, consent was obtained at 61 sites for 218 participants, of whom 203 were randomly assigned at a median of 115 days (IQR 49-265) after intracranial haemorrhage onset. 101 were assigned to start and 102 to avoid oral anticoagulation. Participants were followed up for median of 1·2 years (IQR 0·97-1·95; completeness 97·2%). Starting oral anticoagulation was not non-inferior to avoiding oral anticoagulation: eight (8%) of 101 in the start group versus four (4%) of 102 in the avoid group had intracranial haemorrhage recurrences (adjusted HR 2·42 [95% CI 0·72-8·09]; p=0·152). Serious adverse events occurred in 17 (17%) participants in the start group and 15 (15%) in the avoid group. 22 (22%) patients in the start group and 11 (11%) patients in the avoid group died during the study.

INTERPRETATION

Whether starting oral anticoagulation was non-inferior to avoiding it for people with atrial fibrillation after intracranial haemorrhage was inconclusive, although rates of recurrent intracranial haemorrhage were lower than expected. In view of weak evidence from analyses of three composite secondary outcomes, the possibility that oral anticoagulation might be superior for preventing symptomatic major vascular events should be investigated in adequately powered randomised trials.

FUNDING

British Heart Foundation, Medical Research Council, Chest Heart & Stroke Scotland.

Effect of Hydrocortisone on Mortality and Organ Support in Patients With Severe COVID-19: The REMAP-CAP COVID-19 Corticosteroid Domain Randomized Clinical Trial

IMPORTANCE

Evidence regarding corticosteroid use for severe coronavirus disease 2019 (COVID-19) is limited.

OBJECTIVE

To determine whether hydrocortisone improves outcome for patients with severe COVID-19.

DESIGN, SETTING, AND PARTICIPANTS

An ongoing adaptive platform trial testing multiple interventions within multiple therapeutic domains, for example, antiviral agents, corticosteroids, or immunoglobulin. Between March 9 and June 17, 2020, 614 adult patients with suspected or confirmed COVID-19 were enrolled and randomized within at least 1 domain following admission to an intensive care unit (ICU) for respiratory or cardiovascular organ support at 121 sites in 8 countries. Of these, 403 were randomized to open-label interventions within the corticosteroid domain. The domain was halted after results from another trial were released. Follow-up ended August 12, 2020.

INTERVENTIONS

The corticosteroid domain randomized participants to a fixed 7-day course of intravenous hydrocortisone (50 mg or 100 mg every 6 hours) (n = 143), a shock-dependent course (50 mg every 6 hours when shock was clinically evident) (n = 152), or no hydrocortisone (n = 108).

MAIN OUTCOMES AND MEASURES

The primary end point was organ support-free days (days alive and free of ICU-based respiratory or cardiovascular support) within 21 days, where patients who died were assigned -1 day. The primary analysis was a bayesian cumulative logistic model that included all patients enrolled with severe COVID-19, adjusting for age, sex, site, region, time, assignment to interventions within other domains, and domain and intervention eligibility. Superiority was defined as the posterior probability of an odds ratio greater than 1 (threshold for trial conclusion of superiority >99%).

RESULTS

After excluding 19 participants who withdrew consent, there were 384 patients (mean age, 60 years; 29% female) randomized to the fixed-dose (n = 137), shock-dependent (n = 146), and no (n = 101) hydrocortisone groups; 379 (99%) completed the study and were included in the analysis. The mean age for the 3 groups ranged between 59.5 and 60.4 years; most patients were male (range, 70.6%-71.5%); mean body mass index ranged between 29.7 and 30.9; and patients receiving mechanical ventilation ranged between 50.0% and 63.5%. For the fixed-dose, shock-dependent, and no hydrocortisone groups, respectively, the median organ support-free days were 0 (IQR, -1 to 15), 0 (IQR, -1 to 13), and 0 (-1 to 11) days (composed of 30%, 26%, and 33% mortality rates and 11.5, 9.5, and 6 median organ support-free days among survivors). The median adjusted odds ratio and bayesian probability of superiority were 1.43 (95% credible interval, 0.91-2.27) and 93% for fixed-dose hydrocortisone, respectively, and were 1.22 (95% credible interval, 0.76-1.94) and 80% for shock-dependent hydrocortisone compared with no hydrocortisone. Serious adverse events were reported in 4 (3%), 5 (3%), and 1 (1%) patients in the fixed-dose, shock-dependent, and no hydrocortisone groups, respectively.

CONCLUSIONS AND RELEVANCE

Among patients with severe COVID-19, treatment with a 7-day fixed-dose course of hydrocortisone or shock-dependent dosing of hydrocortisone, compared with no hydrocortisone, resulted in 93% and 80% probabilities of superiority with regard to the odds of improvement in organ support-free days within 21 days. However, the trial was stopped early and no treatment strategy met prespecified criteria for statistical superiority, precluding definitive conclusions.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT02735707.

Effect of Hydrocortisone on Mortality and Organ Support in Patients With Severe COVID-19: The REMAP-CAP COVID-19 Corticosteroid Domain Randomized Clinical Trial

IMPORTANCE

Evidence regarding corticosteroid use for severe coronavirus disease 2019 (COVID-19) is limited.

OBJECTIVE

To determine whether hydrocortisone improves outcome for patients with severe COVID-19.

DESIGN, SETTING, AND PARTICIPANTS

An ongoing adaptive platform trial testing multiple interventions within multiple therapeutic domains, for example, antiviral agents, corticosteroids, or immunoglobulin. Between March 9 and June 17, 2020, 614 adult patients with suspected or confirmed COVID-19 were enrolled and randomized within at least 1 domain following admission to an intensive care unit (ICU) for respiratory or cardiovascular organ support at 121 sites in 8 countries. Of these, 403 were randomized to open-label interventions within the corticosteroid domain. The domain was halted after results from another trial were released. Follow-up ended August 12, 2020.

INTERVENTIONS

The corticosteroid domain randomized participants to a fixed 7-day course of intravenous hydrocortisone (50 mg or 100 mg every 6 hours) (n = 143), a shock-dependent course (50 mg every 6 hours when shock was clinically evident) (n = 152), or no hydrocortisone (n = 108).

MAIN OUTCOMES AND MEASURES

The primary end point was organ support-free days (days alive and free of ICU-based respiratory or cardiovascular support) within 21 days, where patients who died were assigned -1 day. The primary analysis was a bayesian cumulative logistic model that included all patients enrolled with severe COVID-19, adjusting for age, sex, site, region, time, assignment to interventions within other domains, and domain and intervention eligibility. Superiority was defined as the posterior probability of an odds ratio greater than 1 (threshold for trial conclusion of superiority >99%).

RESULTS

After excluding 19 participants who withdrew consent, there were 384 patients (mean age, 60 years; 29% female) randomized to the fixed-dose (n = 137), shock-dependent (n = 146), and no (n = 101) hydrocortisone groups; 379 (99%) completed the study and were included in the analysis. The mean age for the 3 groups ranged between 59.5 and 60.4 years; most patients were male (range, 70.6%-71.5%); mean body mass index ranged between 29.7 and 30.9; and patients receiving mechanical ventilation ranged between 50.0% and 63.5%. For the fixed-dose, shock-dependent, and no hydrocortisone groups, respectively, the median organ support-free days were 0 (IQR, -1 to 15), 0 (IQR, -1 to 13), and 0 (-1 to 11) days (composed of 30%, 26%, and 33% mortality rates and 11.5, 9.5, and 6 median organ support-free days among survivors). The median adjusted odds ratio and bayesian probability of superiority were 1.43 (95% credible interval, 0.91-2.27) and 93% for fixed-dose hydrocortisone, respectively, and were 1.22 (95% credible interval, 0.76-1.94) and 80% for shock-dependent hydrocortisone compared with no hydrocortisone. Serious adverse events were reported in 4 (3%), 5 (3%), and 1 (1%) patients in the fixed-dose, shock-dependent, and no hydrocortisone groups, respectively.

CONCLUSIONS AND RELEVANCE

Among patients with severe COVID-19, treatment with a 7-day fixed-dose course of hydrocortisone or shock-dependent dosing of hydrocortisone, compared with no hydrocortisone, resulted in 93% and 80% probabilities of superiority with regard to the odds of improvement in organ support-free days within 21 days. However, the trial was stopped early and no treatment strategy met prespecified criteria for statistical superiority, precluding definitive conclusions.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT02735707.

Galectin-9 suppresses B cell receptor signaling and is regulated by I-branching of N-glycans

Leukocytes are coated with a layer of heterogeneous carbohydrates (glycans) that modulate immune function, in part by governing specific interactions with glycan-binding proteins (lectins). Although nearly all membrane proteins bear glycans, the identity and function of most of these sugars on leukocytes remain unexplored. Here, we characterize the N-glycan repertoire (N-glycome) of human tonsillar B cells. We observe that naive and memory B cells express an N-glycan repertoire conferring strong binding to the immunoregulatory lectin galectin-9 (Gal-9). Germinal center B cells, by contrast, show sharply diminished binding to Gal-9 due to upregulation of I-branched N-glycans, catalyzed by the β1,6-N-acetylglucosaminyltransferase GCNT2. Functionally, we find that Gal-9 is autologously produced by naive B cells, binds CD45, suppresses calcium signaling via a Lyn-CD22-SHP-1 dependent mechanism, and blunts B cell activation. Thus, our findings suggest Gal-9 intrinsically regulates B cell activation and may differentially modulate BCR signaling at steady state and within germinal centers.

The use of the Hemochron in assessment of heparin reversal after cardiopulmonary bypass

The use of the Hemochron activated clotting time (ACT) for determining adequacy of reversal of heparin following cardiopulmonary bypass was evaluated in 20 patients and compared with standard laboratory tests of coagulation. The commonly used Celite ACT method proved too insensitive to have any useful predictive value in detecting or quantifying residual heparin and removal of the Celite activation rendered the test even less sensitive. In contrast, the partial thromboplastin time with kaolin (PTTK) proved to correlate well with residual heparin ( r = 0.79). It is, therefore, recommended that the use of the Hemochron following protamine administration be abandoned in favour of the PTTK.

SHIP-1 inhibits CD95/APO-1/Fas-induced apoptosis in primary T lymphocytes and T leukemic cells by promoting CD95 glycosylation independently of its phosphatase activity

SHIP-1 (SH2 (Src homology 2)-containing inositol 5'-phosphatase-1) functions as a negative regulator of immune responses by hydrolyzing phosphatidylinositol-3,4,5-triphosphate generated by phosphoinositide-3 (PI 3)-kinase activity. As a result, SHIP-1 deficiency in mice results in myeloproliferation and B-cell lymphoma. On the other hand, SHIP-1-deficient mice have a reduced T-cell population, but the underlying mechanisms are unknown. In this work, we hypothesized that SHIP-1 plays anti-apoptotic functions in T cells upon stimulation of the death receptor CD95/APO-1/Fas. Using primary T cells from SHIP-1(-/-) mice and T leukemic cell lines, we report that SHIP-1 is a potent inhibitor of CD95-induced death. We observed that a small fraction of the SHIP-1 pool is localized to the endoplasmic reticulum (ER), in which it promotes CD95 glycosylation. This post-translational modification requires an intact SH2 domain of SHIP-1, but is independent of its phosphatase activity. The glycosylated CD95 fails to oligomerize upon stimulation, resulting in impaired death-inducing signaling complex (DISC) formation and downstream apoptotic cascade. These results uncover an unanticipated inhibitory function for SHIP-1 and emphasize the role of glycosylation in the regulation of CD95 signaling in T cells. This work may also provide a new basis for therapeutic strategies using compounds inducing apoptosis through the CD95 pathway on SHIP-1-negative leukemic T cells.

The plasma von Willebrand factor O-glycome comprises a surprising variety of structures including ABH antigens and disialosyl motifs

BACKGROUND

von Willebrand factor (VWF) is a key component for maintenance of normal hemostasis. Its glycan moieties, accounting for about 20% of its molecular weight, have been shown to affect many of its properties. Previous studies reported correlations between VWF secretion, half-life and the nature or presence of its N-glycans, and more importantly between VWF plasma level and the type of N-linked ABH antigens. Despite the presence of 10 predicted O-glycosylation sites, the O-glycome remains poorly characterized, impairing the complete elucidation of its influence on VWF functions. So far only a single glycan structure, a disialyl core 1 glycan, has been identified.

OBJECTIVES

To define an exhaustive profile of the VWF O-glycan structures to help the understanding of their role in VWF regulation and properties.

METHODS

Plasma-derived VWF O-linked sugars were isolated and analyzed using state-of-the-art mass spectrometry methodologies.

RESULTS AND CONCLUSIONS

We provide here a detailed analysis of the human plasma-derived VWF O-glycome. Eighteen O-glycan structures including both core 1 and core 2 structures are now demonstrated to be present on VWF. Amongst the newly determined structures are unusual tetra-sialylated core 1 O-glycans and ABH antigen-containing core 2 O-glycans. In conjunction with current models explaining VWF activity, knowledge of the complete O-glycome will facilitate research aimed at providing a better understanding of the influence of glycosylation on VWF functions.

Glycosylation of the phosphate binding protein, PstS, in Streptomyces coelicolor by a pathway that resembles protein O-mannosylation in eukaryotes

Previously mutations in a putative protein O-mannosyltransferase (SCO3154, Pmt) and a polyprenol phosphate mannose synthase (SCO1423, Ppm1) were found to cause resistance to phage, phiC31, in the antibiotic producing bacteria Streptomyces coelicolor A3(2). It was proposed that these two enzymes were part of a protein O-glycosylation pathway that was necessary for synthesis of the phage receptor. Here we provide the evidence that Pmt and Ppm1 are indeed both required for protein O-glycosylation. The phosphate binding protein PstS was found to be glycosylated with a trihexose in the S. coelicolor parent strain, J1929, but not in the pmt(-) derivative, DT1025. Ppm1 was necessary for the transfer of mannose to endogenous polyprenol phosphate in membrane preparations of S. coelicolor. A mutation in ppm1 that conferred an E218V substitution in Ppm1 abolished mannose transfer and glycosylation of PstS. Mass spectrometry analysis of extracted lipids showed the presence of a glycosylated polyprenol phosphate (PP) containing nine repeated isoprenyl units (C(45)-PP). S. coelicolor membranes were also able to catalyse the transfer of mannose to peptides derived from PstS, indicating that these could be targets for Pmt in vivo.

Hallmarks of Caenorhabditis elegans N-glycosylation: complexity and controversy

Caenorhabditis elegans has become one of the most widely used model organisms for a range of molecular cell biological applications and is being increasingly used by glycobiologists. However, a major problem has been the lack of knowledge of the structure of the protein-linked glycans from this organism. In recent years several groups have published structural data, particularly N-glycan structural data. However, some of these data are contradictory. In this review we critically assess all the N-glycan structural data and consider how close we are in our goal of defining the glycome of C. elegans.

Modeling human congenital disorder of glycosylation type IIa in the mouse: conservation of asparagine-linked glycan-dependent functions in mammalian physiology and insights into disease pathogenesis

The congenital disorders of glycosylation (CDGs) are recent additions to the repertoire of inherited human genetic diseases. Frequency of CDGs is unknown since most cases are believed to be misdiagnosed or unrecognized. With few patients identified and heterogeneity in disease signs noted, studies of animal models may provide increased understanding of pathogenic mechanisms. However, features of mammalian glycan biosynthesis and species-specific variations in glycan repertoires have cast doubt on whether animal models of human genetic defects in protein glycosylation will reproduce pathogenic events and disease signs. We have introduced a mutation into the mouse germline that recapitulates the glycan biosynthetic defect responsible for human CDG type IIa (CDG-IIa). Mice lacking the Mgat2 gene were deficient in GlcNAcT-II glycosyltransferase activity and complex N-glycans, resulting in severe gastrointestinal, hematologic, and osteogenic abnormalities. With use of a lectin-based diagnostic screen for CDG-IIa, we found that all Mgat2-null mice died in early postnatal development. However, crossing the Mgat2 mutation into a distinct genetic background resulted in a low frequency of survivors. Mice deficient in complex N-glycans exhibited most CDG-IIa disease signs; however, some signs were unique to the aged mouse or are prognostic in human CDG-IIa. Unexpectedly, analyses of N-glycan structures in Mgat2-null mice revealed a novel oligosaccharide branch on the "bisecting" N-acetylglucosamine. These genetic, biochemical, and physiologic studies indicate conserved functions for N-glycan branches produced in the Golgi apparatus among two mammalian species and suggest possible therapeutic approaches to GlcNAcT-II deficiency. Our findings indicate that human genetic disease due to aberrant protein glycosylation can be modeled in the mouse to gain insights into N-glycan-dependent physiology and the pathogenesis of CDG-IIa.

Isolation and structural determination of novel sulfated hexasaccharides from squid cartilage chondroitin sulfate E that exhibits neuroregulatory activities

Squid cartilage chondroitin sulfate E (CS-E) exhibits various biological activities, including anticoagulant activities, lymphoid regulatory activities, and neuroregulatory activities [Ueoka, C., Kaneda, N., Okazaki, I., Nadanaka, S., Muramatsu, T., and Sugahara, K. (2000) J. Biol. Chem. 275, 37407-37413]. These activities are expressed through molecular interactions with specific proteins, including heparin cofactor II, selectins, CD44, chemokines, and the heparin-binding growth factor midkine. Hence, the sugar sequence information is essential for a better understanding of the CS-E functions. Previously, several novel tetrasaccharides containing the unreported 3-O-sulfated glucuronic acid (GlcA) were isolated after digestion of squid cartilage CS-E with testicular hyaluronidase. In this study, hexasaccharides were isolated to obtain more detailed sequence information, especially around the GlcA(3-O-sulfate) residue, and were characterized by fast atom bombardment mass spectrometry and 500 or 600 MHz (1)H NMR spectroscopy. The findings demonstrate one tetrasulfated and five pentasulfated hexasaccharide sequences, five of them being novel. They were composed of three disaccharide building units of either A [GlcA(beta1-3)GalNAc(4-O-sulfate)], E [GlcA(beta1-3)GalNAc(4,6-O-disulfate)], K [GlcA(3-O-sulfate)(beta1-3)GalNAc(4-O-sulfate)], L [GlcA(3-O-sulfate)(beta1-3)GalNAc(6-O-sulfate)], or M [GlcA(3-O-sulfate)(beta1-3)GalNAc(4,6-O-disulfate)], forming E-A-A, M-A-A, K-L-A, E-E-A, K-K-A, and A-M-A hexasaccharide sequences. The K-L tetrasaccharide sequence is to date unreported. The isolated sequences appear to indicate the occurrence of an unreported GlcA 3-O-sulfotransferase specific for chondroitin sulfate. The obtained sequence information will be useful for investigating the structure-function relationship and biosynthesis of CS-E.

A non-Golgi alpha 1,2-fucosyltransferase that modifies Skp1 in the cytoplasm of Dictyostelium

Skp1 is a subunit of the SCF-E3 ubiquitin ligase that targets cell cycle and other regulatory factors for degradation. In Dictyostelium, Skp1 is modified by a pentasaccharide containing the type 1 blood group H trisaccharide at its core. To address how the third sugar, fucose alpha1,2-linked to galactose, is attached, a proteomics strategy was applied to determine the primary structure of FT85, previously shown to copurify with the GDP-Fuc:Skp1 alpha 1,2-fucosyltransferase. Tryptic-generated peptides of FT85 were sequenced de novo using Q-TOF tandem mass spectrometry. Degenerate primers were used to amplify FT85 genomic DNA, which was further extended by a novel linker polymerase chain reaction method to yield an intronless open reading frame of 768 amino acids. Disruption of the FT85 gene by homologous recombination resulted in viable cells, which had altered light scattering properties as revealed by flow cytometry. FT85 was necessary and sufficient for Skp1 fucosylation, based on biochemical analysis of FT85 mutant cells and Escherichia coli that express FT85 recombinantly. FT85 lacks sequence motifs that characterize all other known alpha 1,2-fucosyltransferases and lacks the signal-anchor sequence that targets them to the secretory pathway. The C-terminal region of FT85 harbors motifs found in inverting Family 2 glycosyltransferase domains, and its expression in FT85 mutant cells restores fucosyltransferase activity toward a simple disaccharide substrate. Whereas most prokaryote and eukaryote Family 2 glycosyltransferases are membrane-bound and oriented toward the cytoplasm where they glycosylate lipid-linked or polysaccharide precursors prior to membrane translocation, the soluble, eukaryotic Skp1-fucosyltransferase modifies a protein that resides in the cytoplasm and nucleus.

FAB-MS characterization of sialyl Lewis x determinants on polylactosamine chains of human airway mucins secreted by patients suffering from cystic fibrosis or chronic bronchitis

Although a large body of structural data exists for bronchial mucins from cystic fibrosis (CF) and chronic bronchitis (CB) patients, little is known about terminal structures carried on poly-N-acetyllactosamine antennae. Such structures are of interest because they are potential ligands for bacterial adhesins and other lectins. In this study, we have used fast atom bombardment mass spectrometry (FAB-MS) to examine terminal sequences released by endo-beta-galactosidase from O-glycans obtained by reductive elimination of bronchial mucins purified from the sputum of 8 CF and 8 CB patients. Our data show that, although the polylactosamine antennae of CF and CB mucins have several terminal sequences in common, they differ significantly in their sialyl Lewis(x) (NeuAcalpha2-3Galbeta1-4[Fucalpha1-3]GlcNAcbeta1-) content. Thus all examined mucins from CF patients carry sialyl Lewis(x) on their polylactosamine antennae, whereas this type of epitope is present on only three out of the eight CB mucins examined, notably in the airways of one CB patient which were heavily infected by Pseudomonas aeruginosa as are the airways of all the CF patients. This suggests that, in airway mucins, the expression of sialyl Lewis(x) on polylactosamine antennae is probably more related to inflammation and infection than to a direct effect of the CF defect.

Differences between neonates and adults in tissue-type-plasminogen activator (t-PA)-catalyzed plasminogen activation with various effectors and in carbohydrate sequences of fibrinogen chains

Our study investigates the effect of fetal and adult soluble fibrin (SF), fetal and adult fibrinogen Aalpha- and gamma-chains, as well as adult CNBr-fibrinogen fragments on tissue-type plasminogen activator (t-PA)-catalyzed plasminogen activation of both fetal and adult Glu-plasminogen types 1 and 2. In addition, we determined carbohydrate sequences of fetal and adult Bbeta- and gamma-chains by mass spectrometric analysis. In the absence of an effector, no substantial differences in the rate of plasmin formation could be seen between the fetal and adult plasminogen types. In the presence of an effector, both fetal Glu-plasminogen types revealed lower values for k(cat app) than the respective adult types. No differences could be seen in the values for K(m app). The resulting differences in catalytic efficiencies between the fetal and adult plasminogen types were much less than previously reported. No differences could be seen between fetal and adult effectors in stimulating t-PA-catalyzed plasminogen activation. Detailed analyses of the activation kinetics revealed a longer initial phase of slow plasmin formation of both fetal Glu-plasminogen types compared to their respective adult types, indicating a slower plasmin-induced modification of CNBr-fibrinogen fragments or SF by fetal plasmin. Mass spectrometric analysis of the N-glycans present on adult and fetal Bbeta- and gamma-fibrinogen chains showed the presence of a major monosialylated biantennary structure with lesser amounts of the disialylated form. In contrast to previous data, we conclude that catalytic efficiency of t-PA-catalyzed plasminogen activation in neonates is only slightly lower than in adults.

Galactan biosynthesis in Mycobacterium tuberculosis. Identification of a bifunctional UDP-galactofuranosyltransferase

The cell wall of Mycobacterium tuberculosis and related genera is unique among prokaryotes, consisting of a covalently bound complex of mycolic acids, D-arabinan and D-galactan, which is linked to peptidoglycan via a special linkage unit consisting of Rhap-(1-->3)-GlcNAc-P. Information concerning the biosynthesis of this entire polymer is now emerging with the promise of new drug targets against tuberculosis. Accordingly, we have developed a galactosyltransferase assay that utilizes the disaccharide neoglycolipid acceptors beta-d-Galf-(1-->5)-beta-D-Galf-O-C(10:1) and beta-D-Galf-(1-->6)-beta-D-Galf-O-C(10:1), with UDP-Gal in conjunction with isolated membranes. Chemical analysis of the subsequent reaction products established that the enzymatically synthesized products contained both beta-D-Galf linkages ((1-->5) and (1-->6)) found within the mycobacterial cell, as well as in an alternating (1-->5) and (1-->6) fashion consistent with the established structure of the cell wall. Furthermore, through a detailed examination of the M. tuberculosis genome, we have shown that the gene product of Rv3808c, now termed glfT, is a novel UDP-galactofuranosyltransferase. This enzyme possesses dual functionality in performing both (1-->5) and (1-->6) galactofuranosyltransferase reactions with the above neoglycolipid acceptors, using membranes isolated from the heterologous host Escherichia coli expressing Rv3808c. Thus, at a biochemical and genetic level, the polymerization of the galactan region of the mycolyl-arabinogalactan complex has been defined, allowing the possibility of further studies toward substrate recognition and catalysis and assay development. Ultimately, this may also lead to a more rational approach to drug design to be explored in the context of mycobacterial infections.

Molecular characterization of the surface layer proteins from Clostridium difficile

Many bacteria express a surface-exposed proteinaceous layer, termed the S-layer, which forms a regular two-dimensional array visible by electron microscopy. Clostridium difficile is unusual in expressing two S-layer proteins (SLPs), which are of varying size in a number of strains. In an approach combining molecular biology with mass spectrometric sequencing strategies, we have identified the structural gene (slpA) for the S-layer from three strains of C. difficile. Both proteins are derived from a common precursor, and processing involves the removal of a signal peptide and a second cleavage to release the two mature SLPs. To our knowledge, this is the first example in which two SLPs have been shown to derive from a single gene product through post-translational processing, rather than from the expression of separate genes. The higher molecular weight (MW) SLP is highly conserved among the three strains, whereas the lower MW SLP shows considerable sequence diversity, reflecting the results from Western blotting. The high-MW SLP shows weak homology to N-acetyl muramoyl-L-alanine amidase from Bacillus subtilis, and both the native SLP from C. difficile and a recombinant protein expressed in Escherichia coli were found to display amidase activity by zymography. The high-MW SLPs showed evidence of glycosylation, whereas the lower MW proteins did not. A family of genes with sequence homology to the amidase domain of the high-MW SLP was identified in the C. difficile strain 630 genome, some of which are located in the same region of the genome as slpA and were shown by reverse transcription-polymerase chain reaction (RT-PCR) analysis to be transcribed.

In vivo glycosylation of mucin tandem repeats

The biochemical and biophysical properties of mucins are largely determined by extensive O-glycosylation of serine- and threonine-rich tandem repeat (TR) domains. In a number of human diseases aberrant O-glycosylation is associated with variations in the properties of the cell surface-associated and secreted mucins. To evaluate in vivo the O-glycosylation of mucin TR domains, we generated recombinant chimeric mucins with TR sequences from MUC2, MUC4, MUC5AC, or MUC5B, which were substituted for the native TRs of epitope-tagged MUC1 protein (MUC1F). These hybrid mucins were extensively O-glycosylated and showed the expected association with the cell surface and release into culture media. The presence of different TR domains within the chimeric mucins appears to have limited influence on their posttranslational processing. Alterations in glycosylation were detailed by fast atom bombardment mass spectrometry and reactivity with antibodies against particular blood-group and tumor-associated carbohydrate antigens. Future applications of these chimeras will include investigations of mucin posttranslational modification in the context of disease.

Mass spectrometric strategies: providing structural clues for helminth glycoproteins

Here we review current knowledge of helminth glycans and introduce parasitologists to the power of the mass spectrometric techniques that have been largely responsible for defining their carbohydrate moieties. A brief overview of glycosylation in other eukaryotes is presented, with a focus on mammalian glycosylation, to facilitate understanding of how parasite structures might be recognized as 'self' or 'foreign' by the immune system of the host.

The failure of different strains of Yersinia pestis to produce lipopolysaccharide O-antigen under different growth conditions is due to mutations in the O-antigen gene cluster

The lipopolysaccharide (LPS) from eight strains of Yersinia pestis which had been cultured at 28 degrees C appeared to be devoid of an O-antigen when analysed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. LPS isolated from three of these strains which had been cultured at 37 degrees C also appeared to be devoid of an O-antigen. When the LPS from Y. pestis strain CO92 was purified and analysed by matrix-assisted laser desorption-ionisation time-of-flight mass spectrometry, the observed signals were in the mass range predicted for molecules containing lipid A plus the core oligosaccharide but lacking an O-antigen. The nucleotide sequence of Y. pestis strain CO92 revealed the presence of a putative O-antigen gene cluster. However, frame-shift mutations in the ddhB, gmd, fcl and ushA genes are likely to prevent expression of the O-antigen thus explaining the loss of phenotype.

Glycoprotein structure determination by mass spectrometry

The human genome encodes 30,000 to 40,000 proteins, and a major challenge is to understand how posttranslational events, such as glycosylation, affect the activities and functions of these proteins in health and disease. Glycosylated proteins are ubiquitous components of extracellular matrices and cellular surfaces where their oligosaccharide moieties are implicated in a wide range of cell-cell and cell-matrix recognition events. The power of ultrahigh-sensitivity mass spectrometric strategies for defining the primary structures of highly complex mixtures of glycoprotein glycoforms is set to revolutionize structural glycobiology in the coming postgenomic era.

The species recognition system: a new corollary for the human fetoembryonic defense system hypothesis

We have previously suggested that the human fetus is protected during human development by a system of both soluble and cell surface associated glycoconjugates that utilize their carbohydrate sequences as functional groups to enable them to evoke tolerance. The proposed model has been referred to as the human fetoembryonic defense system hypothesis (hu-FEDS). In this paradigm, it has previously been proposed that similar oligosaccharides are used to mediate crucial recognition events required during both human sperm-egg binding and immune-inflammatory cell interactions. This vertical integration suggested to us that the sperm-egg binding itself is related to universal recognition events that occur between immune and inflammatory cells, except that in this case recognition of 'species' rather than recognition of 'self' is being manifested. In this paper, we have designated this component of hu-FEDS as the species recognition system (SRS). We propose that the SRS is an integral component of the hu-FEDS used to enable sperm-egg recognition and protection of the gametes from potential immune responses. Recent structural data indicates that the glycan sequences implicated in mediating murine gamete recognition are also expressed on CD45 in activated murine T lymphocytes and cytotoxic T lymphocytes. This overlap supports our contention that there is an overlap between the immune and gamete recognition systems. Therefore the hu-FEDS paradigm may be a subset of a larger model that also applies to other placental mammals. We therefore propose that the hu-FEDS model for protection should in the future be referred to as the eutherian fetoembryonic defense system hypothesis (eu-FEDS) to account for this extension. The possibility exists that the SRS component of eu-FEDS could predate eutherians and extend to all sexually reproducing organisms. Future investigation of the interactions between the immune and gamete recognition system will be required to determine the degree of overlap.

Characterization of the lipopolysaccharide of Yersinia pestis

Lipopolysaccharide (LPS) extracted from eight strains of Yersinia pestis, which had been cultured at 28 or 37 degrees C, reacted equally well, in Western blots, with four monoclonal antibodies generated against the LPS from a single strain of Y. pestis cultured at 28 degrees C. LPS was extracted and purified from Y. pestis strain GB, which had been cultured at 28 degrees C. When the LPS was analysed by SDS-PAGE and MALDI-TOF mass spectrometry it was found to be devoid of an O-antigen. The LPS possessed activity of 2.7 endotoxin units/ng in the Limulus amoebocyte lysate assay. The LPS stimulated the production of TNFalpha and IL-6 from mouse macrophages, but was less active in these assays than LPS isolated from Escherichia coli strain 0111. Y. pestis LPS, either alone or with cholera toxin B subunit, was used to immunize mice. Either immunization schedule resulted in the development of an antibody response to LPS. However, this response did not provide protection against 100 MLD of Y. pestis strain GB.

Genetic remodeling of protein glycosylation in vivo induces autoimmune disease

Autoimmune diseases are among the most prevalent of afflictions, yet the genetic factors responsible are largely undefined. Protein glycosylation in the Golgi apparatus produces structural variation at the cell surface and contributes to immune self-recognition. Altered protein glycosylation and antibodies that recognize endogenous glycans have been associated with various autoimmune syndromes, with the possibility that such abnormalities may reflect genetic defects in glycan formation. We show that mutation of a single gene, encoding alpha-mannosidase II, which regulates the hybrid to complex branching pattern of extracellular asparagine (N)-linked oligosaccharide chains (N-glycans), results in a systemic autoimmune disease similar to human systemic lupus erythematosus. alpha-Mannosidase II-deficient autoimmune disease is due to an incomplete overlap of two conjoined pathways in complex-type N-glycan production. Lymphocyte development, abundance, and activation parameters are normal; however, serum immunoglobulins are increased and kidney function progressively falters as a disorder consistent with lupus nephritis develops. Autoantibody reactivity and circulating immune complexes are induced, and anti-nuclear antibodies exhibit reactivity toward histone, Sm antigen, and DNA. These findings reveal a genetic cause of autoimmune disease provoked by a defect in the pathway of protein N-glycosylation.

Glycoconjugates from Parasitic Helminths: Structure Diversity and Immunobiological Implications

We have provided an account of the progress we and others have made over the last decade on the structural characterization of glycans from parasitic helminths. We hope to have illustrated a few principles and patterns governing helminth glycosylation, as well as the experimental approaches adopted and their associated strengths and limitations. Schistosomes remain the best studied systems but are still punctuated with gaps of knowledge. An important theme developed here is the regulated developmental stage-specific expression of various glycan epitopes and their interplay with immediate host environments for successful parasitism. It is anticipated that more novel or unusual structures will continuously be uncovered in the future and that despite many difficulties, current analytical techniques should be well up to meet the challenge in at least elucidating the major or key glycoconjugates from each of the diverse range of worms. The bottle neck will in fact reside in finding suitable experimental models to test their putative immunobiological functions from which the intricate host-parasite interactions can be delineated and rational vaccine design be achieved. The glycobiology of parasitic helminths is an area waiting to be more fully explored and the rewards should be sweet.

Phosphorylcholine-containing N-glycans of Trichinella spiralis: identification of multiantennary lacdiNAc structures

Although the presence of phosphorylcholine (PC) in Trichinella spiralis is well established, the precise structure of the PC-bearing molecules is not known. In this paper, we report structural studies of N-glycans released from T.spiralis affinity-purified antigens by peptide N-glycosidase F. Three classes of N-glycan structures were observed: high mannose type structures; those which had been fully trimmed to the trimannosyl core and were sub-stoichiometrically fucosylated; and those with a trimannosyl core, with and without core fucosylation, carrying between one and eight N-acetylhexosamine residues. Of the three classes of glycans, only the last was found to be substituted with detectable levels of phosphorylcholine.

Phase variation of a beta-1,3 galactosyltransferase involved in generation of the ganglioside GM1-like lipo-oligosaccharide of Campylobacter jejuni

Ganglioside mimicry by Campylobacter jejuni lipo-oligosaccharide (LOS) is thought to be a critical factor in the triggering of the Guillain-Barré and Miller-Fisher syndrome neuropathies after C. jejuni infection. The combination of a completed genome sequence and a ganglioside GM1-like LOS structure makes C. jejuni NCTC 11168 a useful model strain for the identification and characterization of the genes involved in the biosynthesis of ganglioside-mimicking LOS. Genome analysis identified a putative LOS biosynthetic cluster and, from this, we describe a putative gene (ORF Cj1139c), which we have termed wlaN, with a significant level of similarity to a number of bacterial glycosyltransferases. Mutation of this gene in C. jejuni NCTC 11168 resulted in a LOS molecule of increased electrophoretic mobility, which also failed to bind cholera toxin. Comparison of LOS structural data from wild type and the mutant strain indicated lack of a terminal beta-1,3-linked galactose residue in the latter. The wlaN gene product was demonstrated unambiguously as a beta-1,3 galactosyltransferase responsible for converting GM2-like LOS structures to GM1-like by in vitro expression. We also show that the presence of an intragenic homopolymeric tract renders the expression of a functional wlaN gene product phase variable, resulting in distinct C. jejuni NCTC 11168 cell populations with alternate GM1 or GM2 ganglioside-mimicking LOS structures. The distribution of wlaN among a number of C. jejuni strains with known LOS structure was determined and, for C. jejuni NCTC 12500, similar wlaN gene phase variation was shown to occur, so that this strain has the potential to synthesize a GM1-like LOS structure as well as the ganglioside GM2-like LOS structure proposed in the literature.

Recombinant glycodelin carrying the same type of glycan structures as contraceptive glycodelin-A can be produced in human kidney 293 cells but not in chinese hamster ovary cells

We have produced human recombinant glycodelin in human kidney 293 cells and in Chinese hamster ovary (CHO) cells. Structural analyses by lectin immunoassays and fast atom bombardment mass spectrometry showed that recombinant human glycodelin produced in CHO cells contains only typical CHO-type glycans and is devoid of any of the N, N'-diacetyllactosediamine (lacdiNAc)-based chains previously identified in glycodelin-A (GdA). By contrast, human kidney 293 cells produced recombinant glycodelin with the same type of carbohydrate structures as GdA. The presence of a beta1-->4-N-acetylgalactosaminyltransferase functioning in the synthesis of lacdiNAc-based glycans in human kidney 293 cells is concluded to be the cause of the occurrence of lacdiNAc-based glycans on glycodelin produced in these cells. Furthermore, human kidney 293 cells were found to be particularly suited for the production of recombinant glycodelin when they were cultured in high glucose media. Lowering the glucose concentration and the addition of glucosamine resulted in higher relative amounts of oligomannosidic-type glycans and complex glycans with truncated antennae. Human glycodelin is an attractive candidate for the development of a contraceptive agent, and this study gives valuable information for selecting the proper expression system and cell culture conditions for the production of a correctly glycosylated recombinant form.

Pregnancy-associated changes in the glycosylation of tamm-horsfall glycoprotein. Expression of sialyl Lewis(x) sequences on core 2 type O-glycans derived from uromodulin

Tamm-Horsfall glycoprotein (THP) is a major glycoprotein associated with human urine that binds pro-inflammatory cytokines and also inhibits in vitro T cell proliferation induced by specific antigens. THP derived from human pregnancy urine (designated uromodulin) has previously been shown to be 13-fold more effective as an inhibitor of antigen-induced T cell proliferation than THP obtained from other sources. Structural analysis of human THP and uromodulin has for the first time revealed that these glycoproteins are O-glycosylated. THP from nonpregnant females and males expresses primarily core 1 type O-glycans terminated with either sialic acid or fucose but not the sialyl Lewis(x) epitope. By contrast, the O-glycans linked to uromodulin include unusual core 2 type glycans terminated with one, two, or three sialyl Lewis(x) sequences. The specific association of these unusual carbohydrate sequences with uromodulin could explain its enhanced immunomodulatory effects compared with THP obtained from males and nonpregnant females. Analysis of THP from one of the pregnant females 2 months postpartum showed a reversion of the O-glycan profile to that found for a non-pregnant female. These data suggest that the glycosylation state of uromodulin could be under the regulation of steroidal hormones produced during pregnancy. The significant physiological implications of these observations are discussed.

Modification of a recombinant GPI-anchored metalloproteinase for secretion alters the protein glycosylation

The N-linked glycans of recombinant leishmanolysin (GP63) expressed as a glycosylphosphatidylinositol (GPI)-anchored membrane protein or modified for secretion in Chinese hamster ovary (CHO) cells were analyzed by fast atom bombardment-mass spectrometry (FAB-MS). The glycans isolated from both membrane and secreted protein were predominantly complex biantennary structures. However other aspects of the glycan profiles showed striking differences. The degree of sialylation of the membrane form was greatly reduced and the core fucosylation of biantennary structures was increased compared to the secreted form. Glycans isolated from membrane expressed protein also contained a higher proportion of lactosamine repeats. Residence times in the secretory pathway were similar for both secreted and membrane protein. Glycosylation differences may therefore be due to differences in protein conformation and accessibility to glycosyltransferases or glycosidases. These differences in glycosylation represent an important factor when considering modifying membrane expressed proteins for secreted production.

Structural analysis of murine zona pellucida glycans. Evidence for the expression of core 2-type O-glycans and the Sd(a) antigen

Murine sperm initiate fertilization by binding to specific oligosaccharides linked to the zona pellucida, the specialized matrix coating the egg. Biophysical analyses have revealed the presence of both high mannose and complex-type N-glycans in murine zona pellucida. The predominant high mannose-type glycan had the composition Man(5)GlcNAc(2), but larger oligosaccharides of this type were also detected. Biantennary, triantennary, and tetraantennary complex-type N-glycans were found to be terminated with the following antennae: Galbeta1-4GlcNAc, NeuAcalpha2-3Galbeta1-4GlcNAc, NeuGcalpha2-3Galbeta1-4GlcNAc, the Sd(a) antigen (NeuAcalpha2-3[GalNAcbeta1-4]Galbeta1-4GlcNAc, NeuGcalpha2-3[GalNAcbeta1-4]Galbeta1-4GlcNAc), and terminal GlcNAc. Polylactosamine-type sequence was also detected on a subset of the antennae. Analysis of the O-glycans indicated that the majority were core 2-type (Galbeta1-4GlcNAcbeta1-6[Galbeta1-3]GalNAc). The beta1-6-linked branches attached to these O-glycans were terminated with the same sequences as the N-glycans, except for terminal GlcNAc. Glycans bearing Galbeta1-4GlcNAcbeta1-6 branches have previously been suggested to mediate initial murine gamete binding. Oligosaccharides terminated with GalNAcbeta1-4Gal have been implicated in the secondary binding interaction that occurs following the acrosome reaction. The significant implications of these observations are discussed.

Characterization of the N-linked oligosaccharides of megalin (gp330) from rat kidney

Megalin (gp 330) is a large cell surface receptor expressed on the apical surfaces of epithelial tissues, that mediates the binding and internalization of a number of structurally and functionally distinct ligands. In this paper we report the first detailed structural characterization of megalin-derived oligosaccharides. Using strategies based on mass spectrometric analysis, we have defined the structures of the N-glycans of megalin. The results reveal that megalin glycoprotein is heterogeneously glycosylated. The major N-glycans identified belong to the following two classes: high mannose structures and complex type structures, with complex structures being more abundant than high mannose structures. The major nonreducing epitopes in the complex-type glycans are: GlcNAc, Galbeta1-4GlcNAc (LacNAc), NeuAcalpha2-6Galbeta1-4GlcNAc (sialylated LacNAc), GalNAcbeta1-4[NeuAcalpha2-3]Galbeta1-4GlcNAc (Sd(a)) and Galalpha1-3Galbeta1-4GlcNAc. Most complex structures are characterized by the presence of (alpha1,6)-core fucosylation and the presence of a bisecting GlcNAc residue.

Multiple N-acetyl neuraminic acid synthetase (neuB) genes in Campylobacter jejuni: identification and characterization of the gene involved in sialylation of lipo-oligosaccharide

N-acetyl neuraminic acid (NANA) is a common constituent of Campylobacter jejuni lipo-oligosaccharide (LOS). Such structures often mimic human gangliosides and are thought to be involved in the triggering of Guillain-Barré syndrome (GBS) and Miller-Fisher syndrome (MFS) following C. jejuni infection. Analysis of the C. jejuni NCTC 11168 genome sequence identified three putative NANA synthetase genes termed neuB1, neuB2 and neuB3. The NANA synthetase activity of all three C. jejuni neuB gene products was confirmed by complementation experiments in an Escherichia coli neuB-deficient strain. Isogenic mutants were created in all three neuB genes, and for one such mutant (neuB1) LOS was shown to have increased mobility. C. jejuni NCTC 11168 wild-type LOS bound cholera toxin, indicating the presence of NANA in a LOS structure mimicking the ganglioside GM1. This property was lost in the neuB1 mutant. Gas chromatography-mass spectrometry and fast atom bombardment-mass spectrometry analysis of LOS from wild-type and the neuB1 mutant strain demonstrated the lack of NANA in the latter. Expression of the neuB1 gene in E. coli confirmed that NeuB1 was capable of in vitro NANA biosynthesis through condensation of N-acetyl-D-mannosamine and phosphoenolpyruvate. Southern analysis demonstrated that the neuB1 gene was confined to strains of C. jejuni with LOS containing a single NANA residue. Mutagenesis of neuB2 and neuB3 did not affect LOS, but neuB3 mutants were aflagellate and non-motile. No phenotype was evident for neuB2 mutants in strain NCTC 11168, but for strain G1 the flagellin protein from the neuB2 mutant showed an apparent reduction in molecular size relative to the wild type. Thus, the neuB genes of C. jejuni appear to be involved in the biosynthesis of at least two distinct surface structures: LOS and flagella.

Structural characterization of the N-glycans of Dictyocaulus viviparus: discovery of the Lewis(x) structure in a nematode

This paper reports the first rigorous evidence for the existence of N-linked oligosaccharides in Dictyocaulus viviparus, an economically important nematode that parasitises cattle. Structural strategies based upon fast atom bombardment mass spectrometry were employed to examine detergent extracts of homogenised adult D.viviparus for their N-glycan content. These revealed that detergent-soluble material is rich in high mannose, truncated and complex-type families of N-linked oligosaccharides. Importantly, the most abundant antennae in the complex-type structures were shown to carry the Lewis(x)epitope (Galbeta1-4(Fucalpha1-3)GlcNAc). Although the Lewis(x)moiety occurs in other helminths such as schistosomes, nematodes have previously been thought to lack this epitope. The Lewis(x)epitopes in D.viviparus are carried on bi-, tri-, and tetraantennary glycans and are therefore candidates for recognition events requiring multivalent ligands. There is compelling evidence from schistosome research that glycoconjugates containing Lewis(x)structures are immunomodulators. We propose that the Lewis(x)-rich glycans identified in this study might similarly be involved in D.viviparus host interactions.

Structural characterization of the inflammatory moiety of a variable major lipoprotein of Borrelia recurrentis

Louse-borne relapsing fever, caused by Borrelia recurrentis, provides one of the best documented examples of the causative role of tumor necrosis factor (TNF) in the pathology of severe infection in humans. We have identified the principal TNF-inducing factor of B. recurrentis as a variable major lipoprotein (Vmp). Here we report the complete gene sequence of Vmp, including its lipoprotein leader sequence. Using metabolically labeled forms of the native Vmp we confirm that the TNF inducing properties are associated with the lipid portion of the molecule. Quadrupole orthogonal time of flight mass spectrometry unequivocally locates the lipidic moiety at the NH(2)-terminal cysteine of the native polypeptide, and indicates the existence of three forms which are consistent with the structures C16:0, C16:0, C16:0 glyceryl cysteine; C18:1, C16:0, C16:0 glyceryl cysteine; and C18:0, C16:0, C16:0 glyceryl cysteine. These data provide the first direct evidence that the TNF inducing lipid modification of native Borrelia lipoproteins is a structural homologue of the murein lipoprotein of Escherichia coli.

Molecular cloning and demonstration of an aminopeptidase activity in a filarial nematode glycoprotein

ES-62 is an abundant phosphorylcholine-containing secreted glycoprotein of the filarial nematode Acanthocheilonema viteae. Using an antiserum directed against the parasite molecule, 3 cDNAs of size, approximately 1.5-1.6 kbp were isolated from an A. viteae expression library. Sequence analysis in combination with N-terminal amino acid sequencing of purified ES-62 revealed that each clone contained a full-length cDNA for ES-62 corresponding to 474 amino acid residues but differed in their 5' and 3' untranslated regions. Characterisation of the 5' end of ES-62 mRNA using 5' rapid amplification of cDNA ends showed that it coded for a signal sequence. Several tryptic peptides were independently sequenced using quadruple-time-of-flight mass spectrometry and used to confirm the cDNA sequence. The mature protein was found to contain three potential N-linked glycosylation sites. Comparison of the derived amino acid sequence of ES-62 with the SwissProt database identified a sequence (between amino acid residues approximately 250 and 350 of mature ES-62) with significant similarity to several bacterial/fungal aminopeptidases. Incubation of ES-62 with leucine-7-amino-4-methylcoumarin as substrate confirmed that ES-62 possessed aminopeptidase activity.

Immunogenic glycoconjugates implicated in parasitic nematode diseases

Parasitic nematodes infect billions of people world-wide, often causing chronic infections associated with high morbidity. The greatest interface between the parasite and its host is the cuticle surface, the outer layer of which in many species is covered by a carbohydrate-rich glycocalyx or cuticle surface coat. In addition many nematodes excrete or secrete antigenic glycoconjugates (ES antigens) which can either help to form the glycocalyx or dissipate more extensively into the nematode's environment. The glycocalyx and ES antigens represent the main immunogenic challenge to the host and could therefore be crucial in determining if successful parasitism is established. This review focuses on a few selected model systems where detailed structural data on glycoconjugates have been obtained over the last few years and where this structural information is starting to provide insight into possible molecular functions.

Structural studies of N-glycans of filarial parasites. Conservation of phosphorylcholine-substituted glycans among species and discovery of novel chito-oligomers

N-Type glycans containing phosphorylcholine (PC-glycans), unusual structures found in the important human pathogens filarial nematodes, represent a novel target for chemotherapy. Previous work in our laboratories produced compositional information on the PC-glycan of ES-62, a secreted protein of the rodent parasite Acanthocheilonema viteae. In particular, we established using fast atom bombardment mass spectrometry (MS) analysis that PC was attached to a glycan with a trimannosyl core, with and without core fucosylation, carrying between one and four additional N-acetylglucosamine residues. In the present study, we demonstrate that this structure is conserved among filarial nematodes, including the parasite of humans, Onchocerca volvulus, for which new drugs are most urgently sought. Furthermore, by employing a variety of procedures, including collision-activated dissociation MS-MS analysis and matrix-assisted laser desorption MS analysis, we reveal that surprisingly, filarial nematodes also contain N-linked glycans, the antennae of which are composed of chito-oligomers. To our knowledge, this is the first report of such structures in a eukaryotic glycoprotein.