Use of porcine fibrinogen as a model glycoprotein to study the binding specificity of the three variants of K88 lectin

Regulation of fibrinogen synthesis

The plasma protein fibrinogen is encoded by 3 structural genes (FGA, FGB, and FGG) that are transcribed to mRNA, spliced, and translated to 3 polypeptide chains (Aα, Bβ, and γ, respectively). These chains are targeted for secretion, decorated with post-translational modifications, and assembled into a hexameric "dimer of trimers" (AαBβγ)2. Fully assembled fibrinogen is secreted into the blood as a 340 kDa glycoprotein. Fibrinogen is one of the most prevalent coagulation proteins in blood, and its expression is induced by inflammatory cytokines, wherein circulating fibrinogen levels may increase up to 3-fold during acute inflammatory events. Abnormal levels of circulating fibrinogen are associated with bleeding and thrombotic disorders, as well as several inflammatory diseases. Notably, therapeutic strategies to modulate fibrinogen levels have shown promise in experimental models of disease. Herein, we review pathways mediating fibrinogen synthesis, from gene expression to secretion. Knowledge of these mechanisms may lead to the identification of biomarkers and new therapeutic targets to modulate fibrinogen in health and disease.

Cetacean Intracytoplasmic Eosinophilic Globules: A Cytomorphological, Histological, Histochemical, Immunohistochemical, and Proteomic Characterization

The nature, etiopathogenesis, and clinicopathologic relevance of the prevalent intracytoplasmic eosinophilic globules (IEGs) within hepatocytes of cetaceans are unknown. This study aims to evaluate the presence and characterize the IEGs in the hepatocytes of cetaceans using histochemical and immunohistochemical electron microscopy, Western blot, lectin histochemistry, and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry techniques. A total of 95/115 (83%) animals (16 species) exhibited histologically evident intracytoplasmic round to oval, single to multiple, hyaline eosinophilic globules within the hepatocytes. These globules were largely PAS-positive, diastase resistant, and were immunopositive for fibrinogen (FB, 97%), albumin (Alb, 85%), and α1-antitrypsine (A1AT, 53%). The IEG positivity for FB and A1AT were correlated with live-stranding, hepatic congestion and a good nutritional status. The cetaceans lacking IEGs were consistently dead stranded and had poor body conditions. The IEGs in 36 bycaught cetaceans were, all except one, FB-positive and A1AT-negative. The IEGs exhibited morphologic and compositional variations at the ultrastructural level, suggesting various stages of development and/or etiopathogenesis(es). The glycocalyx analysis suggested an FB- and A1AT-glycosylation pattern variability between cetaceans and other animals. The proteomic analyses confirmed an association between the IEGs and acute phase proteins, suggesting a relationship between acute stress (i.e., bycatch), disease, and cellular protective mechanisms, allowing pathologists to correlate this morphological change using the acute hepatocytic cell response under certain stress conditions.

Urinary Glycopeptide Analysis for the Investigation of Novel Biomarkers

PURPOSE

Urine is a rich source of potential biomarkers, including glycoproteins. Glycoproteomic analysis remains difficult due to the high heterogeneity of glycans. Nevertheless, recent advances in glycoproteomics software solutions facilitate glycopeptide identification and characterization. The aim is to investigate intact glycopeptides in the urinary peptide profiles of normal subjects using a novel PTM-centric software-Byonic.

EXPERIMENTAL DESIGN

The urinary peptide profiles of 238 normal subjects, previously analyzed using CE-MS and CE-MS/MS and/or LC-MS/MS, are subjected to glycopeptide analysis. Additionally, glycopeptide distribution is assessed in a set of 969 patients with five different cancer types: bladder, prostate and pancreatic cancer, cholangiocarcinoma, and renal cell carcinoma.

RESULTS

A total of 37 intact O-glycopeptides and 23 intact N-glycopeptides are identified in the urinary profiles of 238 normal subjects. Among the most commonly identified O-glycoproteins are Apolipoprotein C-III and insulin-like growth factor II, while titin among the N-glycoproteins. Further statistical analysis reveals that three O-glycopeptides and five N-glycopeptides differed significantly in their abundance among the different cancer types, comparing to normal subjects.

CONCLUSIONS AND CLINICAL RELEVANCE

Through the established glycoproteomics workflow, intact O- and N-glycopeptides in human urine are identified and characterized, providing novel insights for further exploration of the glycoproteome with respect to specific diseases.

Glycosylation characterization of human and porcine fibrinogen proteins by lectin-binding biophotonic microarray imaging

Lectin binding has been studied using the particle plasmon light-scattering properties of gold nanoparticles printed into an array format. Performance of the kinetic assay is evaluated from a detailed analysis of the binding of concanavalin A (ConA) and wheat germ agglutinin (WGA) to their target monosaccharides indicating affinity constants in the order of KD ∼10 nM for the lectin-monosaccharide interaction. The detection limits for the lectins following a 200 s injection time were determined as 10 ng/mL or 0.23 nM and 100 ng/mL or 0.93 nM, respectively. Subsequently, a nine-lectin screen was performed on the porcine and human fibrinogen glycoproteins. The observed spectra of lectin-protein specific binding rates result in characteristic patterns that evidently correlate with the structure of the glycans and allow one to distinguish between glycosylation of the porcine and human fibrinogens. The array technology has the potential to perform a multilectin screen of large numbers of proteins providing information on protein glycosylation and their microheterogeneity.

Glycoproteins of drusen and drusen-like lesions

Drusen are a marker of age-related macular degeneration (AMD). Lesions similar to drusen, both in histology and their clinical appearance, are also seen in choroidal tumours, chronic inflammatory and degenerative conditions of the eye, and in mesangiocapillary glomerulonephritis type II (MCGN-II). This study aims to compare the saccharide composition of these drusen-like lesions in the various ocular pathological groups and in MCGN-II. Formalin fixed and paraffin wax embedded tissue from 21 eyes was studied. The histological diagnoses included AMD, retinal detachment, phthisis bulbi following failed retinal detachment surgery, malignant melanoma, long-standing uveitis, glaucoma and MCGN II. Glycosylation was examined using a panel of twenty biotinylated lectins and an avidin-peroxidase DAB-cobalt revealing system, with and without neuraminidase pre-treatment. High mannose, bi/tri-nonbisected and bisected complex N-glycan, N-acetyl glucosaminyl, galactosyl and sialyl residues were found to be expressed by drusen, while treatment with neuraminidase exposed subterminal N-acetyl galactosamine and galactosyl residues. Similar binding patterns were found in the various pathological groups studied. As there was no significant difference in the lectin-binding pattern in drusen in different pathologies, a common pathogenesis or at least a final common pathway for the elaboration of carbohydrate components of drusen is suggested.

Evaluation of receptor binding specificity of Escherichia coli K88 (F4) fimbrial adhesin variants using porcine serum transferrin and glycosphingolipids as model receptors

Diarrheal disease caused by enterotoxigenic Escherichia coli expressing the K88 (F4) fimbrial adhesin (K88 ETEC) is a significant source of mortality and morbidity among newborn and weaned piglets. K88 fimbrial adhesins are filamentous surface appendages whose lectin (carbohydrate-binding) activity allows K88 ETEC to attach to specific glycoconjugates (receptors) on porcine intestinal epithelial cells. There are three variants of K88 adhesin (K88ab, K88ac, and K88ad), which possess different, yet related, carbohydrate-binding specificities. We used porcine serum transferrin (pSTf) and purified glycosphingolipids (GSL) to begin to define the minimal recognition sequence for K88 adhesin variants. We found that K88ab adhesin binds with high affinity to pSTf (dissociation constant, 75 microM), while neither K88ac nor K88ad adhesin recognizes pSTf. Degradation of the N-glycan on pSTf by extensive metaperiodate treatment abolished its interaction with the K88ab adhesin, indicating that the K88ab adhesin binds to the single N-glycan found on pSTf. Using exoglycosidase digestion of the pSTf glycan, we demonstrated that K88ab adhesin recognizes N-acetylglucosamine (GlcNAc) residues in the core of the N-glycan on pSTf. All three K88 variants were found to bind preferentially to GSL containing a beta-linked N-acetylhexosamine (HexNAc), either GlcNAc or N-acetylgalactosamine, in the terminal position or, alternatively, in the penultimate position with galactose in the terminal position. Considering the results from pSTf and GSL binding studies together, we propose that the minimal recognition sequence for the K88 adhesin variants contains a beta-linked HexNAc. In addition, the presence of a terminal galactose beta-linked to this HexNAc residue enhances K88 adhesin binding.

Mycobacterium leprae binds to a 25-kDa phosphorylated glycoprotein of human peripheral nerve

Mycobacterium leprae, the causative agent of leprosy, specifically invades and destroys the peripheral nerve, which results in the main clinical manifestation of the disease. Little is known about the bacteria-nerve protein interaction. We show in the present work that M leprae binds to a 25 kDa glycoprotein from human peripheral nerve. This protein is phosphorylatable and it binds to lectins which have alpha-mannose specificity. This M leprae-protein interaction could be of importance in the pathogenesis of leprosy.

Structural studies on the Escherichia coli O101 lipopolysaccharide found in association with F41 and K99 fimbriae

In this study it was shown that the O101 lipopolysaccharide isolated from Escherichia coli B41 did not contain an O-specific polysaccharide and that its sugar moiety is probably restricted to the core oligosaccharide. It is characterized by the presence of galactose, glucose, N-acetylglucosamine, heptose and 3-deoxy-D-manno-2-octulosonic acid and the fatty acid composition is typical of an Enterobacteriaceae lipopolysaccharide. Methylation analysis indicated terminal non-reducing galactose and glucose and also 1,2-linked glucose which is a substitution pattern typical of an E. coli lipopolysaccharide core oligosaccharide. The obtained structural information is sufficient to explain the previously observed interactions between the O101 lipopolysaccharide and the K99 lectin.

Transferrin associated with the porcine intestinal mucosa is a receptor specific for K88ab fimbriae of Escherichia coli

Putative receptors of Escherichia coli K88 fimbriae are either tightly membrane bound or an integral part of membranes. Thus, proteins associated with piglet small intestinal mucosae were solubilized by a detergent (deoxycholate). A 74-kDa glycoprotein (GP74) purified from enterocyte and brush border membrane preparations was specifically detected in vitro by K88ab fimbriae. GP74 was recognized only in the mucosae of phenotypically adhesive animals. Metaperiodate treatment abolished the recognition, indicating that K88ab fimbriae-GP74 binding required the carbohydrate moiety. This glycoprotein belongs to the transferrin family and differed from the serum transferrin of the same adhesive-phenotype piglets. Unlike intestinal transferrin, serum transferrin was recognized independently of the adhesion phenotype. The glycan moieties of intestinal and serum transferrins differed in their molar compositions. Transferrin GP74 contained one monosialylated and monofucosylated glycan chain of the N-acetyllactosamine type. Intestinal holotransferrin exhibited pI values of 5.2, 5.3, 5.5, and 5.6, whereas serum holotransferrin pI values ranged between 5.4 and 6.2. Since mucosal transferrin was found intimately entrapped on membranes, we hypothesize that a K88ab fimbriae-transferrin-cell transferrin receptor complex might allow the bacteria to adhere to specific sites of the mucosa.