Identification of blood group A/A-Leb/y and B/B-Leb/y active glycotopes co-expressed on the O-glycans isolated from two distinct human ovarian cyst fluids

Prevalence of high affinity naturally occurring IgG2 antibodies against human chorionic gonadotropin and its subunits in patients with ovarian cyst

Naturally occurring antibodies to tumour antigens are gaining interest as clinically important cancer biomarkers for early diagnosis, prognosis and for the development of anti-cancer therapeutics. The glycoprotein αβ heterodimer hormone human chorionic gonadotropin (hCG) and its β subunit (hCGβ) are produced by various cancers, and their increased serum levels correlate with poor prognosis. We have previously reported that patients with benign ovarian cysts, but not the malignant tumours, were characterized by augmented serum levels of naturally-occurring IgG antibodies to hCG and hCGβ. Here we further characterise these antibodies in patients with ovarian cysts. IgG and IgM antibody binding to whole hCG, hCGβ, hCGα, hCGβ C-terminal peptide (hCGβCTP), and the hCGβ core fragment (hCGβCF) were measured in the sera from 36 patients with ovarian cysts and 12 healthy non-pregnant women using a standard ELISA. IgG subclass usage and affinity was also determined together with cross-binding to whole hCG and its subunits of four selected commercial monoclonal antibodies generated against ovarian cyst mucins. Our results showed that 91.7% of the sera tested contained elevated IgG, but not IgM antibodies to one or several antigens, with an overwhelming prevalence of high affinity IgG2 indicating their binding to carbohydrate epitopes and possibly ovarian cyst mucins. Anti-mucin commercial antibody ab212418 (Abcam) produced against Gal1-3GalNAc, exhibited strong cross-binding to hCGαβ, hCGβ, hCGα and hCGβCTP. The protective anti-cancer potential of these antibodies will be further investigated and could lead to the development of novel treatment strategies for ovarian cancer.

Loci and motifs of the GalNAcα1 → 3/O related glycotopes in the mammalian glycoconjugates and their lectin recognition roles

Galα1 → and GalNAcα1 → are the two essential key sugars in human blood group AB active glycotopes, in which GalNAcα1 → related sequences are located at both sides of the nonreducing and the reducing ends of human blood group A active O-glycans. It is also found at the nonreducing ends of GlcNAc N-glycans and glycosphingolipid(GSL) of human blood group A active glycotopes (A_h) and Forssman antigen (F_p). When monosaccharides and their α, β anomers are involved in basic units to express the complex size of the combining sites of the GalNAcα1 → specific lectins, they can be divided into a cavity site to accommodate the GalNAcα → key sugar and a subsite with a wide and broad range of recognition area to adopt the rest part of sugar sequences or glycotopes. The function of the subsite is assumed to act as an enhancement factor to increase its affinity power. The following three points are the theme of this mini review: (1) the loci and distribution of the GalNAcα1 → related glycotopes in mammalian glycoconjugates are illustrated and their chemical structures are advanced by the expression of the disaccharide units and code system; (2) the sizes and motifs of GalNAcα1 → specific lectin-glycan interactions are given and (3) the role of the polyvalent blood group A_h and B_h glycotopes as blood group AB antigens are proposed. These three highlights should provide an essential background required for the advances in this field.

Glycan structures and their recognition roles in the human blood group ABH/Ii, Lea, b, x, y and Sialyl Lea,x active cyst glycoproteins

Human ovarian cyst glycoproteins (HOC, cyst gps) isolated from pseudomucinous type of human ovarian cyst fluids is one of the richest and pioneer sources for studying biosynthesis, structures and functional roles of blood group ABH, Le^a,b,x,y, sLe^a and sLe^x active glycoproteins. After 70⁺ years of exploration, four top highlights are shared. (i) an updated concept of glycotopes and their internal structures in cyst gps was composited; (ii) the unknown codes of new genes in secreted cyst gps were unlocked as Le^x and Le^y; (iii) recognition profiles of cyst glycans and a sialic acid-rich (18%) glycan with lectins and antibodies were shown. (iv) Co-expression of Blood Group A/ A-Le^b/y and B/B-Le^b/y active Glycotopes in the same glycan chains were isolated and illustrated. These are the most advanced achievements since 1980.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: an update for 2009-2010

This review is the sixth update of the original article published in 1999 on the application of MALDI mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2010. General aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, arrays and fragmentation are covered in the first part of the review and applications to various structural typed constitutes the remainder. The main groups of compound that are discussed in this section are oligo and polysaccharides, glycoproteins, glycolipids, glycosides and biopharmaceuticals. Many of these applications are presented in tabular form. Also discussed are medical and industrial applications of the technique, studies of enzyme reactions and applications to chemical synthesis.

Increasing the depth of mass spectrometry-based glycomic coverage by additional dimensions of sulfoglycomics and target analysis of permethylated glycans

Hog or porcine gastric mucin resembles the human source in carrying not only blood group antigens but also the rather rare α4-GlcNAc-capped terminal epitope functionally implicated in protection against Helicobacter pylori infection. Being more readily available and reasonably well characterized, it serves as a good reagent for immunobiological studies, as well as a standard for analytical methodology developments. Current approaches in mass spectrometry (MS)-based glycomic mapping remain vastly inadequate in revealing the full complexity of glycosylation, particularly for cases such as the extremely heterogeneous O-glycosylation of mucosal mucins that can be further sulfated. We demonstrate here a novel concerted workflow that extends the conventional matrix-assisted laser desorption/ionization–mass spectrometry (MALDI-MS) mapping of permethylated glycans in positive ion mode to include a further step of sulfoglycomic analysis in negative ion mode. This was facilitated by introducing a mixed-mode solid-phase extraction step, which allows direct cleanup and simultaneous fractionation of the permethylated glycans into separate non-sulfated and sulfated pools in one single step. By distinct MALDI-MS/MS fragmentation patterns, all previously known structural features of porcine gastric mucin including the terminal epitopes and location of sulfates could be readily defined. We additionally showed that both arms of the core 2 structures could be extended via 6-O-sulfated GlcNAc to yield a series of disulfated O-glycans not previously reported, thus expanding its current glycomic coverage. However, a targeted LC-MSn analysis was required and best suited to dig even deeper into validating the occurrence of very minor structural isomers carrying the Lewis Y epitope implicated by positive antibody binding.

Advances in proximal fluid proteomics for disease biomarker discovery

Although serum/plasma has been the preferred source for identification of disease biomarkers, these efforts have been met with little success, in large part due the relatively small number of highly abundant proteins that render the reliable detection of low abundant disease-related proteins challenging due to the expansive dynamic range of concentration of proteins in this sample. Proximal fluid, the fluid derived from the extracellular milieu of tissues, contains a large repertoire of shed and secreted proteins that are likely to be present at higher concentrations relative to plasma/serum. It is hypothesized that many, if not all, proximal fluid proteins exchange with peripheral circulation, which has provided significant motivation for utilizing proximal fluids as a primary sample source for protein biomarker discovery. The present review highlights recent advances in proximal fluid proteomics, including the various protocols utilized to harvest proximal fluids along with detailing the results from mass spectrometry- and antibody-based analyses.

Mass spectrometric identification of aberrantly glycosylated human apolipoprotein C-III peptides in urine from Schistosoma mansoni-infected individuals

Schistosomiasis is a parasitic infection caused by Schistosoma flatworms, prime examples of multicellular parasites that live in the mammalian host for many years. Glycoconjugates derived from the parasite have been shown to play an important role in many aspects of schistosomiasis, and some of them are present in the circulation of the host. The aim of this study was to identify novel glycoconjugates related to schistosomiasis in urine of Schistosoma mansoni-infected individuals using a combination of glycopeptide separation techniques and in-depth mass spectrometric analysis. Surprisingly, we characterized a heterogeneous population of novel aberrantly O-glycosylated peptides derived from the C terminus of human apolipoprotein C-III (apoC-III) in urine of S. mansoni-infected individuals that were not detected in urine of non-infected controls. The glycan composition of these glycopeptides is completely different from what has been described previously for apoC-III. Most importantly, they lack sialylation and display a high degree of fucosylation. This study exemplifies the potential of mass spectrometry for the identification and characterization of O-glycopeptides without prior knowledge of either the glycan or the peptide sequence. Furthermore, our results indicate for the first time that as a result of S. mansoni infection the glycosylation of a host protein is altered.