Ultrastructure, Carbohydrate, and Amino Acid Analysis of Two Preparations of the Cercarial Glycocalyx of Schistosoma mansoni

Abstract

This study determined the amino acid and carbohydrate composition of 2 cercarial glycocalyx preparations obtained after phenol-water extraction and subsequent gel chromatography. Labeled cercariae were subjected to 85% phenol, thereby dissociating the glycocalyx into the aqueous phase, which was dialyzed and chromatographed on Sepharose CL-2B or -4B in either 4 M guanidine hydrochloride (GuHCl) or 0.1% sodium dodecyl sulfate (SDS). The label eluted primarily in the void volume and was antigenic as tested with rabbit polyclonal antibodies by immunoblotting. Approximately 6 micrograms of protein and 28 micrograms of carbohydrate were obtained from 10(5) cercariae in the antigenic void volume fraction after SDS chromatography. Threonine, serine, and glutamic acid comprised 44% of the amino acid residues of the protein. The predominant sugar was fucose. Galactosamine, glucosamine, galactose, and mannose were also detected. After GuHCl chromatography, free amino acids, predominantly glycine and serine, comprised 17% of the total protein. The carbohydrate composition was similar to that of SDS-chromatographed extracts. Phenol-water extracts eluting in the void volume of Sepharose CL-2B were compared by negative staining and scanning electron microscopy with material obtained from medium in which cercariae shed glycocalyx during transformation to schistosomula. Both the isolated material and the transformation medium contained particles 20-50 nm in diameter, with subunits of 15-20 nm. These studies show that the cercarial glycocalyx is particulate, contains mainly carbohydrate and some protein, and is solubilized by phenol-water extraction.

Changes in surface glycosylation and glycocalyx shedding in Trichobilharzia regenti (Schistosomatidae) during the transformation of cercaria to schistosomulum

“…Moreover, comparison with other schistosomes and non-schistosome trematodes had conclusively shown that extensive fucosylation of the cercarial glycocalyx is unique, and represents a general attribute of all the schistosome species studied so far [44,45,9,22]. In the cercarial glycocalyx of Schistosoma mansoni , Fuc represents more than 50% of the overall saccharide content; other saccharides include Gal/GalNAc, Glc/GlcNAc, Man and xylose [8,11,14]; sialic acid was not confirmed [9]. Moreover, a reduction and gradual disappearance of lectin-recognized Fuc epitopes, and the emergence of epitopes recognized by some Gal/GalNAc-specific lectins (e.g., PNA) was described in the schistosomula of S .…”

“…Much information about the structure of glycocalyx is available from human schistosomes, especially Schistosoma mansoni . The entire surface of the cercarial stage is covered by a 1–2 μm thick glycocalyx unusually rich in fucose residues [7,8]. Saccharide molecules represented by a heterogenous population of highly fucosylated glycans are bound to lipids and proteins on the membrane of the cercarial tegument by O-glycosidic bonds via sphingosine and serine or threonine, respectively [9–12].…”

Schistosoma mansoni host-exposed surface antigens characterized by sera and recombinant antibodies from schistosomiasis-resistant rats

“…It is clear that adult schistosomes have non-protein components exposed at the host/parasite interface (Skelly and Wilson, 2006). Cercariae are known to be coated with a glycocalyx largely composed of carbohydrate (Samuelson and Caulfield, 1985; Caulfield et al, 1987; Khoo et al, 1995) and the exposed surface of living adults is also known to contain substantial carbohydrates (Klabunde et al, 2000). A valuable feature of the schistosome surface binding scFvs is that these binding proteins are reagents that will permit the purification and characterization of these antigens that comprise the critical host/parasite interface on adult schistosomes.…”

Glycoconjugates in Host-Helminth Interactions

“…Secondly, the study of adaptive immunity to eukaryotic pathogens has traditionally focused on protein, rather than glycan antigens. A large portion of the surface-exposed and secreted antigens of helminths consists of glycoconjugates (17, 149, 150). Thus, crucial insights into immunological control of helminth infection lie at the intersection of these two fields, as we will now discuss.…”