The tegument surface membranes of the human blood parasite Schistosoma mansoni: A proteomic analysis after differential extraction

Abstract

The blood fluke Schistosoma mansoni can live for years in the hepatic portal system of its human host and so must possess very effective mechanisms of immune evasion. The key to understanding how these operate lies in defining the molecular organisation of the exposed parasite surface. The adult worm is covered by a syncytial tegument, bounded externally by a plasma membrane and overlain by a laminate secretion, the membranocalyx. In order to determine the protein composition of this surface, the membranes were detached using a freeze/thaw technique and enriched by sucrose density gradient centrifugation. The resulting preparation was sequentially extracted with three reagents of increasing solubilising power. The extracts were separated by 2-DE and their protein constituents were identified by MS/MS, yielding predominantly cytosolic, cytoskeletal and membrane-associated proteins, respectively. After extraction, the final pellet containing membrane-spanning proteins was processed by liquid chromatographic techniques before MS. Transporters for sugars, amino acids, ions and other solutes were found together with membrane enzymes and proteins concerned with membrane structure. The proteins identified were categorised by their function and putative location on the basis of their homology with annotated proteins in other organisms.

Patterns of gene expression in schistosomes: localization by whole mountin situhybridization

“…At the worm surface, the syncytial tegument is connected by cytoplasmic processes to underlying cell bodies which contain the nucleus and molecular machinery necessary for protein synthesis and export. Although Sm29 has no homology to molecules outside of the genus Schistosoma, we can infer that the product is tegument specific, which is an added bonus for our independent proteomic analyses of tegument membrane composition (Braschi et al 2005. Together, these observations imply a role for Sm29 at the tegument surface, possibly in immune evasion.…”

Schistosomes—proteomics studies for potential novel vaccines and drug targets

“…In fact, several proteomics studies have used EST assemblies, or gene prediction data based on the genome, for peptide searches [29][30][31][32] or have used full-length clones of schistosome genes that resulted from further transcriptome sequencing [33]. Using these resources, several strategies have been employed to search for potential novel vaccines and drug targets, as we will describe in detail in the next sections and is summarized in Table 1.…”

Design and testing of PCR primers for the construction of scFv libraries representing the immunoglobulin repertoire of rats

“…First, the targets are only one of probably hundreds of different antigens that are immunogenic during schistosome infection. Secondly, they derive from proteins that are not particularly abundant in the parasites based on proteomic surveys (van Balkom et al, 2005;Braschi et al, 2006). Thirdly, the epitopes derive from a relatively small extracellular loop domain (~10kD) contained within these apical membrane proteins, which are often more difficult than cytosolic or secreted proteins to study as antigens.…”

“…Two schistosome tetraspanin proteins, Sm23 and SmTsp2, were selected to validate the utility of the rat scFv library. These proteins were chosen because they are known to be immunogenic in schistosome infected animals (Wright et al, 1990;Tran et al, 2006) and because they are among the very few integral membrane antigens shown to be present within the host-interactive worm surface tegumental membrane (Braschi et al, 2006;Tran et al, 2006) . Four weeks after S. mansoni infection, rats have a moderate titer of serum antibodies against both Sm23 and SmTsp2 ( Fig.…”