Molecular and immunological characterisation of a polymorphic cytosolic fatty acid binding protein from the human blood fluke of humans, Schistosoma japonicum.

Most organisms obtain their fatty acids through their diet or by de novo synthesis, but human blood flukes belonging to the genus Schistosoma lack the oxygen-dependent pathways required for the synthesis of sterols and fatty acids so they are entirely dependent on their hosts for these and other complex lipids. Fatty acid binding proteins (FABPs) of the FABP/P2/CRABP/CRBP family of beta-barrel cytosolic lipid binding proteins (cLBP) appear to be particularly important to schistosomes in the uptake, transport and compartmentalisation of host-derived fatty acids and may provide important targets for immuno- and chemotherapy. Here we describe the isolation of a set of cDNAs prepared from the Asiatic schistosome, Schistosoma japonicum, which encode two groups of cLBPs based on sequence homology and unique cDNA restriction sites. Representative clones from the two groups, one encoding a complete Sj-FABP (F10), and the other encoding a deletion mutant (F25) were characterised at the nucleic acid level by Southern and Northern hybridisation analysis, and at the protein level by immunoblotting. The presence and size of introns in the genes encoding F10 and F25 were determined and, because of the interest in the Schistosoma mansoni FABP homologue (Sm14) as a putative vaccine candidate, the immunogenicity and protective efficacy of the two proteins were also evaluated. A particularly interesting finding was the degree of Sj-FABP amino acid sequence polymorphism found to occur within the S. japonicum worm population, which appears to be greater than that described from cLBPs from vertebrates or, indeed, any other group of organisms investigated to date.