Ferritins of Schistosoma mansoni: sequence comparison and expression in female and male worms.

Recombinant clones of Schistosoma mansoni cDNA libraries containing the complete coding regions of 2 different ferritin subunits have been isolated and sequenced. This allows for the first time a comparison of ferritin sequences from an invertebrate with those of vertebrates. The deduced amino acid sequences of both Schistosoma ferritin subunit clones show significant homology to vertebrate ferritin H chains. Similarity exceeds 50% identity and includes the recently identified ferroxidase center which is present only in H chains. However, non-conservative substitutions of amino acid residues lining the 3-fold symmetry channel were found, and a gap of 3 successive amino acids unique to the 2 Schistosoma ferritin sequences was identified. Remarkably, for each of the 2 genes, we found a conspicuous difference in the amount of ferritin transcripts between females and males: one of the genes is preferentially expressed in females, the other in males.