Conserved proteins as immunogens: glutathione S-transferase of Schistosoma

Although some immunogenic proteins of parasites evolve rapidly and seem to have no function other than the eliciting o f an immune response, others are proteins that are ordinarily conserved because of functional constraints. The 26 kDa and 28 kDa glutathione S-transferases (GSTs) of Schistosoma would seem to fall in the latter category. However, in the generally more conserved N-terminal portion o f the molecule, the 28 kDa GSTs have evolved over twice as fast at nor-synonymous nucleotide sites as have the 26 kDa GSTs. It is possible that this accelerated rate o f evolution results from natural selection by the host immune system, as discussed here by Austin Hughes.