Aligning Sigma class GSTs of trematodes shows the extent of identity and similarity across this class of GSTs ( Figure S1 ). An amino acid sequence comparison of FhGST-S1 with other trematode GSTs places FhGST-S1 into the Sigma class of GSTs, with identities averaging approximately 45%. Comparison with the most closely matching mammalian GSTs shows sequence identities averaging only approximately 28% (Table S1 ). Despite phylogenetic neighbour-joining trees place mammalian and trematode GSTs within the same broad Sigma class ( Figure S1 ) there remains a distinct separation of the trematode and mammalian clusters.