Crystal structures of three protozoan homologs of tryptophanyl-tRNA synthetase

► Crystal structures of TrpRS homologs from C. parvum, T. brucei, and E. histolytica. ► Protozoan TrpRS homologs differ in substrate order and inferred activation mechanism. ► The E. histolytica homolog, one of three isoforms in the genome, is inactive. ► C. parvum N-terminal domain sequence is related to editing domains of AlaRS and ThrRS.