Alignment of TrpEb_1 from S. typhimurium (Sty) and of TrpEb_2 from P. furiosus (Pfu-2). The sequences are shown as they appear in a comprehensive alignment, including gaps. Invariant residues in each subfamily are highlighted and near-invariant residues (delineated in Table 2) are shaded. Invariant or near-invariant residues common to both subfamilies are boxed. Residues shown in Sty to be relevant to metal coordination or to the binding of indole, serine or PLP are color-coded as indicated at the bottom.