FIGURE 1.

Phylogenetic relationships and structural conservation of the streptococcal superantigens. (A) Unrooted neighbor-joining tree showing phylogenetic relationships of known streptococcal superantigens. The unrooted tree was based on the alignment of amino acid sequences using CLUSTAL W (166) and constructed using MEGA7 (167). The groups indicate a prior classification scheme for the superantigen family (32). (B) Amino acid alignment of five representative streptococcal superantigens. The colors designate distinct domains in the superantigen structure, including the N-terminal α-helix (green), the central α-helix (red), the α3-β8 loop that is unique to the group V superantigens (168), and a C-terminal α-helix that is lacking in a subgroup of group IV. Residues involved in the coordination of a zinc atom important for binding to the MHC class II β-chain are colored magenta. (C) Crystal structures of representative streptococcal superantigens are colored as in panel B.