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Figure 1.
Figure 1. Structural similarity of SEK and other group V
bacterial superantigens. (a) Structure of SEK in the unbound
state. The α3-β8 loop is in orange and the residues
responsible for Zn^2+ coordination and MHC class II binding are
in cyan. (b) Structural comparison of the α3-β8 loop domains
of SEK, SEI and SpeI. Superposition of the main chains of the
α3-β8 loops (left-hand panel). Molecular details of side-chain
positions in the α3-β8 loops (right-hand panels). SEK, SEI and
SpeI are in magenta, green and blue, respectively. The residues
in SEK that interact with TCR, His142 and Tyr158, as well as
corresponding residues in SEI and SpeI are encircled. (c)
Structural comparison of the MHC binding site of SEI and the
putative MHC binding sites of SEK and SpeI. Superposition of SEK
and SpeI with SEI from the SEI-MHC class II crystal structure
(left-hand panel).^21 Close-up view of the Zn^2+ coordination
between SEI residues His169, His207 and Asp209 and the MHC β
subunit residue His81 (middle panel). Close-up views of the
putative SAG-MHC interface formed by the superposed SEK and SpeI
structures (right-hand panels). The MHC α subunit is in yellow,
the MHC β subunit is in red, the zinc ion is in gray, and the
SAG colors are as in (b).
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