Fig. 2.

Structure of SadAK3. (A) The whole crystal structure of SadAK3, including the GCN4-adaptors in gray and the 2 chloride and 2 nitrate anions trapped in the N@d layers. (B) Close-up of the SadA insert. Residues in positions a and d of the N@d layers and the single T@d are shown as sticks. (C–E) Binding details in stereoview upstream the helical bundle, showing I478, T481, N482, and K484 of the single T@d layer (C), I492, N495@d, T496, S498, and a bridging water coordinating nitrate (D) and I506, N509@d, T510, N512, and a bridging water coordinating chloride (E). (F) Sequences of the constructs SadAK3 and SadAK3b. In SadAK3 and SadAK3b residues 479–519 and 483–523 of SadA were fused as an insert between the N- and C-terminal GCN4-pII adaptors. For SadAK3, the fusion was done in register. Relative to SadAK3, the insert of SadAK3b has the first 4 residues deleted and 4 residues added to its end (green boxes). The resulting shift in the sequence is highlighted in gray. For SadAK3 the observed and for SadAK3b the expected core positions (a and d) are highlighted in red. The C-terminal His-tag of SadAK3b (KLHHHHHH) is omitted.