Fig. 1. Sxph structure.

(A) R. catesbeiana Sxph:STX: complex ribbon diagram. Domains are indicated and are colored as follows: N1 (smudge), N2 (limon), thyroglobulin (Thy; bright orange), C1 (marine), and C2 (cyan). STX (red) is shown as space filling. (B) Superposition of Sxph and rabbit transferrin [Protein Data Bank (PDB): 1JNF] (32). Transferrin N-lobe and C-lobe are colored purple and pink, respectively. Sxph Thy1 repeats are not shown. Insets show transferrin Fe³⁺ ligands and Sxph equivalents as sticks. N domain: transferrin (purple) and Sxph (green); C domain: transferrin (pink) and Sxph (blue). STX (red) is shown as space filling. Right hand inset shows distance between the STX center and transferrin Fe³⁺. (C) Cartoon diagram showing unique Sxph disulfide bonds in space filling representation: SS3 (Cys²⁷ to Cys⁴¹⁷) SS4 (Cys⁹¹ to Cys¹¹¹), SS5 (Cys¹²² to Cys¹²⁹), SS6 (Cys¹³¹ to Cys¹⁵³), SS7 (Cys¹⁶¹ to Cys¹⁸³), SS8 (Cys²⁰³ to Cys²²⁵), and SS9 (Cys²³⁴ to Cys⁸²⁵). Colors and labels are the same as in (A).