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Figure 1
Comparison of the structures of RiVax, ricin holotoxin and the RTA 1–33/44–198 R48C/T77C immunogen. (a) Stereoview of the RiVax structure showing the two B-cell epitopes at Asn97–Phe108 and Leu161–Ile175 and the T-­cell epitope at Ile175–Glu185. The Asn97–Phe108 epitope bound by the UNIVAX 70/138 antibody is shown in magenta. The Leu161–Ile175 epitope bound by human neutralizing antibodies characterized by Castelletti et al. (2004BB4) is shown in green. The Ile175–Glu185 T-cell epitope is shown in blue. The active-site residues within this epitope, Glu177 and Arg180, are shown as sticks; Tyr123, another active-site residue, is shown as dark gray sticks. The active-site mutation, Y80A, is shown in cyan. The mutation to the VLS site, V76M, is shown in orange. (b) Structure of the ricin AB toxin determined by Rutenber et al. (1991BB31) (PDB entry 2aai ). The A-chain is depicted by ribbons and the B-chain by tubes. Lactose (colored red) is reversibly bound to the carbohydrate-binding site. The N-linked sugars resolved at the glycosylation sites Asn95 and Asn135 are shown as yellow sticks. The putative immunological epitopes are colored as in (a). (c) Structure of the RTA 1–33/44–198 R48C/T77C disulfide-bonded variant based upon PDB entry 3lc9 (Compton et al., 2011BB7). The epitopes and VLS site are colored as in (a). The helix–turn–helix motif between residues Ile175 and Glu185 (blue) is found to be fully helical in the 1–33/44–198 R48C/T77C variant. (d) Mapping of residues which are believed to be important in T-­cell activation (Castelletti & Colombatti, 2005BB3; shown in cyan) onto the helical segment between Ile175 and Glu185. Residues which do not affect T-cell activation when mutated to alanine are shown in blue. One residue, Arg180, had an intermediate affect on T-cell activation (purple). The figures were produced using PyMOL (DeLano, 2002BB40).

Journal logoBIOLOGICAL
ISSN: 1399-0047
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