Fig 1.

Summary of genetic modifications. (A) Positions of amino acid additions and substitutions (boxed residues) in recombinant A. actinomycetemcomitans CdtA-His₆, CdtB-His₆, and CdtC-His₆. The locations of the histidine and tetracysteine tags and active site in CdtB are underlined. The spacer sequence to improve Lumio green labeling is in italics. Predicted NLSs (25, 30) are in labeled boxes. The location where the wild-type amino acid sequence begins is marked with an arrow. (B) Ribbon backbone structure of the A. actinomycetemcomitans Cdt showing the locations of the mutated sites designated in panel A and in Table 1. The structure was modeled in Chimera 1.6 using Protein Data Bank file accession number 2F2F (37). Side chains are shown only for the amino acids targeted for mutation in sites AD1 in CdtA and AT, R1, and R2 in CdtC. Amino acids designated for mutation in sites A9, A10, and CH-1 in CdtB cluster around a catalytic center marked by a thin orange polygon. Amino acids targeted for mutation in the two NLS sites align along the back side of the structure as designated by the thin green line. (C) The same structure as shown in panel B except that CdtA and CdtC are depicted as a surface model and the heterotrimer is rotated approximately 90° vertically. Only the surface-exposed sites AD1, R1, and R2 are labeled.