FIGURE 5.

Structural model supports the possibility of alternative intersubunit zinc coordination in TbADAT2/3. Using the ADATa (TadA) homodimer (co-crystallized with tRNA anticodon loop) from S. aureus (Protein Data Bank code 2B3J) as a modeling template, two ADAT2/3 heterodimer models were built using the FRankenstein's monster method (22). A, this model represents the heterodimer most like the ADATa homodimer in that each subunit individually coordinates Zn²⁺ (intrasubunit coordination). B, this model represents an alternative “swapped” model, which was built by exchanging parts of ADAT2 and ADAT3 containing the HXE and CXXC motifs; this model supports the possibility of intersubunit zinc coordination. The models are colored by subunits: ADAT2 in dark blue and ADAT3 in dark pink. Active site residues (His, Cys, and Cys) of ADAT2 and ADAT3 are red and green, respectively. In both models, the C-terminal ends are as labeled, and the magenta spheres represent zinc ions.