Figure 2.

Crystal structure of the Antarctic AKNc. (a) Overall structure of AKNc. The CORE (residues 1–38, 69–136, and 143–193), AMP_bind (residues 39–68) and LID (residues 137–142) domains are shown in yellow, blue, and red, respectively. The co-crystallized Ap₅A molecule bound to the active site is shown in black (left), but not in the 120°-rotated model (right), to reveal the AK structure more clearly. The three Val residues for which hydrophobic contacts are suboptimal are highlighted in cyan in stick representations (right). (b,c) Close-up views of the hydrophobic environment around Val28 (b) and Val118/Val173 (c). The Val residues interact hydrophobically with other residues in the CORE domain, but there is room for improvement in hydrophobic packing. The 2mF_obs − DF_calc map is contoured at 1.0 σ.