Figure 1.

Cartoon representation of monomeric WT CIB2 in its Ca²⁺-bound form. The homology model is based on the X-RAY structure of Ca²⁺-bound CIB1 (see section Materials and Methods). The N-terminal region is colored gray, while the C-terminal region (helix 10) is colored yellow. EF1, EF2, EF3, and EF4 are colored green, blue, orange, and magenta, respectively. Asn 121 and Glu 64, found to be involved in an allosteric connection, are represented by sticks, as well as Arg 33, electrostatically interacting with Glu 64. The sequence alignment of CIB2 with CIB1, CIB3, and CIB4 is also shown, restricted to the metal-coordinating EF-hands, namely EF3 and EF4. Amino acids contributing to the coordination of Ca²⁺ according to the canonical pentagonal bipyramid geometry are marked by their respective position and labeled in the zoomed-in protein cartoon on the right.