Figure 1.

The crystal structure of HC1. A, orthogonal views of the structure of rHC1, colored from the N terminus (blue) to C terminus (red), where domains and the bound Mg²⁺ ion are labeled; the dotted orange line denotes residues 631–638, which are not visible in the crystal structure. B, close-up of the MIDAS site, showing metal coordination (black) and an important hydrogen bond (gray). The WT structure is shown in green, and the D298A structure (which lacks the Mg²⁺ ion) is in pink. C, raw SAXS data (orange with black error bars) of a rHC1 monomer (D298A) and back-calculated scattering curves based on the crystal structure of rHC1 alone or the crystal structure with the unstructured/flexible regions modeled in using AllosMod. D, AllosMod model of rHC1 with the N-terminal histidine tag (blue) and residues 35–44, 631–636, and 653–672 (pink) modeled based on SAXS restraints.