FIGURE 1.

IgG1 antibody hinge region structure analysis. a, a close-up view of the hinge region of IgG1b12 (Protein Data Bank code 1HZH). Thr²²⁸-His-Thr in the K chain was modeled into the structure, and the imidazole ring in the K-HC was only shown in a position close to the H-HC. An opposite position is possible but is not shown here. b, the local structure of each upper hinge including Cys²³¹, only Cys (in yellow) and His are labeled. c, structural environments of the imidazole ring. The residues within a distance of 5 Å from the ring are shown here for the H chain and the K chain. The atoms in shadow are those exposed to the solvent.