Fig. 1: Proposed model of His-induced 3D protein crystals and 3D solid arrays in solution by combining His-His interactions and metal coordination.
a Close-up view from three C4 rotation axes of ferritin which are perpendicular to each other. Single His mutation of each ferritin subunit on the protein outer surface nearby the C4 rotation axes were highlighted in red. b Crystal diagram of ferritin induced by His–His interactions along the C4 rotation axes. c Solid 3D assemblies produced by a combination of His-His interactions and metal coordination. d Crystal structure illustration of four pairs of His–His interactions (colored magenta) between two adjacent ferritin molecules. e The action mode of His–His interactions can be adjusted by pH. f Crystal structure revealed that both His-His (colored magenta) interaction and metal coordination of Ni2+ (colored yellow) with glutamic acid (colored cyan) are responsible for the formation 3D protein arrays. g Close-up views of Ni2+ induced metal coordination and His-His interaction in f.
