Abstract
Histidine (His) residues represent versatile motifs for designing protein-protein interactions because the protonation state of the imidazole group of His is the only moiety in protein to be significantly pH dependent under physiological conditions. Here we show that, by the designed His motifs nearby the C4 axes, ferritin nanocages arrange in crystals with a simple cubic stacking pattern. The X-ray crystal structures obtained at pH 4.0, 7.0, and 9.0 in conjunction with thermostability analyses reveal the strength of the π–π interactions between two adjacent protein nanocages can be fine-tuned by pH. By using the crystal structural information as a guide, we constructed 3D protein frameworks in solution by a combination of the relatively weak His–His interaction and Ni2+-participated metal coordination with Glu residues from two adjacent protein nanocages. These findings open up a new way of organizing protein building blocks into 3D protein crystalline frameworks.
Highlights
Histidine (His) residues represent versatile motifs for designing protein-protein interactions because the protonation state of the imidazole group of His is the only moiety in protein to be significantly pH dependent under physiological conditions
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 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 interaction and metal coordination of Ni2+ with glutamic acid are responsible for the formation 3D protein arrays. g Close-up views of Ni2+ induced metal coordination and His-His interaction in f
We wondered whether high-ordered nanocage arrays would be created through π–π interactions after a certain amino acid residue located on the protein exterior surface nearby the C4 rotation axes was replaced with His residue
Summary
Histidine (His) residues represent versatile motifs for designing protein-protein interactions because the protonation state of the imidazole group of His is the only moiety in protein to be significantly pH dependent under physiological conditions. By using the crystal structural information as a guide, we constructed 3D protein frameworks in solution by a combination of the relatively weak His–His interaction and Ni2+-participated metal coordination with Glu residues from two adjacent protein nanocages These findings open up a new way of organizing protein building blocks into 3D protein crystalline frameworks. We believe that highly ordered protein self-assemblies could be constructed by a combination of the aromatic interactions from His residues and protein symmetry By single His mutation on ferritin outer surface close to its C4 symmetry axes as shown, we implemented the His–His interactions within two neighboring protein molecules could be fine-tuned by pH in crystals (Fig. 1b). 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
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