Biomineralization of a Cadmium Chloride Nanocrystal by a Designed Symmetrical Protein

Abstract

We have engineered am etal-binding site into the novel artificial b-propeller protein Pizza. This new Pizza variant carries two nearly identical domains per polypeptide chain, and forms at rimer with three-fold symmetry.T he designed single metal ion binding site lies on the symmetry axis, bonding the trimer together.T wo copies of the trimer associate in the presence of cadmium chloride in solution, and very highresolution X-raycrystallographic analysis reveals ananocrystal of cadmium chloride,s andwiched between two trimers of the protein. This nanocrystal, containing seven cadmium ions lying in ap lane and twelve interspersed chloride ions,i st he smallest reported to date.Our results indicate the feasibility of using rationally designed symmetrical proteins to biomineralizen anocrystals with useful properties.

Observation of gold sub-nanocluster nucleation within a crystalline protein cage

“…Several organic ligands have been developed to stabilize small nanoclusters and crystal structures have been obtained, but the formation mechanism remains unknown464950. Similarly, protein scaffolds are also used for preparing small nanoclusters, but their exact positions, structures and formation mechanisms remain unclear10111213. In this regard, the present work provides a detailed map for studying the mechanism of formation of inorganic materials in the confined protein environment.…”

“…For example, cobalt oxide nanoparticles are fabricated in the ferritin cage and an Fe 3 O 4 nanocluster is formed in Dps-like ferritin1018. The metal oxide/chloride cluster in the symmetric protein scaffold does not grow to generate a larger mineral and thus it can serve as an electron transfer centre1213. Several organic ligands have been developed to stabilize small nanoclusters and crystal structures have been obtained, but the formation mechanism remains unknown464950.…”

“…Thus, it is essential to investigate the formation of sub-nanoclusters in protein scaffolds to gain an understanding of the molecular mechanisms of biomineralization and protein-nanoparticle recognition89. There are only a few reports of X-ray crystal structures of metal oxide/chloride nanostructures such as Fe x O y , W/MoO x and Cd 7 Cl 12 , which are formed within the symmetric cavities of protein scaffolds1011121314. These reports show that the symmetrical environments of protein scaffolds can be used for nanocluster formation.…”

Hierarchical design of artificial proteins and complexes toward synthetic structural biology

“…1l) (Brunette et al 2015;Doyle et al 2015;Park et al 2015;Parmeggiani and Huang 2017). Mou et al also reported a computationally designed symmetric protein homodimer (Mou et al 2015a), and Voet et al reported computationally designed symmetrical β-propeller proteins (Voet et al 2014) and biomineralization of a cadmium chloride nanocrystal using a designed symmetrical protein (Voet et al 2015). Furthermore, Woolfson and colleagues described computational design of water-soluble α-helical barrels (Thomson et al 2014) and recently installed hydrolytic activity into a de novo α-helical barrel comprising seven helices with cysteine-histidine-glutamate catalytic triads (Burton et al 2016).…”

A protein sequence fitness function for identifying natural and nonnatural proteins

“…Creating a protein to perform a predefined or novel biological function(s) is often considered as protein design. In general, protein design is formulated as composing an amino acid sequence which should ideally fold into a stable structure, meant to perform some biological function(s) 9‐13 . The goals of protein design include either desired optimization of certain characteristics such as stability, solubility, and binding affinity or designing entirely novel sequences resulting into novel structures or attaining remedial or industrial utilities 14‐17 .…”