Abstract
Cage-shaped protein (CSP) complexes are frequently used in bionanotechnology, and they have a variety of different architectures and sizes. The smallest cage-shaped protein, Dps (DNA binding protein from starved cells), can naturally form iron oxide biominerals in a multistep process of ion attraction, translocation, oxidation, and nucleation. The structural basis of this biomineralization mechanism is still unclear. The aim of this paper is to further develop understanding of this topic. Time-resolved metal translocation of Yb3+ ions has been investigated on Dps surfaces using X-ray crystallography. The results reveal that the soak time of protein crystals with Yb3+ ions strongly affects metal positions during metal translocation, in particular, around and inside the ion translocation pore. We have trapped a dynamic state with ongoing translocation events and compared this to a static state, which is reached when the cavity of Dps is entirely filled by metal ions and translocation is therefore blocked. By comparison with La3+ and Co2+ datasets, the time-dependence together with the coordination sphere chemistry primarily determine metal−protein interactions. Our data can allow structure-based protein engineering to generate CSPs for the production of tailored nanoparticles.
Highlights
The results reveal that the soak time of protein crystals with Yb3+ ions strongly affects metal positions during metal translocation, in particular, around and inside the ion translocation pore
We have trapped a dynamic state with ongoing translocation events and compared this to a static state, which is reached when the cavity of Dps is entirely filled by metal ions and translocation is blocked
Biomineralization in Dps proteins is time dependent and a multistep process starting with ion attraction, by negatively charged residues, toward the surface of the protein
Summary
Cage-shaped proteins (CSPs) of various sizes are used as molecular carriers for organic molecules in, e.g., anti-cancer therapy and imaging [1,2]. The formation of defined metal nanoparticles for nanobiotechnology applications used in memory storage and hydrothermal processes are other important fields for CSP applications [3]. Two independent surface areas in CSPs may be modified to achieve new functionalities: the outer surface in order to make CSPs target specific, and the inner surface to alter, e.g., mineralization kinetics and nucleation. The outer surface of CSPs can be functionalized, e.g., with antibodies, peptides, or organic molecules to generate cages targeting receptors [4,5]. Many CSPs are known to be involved in iron-oxide assembly in cells and can be broadly used for the formation of metal-oxide/sulfide nanoparticles in the range of 5 to 50 nm
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