Self-Assembly of Electrostatic Cocrystals from Supercharged Fusion Peptides and Protein Cages

Abstract

Self-assembly is a convenient process to arrange complex biomolecules into large hierarchically ordered structures. Electrostatic attraction between the building blocks is a particularly interesting driving force for the assembly process, as it is easily tunable and reversible. Large biomolecules with high surface charge density, such as proteins and protein cages, are very promising building blocks due to their uniform size and shape. Assemblies of functional molecules with well-defined nanostructures have wide-ranging applications but are difficult to produce precisely by synthetic methods. Furthermore, obtaining highly ordered structures is an important prerequisite for X-ray structure analysis. Here we show how negatively charged ferritin and viral protein cages can adopt specific cocrystal structures with supercharged cationic polypeptides (SUPs, K72) and their recombinant fusions with green fluorescent protein (GFP-K72). The cage structures and recombinant proteins self-assemble in aqueous solution to large ordered structures, where the structure morphology and size are controlled by the ratio of oppositely charged building blocks and the electrolyte concentration. Both ferritin and viral cages form cocrystals with face centered cubic structure and lattice constants of 14.0 and 28.5 nm, respectively. The crystals are porous and the cationic recombinant proteins occupy the voids between the cages. Such systems resemble naturally occurring occlusion bodies and may serve as protecting agents as well as aid the structure determination of biomolecules by X-ray scattering.

From stars to stripes: RNA‐directed shaping of plant viral protein templates—structural synthetic virology for smart biohybrid nanostructures

“…The resulting planar and 3D disk arrays may be developed into versatile lattices and crystals for ordering, storing and converting suitable molecules. If co‐crystallization with catalytically active nanoparticles or enzymes was possible in analogy to assemblies with spherical viruses or ferritin (Chakraborti et al, ; Korpi et al, ; Mikkilä et al, ), active materials might be generated that profit from high definition due to a long‐range order of their constituents.…”

“…A controlled supracolloidal assembly of regular composites with proteins as major shape‐directing agents demands for an exceptionally careful adjustment of many parameters. Therefore, highly ordered structures have so far been achieved for a few systems only, which include plant virus capsids with or without nucleic acid content (Korpi et al, ; Kostiainen et al, ; Liljeström et al, ; Mikkilä et al, ). To stay with examples based on TMV, the products resulting from co‐assembly of positively charged AuNPs and complete virions are shown in Figure : twisted superlattice wires (Liljeström et al, ).…”

Highly ordered protein cage assemblies: A toolkit for new materials

“…Schematic (top) and transmission electron microscope (TEM) images (bottom) of free magnetoferritin self‐assembly with cationic dendrons and disassembly back to nanoparticles (NPs) after exposure to ultraviolet (UV) radiation (Reprinted with permission from Liljeström et al (). Copyright 2017 Nature, Korpi et al (). Copyright 2018 American Chemical Society, Beyeh et al ().…”

“…Apoferritin (aFt) Electrostatic Au nanoparticles (AuNP) Kostiainen et al (2013) Polypeptides Bellapadrona et al (2015); Korpi et al (2018) Dendrons and dendrimers Liljeström, Seitsonen, & Kostiainen (2015); Välimäki et al (2015) Protein Künzle, Eckert, and Beck (2016); Lach, Künzle, and Beck (2017) Small cyclic molecules Beyeh et al (2018) Organic dye Mikkilä et al (2016) Ce 3+ Okuda, Suzumoto, and Yamashita (2011)…”

“…Protein scaffold-based materials can also be physically active in addition to having chemical properties. Many hollow scaffolds can be filled with magnetic particles to introduce magnetic responses in addition to the protein properties initially Korpi et al (2018). Copyright 2018 American Chemical Society, Beyeh et al (2018).…”