Connectability of protein cages

Designed, Programmable Protein Cages Utilizing Diverse Metal Coordination Geometries Show Reversible, pH-Dependent Assembly

The rational design and production of a novel series of engineered protein cages are presented, which have emerged as versatile and adaptable platforms with significant applications in biomedicine. These protein cages are assembled from multiple protein subunits, and precise control over their interactions is crucial for regulating assembly and disassembly, such as the on-demand release of encapsulated therapeutic agents. This approach employs a homo-undecameric, ring-shaped protein scaffold with strategically positioned metal binding sites. These engineered proteins can self-assemble into highly stable cages in the presence of cobalt or zinc ions. Furthermore, the cages can be disassembled on demand by employing external triggers such as chelating agents and changes in pH. Interestingly, for certain triggers, the disassembly process is reversible, allowing the cages to reassemble upon reversal or outcompeting of triggering conditions/agents. This work offers a promising platform for the development of advanced drug delivery systems and other biomedical applications.

Reengineering of an Artificial Protein Cage for Efficient Packaging of Active Enzymes

Protein cages that readily encapsulate active enzymes of interest present useful nanotools for delivery and catalysis, wherein those with programmable disassembly characteristics serve as particularly attractive platforms. Here, a general guest packaging system based on an artificial protein cage, TRAP-cage, the disassembly of which can be induced by the addition of reducing agents, is established. In this system, TRAP-cage with SpyCatcher moieties in the lumen is prepared using genetic modification of the protein building block and assembled into a cage structure with either monovalent gold ions or molecular crosslinkers. The resulting protein cage can efficiently capture guest proteins equipped with a SpyTag by simply mixing them in an aqueous solution. This post-assembly loading system, which circumvents the exposure of guests to thiol-reactive crosslinkers, enables the packaging of enzymes possessing a catalytic cysteine or a metal cofactor while retaining their catalytic activity.

Anticancer Activity of Reconstituted Ribonuclease S-Decorated Artificial Viral Capsid

Ribonuclease S (RNase S) is an enzyme that exhibits anticancer activity by degrading RNAs within cancer cells; however, the cellular uptake efficiency is low due to its small molecular size. Here we generated RNase S-decorated artificial viral capsids with a size of 70-170 nm by self-assembly of the β-annulus-S-peptide followed by reconstitution with S-protein at neutral pH. The RNase S-decorated artificial viral capsids are efficiently taken up by HepG2 cells and exhibit higher RNA degradation activity in cells compared with RNase S alone. Cell viability assays revealed that RNase S-decorated capsids have high anticancer activity comparable to that of standard anticancer drugs.

Shape-Morphing of an Artificial Protein Cage with Unusual Geometry Induced by a Single Amino Acid Change

Artificial protein cages are constructed from multiple protein subunits. The interaction between the subunits, notably the angle formed between them, controls the geometry of the resulting cage. Here, using the artificial protein cage, “TRAP-cage”, we show that a simple alteration in the position of a single amino acid responsible for Au(I)-mediated subunit–subunit interactions in the constituent ring-shaped building blocks results in a more acute dihedral angle between them. In turn, this causes a dramatic shift in the structure from a 24-ring cage with an octahedral symmetry to a 20-ring cage with a C2 symmetry. This symmetry change is accompanied by a decrease in the number of Au(I)-mediated bonds between cysteines and a concomitant change in biophysical properties of the cage.

Chemically induced protein cage assembly with programmable opening and cargo release

Engineered protein cages are promising tools that can be customized for applications in medicine and nanotechnology. A major challenge is developing a straightforward strategy for endowing cages with bespoke, inducible disassembly. Such cages would allow release of encapsulated cargoes at desired timing and location. Here, we achieve such programmable disassembly using protein cages, in which the subunits are held together by different molecular cross-linkers. This modular system enables cage disassembly to be controlled in a condition-dependent manner. Structural details of the resulting cages were determined using cryo–electron microscopy, which allowed observation of bridging cross-linkers at intended positions. Triggered disassembly was demonstrated by high-speed atomic force microscopy and subsequent cargo release using an encapsulated Förster resonance energy transfer pair whose signal depends on the quaternary structure of the cage.

Protein Assembly by Design

Proteins are nature's primary building blocks for the construction of sophisticated molecular machines and dynamic materials, ranging from protein complexes such as photosystem II and nitrogenase that drive biogeochemical cycles to cytoskeletal assemblies and muscle fibers for motion. Such natural systems have inspired extensive efforts in the rational design of artificial protein assemblies in the last two decades. As molecular building blocks, proteins are highly complex, in terms of both their three-dimensional structures and chemical compositions. To enable control over the self-assembly of such complex molecules, scientists have devised many creative strategies by combining tools and principles of experimental and computational biophysics, supramolecular chemistry, inorganic chemistry, materials science, and polymer chemistry, among others. Owing to these innovative strategies, what started as a purely structure-building exercise two decades ago has, in short order, led to artificial protein assemblies with unprecedented structures and functions and protein-based materials with unusual properties. Our goal in this review is to give an overview of this exciting and highly interdisciplinary area of research, first outlining the design strategies and tools that have been devised for controlling protein self-assembly, then describing the diverse structures of artificial protein assemblies, and finally highlighting the emergent properties and functions of these assemblies.

Virus-Based Supramolecular Structure and Materials: Concept and Prospects

Rodlike and spherelike viruses are various monodisperse nanoparticles that can display small molecules or polymers with unique distribution following chemical modifications. Because of the monodisperse property, aggregates in synthetic protein-polymer nanoparticles could be eliminated, thus improving the probability for application in protein-polymer drug. In addition, the monodisperse virus could direct the growth of metal materials or inorganic materials, finding applications in hydrogel, drug delivery, and optoelectronic and catalysis materials. Benefiting from the advantages, the virus or viruslike particles have been widely explored in the field of supramolecular chemistry. In this review, we describe the modification and application of virus and viruslike particles in surpramolecular structures and biomedical research.

Protein cages as building blocks for superstructures

Proteins naturally self-assemble to function. Protein cages result from the self-assembly of multiple protein subunits that interact to form hollow symmetrical structures with functions that range from cargo storage to catalysis. Driven by self-assembly, building elegant higher-order superstructures with protein cages as building blocks has been an increasingly attractive field in recent years. It presents an engineering challenge not only at the molecular level but also at the supramolecular level. The higher-order constructs are proposed to provide access to diverse functional materials. Focussing on design strategy as a perspective, current work on protein cage supramolecular self-assembly are reviewed from three principles that are electrostatic, metal-ligand coordination and inherent symmetry. The review also summarises possible applications of the superstructure architecture built using modified protein cages.