Encapsulin Based Self-Assembling Iron-Containing Protein Nanoparticles for Stem Cells MRI Visualization

Semisynthetic ferritin-based nanoparticles with high magnetic anisotropy for spatial magnetic manipulation and inductive heating

The human iron storage protein ferritin represents an appealing template to obtain a semisynthetic magnetic nanoparticle (MNP) for spatial manipulation or inductive heating applications on a nanoscale. Ferritin consists of a protein cage of well-defined size (12 nm), which is genetically modifiable and biocompatible, and into which a magnetic core is synthesised. Here, we probed the magnetic response and hence the MNP's suitability for (bio-)nanotechnological or nanomedical applications when the core is doped with 7% cobalt or 7% zinc in comparison with the undoped iron oxide MNP. The samples exhibit almost identical core and hydrodynamic sizes, along with their tunable magnetic core characteristics as verified by structural and magnetic characterisation. Cobalt doping significantly increased the MNP's anisotropy and hence the heating power in comparison with other magnetic cores with potential application as a mild heat mediator. Spatial magnetic manipulation was performed with MNPs inside droplets, the cell cytoplasm, or the cell nucleus, where the MNP surface conjugation with mEGFP and poly(ethylene glycol) gave rise to excellent intracellular stability and traceability within the complex biological environment. A magnetic stimulus (smaller than fN forces) results in the quick and reversible redistribution of the MNPs. The obtained data suggest that semisynthetic ferritin MNPs are highly versatile nanoagents and promising candidates for theranostic or (bio-)nanotechnological applications.

Extraordinary Titer and Broad Anti-SARS-CoV-2 Neutralization Induced by Stabilized RBD Nanoparticles from Strain BA.5

The receptor-binding domain (RBD) of the SARS-CoV-2 spike is a primary target of neutralizing antibodies and a key component of licensed vaccines. Substantial mutations in RBD, however, enable current variants to escape immunogenicity generated by vaccination with the ancestral (WA1) strain. Here, we produce and assess self-assembling nanoparticles displaying RBDs from WA1 and BA.5 strains by using the SpyTag:SpyCatcher system for coupling. We observed both WA1- and BA.5-RBD nanoparticles to degrade substantially after a few days at 37 °C. Incorporation of nine RBD-stabilizing mutations, however, increased yield ~five-fold and stability such that more than 50% of either the WA1- or BA.5-RBD nanoparticle was retained after one week at 37 °C. Murine immunizations revealed that the stabilized RBD-nanoparticles induced ~100-fold higher autologous neutralization titers than the prefusion-stabilized (S2P) spike at a 2 μg dose. Even at a 25-fold lower dose where S2P-induced neutralization titers were below the detection limit, the stabilized BA.5-RBD nanoparticle induced homologous titers of 12,795 ID50 and heterologous titers against WA1 of 1767 ID50. Assessment against a panel of β-coronavirus variants revealed both the stabilized BA.5-RBD nanoparticle and the stabilized WA1-BA.5-(mosaic)-RBD nanoparticle to elicit much higher neutralization breadth than the stabilized WA1-RBD nanoparticle. The extraordinary titer and high neutralization breadth elicited by stabilized RBD nanoparticles from strain BA.5 make them strong candidates for next-generation COVID-19 vaccines.

Encapsulins: Nanotechnology's future in a shell

Encapsulins, virus capsid-like bacterial nanocompartments have emerged as promising tools in medicine, imaging, and material sciences. Recent work has shown that these protein-bound icosahedral 'organelles' possess distinct properties that make them exceptionally usable for nanotechnology applications. A key factor contributing to their appeal is their ability to self-assemble, coupled with their capacity to encapsulate a wide range of cargos. Their genetic manipulability, stability, biocompatibility, and nano-size further enhance their utility, offering outstanding possibilities for practical biotechnology applications. In particular, their amenability to engineering has led to their extensive modification, including the packaging of non-native cargos and the utilization of the shell surface for displaying immunogenic or targeting proteins and peptides. This inherent versatility, combined with the ease of expressing encapsulins in heterologous hosts, promises to provide broad usability. Although mostly not yet commercialized, encapsulins have started to demonstrate their vast potential for biotechnology, from drug delivery to biofuel production and the synthesis of valuable inorganic materials. In this review, we will initially discuss the structure, function and diversity of encapsulins, which form the basis for these emerging applications, before reviewing ongoing practical uses and highlighting promising applications in medicine, engineering and environmental sciences.

Magnetic and Fluorescent Dual-Labeled Genetically Encoded Targeted Nanoparticles for Malignant Glioma Cell Tracking and Drug Delivery

Human glioblastoma multiforme (GBM) is a primary malignant brain tumor, a radically incurable disease characterized by rapid growth resistance to classical therapies, with a median patient survival of about 15 months. For decades, a plethora of approaches have been developed to make GBM therapy more precise and improve the diagnosis of this pathology. Targeted delivery mediated by the use of various molecules (monoclonal antibodies, ligands to overexpressed tumor receptors) is one of the promising methods to achieve this goal. Here we present a novel genetically encoded nanoscale dual-labeled system based on Quasibacillus thermotolerans (Qt) encapsulins exploiting biologically inspired designs with iron-containing nanoparticles as a cargo, conjugated with human fluorescent labeled transferrin (Tf) acting as a vector. It is known that the expression of transferrin receptors (TfR) in glioma cells is significantly higher compared to non-tumor cells, which enables the targeting of the resulting nanocarrier. The selectivity of binding of the obtained nanosystem to glioma cells was studied by qualitative and quantitative assessment of the accumulation of intracellular iron, as well as by magnetic particle quantification method and laser scanning confocal microscopy. Used approaches unambiguously demonstrated that transferrin-conjugated encapsulins were captured by glioma cells much more efficiently than by benign cells. The resulting bioinspired nanoplatform can be supplemented with a chemotherapeutic drug or genotherapeutic agent and used for targeted delivery of a therapeutic agent to malignant glioma cells. Additionally, the observed cell-assisted biosynthesis of magnetic nanoparticles could be an attractive way to achieve a narrow size distribution of particles for various applications.

Modification and Production of Encapsulin

Encapsulins are a class of protein nanocages that are found in bacteria, which are easy to produce and engineer in E. coli expression systems. The encapsulin from Thermotoga maritima (Tm) is well studied, its structure is available, and without modification it is barely taken up by cells, making it promising candidates for targeted drug delivery. In recent years, encapsulins are engineered and studied for potential use as drug delivery carriers, imaging agents, and as nanoreactors. Consequently, it is important to be able to modify the surface of these encapsulins, for example, by inserting a peptide sequence for targeting or other functions. Ideally, this is combined with high production yields and straightforward purification methods. In this chapter, we describe a method to genetically modify the surface of Tm and Brevibacterium linens (Bl) encapsulins, as model systems, to purify them and characterize the obtain nanocages.

Encapsulins: Structure, Properties, and Biotechnological Applications

In 1994 a new class of prokaryotic compartments was discovered, collectively called "encapsulins" or "nanocompartments". Encapsulin shell protomer proteins self-assemble to form icosahedral structures of various diameters (24-42 nm). Inside of nanocompartments shells, one or several cargo proteins, diverse in their functions, can be encapsulated. In addition, non-native cargo proteins can be loaded into nanocompartments, and shell surfaces can be modified via various compounds, which makes it possible to create targeted drug delivery systems, labels for optical and MRI imaging, and to use encapsulins as bioreactors. This review describes a number of strategies of encapsulins application in various fields of science, including biomedicine and nanobiotechnologies.

Myxococcus xanthus Encapsulin as a Promising Platform for Intracellular Protein Delivery

Introducing a new genetically encoded material containing a photoactivatable label as a model cargo protein, based on Myxococcus xanthus (Mx) encapsulin system stably expressed in human 293T cells. Encapsulin from Mx is known to be a protein-based container for a ferritin-like cargo in its shell which could be replaced with an exogenous cargo protein, resulting in a modified encapsulin system. We replaced Mx natural cargo with a foreign photoactivatable mCherry (PAmCherry) fluorescent protein and isolated encapsulins, containing PAmCherry, from 293T cells. Isolated Mx encapsulin shells containing photoactivatable label can be internalized by macrophages, wherein the PAmCherry fluorescent signal remains clearly visible. We believe that a genetically encoded nanocarrier system obtained in this study, can be used as a platform for controllable delivery of protein/peptide therapeutics in vitro.

Engineered Protein Nanocages for Concurrent RNA and Protein Packaging In Vivo

Protein nanocages have emerged as an important engineering platform for biotechnological and biomedical applications. Among naturally occurring protein cages, encapsulin nanocompartments have recently gained prominence due to their favorable physico-chemical properties, ease of shell modification, and highly efficient and selective intrinsic protein packaging capabilities. Here, we expand encapsulin function by designing and characterizing encapsulins for concurrent RNA and protein encapsulation in vivo. Our strategy is based on modifying encapsulin shells with nucleic acid-binding peptides without disrupting the native protein packaging mechanism. We show that our engineered encapsulins reliably self-assemble in vivo, are capable of efficient size-selective in vivo RNA packaging, can simultaneously load multiple functional RNAs, and can be used for concurrent in vivo packaging of RNA and protein. Our engineered encapsulation platform has potential for codelivery of therapeutic RNAs and proteins to elicit synergistic effects and as a modular tool for other biotechnological applications.

New Approach to Non-Invasive Tumor Model Monitoring via Self-Assemble Iron Containing Protein Nanocompartments

According to the World Health Organization, breast cancer is the most common oncological disease worldwide. There are multiple animal models for different types of breast carcinoma, allowing the research of tumor growth, metastasis, and angiogenesis. When studying these processes, it is crucial to visualize cancer cells for a prolonged time via a non-invasive method, for example, magnetic resonance imaging (MRI). In this study, we establish a new genetically encoded material based on Quasibacillus thermotolerans (Q.thermotolerans, Qt) encapsulin, stably expressed in mouse 4T1 breast carcinoma cells. The label consists of a protein shell containing an enzyme called ferroxidase. When adding Fe2+, a ferroxidase oxidizes Fe2+ to Fe3+, followed by iron oxide nanoparticles formation. Additionally, genes encoding mZip14 metal transporter, enhancing the iron transport, were inserted into the cells via lentiviral transduction. The expression of transgenic sequences does not affect cell viability, and the presence of magnetic nanoparticles formed inside encapsulins results in an increase in T2 relaxivity.