Magnetic immobilization of a quorum sensing signal hydrolase, AiiA

Magnetizing Biotech-Advances in (In Vivo) Magnetic Enzyme Immobilization

Industrial biocatalysis, a multibillion dollar industry, relies on the selectivity and efficacy of enzymes for efficient chemical transformations. However, enzymes, evolutionary adapted to mild biological conditions, often struggle in industrial processes that require harsh reaction conditions, resulting in reduced stability and activity. Enzyme immobilization, which addresses challenges such as enzyme reuse and stability, has therefore become a vital strategy for improving enzyme use in industrial applications. Traditional immobilization techniques rely on the confinement or display of enzymes within/on organic or inorganic supports, while recent advances in synthetic biology have led to the development of solely biological in vivo immobilization methods that streamline enzyme production and immobilization. These methods offer added benefits in terms of sustainability and cost efficiency. In addition, the development and use of multifunctional materials, such as magnetic (nano)materials for enzyme immobilization, has enabled improved separation and purification processes. The combination of both "worlds," opens up new avenues in both (industrial) biocatalysis, fundamental science, and biomedicine. Therefore, in this review, we provide an overview of established and recently emerging methods for the generation of magnetic protein immobilizates, placing a special focus on in vivo immobilization solutions.

Unexpected divergence in magnetoreceptor MagR from robin and pigeon linked to two sequence variations

Birds exhibit extraordinary mobility and remarkable navigational skills, obtaining guidance cues from the Earth's magnetic field for orientation and long-distance movement. Bird species also show tremendous diversity in navigation strategies, with considerable differences even within the same taxa and among individuals from the same population. The highly conserved iron and iron-sulfur cluster binding magnetoreceptor (MagR) protein is suggested to enable animals, including birds, to detect the geomagnetic field and navigate accordingly. Notably, MagR is also implicated in other functions, such as electron transfer and biogenesis of iron-sulfur clusters, raising the question of whether variability exists in its biochemical and biophysical features among species, particularly birds. In the current study, we conducted a comparative analysis of MagR from two different bird species, including the migratory European robin and the homing pigeon. Sequence alignment revealed an extremely high degree of similarity between the MagRs of these species, with only three sequence variations. Nevertheless, two of these variations underpinned significant differences in metal binding capacity, oligomeric state, and magnetic properties. These findings offer compelling evidence for the marked differences in MagR between the two avian species, potentially explaining how a highly conserved protein can mediate such diverse functions.

A Rationally Designed Building Block of the Putative Magnetoreceptor MagR

The ability of animals to perceive guidance cues from Earth's magnetic field for orientation and navigation has been supported by a wealth of behavioral experiments, yet the nature of this sensory modality remains fascinatingly unresolved and wide open for discovery. MagR has been proposed as a putative magnetoreceptor based on its intrinsic magnetism and its complexation with a previously suggested key protein in magnetosensing, cryptochrome, to form a rod-like polymer structure. Here, we report a rationally designed single-chain tetramer of MagR (SctMagR), serving as the building block of the hierarchical assembly of MagR polymer. The magnetic trapping experiment and direct magnetic measurement of SctMagR demonstrated the possibility of magnetization of nonmagnetic cells via overexpressing a single protein, which has great potential in various applications. SctMagR, as reported in this study, serves as a prototype of designed magnetic biomaterials inspired by animal magnetoreception. The features of SctMagR provide insights into the unresolved origin of the intrinsic magnetic moment, which is of considerable interest in both biology and physics. © 2022 Bioelectromagnetics Society.

Tag-mediated single-step purification and immobilization of recombinant proteins toward protein-engineered advanced materials

Background

The potential applications of protein-engineered functional materials are so wide and exciting that the interest in these eco-friendly advanced materials will further expand in the future. Tag-mediated protein purification/immobilization technologies have emerged as green and cost-effective approaches for the fabrication of such materials. Strategies that combine the purification and immobilization of recombinant proteins/peptides onto/into natural, synthetic or hybrid materials in a single-step are arising and attracting increasing interest.

Aim of Review

This review highlights the most significant advances of the last 5 years within the scope of tag-mediated protein purification/immobilization and elucidates their contributions for the development of efficient single-step purification and immobilization strategies. Recent progresses in the field of protein-engineered materials created using innovative protein-tag combinations and future opportunities created by these new technologies are also summarized and identified herein.

Key Scientific Concepts of Review

Protein purification/immobilization tags present a remarkable ability to establish specific non-covalent/covalent interactions between solid materials and biological elements, which prompted the creation of tailor-made and advanced functional materials, and of next-generation hybrid materials. Affinity tags can bind to a wide range of materials (of synthetic, natural or hybrid nature), being most suitable for protein purification. Covalently binding tags are most suitable for long-term protein immobilization, but can only bind naturally to protein-based materials. Hybrid affinity-covalently binding tags have allowed efficient one-step purification and immobilization of proteins onto different materials, as well as the development of innovative protein-engineered materials. Self-aggregating tags have been particularly useful in combination with other tags for generating protein-engineered materials with self-assembling, flexible and/or responsive properties. While these tags have been mainly explored for independent protein purification, immobilization or functionalization purposes, efficient strategies that combine tag-mediated purification and immobilization/functionalization in a single-step will be essential to guarantee the sustainable manufacturing of advanced protein-engineered materials.

Modulation of MagR magnetic properties via iron-sulfur cluster binding

Iron-sulfur clusters are essential cofactors found in all kingdoms of life and play essential roles in fundamental processes, including but not limited to respiration, photosynthesis, and nitrogen fixation. The chemistry of iron-sulfur clusters makes them ideal for sensing various redox environmental signals, while the physics of iron-sulfur clusters and its host proteins have been long overlooked. One such protein, MagR, has been proposed as a putative animal magnetoreceptor. It forms a rod-like complex with cryptochromes (Cry) and possesses intrinsic magnetic moment. However, the magnetism modulation of MagR remains unknown. Here in this study, iron-sulfur cluster binding in MagR has been characterized. Three conserved cysteines of MagR play different roles in iron-sulfur cluster binding. Two forms of iron-sulfur clusters binding have been identified in pigeon MagR and showed different magnetic properties: [3Fe-4S]-MagR appears to be superparamagnetic and has saturation magnetization at 5 K but [2Fe-2S]-MagR is paramagnetic. While at 300 K, [2Fe-2S]-MagR is diamagnetic but [3Fe-4S]-MagR is paramagnetic. Together, the different types of iron-sulfur cluster binding in MagR attribute distinguished magnetic properties, which may provide a fascinating mechanism for animals to modulate the sensitivity in magnetic sensing.

Revisiting the Potential Functionality of the MagR Protein

Recent findings have sparked great interest in the putative magnetic receptor protein MagR. However, in vivo experiments have revealed no magnetic moment of MagR at room temperature. Nevertheless, the interaction of MagR and MagR fusion proteins with silica-coated magnetite beads have proven useful for protein purification. In this study, we recombinantly produced two different MagR proteins in Escherichia coli BL21(DE3) to (1) expand earlier protein purification studies, (2) test if MagR can magnetize whole E. coli cells once it is expressed to a high cytosolic, soluble titer, and (3) investigate the MagR-expressing E. coli cells’ magnetic properties at low temperatures. Our results show that MagR induces no measurable, permanent magnetic moment in cells at low temperatures, indicating no usability for cell magnetization. Furthermore, we show the limited usability for magnetic bead-based protein purification, thus closing the current knowledge gap between theoretical considerations and empirical data on the MagR protein.

Intrinsically Magnetic Cells: A Review on Their Natural Occurrence and Synthetic Generation

The magnetization of non-magnetic cells has great potential to aid various processes in medicine, but also in bioprocess engineering. Current approaches to magnetize cells with magnetic nanoparticles (MNPs) require cellular uptake or adsorption through in vitro manipulation of cells. A relatively new field of research is "magnetogenetics" which focuses on in vivo production and accumulation of magnetic material. Natural intrinsically magnetic cells (IMCs) produce intracellular, MNPs, and are called magnetotactic bacteria (MTB). In recent years, researchers have unraveled function and structure of numerous proteins from MTB. Furthermore, protein engineering studies on such MTB proteins and other potentially magnetic proteins, like ferritins, highlight that in vivo magnetization of non-magnetic hosts is a thriving field of research. This review summarizes current knowledge on recombinant IMC generation and highlights future steps that can be taken to succeed in transforming non-magnetic cells to IMCs.

Magnetic immobilization of a quorum sensing signal hydrolase, AiiA

Magnetic immobilization of quorum sensing (QS) signal hydrolases provides a convenient solution for quenching QS process that is essential for bacterial biofilm formation and antimicrobial resistance. In the present study, a QS signal hydrolase, AiiA, was fused with a magnetic protein, MagR, and expressed in Escherichia coli. Magnetic immobilization of AiiA was achieved on Fe₃ O₄ -SiO₂ iron beads and was confirmed via SDS-PAGE, zeta potential measurement, FTIR spectrometry, and SEM analysis. The magnetic immobilized AiiA exhibited activity in degrading the quorum sensing signal, C6-HSL. This study opens a new avenue to actively immobilize enzymes via magnetic interaction and quench quorum sensing.