Luminescent bio-sensors via co-assembly of hen egg white lysozyme with Eu3+/Tb3+-complexes

Protein crystals have advantageous properties as framework materials, such as porosity and organized, high-density functional groups with the potential for guest specificity. Thus, protein crystal materials open up vast opportunities for fluorescent species doping and drug sensing. In this work, we explore this frontier by combining two lanthanide complexes with hen egg white lysozyme (HEWL) and directly obtaining co deposited structures in one step using an anti-solvent method different from the previous two-step method. Cross-linking of the protein was achieved using glutaraldehyde, ensuring the stability of the assembly in diverse solvent environments. The use of glutaraldehyde achieved protein cross-linking, ensuring the stability of the components in various solvent environments, including no leakage of fluorescent substances in ultrapure water and anhydrous ethanol. Differential fluorescence quenching effects of amino acids on the two doped luminescent complexes were observed. Introduction of amino acids, varying in concentration and type, resulted in distinct fluorescence enhancement or quenching effects on the protein assembly loaded with the complexes, and the detection results are reflected through different fitting equations and parameters. By exploring the application of this hybrid material for amino acid detection, this work lays the groundwork for broader applications.

Hyper-Expandable Cross-Linked Protein Crystals as Scaffolds for Catalytic Reactions

Scaffolding catalytic reactions within porous materials is a powerful strategy to enhance the reaction rates of multicatalytic systems. However, it remains challenging to develop materials with high porosity, high diversity of functional groups within the pores, and guest-adaptive tunability. Furthermore, it is challenging to capture large catalysts such as enzymes within porous materials. Protein-based materials are promising candidates to overcome these limitations, owing to their large pore sizes and potential for stimuli-responsive adaptability. In this work, hydrogel beads were generated from cross-linked lysozyme crystals. These swellable lysozyme cross-linked crystals (SLCCs) expand more than 10 mL per gram of crystal following a simple treatment in ethanol, followed by the addition of water. SLCCs are sensitive to the solution environment and change their extent of swelling from adjusting the concentration and identity of the ions in the solution, or by changing the flexibility of the protein backbone, such as adding dithiothreitol to reduce the protein disulfide bonds. SLCCs can adsorb a wide range of catalysts ranging from transition metal complexes to large biomacromolecules, such as the 160 kDa enzyme glucose oxidase (GOx). Transition metal catalysts and enzymes captured within SLCCs maintained their catalytic activity and exhibited minimal leaching. We performed a cascade reaction by adsorbing GOx and the transition metal catalyst Fe-TAML into SLCCs, resulting in enhanced activity compared to a free-floating reaction. SLCCs offer a promising combination of attributes as scaffolds for multicatalytic reactions, including gram-scale batch preparation, tunable expansion to greater than 20-fold in volume, guest-responsive adaptable behavior, and facile capture of a wide array of small molecule and enzyme-catalysts.

Characterization of Guest DNA Transport and Adsorption within Host Porous Protein Crystals

Nucleic acid transport through protein-based pores is a well-characterized phenomenon due in part to advancements in nanopore sequencing. A less studied area is nucleic acid transport through extended protein-based channels, where the additional surface area and increased contact time allow for the study of prolonged binding interactions. Porous protein crystals composed of "CJ", a putative polyisoprenoid-binding protein from Campylobacter jejuni, represent a favorable, highly ordered material for studying DNA transport and binding/unbinding along protein-based channels. These crystals adopt a hexagonal prism habit and contain a densely packed hexagonal array of 13 nm diameter axial nanopores that run from the top to the bottom of the crystal. After cross-linking, the crystals are easily manipulated for experimentation. An adsorption isotherm between host crystals and guest double-stranded 8 base pair DNA (8mer) revealed a high equilibrium adsorption constant of 206 ± 30 L/g. Fluorescence confocal microscopy tracked the loading of guest DNA into host crystals predominately along the major axial crystal nanopores. Four different computational models based on the finite volume (FV) method were assessed to model the transport process for guest 8mer and 15mer dsDNA loading into empty host crystals in terms of fundamental parameters, such as the intrapore diffusion constant. Fitting the models to the data revealed that the most basic FV model sufficed to describe the observed loading behavior, characterized by a single effective diffusion coefficient. Leveraging Fick's first law, we more directly fit a numerical range for the observed intrapore diffusion coefficient as a function of time, position within the crystal, and relative guest concentration. This new transport analysis strategy was applied to both out-of-equilibrium loading and fluorescence recovery after photobleaching (FRAP) experiments. The intrapore diffusion constants are comparable between 8mer and 15mer dsDNA and were found to be 2 orders of magnitude faster for DNA loading into empty crystals than that observed in FRAP experiments, which averaged (10 ± 4) × 10-11 cm2/s.

Conditionally designed luminescent DNA crystals doped by Ln3+(Eu3+/Tb3+) complexes or fluorescent proteins with smart drug sensing property

In this work, a designed porous DNA crystal with high intrinsic biocompatibility was used as the scaffold material to load fluorescent guest molecules to detect anti-cancer drugs. It is shown here that the synthesized crystals have the characteristics consistent with the designed large solvent channels, and can therefore accommodate guest molecules such as fluorescent proteins that cannot be accommodated by less porous crystals. Eu(TTA)₃phen and Tb(acac)₃phen lanthanide complexes were individually noncovalently loaded into the porous crystals, resulting in hybrid luminescent DNA crystals. Emodin, an anti-cancer, anti-tumor, anti-inflammatory drug, was found to quench lanthanide complexes in solution or in crystals. Notably, emodin is the active ingredient of Lianhua Qingwen Capsule, an anti-COVID-19 drug candidate. Therefore, the porous DNA crystals reported here have potential applications as a biocompatible and theranostic delivery biomaterial for functional macromolecules.

Multilayered Ordered Protein Arrays Self-Assembled from a Mixed Population of Virus-like Particles

Biology shows many examples of spatially controlled assembly of cells and biomacromolecules into hierarchically organized structures, to which many of the complex biological functions are attributed. While such biological structures have inspired the design of synthetic materials, it is still a great challenge to control the spatial arrangement of individual building blocks when assembling multiple types of components into bulk materials. Here, we report self-assembly of multilayered, ordered protein arrays from mixed populations of virus-like particles (VLPs). We systematically tuned the magnitude of the surface charge of the VLPs via mutagenesis to prepare four different types of VLPs for mixing. A mixture of up to four types of VLPs selectively assembled into higher-order structures in the presence of oppositely charged dendrimers during a gradual lowering of the ionic strength of the solution. The assembly resulted in the formation of three-dimensional ordered VLP arrays with up to four distinct layers including a central core, with each layer comprising a single type of VLP. A coarse-grained computational model was developed and simulated using molecular dynamics to probe the formation of the multilayered, core-shell structure. Our findings establish a simple and versatile bottom-up strategy to synthesize multilayered, ordered materials by controlling the spatial arrangement of multiple types of nanoscale building blocks in a one-pot fabrication.

Production of Cross-Linked Lipase Crystals at a Preparative Scale

The autoimmobilization of enzymes via cross-linked enzyme crystals (CLECs) has regained interest in recent years, boosted by the extensive knowledge gained in protein crystallization, the decrease of cost and laboriousness of the process, and the development of potential applications. In this work, we present the crystallization and preparative-scale production of reinforced cross-linked lipase crystals (RCLLCs) using a commercial detergent additive as a raw material. Bulk crystallization was carried out in 500 mL of agarose media using the batch technique. Agarose facilitates the homogeneous production of crystals, their cross-linking treatment, and their extraction. RCLLCs were active in an aqueous solution and in hexane, as shown by the hydrolysis of p-nitrophenol butyrate and α-methylbenzyl acetate, respectively. RCLLCs presented both high thermal and robust operational stability, allowing the preparation of a packed-bed chromatographic column to work in a continuous flow. Finally, we determined the three-dimensional (3D) models of this commercial lipase crystallized with and without phosphate at 2.0 and 1.7 Å resolutions, respectively.

In Situ Absorption and Fluorescence Microspectroscopy Investigation of the Molecular Incorporation Process into Single Nanoporous Protein Crystals

Protein crystals exhibit distinct three-dimensional structures, which contain well-ordered nanoporous solvent channels, providing a chemically heterogeneous environment. In this paper, the incorporation of various molecules into the solvent channels of native hen egg-white lysozyme crystals was demonstrated using fluorescent dyes, including acridine yellow G, rhodamine 6G, and eosin Y. The process was evaluated on the basis of absorption and fluorescence microspectroscopy at a single-crystal level. The molecular loading process was clearly visualized as a function of time, and it was determined that the protein crystals could act as nanoporous materials. It was found that the incorporation process is strongly dependent on the molecular charge, leading to heterogeneous molecular aggregation, which suggests host-guest interaction of protein crystals from the viewpoint of nanoporous materials.