Crystallization control of thermal stability and morphology of hen egg white lysozyme crystals by ionic liquids

Thermofluor-Based Optimization Strategy for the Stabilization of Recombinant Human Soluble Catechol-O-Methyltransferase

Catechol-O-methyltransferase (COMT) has been involved in a number of medical conditions including catechol-estrogen-induced cancers and a great range of cardiovascular and neurodegenerative diseases such as Parkinson's disease. Currently, Parkinson's disease treatment relies on a triple prophylaxis, involving dopamine replacement by levodopa, the use of aromatic L-amino acid decarboxylase inhibitors, and the use of COMT inhibitors. Typically, COMT is highly thermolabile, and its soluble isoform (SCOMT) loses biological activity within a short time span preventing further structural and functional trials. Herein, we characterized the thermal stability profile of lysate cells from Komagataella pastoris containing human recombinant SCOMT (hSCOMT) and enzyme-purified fractions (by Immobilized Metal Affinity Chromatography-IMAC) upon interaction with several buffers and additives by Thermal Shift Assay (TSA) and a biological activity assessment. Based on the obtained results, potential conditions able to increase the thermal stability of hSCOMT have been found through the analysis of melting temperature (T_m) variations. Moreover, the use of the ionic liquid 1-butyl-3-methylimidazolium chloride [C₄mim]Cl (along with cysteine, trehalose, and glycerol) ensures complete protein solubilization as well as an increment in the protein Tm of approximately 10 °C. Thus, the developed formulation enhances hSCOMT stability with an increment in the percentage of activity recovery of 200% and 70% when the protein was stored at 4 °C and -80 °C, respectively, for 12 h. The formation of metanephrine over time confirmed that the enzyme showed twice the productivity in the presence of the additive. These outstanding achievements might pave the way for the development of future hSCOMT structural and biophysical studies, which are fundamental for the design of novel therapeutic molecules.

Avian Egg: A Multifaceted Biomaterial for Tissue Engineering

Most components in avian eggs, offering a natural and environmentally friendly source of raw materials, hold great potential in tissue engineering. An avian egg consists of several beneficial elements: the protective eggshell, the eggshell membrane, the egg white (albumen), and the egg yolk (vitellus). The eggshell is mostly composed of calcium carbonate and has intrinsic biological properties that stimulate bone repair. It is a suitable precursor for the synthesis of hydroxyapatite and calcium phosphate, which are particularly relevant for bone tissue engineering. The eggshell membrane is a thin protein-based layer with a fibrous structure and is constituted of several valuable biopolymers, such as collagen and hyaluronic acid, that are also found in the human extracellular matrix. As a result, the eggshell membrane has found several applications in skin tissue repair and regeneration. The egg white is a protein-rich material that is under investigation for the design of functional protein-based hydrogel scaffolds. The egg yolk, mostly composed of lipids but also diverse essential nutrients (e.g., proteins, minerals, vitamins), has potential applications in wound healing and bone tissue engineering. This review summarizes the advantages and status of each egg component in tissue engineering and regenerative medicine, but also covers their current limitations and future perspectives.

Ionic Liquids as Protein Crystallization Additives

Among its attributes, the mythical philosopher’s stone is supposedly capable of turning base metals to gold or silver. In an analogous fashion, we are finding that protein crystallization optimization using ionic liquids (ILs) often results in the conversion of base protein precipitate to crystals. Recombinant inorganic pyrophosphatases (8 of the 11 proteins) from pathogenic bacteria as well as several other proteins were tested for optimization by 23 ILs, plus a dH₂O control, at IL concentrations of 0.1, 0.2, and 0.4 M. The ILs were used as additives, and all proteins were crystallized in the presence of at least one IL. For 9 of the 11 proteins, precipitation conditions were converted to crystals with at least one IL. The ILs could be ranked in order of effectiveness, and it was found that ~83% of the precipitation-derived crystallization conditions could be obtained with a suite of just eight ILs, with the top two ILs accounting for ~50% of the hits. Structural trends were found in the effectiveness of the ILs, with shorter-alkyl-chain ILs being more effective. The two top ILs, accounting for ~50% of the unique crystallization results, were choline dihydrogen phosphate and 1-butyl-3-methylimidazolium tetrafluoroborate. Curiously, however, a butyl group was present on the cation of four of the top eight ILs.

Conformational Stability and Dynamics in Crystals Recapitulate Protein Behavior in Solution

A growing body of evidences has established that in many cases proteins may preserve most of their function and flexibility in a crystalline environment, and several techniques are today capable to characterize molecular properties of proteins in tightly packed lattices. Intriguingly, in the case of amyloidogenic precursors, the presence of transiently populated states (hidden to conventional crystallographic studies) can be correlated to the pathological fate of the native fold; the low fold stability of the native state is a hallmark of aggregation propensity. It remains unclear, however, to which extent biophysical properties of proteins such as the presence of transient conformations or protein stability characterized in crystallo reflect the protein behavior that is more commonly studied in solution. Here, we address this question by investigating some biophysical properties of a prototypical amyloidogenic system, β2-microglobulin in solution and in microcrystalline state. By combining NMR chemical shifts with molecular dynamics simulations, we confirmed that conformational dynamics of β2-microglobulin native state in the crystal lattice is in keeping with what observed in solution. A comparative study of protein stability in solution and in crystallo is then carried out, monitoring the change in protein secondary structure at increasing temperature by Fourier transform infrared spectroscopy. The increased structural order of the crystalline state contributes to provide better resolved spectral components compared to those collected in solution and crucially, the crystalline samples display thermal stabilities in good agreement with the trend observed in solution. Overall, this work shows that protein stability and occurrence of pathological hidden states in crystals parallel their solution counterpart, confirming the interest of crystals as a platform for the biophysical characterization of processes such as unfolding and aggregation.

Ionic liquids as biocompatible stabilizers of proteins

Ionic liquids (ILs) have recently emerged as versatile solvents and additives in the field of biotechnology, particularly as stabilizers of proteins and enzymes. Of interest to the biotechnology industry is the formulation of stable biopharmaceuticals, therapeutic proteins, and vaccines which have revolutionized the treatment of many diseases including debilitating conditions such as cancers and auto-immune diseases. The stabilization of therapeutic proteins is typically achieved using additives that prevent unfolding and aggregation of these proteins during manufacture, transport, and long-term storage. To determine if ILs could be used in the formulation of stable therapeutic proteins, a thorough understanding of the effects of ILs on protein stability is needed, as well as understanding the toxicity of ILs on humans, and other considerations for formulation development such as viscosity and osmolality. In this review, we summarize recent developments on the stabilization of proteins and enzymes using ILs, with emphasis on identifying biocompatible ILs that may be suitable for the formulation of stable biopharmaceuticals in the future.

Manipulating crystallization in lysozyme and supramolecular self-arrangement in solution using ionic liquids

It was found that ILs exerted impact on intermolecular interactions for lysozyme in solution and brought about distinct evolution in secondary structures of supermolecules during self-assembly in this work.

Superior Catalytic Performance of Gold Nanoparticles Within Small Cross-Linked Lysozyme Crystals

Bionanomaterials synthesized by bioinspired templating methods have emerged as a novel class of composite materials with varied applications in catalysis, detection, drug delivery, and biomedicine. In this study, two kinds of cross-linked lysozyme crystals (CLLCs) with different sizes were applied for the in situ growth of Au nanoparticles (AuNPs). The resulting composite materials were characterized by light microscopy, scanning electron microscopy, transmission electron microscopy, thermogravimetric analysis, and X-ray photoelectron spectroscopy. The catalytic properties of the prepared materials were examined in the catalytic reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP). It was found that the size of the AuNPs increased with an increase in Au loading for both small and large crystals. In addition, small crystals favored homogeneous adsorption and distribution of the metal precursors. And the size of the AuNPs within small crystals could be maintained below 2.5 nm by managing the HAuCl₄/lysozyme molar ratio. Furthermore, the lysozyme functional groups blocked the AuNP activity sites, therefore reducing their catalytic activity. This effect was more pronounced for small AuNPs. Moreover, the mass transfer of reactants (4-NP) from solution to AuNPs within the crystals restricted their catalytic reduction, leading to superior catalytic performance of the AuNPs within small cross-linked lysozyme crystals (Au@S-CLLCs) compared to those within large cross-linked lysozyme crystals (Au@L-CLLCs) at similar Au loadings. Finally, an increase in Au loading clogged the crystal channels with increased quantities of larger AuNPs, thus impeding the catalytic performance of Au@S-CLLCs.

Cross-linked lysozyme crystal templated synthesis of Au nanoparticles as high-performance recyclable catalysts

Bio-nanomaterials fabricated using a bioinspired templating technique represent a novel class of composite materials with diverse applications in biomedical, electronic devices, drug delivery, and catalysis. In this study, Au nanoparticles (NPs) are synthesized within the solvent channels of cross-linked lysozyme crystals (CLLCs) in situ without the introduction of extra chemical reagents or physical treatments. The as-prepared AuNPs-in-protein crystal hybrid materials are characterized by light microscopy, transmission electron microscopy, x-ray diffraction, and Fourier-transform infrared spectroscopy analyses. Small AuNPs with narrow size distribution reveal the restriction effects of the porous structure in the lysozyme crystals. These composite materials are proven to be active heterogeneous catalysts for the reduction of 4-nitrophenol to 4-aminophenol. These catalysts can be easily recovered and reused at least 20 times because of the physical stability and macro-dimension of CLLCs. This work is the first to use CLLCs as a solid biotemplate for the preparation of recyclable high-performance catalysts.