Structural peculiarities of lysozyme - PLURONIC complexes at the aqueous-air and liquid-liquid interfaces and in the bulk of aqueous solution

Lysozyme binding with amikacin and levofloxacin studied by tritium probe, fluorescence spectroscopy and molecular docking

Lysozyme complexes with amikacin and levofloxacin were studied by spectroscopy approaches as well as using a tritium probe. Tritium was used as a labeling agent to trace labeled compound concentration in a system of two immiscible liquids and in the atomic form to determine the possible position of the binding site. Co-adsorption of protein and drug at the liquid-liquid interface was analyzed by scintillation phase method that allowed us to directly determine the amount of protein and drug in the mixed adsorption layer. Also, tensiometric measuring of the interfacial tension was used for calculation of binding parameters accordingly to Fainerman model. The treatment of complexes with atomic tritium followed by trypsinolysis and analysis of tritium distribution in the lysozyme peptides reveals the binding sites, binding energies in which were analyzed using molecular docking. Formation of complexes with amikacin and levofloxacin preserves secondar structure of protein. However, the formation of complex with amikacin leads to the almost total loss of the enzymatic activity of lysozyme and the redshift of the maximum on the lysozyme fluorescence band. A slight decrease in the distribution coefficient of lysozyme in the presence of amikacin assumes that the complex has higher hydrophilicity in comparison to lysozyme without additives. The most favorable for binding were the positions of the active centers that included amino acids Asp52 and Glu35, as well as in the vicinity of peptide His15-Arg21, with the participation of amino acids Tyr20, Arg14. In the case of levofloxacin, the formation of lysozyme-ligand complex in aqueous solution is possible without changing the microenvironment of the active center of the protein. Binding of levofloxacin to the active center of the enzyme was the most favorable, but Asp52 and Glu35 that are responsible for the enzymatic activity of lysozyme, were not affected.

Anionic Hyperbranched Amphiphilic Polyelectrolytes as Nanocarriers for Antimicrobial Proteins and Peptides

This manuscript presents the synthesis of hyperbranched amphiphilic poly (lauryl methacrylate-co-tert-butyl methacrylate-co-methacrylic acid), H-P(LMA-co-tBMA-co-MAA) copolymers via reversible addition fragmentation chain transfer (RAFT) copolymerization of tBMA and LMA, and their post-polymerization modification to anionic amphiphilic polyelectrolytes. The focus is on investigating whether the combination of the hydrophobic characters of LMA and tBMA segments, as well as the polyelectrolyte and hydrophilic properties of MAA segments, both distributed within a unique hyperbranched polymer chain topology, would result in intriguing, branched copolymers with the potential to be applied in nanomedicine. Therefore, we studied the self-assembly behavior of these copolymers in aqueous media, as well as their ability to form complexes with cationic proteins, namely lysozyme (LYZ) and polymyxin (PMX). Various physicochemical characterization techniques, including size exclusion chromatography (SEC) and proton nuclear magnetic resonance (1H-NMR), verified the molecular characteristics of these well-defined copolymers, whereas light scattering and fluorescence spectroscopy techniques revealed promising nanoparticle (NP) self- and co-assembly properties of the copolymers in aqueous media.

Hyperbranched Copolymers of Methacrylic Acid and Lauryl Methacrylate H-P(MAA-co-LMA): Synthetic Aspects and Interactions with Biorelevant Compounds

The synthesis of novel copolymers using one-step reversible addition-fragmentation chain transfer (RAFT) copolymerization of biocompatible methacrylic acid (MAA), lauryl methacrylate (LMA), and difunctional ethylene glycol dimethacrylate (EGDMA) as a branching agent is reported. The obtained amphiphilic hyperbranched H-P(MAA-co-LMA) copolymers are molecularly characterized by size exclusion chromatography (SEC), FTIR, and ¹H-NMR spectroscopy, and subsequently investigated in terms of their self-assembly behavior in aqueous media. The formation of nanoaggregates of varying size, mass, and homogeneity, depending on the copolymer composition and solution conditions such as concentration or pH variation, is demonstrated by light scattering and spectroscopic techniques. Furthermore, drug encapsulation properties are studied by incorporating the low bioavailability drug, curcumin, in the nano-aggregate hydrophobic domains, which can also act as a bioimaging agent. The interaction of polyelectrolyte MAA units with model proteins is described to examine protein complexation capacity relevant to enzyme immobilization strategies, as well as explore copolymer self-assembly in simulated physiological media. The results confirm that these copolymer nanosystems could provide competent biocarriers for imaging and drug or protein delivery/enzyme immobilization applications.

Hyperbranched Polyelectrolyte Copolymers as Novel Candidate Delivery Systems for Bio-Relevant Compounds

In this study, reversible addition-fragmentation chain transfer (RAFT) polymerization is utilized in order to synthesize novel hyperbranched poly(oligoethylene glycol) methyl ether methacrylate-co-tert-butyl methacrylate-co-methacrylic acid) (H-[P(OEGMA-co-tBMA-co-MAA)]) copolymers in combination with selective hydrolysis reactions. The copolymers showing amphiphilicity induced by the polar OEGMA and hydrophobic tBMA monomeric units, and polyelectrolyte character due to MAA units, combined with unique macromolecular architecture were characterized by physicochemical techniques, such as size exclusion chromatography (SEC) and ¹H-NMR spectroscopy. The hyperbranched copolymers were investigated in terms of their ability to self-assemble into nanostructures when dissolved in aqueous media. Dynamic light scattering and fluorescence spectroscopy revealed multimolecular aggregates of nanoscale dimensions with low critical aggregation concentration, the size and mass of which depend on copolymer composition and solution conditions, whereas zeta potential measurements indicated pH sensitive features. In addition, aiming to evaluate their potential use as nanocarriers, the copolymers were studied in terms of their drug encapsulation and protein complexation ability utilizing curcumin and lysozyme, as a model hydrophobic drug and a model cationic protein, respectively.

Role of protein-copolymer assembly in controlling micellization process of amphiphilic triblock copolymer

HYPOTHESIS

Triblock copolymer poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) (PEG-PPG-PEG) forms a well-known micellar assembly at a particular temperature. Apart from regular assembly within the copolymer, it is crucial to explore additional assembly behaviour via simple exposure of proteins which unveils biased interactions with blocks of copolymer. The current work focuses on the examination of Pluronic F108 i.e. PEG-PPG-PEG with two different proteins i.e. α-chymotrypsin (CT) and lysozyme (LSZ), aiming at probing the critical micellization temperature (CMT) and molecular level interactions.

EXPERIMENTS

Potential role of protein-copolymer assembly formation at a particular concentration of protein in modulating CMT was shown by a systematic experimental approach combined with a series of physicochemical methods. The sophisticated multiple techniques include fluorescence spectroscopy, Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, dynamic light scattering (DLS), zeta potential measurements, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Furthermore, molecular docking studies were also employed to correlate theoretical insights with experimental findings.

FINDINGS

CT and LSZ decrease CMT in regular concentration-dependent manner except for particular concentration (1.5 mg/mL) of LSZ which shows anomalous behaviour in steady-state fluorescence spectroscopy, temperature dependent fluorescence spectroscopy, Raman spectroscopy and DLS measurements. SEM and TEM results clearly reveal protein-copolymer assembly formation. The assembled structure has different biophysical properties. Docking studies elucidate several bio macromolecular interactions which can be involved in assembly formation. Based on obtained results from biophysical techniques mechanism of CMT variation was deduced. Obtained results can be useful in biosensors and targeted drug delivery systems.

Lysozyme-dalargin self-organization at the aqueous-air and liquid-liquid interfaces

An experimental study of protein-peptide binding was performed by means of radiochemical and spectroscopic methods. Lysozyme and dalargin were chosen due to their biological and physiological importance. By means of tensiometry and radiochemical assays, it was found that dalargin possesses rather high surface activity at the aqueous-air and aqueous-p-xylene interfaces to be substituted by protein. Dalargin forms a hydrophobic complex with lysozyme in which the secondary structure of lysozyme is preserved. When lysozyme forms a mixed adsorption layer with dalargin at the aqueous-air surface, the peptide prevents protein from concentrating in the subsurface monolayer. In the presence of p-xylene protein in the interface, reorganization occurs quickly, so there is no lag in the interfacial tension time dependence. The interfacial tension in this case is controlled by protein and/or protein-peptide complexes. An increase in the enzymatic activity of lysozyme in the presence of dalargin was confirmed by a docking model that suggests the formation of hydrogen bonds between dalargin and amino acid residues in the active site.