Fourier transform infrared spectroscopy as a tool to study structural properties of cytochromes P450 (CYPs)

Preparation of a novel metallothionein-AuNP composite material by genetic modification and AuS covalent combination

Metallothionein (MTs) can be used in the prevention and treatment of tumors and diabetes due to its antioxidant properties. However, it is necessary to solve its non-transmembrane properties and further improve its antioxidant activity, increase its fluorescence visualization and enhance its stability to meet practical applications in the biomedical field. Here, we report the preparation of a novel metallothionein-AuNP composite material with high transmembrane ability, fluorescence visualization, antioxidant activity, and stability by genetic modification (introducing transduction peptide TAT, fluorescence tag GFP and increasing sulfydryl groups) and immobilization technology (covalently bonding with AuNPs). The transmembrane activity of modified proteins was verified by immunofluorescence. Increasing the sulfhydryl content within a certain range can enhance the antioxidant activity of the protein. In addition, GFP were used to further simplify the imaging of the metallothionein-AuNP composite in cells. XPS results indicated that AuNPs can immobilize metallothionein through AuS covalent bonds. TGA characterization and degradation experiments showed that thermal and degradation stability of the immobilized material was significantly improved. This work provides new ideas to construct metallothionein composites with high transmembrane ability, antioxidant activity, fluorescence visualization and stability to meet novel applications in the biomedical field.

Influence of cytochrome P450 3A4 and membrane lipid composition on doxorubicin activity

Drug resistance is known to depend on the interactions with cell membranes and other molecules such as human cytochromes P450 (CYPs) which are anchored on the endoplasmic reticulum (ER) membrane and involved in the metabolism of anticancer drugs. In this study, we determined the influence from cytochrome P450 3A4 (CYP3A4) on the interaction between the drug doxorubicin (DOX) and Langmuir monolayers mimicking cell membranes. The lipid composition was varied by changing the relative concentrations of cholesterol (Chol), 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine (DPPE), and L-α-phosphatidylinositol (PI). Three compositions were studied in detail which represented a healthy cell membrane and cancerous cell membranes. DOX induced an expansion in the surface pressure isotherms for all monolayers, with stronger effect for the composition of cancerous cell with a high Chol content, thus confirming the relevance of lipid composition. This effect decreased considerably when CYP3A4 was incorporated with the formation of CYP3A4-DOX complexes, according to results from polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS) measurements. Taken together, these results support the hypothesis of CYP3A4 being involved in drug resistance, which may be exploited to design strategies to enhance chemotherapy efficacy.

The impact of camptothecin-encapsulated poly(lactic-co-glycolic acid) nanoparticles on the activity of cytochrome P450 in vitro

Background

Poly(lactic-co-glycolic acid) (PLGA) has emerged as a promising anticancer drug delivery scaffold. Camptothecin (CPT) has been fabricated into a variety of nanosized formulations to improve drug action. We report an experimental study on the effect of CPT-encapsulated PLGA (PLGA-CPT) nanoparticles (NPs) on drug-metabolizing cytochrome P450 enzyme, CYP3A4.

Materials and methods

PLGA-CPT NPs were prepared by a single emulsion–solvent evaporation method.

Results

Transmission electron micrography showed that the NPs had a round and regular shape with a mean diameter of 94.6±5.7 nm. An in vitro drug release study showed that CPT was continuously released for 48 h. PLGA-CPT NPs showed greater cytotoxic effects on the HepG2 cell line compared with an equal dose of free CPT. Correlation with 4-h uptake data suggested that this was due to a higher cellular uptake amount of CPT from PLGA-CPT NPs than from free CPT. PLGA-CPT NPs tended to inhibit CYP3A4 activity isolated from HepG2 cells. However, PLGA-CPT NPs had no effect on the CYP3A4 mRNA levels. Furthermore, the interaction between PLGA-CPT NPs and CYP3A4 was investigated by ultraviolet–visible absorption spectroscopy and fluorescence spectroscopy.

Conclusion

Taken together, the results demonstrate that CYP3A4 may be inhibited by PLGA-CPT NPs and interference with biotransformation should be considered when using NPs as drug delivery vesicles.

Changes in secondary structure of myofibrillar protein and its relationship with water dynamic changes during storage of battered and deep-fried pork slices

Fourier transform infrared spectroscopy was used to analyze the changes of secondary structure of myofibrillar proteins in short-term storage of battered and deep-fried pork slices. These changes were combined with low-field NMR analysis results to analyze the correlation between secondary structure and dynamic changes of water content. The results showed that the number of α-helix and β-sheet decreased by 22.90 and 16.54% respectively, and the orderly structure changed to the disorder structure. The correlation results show that NMR spin-spin relaxation time (T₂₁) has a high negative correlation with α-helix, β-sheet, and has a high positive correlation with irregular curl and β-turn. The population of immobile water (P₂₂) has a very high positive correlation with α-helix, β-sheet, and has a relatively high negative correlation with irregular curl and β-turn. The immobilized water plays an important role in maintaining the secondary structure.

Soybean peroxidase immobilized onto silica-coated superparamagnetic iron oxide nanoparticles: Effect of silica layer on the enzymatic activity

Peroxidase immobilization onto magnetic supports is considered an innovative strategy for the development of technologies that involves enzymes in wastewater treatment. In this work, magnetic biocatalysts were prepared by immobilization of soybean peroxidase (SBP) onto different silica-coated superparamagnetic iron oxide nanoparticles. The obtained magnetic biocatalysts were tested for the degradation of malachite green (MG), a pollutant often found in industrial wastewaters and with significant drawbacks for the human and environmental health. A deep physicochemical characterization of the materials was performed by means of X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), High Resolution-Transmission Electron Microscope (HR-TEM) and magnetization measurements among others techniques. Results showed high immobilization yield of SBP onto nanomaterials with excellent properties for magnetic recoverability. A partial loss of activity with respect to free SBP was observed, compatible with the modification of the conformational structure of the enzyme after immobilization. The structural modification depended on the amount (and thickness) of silica present in the hybrid materials and the activity yield of 43% was obtained for the best biocatalyst. Thermal stability and reusability capacity were also evaluated.

Dynamics and flexibility of human aromatase probed by FTIR and time resolved fluorescence spectroscopy

Human aromatase (CYP19A1) is a steroidogenic cytochrome P450 converting androgens into estrogens. No ligand-free crystal structure of the enzyme is available to date. The crystal structure in complex with the substrate androstenedione and the steroidal inhibitor exemestane shows a very compact conformation of the enzyme, leaving unanswered questions on the conformational changes that must occur to allow access of the ligand to the active site. As H/D exchange kinetics followed by FTIR spectroscopy can provide information on the conformational changes in proteins where solvent accessibility is affected, here the amide I region was used to measure the exchange rates of the different elements of the secondary structure for aromatase in the ligand-free form and in the presence of the substrate androstenedione and the inhibitor anastrozole. Biphasic exponential functions were found to fit the H/D exchange data collected as a function of time. Two exchange rates were assigned to two populations of protons present in different flexible regions of the protein. The addition of the substrate androstenedione and the inhibitor anastrozole lowers the H/D exchange rates of the α-helices of the enzyme when compared to the ligand-free form. Furthermore, the presence of the inhibitor anastrozole lowers exchange rate constant (k₁) for β-sheets from 0.22±0.06 min⁻¹ for the inhibitor-bound enzyme to 0.12±0.02 min⁻¹ for the free protein. Dynamics effects localised in helix F were studied by time resolved fluorescence. The data demonstrate that the fluorescence lifetime component associated to Trp224 emission undergoes a shift toward longer lifetimes (from ≈5.0 to ≈5.5 ns) when the substrate or the inhibitor are present, suggesting slower dynamics in the presence of ligands. Together the results are consistent with different degrees of flexibility of the access channel and therefore different conformations adopted by the enzyme in the free, substrate- and inhibitor-bound forms.

Super-resolved FT-IR spectroscopy: Strategies, challenges, and opportunities for membrane biophysics

Direct correlation of molecular conformation with local structure is critical to studies of protein- and peptide-membrane interactions, particularly in the context of membrane-facilitated aggregation, and disruption or disordering. Infrared spectroscopy has long been a mainstay for determining molecular conformation, following folding dynamics, and characterizing reactions. While tremendous advances have been made in improving the spectral and temporal resolution of infrared spectroscopy, it has only been with the introduction of scanned-probe techniques that exploit the raster-scanning tip as either a source, scattering tool, or measurement probe that researchers have been able to obtain sub-diffraction limit IR spectra. This review will examine the history of correlated scanned-probe IR spectroscopies, from their inception to their use in studies of molecular aggregates, membrane domains, and cellular structures. The challenges and opportunities that these platforms present for examining dynamic phenomena will be discussed. This article is part of a Special Issue entitled: FTIR in membrane proteins and peptide studies.