Conformation of the Z19 prolamin by FTIR, NMR, and SAXS

Research advances in Zein-based nano-delivery systems

Zein is the main vegetable protein from maize. In recent years, Zein has been widely used in pharmaceutical, agriculture, food, environmental protection, and other fields because it has excellent biocompatibility and biosafety. However, there is still a lack of systematic review and research on Zein-based nano-delivery systems. This paper systematically reviews preparation and modification methods of Zein-based nano-delivery systems, based on the basic properties of Zein. It discusses the preparation of Zein nanoparticles and the influencing factors in detail, as well as analyzing the advantages and disadvantages of different preparation methods and summarizing modification methods of Zein nanoparticles. This study provides a new idea for the research of Zein-based nano-delivery system and promotes its application.

Conformations of a highly expressed Z19 α-zein studied with AlphaFold2 and MD simulations

α-zeins are amphiphilic maize seed storage proteins with material properties suitable for a multitude of applications e.g., in renewable plastics, foods, therapeutics and additive manufacturing (3D-printing). To exploit their full potential, molecular-level insights are essential. The difficulties in experimental atomic-resolution characterization of α-zeins have resulted in a diversity of published molecular models. However, deep-learning α-zein models are largely unexplored. Therefore, this work studies an AlphaFold2 (AF2) model of a highly expressed α-zein using molecular dynamics (MD) simulations. The sequence of the α-zein cZ19C2 gave a loosely packed AF2 model with 7 α-helical segments connected by turns/loops. Compact tertiary structure was limited to a C-terminal bundle of three α-helices, each showing notable agreement with a published consensus sequence. Aiming to chart possible α-zein conformations in practically relevant solvents, rather than the native solid-state, the AF2 model was subjected to MD simulations in water/ethanol mixtures with varying ethanol concentrations. Despite giving structurally diverse endpoints, the simulations showed several patterns: In water and low ethanol concentrations, the model rapidly formed compact globular structures, largely preserving the C-terminal bundle. At ≥ 50 mol% ethanol, extended conformations prevailed, consistent with previous SAXS studies. Tertiary structure was partially stabilized in water and low ethanol concentrations, but was disrupted in ≥ 50 mol% ethanol. Aggregated results indicated minor increases in helicity with ethanol concentration. β-sheet content was consistently low (∼1%) across all conditions. Beyond structural dynamics, the rapid formation of branched α-zein aggregates in aqueous environments was highlighted. Furthermore, aqueous simulations revealed favorable interactions between the protein and the crosslinking agent glycidyl methacrylate (GMA). The proximity of GMA epoxide carbons and side chain hydroxyl oxygens simultaneously suggested accessible reactive sites in compact α-zein conformations and pre-reaction geometries for methacrylation. The findings may assist in expanding the applications of these technologically significant proteins, e.g., by guiding chemical modifications.

Integrated multi-spectroscopic and molecular modeling techniques to study the formation mechanism of hidden zearalenone in maize

Hidden mycotoxins have been reported to be "protected" by macromolecular substances to escape routine determination, but release to free mycotoxins under gastrointestinal conditions. Nowadays, the hidden zearalenone (ZEN) that binding with macromolecular zein has been found in maize. However, the binding mechanism of ZEN with zein in maize has not been clarified. In this study, the formation of ZEN-zein complex was investigated applying ultrafiltration, multi-spectroscopic and molecular modeling techniques. The steady-state and transient fluorescence analysis suggested the ZEN could interact with zein to form the complex driven by hydrophobic force and hydrogen bonds, which is in accordance with the molecular modeling studies. The conformational changes of zein induced by binding with ZEN were revealed by Fourier transform infrared spectroscopy (FTIR) and circular dichroism (CD). Elucidating the binding mechanism between zein and ZEN could help the development of detecting hidden ZEN and guarantee the safety of maize products.

Role of zein incorporation on hydrophobic drug-loading capacity and colloidal stability of phospholipid nanoparticles

Liposome, phosphatidylcholine nanoparticle (PC-NP), is an attractive colloidal carrier of hydrophobic drugs but its clinical development is often limited by low drug-loading capacity and the physical instability. Zein is a water-insoluble amphiphilic protein obtained from the corn. We herein investigated a possibility to develop zein-phosphatidylcholine hybrid nanoparticle (Z/PC-NP) as an advanced hydrophobic drug carrier. By employing the conventional liposome preparation method with the addition of zein, Z/PC-NP were produced. The extent of zein incorporation in PC-NP was affected by PC composition. DSC demonstrated the lowered phase transition temperature of PC by zein and FTIR showed the appearance of weakened but clear amide bonds of zein as well as increased levels of heterogeneous hydrogen bonding of Z/PC-NP compared to PC-NP. DLS, TEM and cryo-TEM studies suggested Z/PC-NP to be spherical nanoparticles composed of a zein core and a zein-PC hybrid shell. Z/PC-NP exhibited a higher loading capacity for hydrophobic model drugs (paclitaxel, docetaxel, celecoxib and curcumin), than did the zein nanoparticle and PC-NP, while exhibiting an intermediate drug release rate. The serum stability and the storage stability of Z/PC-NP were greater than those of PC-NP. Zein functioned as a cryoprotectant of PC-NP during freeze-drying. Z/PC-NP may provide a promising nanoparticle carrier of hydrophobic drugs.

One-step formation of a double Pickering emulsion via modulation of the oil phase composition

A facile one-step emulsification strategy was developed to generate a food-grade W/O/W double Pickering emulsion by using corn-peptide-functionalized calcium phosphate particles (CP-CaP) as emulsifier.

Pickering Emulsion Gels Prepared by Hydrogen-Bonded Zein/Tannic Acid Complex Colloidal Particles

Food-grade colloidal particles and complexes, which are formed via modulation of the noncovalent interactions between macromolecules and natural small molecules, can be developed as novel functional ingredients in a safe and sustainable way. For this study was prepared a novel zein/tannic acid (TA) complex colloidal particle (ZTP) based on the hydrogen-bonding interaction between zein and TA in aqueous ethanol solution by using a simple antisolvent approach. Pickering emulsion gels with high oil volume fraction (φ(oil) > 50%) were successfully fabricated via one-step homogenization. Circular dichroism (CD) and small-angle X-ray scattering (SAXS) measurements, which were used to characterize the structure of zein/TA complexes in ethanol solution, clearly showed that TA binding generated a conformational change of zein without altering their supramolecular structure at pH 5.0 and intermediate TA concentrations. Consequently, the resultant ZTP had tuned near neutral wettability (θ(ow) ∼ 86°) and enhanced interfacial reactivity, but without significantly decreased surface charge. These allowed the ZTP to stabilize the oil droplets and further triggered cross-linking to form a continuous network among and around the oil droplets and protein particles, leading to the formation of stable Pickering emulsion gels. Layer-by-layer (LbL) interfacial architecture on the oil-water surface of the droplets was observed, which implied a possibility to fabricate hierarchical interface microstructure via modulation of the noncovalent interaction between hydrophobic protein and natural polyphenol.

Fabrication and characterization of electrospun zein/Ag nanocomposite mats for wound dressing applications

Wound dressing is a very important factor in the process of wound healing as proper wound care can accelerate the recovery of the wound. In this study, zein nanofibrous mats with fiber diameters around 350-500 nm were prepared by electrospinning and silver (Ag) nanoparticles around 20 nm were concurrently synthesized in situ into the mats. The electrospun nanofibers were characterized by Field Emission-Scanning Electron Microscopy (FE-SEM), Transmission Electron Microscopy (TEM), Fourier Transform Infrared Spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analysis. Cell viability and activity of fibroblasts cells in zein/Ag mats were also evaluated and results demonstrated good cytocompatibility and attachment of cells on the composite nanofibers. Also, the bactericidal activity of the fabricated mats against gram-positive Staphylococcus aureus (S. aureus) and gram-negative Escherichia coli (E. coli) was investigated via zone of inhibition test and results showed high anti-bacterial performance.

Formation and Mechanism of Superhydrophobic/Hydrophobic Surfaces Made from Amphiphiles through Droplet-Mediated Evaporation-Induced Self-Assembly

Superhydrophobic/hydrophobic surfaces have attracted wide attention because of their broad applications in various regions, including coating, textile, packaging, electronic devices, and bioengineering. Many studies have been focused on the fabrication of superhydrophobic/hydrophobic surfaces using natural materials. In this paper, superhydrophobic/hydrophobic surfaces were formed by an amphiphilic natural protein, zein, using electrospinning. Water contact angle (WCA) and scanning electron microscopy (SEM) were used to characterize the hydrophobicity and surface morphology of the electrospun structures. The highest WCA of the zein electrospun surfaces could reach 155.5 ± 1.4°. To further understand the mechanism of superhydrophobic surface formation from amphiphiles using electrospinning, a synthetic amphiphilic polymer was selected, and also, a method similar to electrospinning, spray drying, was tried. The electrospun amphiphilic polymer surface showed a high hydrophobicity with a WCA of 141.4 ± 0.7°. WCA of the spray-dried zein surface could reach 125.3 ± 2.1°. The secondary structures of the zein in the electrospun film and cast-dried film were studied using ATR-FTIR, showing that α-helix to β-sheet transformation happened during the solvent evaporation in the cast drying process but not in the electrospinning process. A formation mechanism was proposed on the basis of the orientation of the amphiphiles during the solvent evaporation of different fabrication methods. The droplet-based or jet-based evaporation during electrospinning and spray drying led to the formation of the superhydrophobic/hydrophobic surface by the accumulation of the hydrophobic groups of the amphiphiles on the surface, while the surface-based evaporation during cast drying led to the formation of the hydrophilic surface by the accumulation of the hydrophilic groups of the amphiphiles on the surface.

Electrospun antibacterial polyurethane-cellulose acetate-zein composite mats for wound dressing

In this study, an antibacterial electrospun nanofibrous scaffolds with diameters around 400-700 nm were prepared by physically blending polyurethane (PU) with two biopolymers such as cellulose acetate (CA) and zein. Here, PU was used as the foundation polymer, was blended with CA and zein to achieve desirable properties such as better hydrophilicity, excellent cell attachment, proliferation and blood clotting ability. To prevent common clinical infections, an antimicrobial agent, streptomycin sulfate was incorporated into the electrospun fibers and its antimicrobial ability against the gram negative and gram positive bacteria were examined. The interaction between fibroblasts and the PU-CA and PU-CA-zein-drug scaffolds such as viability, proliferation, and attachment were characterized. PU-CA-zein-drug composite nanoscaffold showed enhanced blood clotting ability in comparison with pristine PU nanofibers. The presence of CA and zein in the nanofiber membrane improved its hydrophilicity, bioactivity and created a moist environment for the wound, which can accelerate wound recovery.

Propriedades mecânicas e molhabilidade de filmes de zeínas extraídas de glúten de milho

Zeínas são proteínas de reserva do milho (prolaminas), que podem ser extraídas através de solubilização em meio alcoólico. Essas proteínas são altamente hidrofóbicas, com elevado grau de polimerização. Neste estudo, zeínas do tipo a (massa molecular entre 10 e 22 kDa) foram extraídas do glúten do milho e caracterizadas com respeito às suas principais bandas de absorção espectroscópica na região do infravermelho. Blendas de zeínas com ácido oléico (AO) como plastificante foram avaliadas em diversas proporções e filmes processados por casting sobre superfície apolar. Filmes de zeínas sem plastificante mostraram-se inviáveis para manipulação e medidas, mas a adição de 1 e 2% em massa de AO proporcionou um significativo aumento do módulo de elasticidade, segundo análise realizada por DMA. A presença de plastificante introduz também irregularidades superficiais e leva a uma perda das características hidrofóbicas dessas proteínas.

Engineering zein films with controlled surface morphology and hydrophilicity

A new method to engineer zein films with controlled surface morphology and hydrophilicity has been developed. The resulting surface morphology and surface hydrophilicity have been studied by tapping mode atomic force microscopy (TP-AFM) and a combination of water contact angle measurements and X-ray photoelectron spectroscopy (XPS), respectively. Our AFM results revealed that zein films cast from acetic acid showed much smoother surfaces as compared to those cast from ethanol aqueous solutions. Furthermore, zein films of controlled hydrophilicity have been engineered through the use of UV/ozone treatment, which can efficiently decrease the water contact angles of zein films from approximately 80 degrees to less than 10 degrees within 130 s. XPS results suggest that the difference in surface hydrophilicity of zein films is due to the difference in surface elemental composition, and UV/ozone treatment converted some of the surface methyl groups mainly to carbonyl groups, therefore decreasing the water contact angles and increasing the surface hydrophilicity of zein films. This research opens up new opportunities of using zein as barrier materials and delivery vehicles for functional food ingredients, drugs, and dietary supplements.

Cloning and structural analysis of an Indian little millet (Panicum sumatrense) zein-like storage protein: implications for molecular assembly

Zeins are prolamin storage proteins that accumulate in kernel endosperm of several cereals. For cloning of genes coding for zein-like proteins that accumulate in enhanced quantities in the filling stages of little millet (Panicum sumatrense Roth.) developing grains, RT-PCR was performed using specific primers. A 750-bp cDNA was directly sequenced and in silico analysis showed high identity degree to alpha-prolamins. This family is composed of zeins from Zea mays, coixins from Coix lachryma-jobi, and alpha-kafirins from Sorghum bicolor. The putative conserved domain of zein-like proteins was identified by primary structure comparisons. Furthermore, threading analyses indicated that the millet zein-like protein forms an anti-parallel alpha-helical hairpin with two opposite surfaces: one hydrophobic and the other hydrophilic that probably could be involved in protein storage assembly. Knowledge about zein-like alpha-prolamins in little millet will lead to cloning and transfer of this gene to other major food crops, such as cereals and legumes, with inferior nutritional quality for monogastric animals.

Effect of temperature and pH on the secondary structure and processes of oligomerization of 19 kDa alpha-zein

Highly hydrophobic protein Z19 zein shows a tendency towards oligomerization. The role of temperature and pH on the oligomerization process was studied monitoring the secondary structure content and the appearance of aggregates by Circular Dichroism Spectroscopy (CD) and Dinamic Light Scattering (DLS). Z19 zein suffers irreversible thermal denaturalization, as demonstrated by far-UV CD measurements. DLS data indicate that this denaturalization is accompanied by oligomerization processes which are strongly dependent on temperature. The aggregates that appear when the sample is heated maintain a certain amount of their native structure. Oligomers, showing high stability to temperature changes and other denaturing conditions with molecular weights of 45, 66 kDa and higher, were detected by SDS-PAGE. The secondary structure strongly depends on pH. Thus, at pH above pI (6.8), all the protein structure is in alpha helix. The formation of disulfide bonds plays an important role in the aggregation process, since most of the sulfhydryls in the protein (97.52%) form disulfide bonds and only 2.47% of them are free and superficially exposed. The sensitivity towards thermal denaturalization is also affected by pH rises.

Structural characterization of alpha-zein

A variety of published physical measurements, computational algorithms, and structural modeling methods have been used to create a molecular model of 19 kDa alpha-zein (Z19). Zetaeins are water-insoluble storage proteins found in corn protein bodies. Analyses of the protein sequence using probability algorithms, structural studies by circular dichroism, infrared spectroscopy, small-angle X-ray scattering (SAXS), light scattering, proton exchange, NMR, and optical rotatory dispersion experiments suggest that Z19 has approximately 35-60% helical character, made up of nine helical segments of about 20 amino acids with glutamine-rich "turns" or "loops". SAXS and light-scattering experiments suggest that in alcohol/water mixtures alpha-zein exists as an oblong structure with an axial ratio of approximately 6:1. Furthermore, ultracentifugation, birefringence, dielectric, and viscosity studies indicate that alpha-zein behaves as an asymmetric particle with an axial ratio of from 7:1 to 28:1. Published models of alpha-zein to date have not been consistent with the experimental data, and for this reason the structure was re-examined using molecular mechanics and dynamics simulations creating a new three-dimensional (3D) structure for Z19. From the amino acid sequence and probability algorithms this analysis suggested that alpha-zein has coiled-coil tendencies resulting in alpha-helices with about four residues per turn in the central helical sections with the nonpolar residue side chains forming a hydrophobic face inside a triple superhelix. The nine helical segments of the 19 kDa protein were modeled into three sets of three interacting coiled-coil helices with segments positioned end to end. The resulting structure lengthens with the addition of the N- and C-terminal sections, to give an axial ratio of approximately 6 or 7:1 in agreement with recent experiments. The natural carotenoid, lutein, is found to fit into the core of the triple-helical segments and help stabilize the configuration. Molecular dynamics simulations with explicit methanol/water molecules as solvent have been carried out to refine the 3D structure.

Effects of Processing on the Structure of Zein/Oleic Acid Films Investigated by X-Ray Diffraction

Zein films plasticized with oleic acid were formed by solution casting, by the stretching of moldable resins, and by blown film extrusion. The effects of the forming process on film structure were investigated by X-ray diffraction. Wide-angle X-ray scattering (WAXS) patterns showed d-spacings at 4.5 and 10 A, which were attributed to the zein alpha-helix backbone and inter-helix packing, respectively. The 4.5 A d-spacing remained stable under processing while the 10 A d-spacing varied with processing treatment. Small-angle X-ray scattering (SAXS) detected a long-range periodicity for the formed films but not for unprocessed zein, which suggests that the forming process-promoted film structure development is possibly aided by oleic acid. The SAXS d-spacing varied among the samples (130-238 A) according to zein origin and film-forming method. X-ray scattering data suggest that the zein molecular structure resists processing but the zein supramolecular arrangements in the formed films are dependent on processing methods. Structural model for a zein molecular aggregate (based on Matsushima et al.10). Rectangular prisms of individual zein molecules are hexagonally aligned parallel to each other.

Characterization of a 19 kDa alpha-zein of high purity

A highly pure alpha-zein was extracted from corn flour using ethanol (95%). Subsequently, ion-exchange chromatography was performed, using SP-Sepharose that yielded a highly homogeneous protein. This protein migrated as a single band in 20% SDS-PAGE and in pH gradient gels, showing an isoelectric point of 6.8. Mass spectrometry (MALDI-TOF-MS) showed a single peak with a molecular mass of 24 535 Da. It was identified as Z19, when comparing the sequence obtained in an automatic Edman sequencer with the Swissprot database using BLAST. The molar extinction coefficient, determined by dry weight in 70% methanol, was 12 415.49 M(-1) cm(-1) at 280 nm. Light scattering showed its presence in a monodispersed state of 44-66 kDa aggregates in methanol (70%). Circular dichroism spectra allowed the estimation of an alpha-helix content that was lower than the one found for a mixture of two alpha-zeins but with a higher content of beta sheets.

Interaction of Two Prolamins with 1-13C Oleic Acid by 13C NMR

In this paper, we analyzed the interaction of Z19 prolamin from a BR451 maize variety and pennisetin from a BRS1501 pearl millet variety with 1-(13)C-enriched oleic acid (OA) by (13)C NMR in solution. In both proteins, we identified the presence of free fatty acids by NMR in solid state and solution. The interactions were analyzed at the protein/OA molar ratios of 1:1 and 1:4. In the Z19/OA 1:1 mixture in 70% ethanol and 30% D(2)O, the chemical shift of OA C1 was 182.9 ppm, about 3 ppm above that of the pure OA in the same solvent. In contrast, upon addition of OA to the pennisetin (1:1), the chemical-shift value slightly decreased by less than 1 ppm. The chemical-shift titration curve of OA C1 in an apparent pH range of 5.5-7.3 shifted by approximately 0.3 pH units toward higher pH values in the pennisetin/OA 1:1 complex relative to the pure OA. The results obtained for the pennisetin/OA 1:4 mixture were similar to the complexes at a 1:1 molar ratio. A significant difference was observed between the 1:1 and 1:4 curves for Z19. The titration curve for Z19/OA 1:1 suggested specific binding at the sites with electrostatic interaction.