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Although apoferritin has been widely utilized as a new class of natural protein nanovehicles for encapsulation and delivery of nutraceuticals, its ability to remove metal heavy ions has yet to be explored. In this study, for the first time, we demonstrated that the ferritin from kuruma prawns (Marsupenaeus japonicus), named MjF, has a pronouncedly larger ability to resist denaturation induced by Cd2+ and Hg2+ as compared to its analogue, human H-chain ferritin (HuHF), despite the fact that these two proteins share a high similarity in protein structure. Treatment of HuHF with Cd2+ or Hg2+ at a metal ion/protein shell ratio of 100/1 resulted in marked protein aggregation, while the MjF solution was kept constantly clear upon treatment with Cd2+ and Hg2+ at different protein shell/metal ion ratios (50/1, 100/1, 250/1, 500/1, 1000/1, and 2500/1). Structural comparison analyses in conjunction with the newly solved crystal structure of the complex of MjF plus Cd2+ or Hg2+ revealed that cysteine (Cys) is a major residue responsible for such binding, and that the large difference in the ability to resist denaturation induced by these two heavy metal ions between MjF and HuHF is mainly derived from the different positions of Cys residues in these two proteins; namely, Cys residues in HuHF are located on the outer surface, while Cys residues from MjF are buried within the protein shell. All of these findings raise the high possibility that prawn ferritin, as a food-derived protein, could be developed into a novel bio-template to remove heavy metal ions from contaminated food systems. [ABSTRACT FROM AUTHOR]

Dried abalones are precious products, in which candy abalone is the most treasured one, owing to its unique taste. After rehydration and simmering, the core part tastes extraordinarily tender and viscoelastic, just like a soft candy which may almost melt in mouth. However, the reason for this has yet to be elucidated. The purpose of this study is to research the formation mechanism of the candy-like core in candy abalone. First of all, we characterized the viscoelasticity, microstructure and protein changes of candy abalone during the simmering process. The texture results indicated that the springiness and adhesiveness of candy abalone showed an increase. Scanning and transmission electron microscopy suggested that myofibrillar protein in candy abalone formed a dense three-dimensional network hydrogel structure. Sodium dodecyl sulfate–polyacrylamide gel electrophoresis revealed such a hydrogel structure might be derived from the degradation of the myofibrillar protein during the drying process. Also, we identified degraded peptides mainly stemmed from paramyosin by mass spectrometry. Moreover, molecular dynamics simulation revealed that the hydrogen bonds and hydrophobic interactions are mainly responsible for the self-assembly of peptides during the rehydration and simmering stages. Different from reported protein hydrogels, the rheological and morphological properties of the formed peptide hydrogels in candy abalone have significant changes. In this study, we found that the myofibrillar protein of fresh abalone degraded into peptides during the drying process, which further cross-linked to form a peptide hydrogel during the rehydration and simmering stages, thereby producing a unique viscoelastic candy-like core in candy abalone. [ABSTRACT FROM AUTHOR]

Background: Protein nanocages have emerged as popular nanocarriers for either drug delivery or biotemplates for the preparation of nanomaterials. However, only three interfaces, namely exterior surface, intersubunit and inner cavity, have been used as reaction sites for the above purposes with all known protein nanocages. On the other hand, how to control the site of Au NCs formed within a targeted protein template while maintaining the functionality of protein itself remains challenging. Results: In this work, inspired by compartmentalization in living systems, we firstly come up with the conception of "intrasubunit interfaces", located within subunit of protein nanocage. We built a new, specific compartment for fabrication of gold nanoclusters by genetic modification of the inherent ferroxidase center located within four-α-helix bundle of each ferritin subunit. This newly built compartment not only realizes the site-directed synthesis of gold nanoclusters but also has no effect on the functionality of ferritin itself such as encapsulation by its inner cavity. These redesigned composites can be further applied as fluorescent imaging agent and carriers for preparation of hybrid nanomaterials. Conclusions: The designing strategy of intrasubunit interfaces opens a new way for future applications of cage-like proteins. [ABSTRACT FROM AUTHOR]

Protein lattices that shift the structure and shape anisotropy in response to environmental cues are closely coupled to potential functionality. However, to design and construct shape‐anisotropic protein arrays from the same building blocks in response to different external stimuli remains challenging. Here, by a combination of the multiple, symmetric interaction sites on the outer surface of protein nanocages and the tunable features of phenylalanine‐phenylalanine interactions, a protein engineering approach is reported to construct a variety of superstructures with shape anisotropy, including 3D cubic, 2D hexagonal layered, and 1D rod‐like crystalline protein nanocage arrays by using one single protein building block. Notably, the assembly of these crystalline protein arrays is reversible, which can be tuned by external stimuli (pH and ionic strength). The anisotropic morphologies of the fabricated macroscopic crystals can be correlated with the Å‐to‐nm scale protein arrangement details by crystallographic elucidation. These results enhance the understanding of the freedom offered by an object's symmetry and inter‐object π−π stacking interactions for protein building blocks to assemble into direction‐ and shape‐anisotropic biomaterials. [ABSTRACT FROM AUTHOR]

The artificial photoreduction of CO 2 into fuels with precious metal-based photosensitizers such as Ru, Re, and Ir represents a potential way to minimize global warming caused by the growing concentration of CO 2 , but these noble metal-based photosensitizers present unsustainable and negative environmental impact issues, thereby limiting their applications. Herein, bioinspired by the inherent ability of Escherichia coli ferritin (EcBFR) to bind to hemin, we constructed a photocatalytic-CO 2 -conversion platform by using a single shell-like EcBFR molecule where up to 12 of hemin molecules can be incorporated into its intersubunit interfaces as photosensitizers, while the semiconductor photocatalysts nanoferrihydrites are catalytically synthesized and encapsulated within the protein inner cavity. Consequently, the constructed platform can selectively, effectively reduce CO 2 to formic acid with 1-benzyl-1,4-dihydronicotinamide (BNAH) as the electron donor in aqueous solution under mild conditions. To improve the recyclability of the above platform, we designed a three-dimensional (3D) protein crystalline framework with the above constructed hybrid molecules as building blocks through π-π interactions. Notably, such protein framework enables the recyclability to be improved up to at least 5 cycles as compared to the individual protein nanocage. All these findings pave the way for CO 2 photoreduction by naturally occurring heme as the photosensitizer in an environmentally friendly manner. [Display omitted] • Escherichia coli ferritin (EcBFR) was explored as a CO 2 photocatalytic platform. • The photosensitizer hemin and biocatalyst ferrihydrite were integrated into a single protein nanocage for CO 2 photocatalysis. • The constructed photocatalytic platform selectively reduced CO 2 to formic acid. • Designed 3D protein crystalline frameworks facilitate high recyclability. [ABSTRACT FROM AUTHOR]

• Protein hydrogel was constructed with native paramyosin and natural crosslinkers. • PM hydrogels show an injectable and reversible characteristic. • PM gelation trigged by different crosslinkers show various rheological properties. • C3G photostability improved upon its encapsulation within the PM hydrogel. • PM hydrogels could effectively expedite wound healing of the skin in mice. Protein hydrogels with multifunction including tunable mechanical property, sustained drug release and excellent biocompatibility have shown considerable promise in biological applications. However, these hydrogels are usually generated using denatured or modified protein molecules, it remains challenging to construct injectable hydrogel based on native protein as building blocks. Here, a native nanofibrous protein, paramyosin (PM) was utilized as building blocks to create hydrogels under mild conditions, taking advantage of Zn2+-mediated metal coordination with His-Glu motifs located on the exterior surface of the protein. The bioactive substance cyanidin-3- O -galactoside was shielded from light-induced degradation by being enclosed in the native PM hydrogels. Moreover, the rheological property and biological activity of construction PM hydrogels were improved through noncovalent interactions with natural polyphenols, such as proanthocyanidins. Importantly, all of these manufactured native hydrogels endow good biocompatibility, reversible sol–gel transforming behavior, great stability, and considerably speed up the healing of wounds in mice with skin injuries. Overall, these hydrogels derived from natural protein not only demonstrates beneficial qualities that are very effective in encouraging wound healing, but also offers a straightforward and repeatable gelation approach to produce protein hydrogel employed in biomedical applications. [ABSTRACT FROM AUTHOR]

Histidine (His) residues represent versatile motifs for designing protein-protein interactions because the protonation state of the imidazole group of His is the only moiety in protein to be significantly pH dependent under physiological conditions. Here we show that, by the designed His motifs nearby the C4 axes, ferritin nanocages arrange in crystals with a simple cubic stacking pattern. The X-ray crystal structures obtained at pH 4.0, 7.0, and 9.0 in conjunction with thermostability analyses reveal the strength of the π–π interactions between two adjacent protein nanocages can be fine-tuned by pH. By using the crystal structural information as a guide, we constructed 3D protein frameworks in solution by a combination of the relatively weak His–His interaction and Ni2+-participated metal coordination with Glu residues from two adjacent protein nanocages. These findings open up a new way of organizing protein building blocks into 3D protein crystalline frameworks. Controlling protein–protein interactions through non-covalent bonding is desirable for the assembly of protein arrays. Here the authors demonstrate that pH-tunable π–π stacking interactions between Histidine motifs can direct the assembly of 3D protein arrays. [ABSTRACT FROM AUTHOR]