Inhibition of In Vitro Amylolysis of Wheat Starch by Gluten Peptides.

The effect of gluten peptides (GPs) isolated from a gluten proteolysate on in vitro amylolysis of gelatinized wheat starch was investigated. GPs in a pepsin hydrolysate were fractionated into fractions with molecular weights (MWs) of 500-3000, 3500-7000, 10-17, and 35-48 kDa. The fractions containing peptides with MW > 10 kDa had a strong inhibitory effect on enzyme activity and amylolysis of starch, whereas GPs with MW <10 kDa had no inhibitory effect. Binding constants estimated by surface plasmon resonance showed that peptides in the fractions with MW > 10 kDa bound more strongly to α-amylase, in contrast to peptides of MW <10 kDa. Significant correlations were observed between digestion parameters and equilibrium binding affinity. We conclude that peptides with MW >10 kDa in a pepsin digest of gluten have a strong inhibitory effect on in vitro enzymatic hydrolysis of starch due to their strong binding affinity to α-amylase.

Peptidomics comparison of plant-based meat alternatives and processed meat after in vitro digestion.

Plant-based meat alternatives (PMAs) is a new type of food that meets people's health needs, but the lack of awareness of its nutritional properties limits product development and promotion. Here, we compared the similarities and differences of the nutritional properties of PMAs and meat before and after in vitro simulation of gastrointestinal digestion by chemical composition analysis, peptidomics and bioactivity tests. The molecular weights of Plant-based meat alternatives derived peptides (PDPs) as well as meat-derived peptides (MDPs) in the beef and pork groups were mainly concentrated in the low mass range from 800 Da to 1500 Da. The principal component analysis indicated that the composition of MDPs in the beef and pork groups significantly differed from PDPs but overlapped slightly with the chicken group. Also, there were very few common peptides among them. The proportion of high-biological-scoring peptides (33.3%-40%) in PDPs was more than that in MDPs (4.8%-20.8%). PDPs were predicted to have higher antibacterial activity than others. PDPs and MDPs showed a certain antioxidant capacity and angiotensin converting enzyme inhibitory activity (62.2%-92.5%) in vitro. Some peptides weakly inhibited the growth of Escherichia coli (ATCC 25922) and Staphylococcus aureus (ATCC 25923) while promoting the growth of probiotics. This research provides a theoretical basis for in-depth exploration of the nutritional characteristics of PMAs.

His-Mediated Reversible Self-Assembly of Ferritin Nanocages through Two Different Switches for Encapsulation of Cargo Molecules.

Protein nanocages represent a class of nanovehicles for a variety of applications. However, precise manipulation of self-assembly behavior of these protein nanocages in response to multiple external stimuli for custom-tailored applications remains challenging. Herein, we established a simple but effective strategy for controlling protein nanocage self-assembly that combines a dual property of His motifs (their significantly pH-dependent protonation state and their capacity to coordinate with transition metals) with its high symmetry. With this strategy, we enabled two different ferritin nanocages to disassemble into protein tetramers under neutral solution by introducing His6 motifs at the 4-fold channel interfaces. Notably, these tetramers are able to self-assemble into ferritin-like protein nanocages in response to multiple external stimuli such as transition metal ions and pH, and vice versa, indicative of a reversible self-assembly process. Furthermore, such His-mediated reversible protein self-assembly has been explored for encapsulation of bioactive cargo molecules within these reconstituted protein nanocages with higher loading efficiency under milder conditions as compared to the reported acid denaturation encapsulation method for ferritin.

Converting histidine-induced 3D protein arrays in crystals into their 3D analogues in solution by metal coordination cross-linking.

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.

Structural Insight into Binary Protein Metal-Organic Frameworks with Ferritin Nanocages as Linkers and Nickel Clusters as Nodes.

Metal-organic frameworks (MOFs) hold great promise for numerous applications. However, proteins, carriers of biological functions in living systems, have not yet been fully explored as building blocks for the construction of MOFs. This work presents a strategy for the fabrication of binary MOFs. Considering octahedral ferritin symmetry, four His2 (His-His) motifs were first incorporated into the exterior surface of a ferritin nanocage near each C4 channel, yielding protein linkers with multiple metal-binding sites (bisH-SF). Secondly, by adding nickel ions to bisH-SF solutions triggers the self-assembly of ferritin nanocages into a porous 3D crystalline MOF with designed protein lattice, where two adjacent ferritin molecules along the C4 symmetry axes are bridged by four dinuclear or tetranuclear nickel clusters depending on Ni2+ concentration. This work provides a simple approach for precise control over a binary protein-metal crystalline framework, and the resulting MOFs exhibited inherent ferroxidase activity and peroxidase-like catalytic activity.

Improvement of butanol production by the development and co-culture of C. acetobutylicum TSH1 and B. cereus TSH2.

Butanol fermentation comprises two successive and distinct stages, namely acidogenesis and solventogenesis. The current lack of clarity regarding the underlying metabolic regulation of fermentation impedes improvements in biobutanol production. Here, a proteomics study was performed in the acidogenesis phase, the lowest pH point (transition point), and the solventogenesis phase in the butanol-producing symbiotic system TSH06. Forty-two Clostridium acetobutylicum proteins demonstrated differential expression levels at different stages. The protein level of butanol dehydrogenase increased in the solventogenesis phase, which was in accordance with the trend of butanol concentration. Stress proteins were upregulated either at the transition point or in the solventogenesis phase. The cell division-related protein Maf was upregulated at the transition point. We disrupted the maf gene in C. acetobutylicum TSH1, and Bacillus cereus TSH2 was added to form a new symbiotic system. TSH06△maf produced 13.9 ± 1.0 g/L butanol, which was higher than that of TSH06 (12.3 ± 0.9 g/L). Butanol was furtherly improved in fermentation at variable temperature with neutral red addition for both TSH06 and TSH06△maf. The butanol titer of the maf deletion strain was higher than that of the wild type, although the exact mechanism remains to be determined.

ARTP mutation and genome shuffling of ABE fermentation symbiotic system for improvement of butanol production.

Butanol is an ideal renewable biofuel which possesses superior fuel properties. Previously, butanol-producing symbiotic system TSH06 was isolated in our lab, with microoxygen tolerance ability. To boost butanol yield for large-scale industrial production, TSH06 was used as parental strain and subjected to atmospheric and room temperature plasma (ARTP) and four rounds of genome shuffling (GS). ARTP mutant and GS strain were co-cultured with facultative anaerobic Bacillus cereus TSH2 to form a symbiotic system with microoxygen tolerance, which was then subjected to fermentation. Relative messenger RNA (mRNA) level of key enzyme gene was measured by real-time PCR. The highest butanol titer of TS4-30 reached 15.63 g/L, which was 34% higher than TSH06 (12.19 g/L). Compared with parental strain, mRNA of acid-forming gene in TS4-30 decreased in acidogenesis phase, while solvent-forming gene increased in solventogenesis phase. This gene expression pattern was consistent with high butanol yield and low acid level in TS4-30. In summary, symbiotic system TS4-30 was obtained with butanol titer improvement and microoxygen tolerance.

Interactions between Bacillus cereus CGMCC 1.895 and Clostridium beijerinckii NCIMB 8052 in coculture for butanol production under nonanaerobic conditions.

Low oxygen tolerance and substrate restriction continues to hamper the process of biobutanol industrialization. In this work, butanol fermentation with cocultures of Bacillus cereus China General Microbiological Culture Collection Center (CGMCC) 1.895 and Clostridium beijerinckii NCIMB 8052 under nonanaerobic conditions was investigated, and the interactions between these two strains were examined. The addition of B. cereus CGMCC 1.895 resulted in higher oxygen tolerance and a wider range of substrate utilization, compared with the pure culture of C. beijerinckii NCIMB 8052. Butanol concentration reached 10.49 g/L with an optimized inoculation size of 90% under nonanaerobic conditions, and this concentration was close to that of pure C. beijerinckii NCIMB 8052 culture under anaerobic conditions. Dynamic relative abundance analysis demonstrated that the ratio of C. beijerinckii NCIMB 8052 accounted for nearly 99% of the cocultured cells. Furthermore, the substrate utilization range was expanded, allowing the use of corn mash for butanol production. The final concentration of butanol and total solvents was 6.78 and 10.52 g/L, respectively. Coculture also was performed successfully in a 5-L fermenter and 8.75 g/L butanol was obtained. Dynamic dissolved oxygen analysis demonstrated that B. cereus consumed the dissolved oxygen in the broth and resulted in the anaerobic condition for C. beijerinckii.

Isolation and characterisation of non-anaerobic butanol-producing symbiotic system TSH06.

Butanol-producing microorganisms are all obligate anaerobes. In this study, a unique symbiotic system TSH06 was isolated to be capable of producing butanol under non-anaerobic condition. Denaturing gradient gel electrophoresis (DGGE) analysis of 16S ribosomal RNA (rRNA) revealed that two strains coexist in TSH06. The two strains were identical to Clostridium acetobutylicum and Bacillus cereus, respectively. They were isolated individually and named as C. acetobutylicum TSH1 and B. cereus TSH2. C. acetobutylicum TSH1 is a butanol-producing, obligate anaerobic strain. Facultative anaerobic B. cereus TSH2 did not possess the ability of butanol production; however, it offered C. acetobutylicum TSH1 the viability under non-anaerobic condition. Moreover, B. cereus TSH2 enhanced butanol yield and speed of fermentation. TSH06 produced 12.97 g/L butanol and 15.39 g/L total solvent under non-anaerobic condition, which is 25 and 24 %, respectively, higher than those of C. acetobutylicum TSH1. In addition, TSH06 produced butanol faster under non-anaerobic condition than under anaerobic condition. Butanol accounted for more than 80 % of total solvent, which is higher than the known report. TSH06 was stable during passage. In all, TSH06 is a promising candidate for industrialisation of biobutanol with high yield, high butanol proportion, easy-handling and time-saving system. These results demonstrated the potential advantage of symbiosis. This study also provides a promising strategy for butanol fermentation.