Seasonal spermatogenesis, epididymal storage, and creatine kinase expression in Pelodiscus sinensis.

The soft-shelled turtle, Pelodiscus sinensis, is an important economic aquaculture species. Its reproduction exhibits seasonality; however, there is a lack of systematic studies focused on sperm maturation and epididymal storage. The testes and epididymides of P. sinensis were sampled from March to December. The seasonal reproduction and maturation of the spermatozoa were examined by anatomy, hematoxylin and eosin staining, AB-PAS staining, and immunohistochemistry. Spermatogenesis exhibited obvious seasonality in P. sinensis. It was found that the spermatogenic epithelium was most active during June to September, whereas the diameter of the epididymal tubules was smallest during June to October. As key enzymes of ATP metabolism, creatine kinases were highly expressed in the epididymal tubule epithelium during the breeding season, which may be important for the regulation of sperm maturation. In addition, the epididymal tubule epithelium changed with the season in June to September, the epididymal tubule epithelium proliferated to form villous structures, and secreted a large number of glycoproteins, which may be related to the rapid maturation of sperm during the breeding season. In conclusion, this study provided insights into the spermatogenesis of P. sinensis through histological analysis and enriched our understanding of reproduction in reptiles.

Body mass index and outcomes of patients with cardiogenic shock: A systematic review and meta-analysis.

BACKGROUND: Cardiogenic shock continues to be a highly morbid complication that affects around 7%-10% of patients with acute myocardial infarction or heart failure. Similarly, obesity has become a worldwide epidemic. AIM: To analyze the impact of higher body mass index (BMI) on outcomes of patients with cardiogenic shock. METHODS: A systematic and comprehensive search was undertaken on the electronic databases of PubMed, Embase, ScienceDirect, CENTRAL, and Google Scholar for all types of studies comparing mortality outcomes of patients with cardiogenic shock based on BMI. All studies defined overweight or obese patients based on the World Health Organization BMI criteria. The data were then extracted and assessed on the basis of the Reference Citation Analysis (https://www.referencecitationanalysis.com/). RESULTS: Five studies were included. On pooled analysis of multivariable-adjusted ratios, we noted a statistically significantly reduced risk of mortality in overweight/obese vs normal patients (three studies; odds ratio [OR] = 0.92, 95% confidence interval [CI]: 0.85-0.98, I 2 = 85%). On meta-analysis, we noted that crude mortality rates did not significantly differ between overweight/obese and normal patients after cardiogenic shock (OR = 0.95, 95%CI: 0.79-1.15, I 2 = 99%). The results were not stable on sensitivity analysis and were associated with substantial heterogeneity. CONCLUSION: Current evidence on the association between overweight/obesity and mortality after cardiogenic shock is scarce and conflicting. The obesity paradox might exist in patients with cardiogenic shock but could be confounded by the use of mechanical circulatory support. There is a need for further studies to clarify this relationship.

A study of Pb2+ induced unfolding and aggregation of arginine kinase from Euphausia superba: kinetics and computational simulation integrating study.

Arginine kinase is a crucial phosphagen kinase in invertebrates, which is associated to the environmental stress response, plays a key role in cellular energy metabolism. In this study, we investigated the Pb2+-induced inhibition and aggregation of Euphausia superba arginine kinase (ESAK) and found that significantly inactivated ESAK in a dose-dependent manner (IC50 = 0.058 ± 0.002 mM). Spectrofluorimetry results showed that Pb2+ induced tertiary structural changes via the internal polarity increased and the non-polarity decreased in ESAK and directly induced ESAK aggregation. The ESAK aggregation process induced by Pb2+ occurred with multi-phase kinetics. The addition of osmolytes did not show protective effect on Pb2+-induced inactivation of ESAK. The computational molecular dynamics (MD) simulation showed that three Pb2+ interrupt the entrance of the active site of ESAK and it could be the reason on the loss of activity of ESAK. Several important residues of ESAK were detected that were importantly contributed the conformation and catalytic function of ESAK. Our study showed that Pb2+-induced misfolding of ESAK and the complete loss of activity irreversibly, which cannot be recovered by osmolytes.Communicated by Ramaswamy H. Sarma.

Seasonal expression of cytoplasmic creatine kinase in the epididymal epithelium of Pelodiscus sinensis.

During hibernation of Pelodiscus sinensis, sperm mature and are stored in the epididymis. We investigated seasonal changes in the morphology of epithelial cells of the epididymis of P. sinensis and changes in expression of cytoplasmic creatine kinase (CK). We found that the epididymal epithelium proliferates rapidly to form multiple layers from June to September, while the epididymal epithelial cells are arranged in a single layer from October to May. From the March before the mating period to the end of the mating period in September, a large amount of neutral glycoprotein is secreted in the epididymal epithelium and in the sperm aggregation area; after October, the glycoprotein in the epididymis decreases. At sperm maturation, cytoplasmic CK is expressed abundantly in the villous epithelium, which is formed by proliferation of epididymal epithelial cells. During hibernation and reproduction, the epididymal epithelium of P. sinensis exhibits different proliferation and secretion patterns as the animal adapts to two types of sperm storage. Cytoplasmic CK may participate in regulating the energy metabolism of the epididymal epithelium; it is an important enzyme for regulating sperm maturation.

Detection of Melanogenesis and Anti-Apoptosis-Associated Melanoma Factors: Array CGH and PPI Mapping Integrating Study.

BACKGROUND: We investigated melanogenesis- and anti-apoptosis-related melanoma factors in melanoma cells (TXM1, TXM18, A375P, and A375SM). OBJECTIVE: To find melanoma associated hub factor, high-throughput screening-based techniques integrating with bioinformatics were investigated. METHODS: Array CGH analysis was conducted with a commercial system. Total genomic DNAs prepared individually from each cell line with control DNA were properly labeled with Cy3-dCTP and Cy5-dCTP and hybridizations and subsequently performed data treatment by the log2 green (G; test) to red (R; reference) fluorescence ratios (G/R). Gain or loss of copy number was judged by spots with log2-transformed ratios. PPI mapping analysis of detected candidate genes based on the array CGH results was conducted using the human interactome in the STRING database. Energy minimization and a short Molecular Dynamics (MD) simulation using the implicit solvation model in CHARMM were performed to analyze the interacting residues between YWHAZ and YWHAB. RESULTS: Three genes (BMP-4, BFGF, LEF-1) known to be involved in melanogenesis were found to lose chromosomal copy numbers, and Chr. 6q23.3 was lost in all tested cell lines. Ten hub genes (CTNNB1, PEX13, PEX14, PEX5, IFNG, EXOSC3, EXOSC1, EXOSC8, UBC, and PEX10) were predicted to be functional interaction factors in the network of the 6q23.3 locus. The apoptosis-associated genes E2F1, p50, BCL2L1, and BIRC7 gained, and FGF2 lost chromosomal copy numbers in the tested melanoma cell lines. YWHAB, which gained chromosomal copy numbers, was predicted to be the most important hub protein in melanoma cells. Molecular dynamics simulations for binding YWHAB and YWHAZ were conducted, and the complex was predicted to be energetically and structurally stable through its 3 hydrogen-bond patterns. The number of interacting residues is 27. CONCLUSION: Our study compares genome-wide screening interactomics predictions for melanoma factors and offers new information for understanding melanogenesis- and anti-apoptosis-associated mechanisms in melanoma. Especially, YWHAB was newly detected as a core factor in melanoma cells.

Transcriptomic profile of human erythroleukemia cells in response to Sargassum fusiforme polysaccharide and its structure analysis.

Sargassum fusiforme (S. fusiforme) has been used as an ingredient in Chinese herbal medicine for thousands of years. However, there are a limited number of studies concerning its therapeutic mechanism. High performance gel permeation chromatography (HPGPC) analysis showed that the average molecular weight of the S. fusiforme polysaccharide, SFPS 191212, is 43 kDa. SFPS 191212 is composed of mannose, rhamnose, galactose, xylose, glucose, and fucose (at a molar ratio: 2.1 : 2.9 : 1.8 : 15.5 : 4.6 : 62.5) with α- and ß-configurations. The present research evaluated the anti-tumor potential of the S. fusiforme polysaccharide in human erythroleukemia (HEL) cells in vitro. To explore the SFPS 191212's apoptosis mechanism in HEL cells, transcriptome analysis was performed on HEL cells that were incubated with SFPS 191212. The inhibitory effect of SFPS 191212 on HEL cell growth was also analyzed. It was found that SFPS 191212 inhibited HEL cell proliferation, reduced cell viability in a concentration-dependent manner, and induced an insignificant toxic effect on normal human embryonic lung (MRC-5) cells. Compared with the control group, transcriptome analysis identified a total of 598 differentially expressed genes (DEGs), including 243 up-regulated genes and 355 down-regulated genes. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses were performed on all DEGs, and 900 GO terms and 52 pathways were found to be significantly enriched. Finally, 23 DEGs were randomly selected and confirmed by quantitative real-time polymerase chain reaction (qRT-PCR). Moreover, SFPS 191212 down-regulated the PI3K/Akt signal transduction pathway. Our results provide a framework for understanding the effect of SFPS 191212 on cancer cells and can serve as a resource for delineating the anti-tumor mechanisms of S. fusiforme.

A Knock-Down Cell-Based Study for the Functional Analysis of Chloride Intracellular Channel 1 (CLIC1): Integrated Proteomics and Microarray Study.

BACKGROUND: Previously, we detected that chloride intracellular channel 1 (CLIC1) was involved in the pathogenesis of atopic dermatitis (AD). OBJECTIVE: In this study, we aimed to use high-throughput screening (HTS) approaches to identify critical factors associated with the function of CLIC1 in knock-down cells. METHODS: We down-regulated CLIC1 in human A549 cells via siRNA and then conducted serial HTS studies, including proteomics integrated with a microarray and the implementation of bioinformatics algorithms. RESULTS: Together, these approaches identified several important proteins and genes associated with the function of CLIC1. These proteins and genes included tumor rejection antigen (gp96) 1, nucleophosmin, annexin I, keratin 1 and 10, FLNA protein, enolase 1, and metalloprotease 1, which were found using two-dimensional electrophoresis (2-DE) proteomics. Separately, NTNG1, SEMA5A, CLEC3A, GRPR, GNGT2, GRM5, GRM7, DNMT3B, CXCR5, CCL11, CD86, IL2, MNDA, TLR5, IL23R, DPP6, DLGAP1, CAT, GSTA1, GSTA2, GSTA5, CYP2E1, ADH1A, ESR1, ARRDC3, A1F1, CCL5, CASP8, DNTT, SQSTM1, PCYT1A, and SLCO4C1 were found using a DNA microarray integrated with PPI mapping. CONCLUSION: CCL11 is thought to be a particularly critical gene among the candidate genes detected in this study. By integrating the datasets and utilizing the strengths of HTS, we obtained new insights into the functional role of CLIC1, including the use of CLIC1-associated applications in the treatment of human diseases such as AD.

Functional study of acetaldehyde dehydrogenase 1 (ALDH1) in keratinocytes: microarray integrating bioinformatics approaches.

The function of acetaldehyde dehydrogenase 1 (ALDH1) has been gradually elucidated in several diseases, especially in various cancers. However, the role of ALDH1 in skin-related diseases has been mostly unknown. Previously, we found that ALDH1 is involved in the pathogenesis of atopic dermatitis (AD). In this study, we used high-throughput screening (HTS) approaches to identify critical factors associated with ALDH1 in human keratinocytes to reveal its functions in skin. We overexpressed ALDH1 in human HaCaT keratinocytes and then conducted serial HTS studies, a DNA microarray and antibody array integrated with bioinformatics algorithms. Together, those tests identified several novel genes associated with the function of ALDH1 in keratinocytes, as well as AD, including CTSG and CCL11. In particular, GNB3, GHSR, TAS2R9, FFAR1, TAS2R16, CCL21, GPR32, NPFFR1, GPR15, FBXW12, CCL19, EDNRA, FFAR3, and RXFP3 proteins were consistently detected as hub proteins in the PPI maps. By integrating the datasets obtained from these HTS studies and using the strengths of each method, we obtained new insights into the functional role of ALDH1 in skin keratinocytes. The approach used here could contribute to the clinical understanding of ALDH1-associated applications for the treatment of AD.Communicated by Ramaswamy H. Sarma.

Tyrosinase-mediated melanogenesis in melanoma cells: Array comparative genome hybridization integrating proteomics and bioinformatics studies.

We investigated the tyrosinase-associated melanogenesis in melanoma cells by using OMICS techniques. We characterized the chromosome copy numbers, including Chr 11q21 where the tyrosinase gene is located, from several melanoma cell lines (TXM13, G361, and SK-MEL-28) by using array CGH. We revealed that 11q21 is stable in TXM13 cells, which is directly related to a spontaneous high melanin pigment production. Meanwhile, significant loss of copy number of 11q21 was found in G361 and SK-MEL-28. We further profiled the proteome of TXM13 cells by LC-ESI-MSMS and detected more than 900 proteins, then predicted 11 hub proteins (YWHAZ; HSP90AA1; HSPA5; HSPA1L; HSPA9; HSP90B1; HSPA1A; HSPA8; FKSG30; ACTB; DKFZp686DQ972) by using an interactomic algorithm. YWHAZ (25% interaction in the network) is thought to be a most important protein as a linking factor between tyrosinase-triggered melanogenesis and melanoma growth. Bioinformatic tools were further applied for revealing various physiologic mechanisms and functional classification. The results revealed clues for the spontaneous pigmentation capability of TXM13 cells, contrary to G361 and SK-MEL-28 cells, which commonly have depigmentation properties during subculture. Our study comparatively conducted the genome-wide screening and proteomic profiling integrated interactomics prediction for TXM13 cells and suggests new insights for studying both melanogenesis and melanoma.

Biochemical Study of Fibrinolytic Protease from Euphausia superba Possessing Multifunctional Serine Protease Activity.

BACKGROUND: Fibrinolytic protease from Euphausia superba (EFP) was isolated. OBJECTIVE: Biochemical distinctions, regulation of the catalytic function, and the key residues of EFP were investigated. METHODS: The serial inhibition kinetic evaluations coupled with measurements of fluorescence spectra in the presence of 4-(2-aminoethyl) benzene sulfonyl fluoride hydrochloride (AEBSF) was conducted. The computational molecular dynamics (MD) simulations were also applied for a comparative study. RESULTS: The enzyme behaved as a monomeric protein with a molecular mass of about 28.6 kD with Km BApNA = 0.629 ± 0.02 mM and kcat/Km BApNA = 7.08 s-1/mM. The real-time interval measurements revealed that the inactivation was a first-order reaction, with the kinetic processes shifting from a monophase to a biphase. Measurements of fluorescence spectra showed that serine residue modification by AEBSF directly caused conspicuous changes of the tertiary structures and exposed hydrophobic surfaces. Some osmolytes were applied to find protective roles. These results confirmed that the active region of EFP is more flexible than the overall enzyme molecule and serine, as the key residue, is associated with the regional unfolding of EFP in addition to its catalytic role. The MD simulations were supportive to the kinetics data. CONCLUSION: Our study indicated that EFP has an essential serine residue for its catalyst function and associated folding behaviors. Also, the functional role of osmolytes such as proline and glycine that may play a role in defense mechanisms from environmental adaptation in a krill's body was suggested.

Effect of Sargassum fusiforme polysaccharide on apoptosis and its possible mechanism in human erythroleukemia cells.

This study aimed to investigate the effects of Sargassum fusiforme polysaccharide (SFPS I, II, and III) on the apoptosis and regulation of human erythroleukemia (HEL) cells. The effect of different doses of SFPS on HEL cell growth was detected using the Cell Counting Kit-8 method, and apoptosis was detected by Hoechst staining. Cell cycle distribution and apoptosis were detected using flow cytometry. Expression of the cell cycle gene, p53, antiapoptotic genes, Bcl-xL and Bcl-2, and pro-apoptotic genes, Bax, Bad, and Caspase-3, as well as the expression of the corresponding proteins, were detected using real-time quantitative polymerase chain reaction (qPCR) and Western blot. The results showed that SFPS II and III decreased HEL cell viability and induced HEL cell apoptosis. Different concentrations of SFPS (I, II, and III) were detected that induced much less toxic effect in normal human embryonic lung (MRC-5) cells, and SFPS I increased cell proliferation, indicating its favorable selectivity towards cancer cells. The mechanism by which SFPS induced apoptosis was also found to be related to the induction of cell cycle arrest in the G0/G1 phase and the increased expression of apoptosis-related genes and proteins. We concluded that SFPS induces HEL cell apoptosis, possibly via activation of the Caspase pathway, providing the theoretical basis for the development of SFPS-based anti-tumor drug products.

Thermal stable characteristics of acid- and pepsin-soluble collagens from the carapace tissue of Chinese soft-shelled turtle (Pelodiscus sinensis).

The carapace from the Chinese soft-shelled turtle (Pelodiscus sinensis) is used as a traditional Chinese medicine. Acid-soluble collagen (ASC) and pepsin-soluble collagen (PSC) from turtle carapace were isolated and characterized to screen novel collagen material in this study. Yields of 1.0% and 2.8% were obtained for ASC and PSC which contained glycine as the major amino acid and had high imino acid content. Both collagens had maximum ultraviolet absorption peaks of 220 nm. SDS-PAGE revealed that the structure of both collagens was similar, belonging to type I collagen. Relative viscosities of collagens were decreased as the temperature increased. Collagens showed minimum solubility at pH 8 and maximum solubility at a salt concentration of 3%. The denaturation temperature (Td) of PSC was higher whereas the melting temperature was lower than that of ASC. Both ASC and PSC appeared to be spongy like microstructure with fibrillar pores shown by scanning electron microscopy. The results suggest that collagens isolated from turtle carapace has high thermal stability with potential uses as new substitute for mammalian collagen in medicinal, food or biomaterial fields. However, their biological or pharmacological activities are needed to be further studied.

Comparative studies of the expression of creatine kinase isoforms under immune stress in Pelodiscus sinensis.

The expression and localization of different isoforms of creatine kinase in Pelodiscus sinensis (PSCK) were studied to reveal the role of PSCK isozymes (PSCK-B, PSCK-M, PSCK-S) under bacterial infection-induced immunologic stress. The computational molecular dynamics simulations predicted that PSCK-S would mostly possess a kinase function in a structural aspect when compared to PSCK-B and PSCK-M. The assay of biochemical parameters such as total superoxide dismutase (T-SOD), lactate dehydrogenase (LDH), malondialdehyde (MDA), catalase (CAT), and the content of ATP were measured along with total PSCK activity in different tissue samples under bacterial infection. The expression detections of PSCK isozymes in vitro and in vivo were overall well-matched where PSCK isozymes were expressed differently in P. sinensis tissues. The results showed that PSCK-B mostly contributes to the spleen, followed by the liver and myocardium; PSCK-M mostly contributes to the liver, followed by the myocardium and skeletal muscle, while PSCK-S contributes to the spleen and is uniquely expressed in skeletal muscle. Our study suggests that the various alterations of PSCK isozymes in tissues of P. sinensis are prone to defense the bacterial infection and blocking energetic imbalance before severe pathogenesis turned on in P. sinensis.

Enhanced stability of a rumen-derived xylanase using SpyTag/SpyCatcher cyclization.

Microbiota from herbivore rumen is of great interest for mining glycoside hydrolases for lignocellulosic biomass biorefinement. We previously isolated a highly active but poorly thermostable xylanase (LXY) from a rumen fluid fosmid library of Hu sheep, a local high-reproductive species in China. In this study, we used a universal enzyme-engineering strategy called SpyTag/SpyCatcher molecular cyclization to improve LXY stability via isopeptide-bond-mediated ligation. Both linear and cyclized LXY (L- and C-LXY, respectively) shared similar patterns of optimal pH and temperature, pH stability, and kinetic constants (km and Vmax). However, the C-LXY showed enhanced thermostability, ion stability, and resilience to aggregation and freeze-thaw treatment than L-LXY, without compromise of its catalytic efficiency. Circular dichroism and intrinsic and 8-anilino-1-naphthalenesulfonic acid-binding fluorescence analysis indicated that the cyclized enzyme was more capable of maintaining its secondary and tertiary structures than the linear enzyme. Taken together, these results promote the cyclized enzyme for potential applications in the feed, food, paper pulp, and bioenergy industries.

Inhibitory effect of α-ketoglutaric acid on α-glucosidase: integrating molecular dynamics simulation and inhibition kinetics.

The inhibition of α-glucosidase is used as a key clinical approach to treat type 2 diabetes mellitus and thus, we assessed the inhibitory effect of α-ketoglutaric acid (AKG) on α-glucosidase with both an enzyme kinetic assay and computational simulations. AKG bound to the active site and interacted with several key residues, including ASP68, PHE157, PHE177, PHE311, ARG312, TYR313, ASN412, ILE434 and ARG439, as detected by protein-ligand docking and molecular dynamics simulations. Subsequently, we confirmed the action of AKG on α-glucosidase as mixed-type inhibition with reversible and rapid binding. The relevant kinetic parameter IC50 was measured (IC50 = 1.738 ± 0.041 mM), and the dissociation constant was determined (Ki Slope = 0.46 ± 0.04 mM). Regarding the relationship between structure and activity, a high AKG concentration induced the slight modulation of the shape of the active site, as monitored by hydrophobic exposure. This tertiary conformational change was linked to AKG inhibition and mostly involved regional changes in the active site. Our study provides insight into the functional role of AKG due to its structural property of a hydroxyphenyl ring that interacts with the active site. We suggest that similar hydroxyphenyl ring-containing compounds targeting key residues in the active site might be potential α-glucosidase inhibitors. AbbreviationsAKGalpha-ketoglutaric acidpNPG4-nitrophenyl-α-d-glucopyranosideANS1-anilinonaphthalene-8-sulfonateMDmolecular dynamics.Communicated by Ramaswamy H. Sarma.

Screening and analysis of agouti signaling protein interaction partners in Pelodiscus sinensis suggests a role in lipid metabolism.

Agouti signaling protein (ASP) is a secreted paracrine protein that has been widely reported to function in melanogenesis and obesity and could potentially be a core protein that regulates the color and fatty phenotype of P. sinensis. In this study, we screened out interacting proteins of ASP by combined co-immunoprecipitation mass spectrometry (CoIP-MS), yeast two hybrid (Y2H) analysis, and computational predictions. We performed docking of ASP with its well-known receptor melanocortin receptor 4 (MC4R) to predict the binding capacity and to screen out actual ASP interacting proteins, CoIP-MS was performed where identified 32 proteins that could bind with ASP and Y2H confirmed seven proteins binding with ASP directly. CoIP-MS and Y2H screening results including PPI prediction revealed that vitronectin (VTN), apolipoprotein A1 (APOA1), apolipoprotein B (APOB), and filamin B (FLNB) were the key interacting proteins of ASP. VTN, APOA1, and APOB are functional proteins in lipid metabolism and various skin disorders, suggesting ASP may function in lipid metabolism through these partners. This study provided protein-protein interaction information of ASP, and the results will promote further research into the diverse roles of ASP, as well as its binding partners, and their function in different strains of P. sinensis.

The inhibitory effect of pyrogallol on tyrosinase activity and structure: Integration study of inhibition kinetics with molecular dynamics simulation.

Pyrogallol is naturally found in aquatic plant and has been proposed as a substrate of tyrosinase. In this study, we evaluated the dual effect of pyrogallol on tyrosinase as an inhibitor in the presence of L­DOPA simultaneously via integrating methods of enzyme kinetics and computational molecular dynamics (MD) simulations. Pyrogallol was found to be a reversible inhibitor of tyrosinase in the presence of L­DOPA and its induced mechanism was the parabolic non-competitive inhibition type (IC50 = 0.772 ±â€¯0.003 mM and Ki = 0.529 ±â€¯0.022 mM). Kinetic measurements by real-time interval assay showed that pyrogallol induced rapid inactivation process composing with slight activations at the low dose. Spectrofluorimetry studies showed that pyrogallol mainly induced regional changes in the active site of tyrosinase accompanying with hydrophobic disruption at high dose. The computational MD simulations further revealed that pyrogallol could interact with several residues near the tyrosinase active site pocket such as HIS61, HIS85, HIS259, ASN260, HIS263, VAL283, and ALA296. Our study provides insight into the mechanism by which hydroxyl group composing pyrogallol inhibit tyrosinase and pyrogallol is a potential natural anti-pigmentation agent.

Inhibitory effect of phloroglucinol on α-glucosidase: Kinetics and molecular dynamics simulation integration study.

Regulation of α-glucosidase (EC 3.2.1.20) and its inhibitors is of great interest to researchers due to its clinical relevance as a target enzyme for the treatment of α-glucosidase-mediated diseases, such as type 2 diabetes mellitus and Pompe disease. In this study, we conducted a phloroglucinol-induced inhibition kinetics assay and performed computational molecular dynamics (MD) simulations to assess binding manner in α-glucosidase. The results showed that phloroglucinol reversibly inhibited α-glucosidase in a dose-dependent but non-competitive manner (Ki=2.07±0.16mM). Interestingly, the maximum peak wavelength and the hydrophobic surface remained unchanged during the inhibition reaction, with computational MD simulations further revealing that phloroglucinol bound in front of the active site pocket rather than in the α-glucosidase active site. Therefore, we speculate that phloroglucinol-specific inhibition is mild and the inhibitor likely binds to a single binding site near but not in the active site. Our study provided insight into the effects and mechanisms associated with a mild inhibitor of α-glucosidase activity and promotes fundamental research and potential applications of inhibitors for treatment of α-glucosidase-mediated clinical disease.

SpyTag/SpyCatcher molecular cyclization confers protein stability and resilience to aggregation.

The capacities for thermal and inhibitor tolerance are critical for industrial enzymes and loss of activity is a major challenge in deploying natural enzymes for commercial applications. Protein engineering approaches, such as site-directed mutagenesis and directed evolution, have been devoted to modifying natural enzymes. Recently, a post-translation protein engineering strategy, the SpyTag/SpyCatcher system, was introduced. Here, we have generated a thermo- and ion-tolerant cyclized xylanase (C-TFX) by fusing the SpyTag and SpyCatcher peptides to its N- and C- terminus respectively. Compared with the linear enzyme, C-TFX retained greater residual activity after heating or metal ion exposure. Intrinsic fluorescence and circular dichroism analysis revealed that the isopeptide bond mediated by SpyTag/SpyCatcher cyclization contributed to enhanced thermo- and ion-stability, probably by stabilizing its secondary and conformational structure. In addition, the heat-challenged C-TFX was observed to degrade natural lignocellulosic substrates efficiently. The cyclized xylanase was more stable and resistent to denaturation and aggregation than the linear enzyme. The "superglue" SpyTag/SpyCatcher cyclization system enables the enzyme to maintain its structural conformation, which will be of particular interest in engineering of enzymes for industrial application such as feed additives and functional oligosaccharides production.

Hydrogen peroxide (H2O2) irreversibly inactivates creatine kinase from Pelodiscus sinensis by targeting the active site cysteine.

Creatine kinase (EC 2.7.3.2, CK) plays an important role in cellular energy metabolism and homeostasis by catalysing the transfer of phosphate between ATP and creatine phosphate. In this study, we investigated the effects of H2O2 on PSCKM (muscle type creatine kinase from Pelodiscus sinensis) by the integrating method between enzyme kinetics and docking simulations. We found that H2O2 strongly inactivated PSCKM (IC50=0.25mM) in a first-order kinetic process, and targeted the active site cysteine directly. A conformational study showed that H2O2 did not induce the tertiary structural changes in PSCKM with no extensive exposure of hydrophobic surfaces. Sequential docking simulations between PSCKM and H2O2 indicated that H2O2 interacts with the ADP binding region of the active site, consistent with experimental results that demonstrated H2O2-induced inactivation. Our study demonstrates the effect of H2O2 on PSCKM enzymatic function and unfolding, and provides important insight into the changes undergone by this central metabolic enzyme in ectothermic animals in response to the environment.