OBJECTIVE: Aeromonas has recently been recognized as an emerging human pathogen. Aeromonas-associated diarrhea is a phenomenon occurring worldwide. This study was designed to determine the prevalence, genetic diversity, antibiotic resistance, and pathogenicity of Aeromonas strains isolated from food products in Shanghai. METHODS: Aeromonas isolates ( n = 79) collected from food samples were analyzed using concatenated gyrB- cpn60 sequencing. The antibiotic resistance of these isolates was determined using antimicrobial susceptibility testing. Pathogenicity was assessed using β-hemolytic, extracellular protease, virulence gene detection, C. elegans liquid toxicity (LT), and cytotoxicity assays. RESULTS: Eight different species were identified among the 79 isolates. The most prevalent Aeromonas species were A. veronii [62 (78.5%)], A. caviae [6 (7.6%)], A. dhakensis [3 (3.8%)], and A. salmonicida [3 (3.8%)]. The Aeromonas isolates were divided into 73 sequence types (STs), of which 65 were novel. The isolates were hemolytic (45.6%) and protease-positive (81.0%). The most prevalent virulence genes were act (73.4%), fla (69.6%), aexT (36.7%), and ascV (30.4%). The results of C. elegans LT and cytotoxicity assays revealed that A. dhakensis and A. hydrophila were more virulent than A. veronii, A. caviae, and A. bivalvium. Antibiotic resistance genes [ tetE, blaTEM, tetA, qnrS, aac(6)-Ib, mcr -1, and mcr-3] were detected in the isolates. The multidrug-resistance rate of the Aeromonas isolates was 11.4%, and 93.7% of the Aeromonas isolates were resistant to cefazolin. CONCLUSION The taxonomy, antibiotic resistance, and pathogenicity of different Aeromonas species varied. The Aeromonas isolates A. dhakensis and A. hydrophila were highly pathogenic, indicating that food-derived Aeromonas isolates are potential risks for public health and food safety. The monitoring of food quality and safety will result in better prevention and treatment strategies to control diarrhea illnesses in China.
Aeromonas/genetics* ; Animals ; Anti-Bacterial Agents/pharmacology* ; Caenorhabditis elegans ; Cefazolin ; China/epidemiology* ; Diarrhea ; Drug Resistance, Multiple, Bacterial/genetics* ; Genetic Variation ; Humans ; Peptide Hydrolases/genetics* ; Virulence/genetics*

Proteases are widely found in organisms participating in the decomposition of proteins to maintain the organisms' normal life activities. Protease inhibitors regulate the activities of target proteases by binding to their active sites, thereby affecting protein metabolism. The key amino acid mutations in proteases and protease inhibitors can affect their physiological functions, stability, catalytic activity, and inhibition specificity. More active, stable, specific, environmentally friendly and cheap proteases and protease inhibitors might be obtained by excavating various natural mutants of proteases and protease inhibitors, analyzing their key active sites by using protein engineering methods. Here, we review the studies on proteases' key active sites and protease inhibitors to deepen the understanding of the active mechanism of proteases and their inhibitors.
Binding Sites ; Catalytic Domain ; Endopeptidases ; Peptide Hydrolases/genetics* ; Protease Inhibitors ; Proteins

The main protease (Mpro) of SARS-CoV-2 is a highly conserved and mutation-resistant coronaviral enzyme, which plays a pivotal role in viral replication, making it an ideal target for the development of novel broad-spectrum anti-coronaviral drugs. In this study, a codon-optimized Mpro gene was cloned into pET-21a and pET-28a expression vectors. The recombinant plasmids were transformed into E. coli Rosetta(DE3) competent cells and the expression conditions were optimized. The highly expressed recombinant proteins, Mpro and Mpro-28, were purified by HisTrapTM chelating column and its proteolytic activity was determined by a fluorescence resonance energy transfer (FRET) assay. The FRET assay showed that Mpro exhibits a desirable proteolytic activity (25 000 U/mg), with Km and kcat values of 11.68 μmol/L and 0.037/s, respectively. The specific activity of Mpro is 25 times that of Mpro-28, a fusion protein carrying a polyhistidine tag at the N and C termini, indicating additional residues at the N terminus of Mpro, but not at the C terminus, are detrimental to its proteolytic activity. The preparation of active SARS-CoV-2 Mpro through codon-optimization strategy might facilitate the development of the rapid screening assays for the discovery of broad-spectrum anti-coronaviral drugs targeting Mpro.
COVID-19 ; Codon/genetics* ; Cysteine Endopeptidases/genetics* ; Escherichia coli/genetics* ; Humans ; Peptide Hydrolases ; SARS-CoV-2 ; Viral Nonstructural Proteins/genetics*

The general secretory (Sec) pathway represents a common mechanism by which bacteria secrete proteins, including virulence factors, into the extracytoplasmic milieu. However, there is little information about this system, as well as its associated secretory proteins, in relation to the fire blight pathogen Erwinia amylovora. In this study, data mining revealed that E. amylovora harbors all of the essential components of the Sec system. Based on this information, we identified putative Sec-dependent secretory proteases in E. amylovora on a genome-wide scale. Using the programs SignalP, LipoP, and Phobius, a total of 15 putative proteases were predicted to contain the N-terminal signal peptides (SPs) that might link them to the Sec-dependent pathway. The activities of the predicted SPs were further validated using an Escherichia coli-based alkaline phosphatase (PhoA) gene fusion system that confirmed their extracytoplasmic property. Transcriptional analyses showed that the expression of 11 of the 15 extracytoplasmic protease genes increased significantly when E. amylovora was used to inoculate immature pears, suggesting their potential roles in plant infection. The results of this study support the suggestion that E. amylovora might employ the Sec system to secrete a suite of proteases to enable successful infection of plants, and shed new light on the interaction of E. amylovora with host plants.
Erwinia amylovora/metabolism* ; Escherichia coli/genetics* ; Peptide Hydrolases/genetics* ; Plant Diseases/microbiology* ; Pyrus/microbiology*

The storage and transportation of raw milk at low temperatures promote the growth of psychrotrophic bacteria and the production of thermo-stable enzymes, which pose great threats to the quality and shelf-life of dairy products. Though many studies have been carried out on the spoilage potential of psychrotrophic bacteria and the thermo-stabilities of the enzymes they produce, further detailed studies are needed to devise an effective strategy to avoid dairy spoilage. The purpose of this study was to explore the spoilage potential of psychrotrophic bacteria from Chinese raw milk samples at both room temperature (28 °C) and refrigerated temperature (7 °C). Species of Yersinia, Pseudomonas, Serratia, and Chryseobacterium showed high proteolytic activity. The highest proteolytic activity was shown by Yersinia intermedia followed by Pseudomonas fluorescens (d). Lipolytic activity was high in isolates of Acinetobacter, and the highest in Acinetobacter guillouiae. Certain isolates showed positive β-galactosidase and phospholipase activity. Strains belonging to the same species sometimes showed markedly different phenotypic characteristics. Proteases and lipases produced by psychrotrophic bacteria retained activity after heat treatment at 70, 80, or 90 °C, and proteases appeared to be more heat-stable than lipases. For these reasons, thermo-stable spoilage enzymes produced by a high number of psychrotrophic bacterial isolates from raw milk are of major concern to the dairy industry. The results of this study provide valuable data about the spoilage potential of bacterial strains in raw milk and the thermal resistance of the enzymes they produce.
Animals ; Bacteria/genetics* ; Bacterial Proteins/chemistry* ; Biofilms ; Cold Temperature ; Dairy Products ; Endopeptidases/chemistry* ; Enzyme Stability ; Food Microbiology ; Hot Temperature ; Lipase/chemistry* ; Milk/microbiology* ; Peptide Hydrolases/chemistry* ; Phospholipases/chemistry* ; RNA, Ribosomal, 16S/genetics* ; Raw Foods/microbiology* ; beta-Galactosidase/chemistry*

SARS coronavirus (SARS-CoV) develops an antagonistic mechanism by which to evade the antiviral activities of interferon (IFN). Previous studies suggested that SARS-CoV papain-like protease (PLpro) inhibits activation of the IRF3 pathway, which would normally elicit a robust IFN response, but the mechanism(s) used by SARS PLpro to inhibit activation of the IRF3 pathway is not fully known. In this study, we uncovered a novel mechanism that may explain how SARS PLpro efficiently inhibits activation of the IRF3 pathway. We found that expression of the membrane-anchored PLpro domain (PLpro-TM) from SARS-CoV inhibits STING/TBK1/IKKε-mediated activation of type I IFNs and disrupts the phosphorylation and dimerization of IRF3, which are activated by STING and TBK1. Meanwhile, we showed that PLpro-TM physically interacts with TRAF3, TBK1, IKKε, STING, and IRF3, the key components that assemble the STING-TRAF3-TBK1 complex for activation of IFN expression. However, the interaction between the components in STING-TRAF3-TBK1 complex is disrupted by PLpro-TM. Furthermore, SARS PLpro-TM reduces the levels of ubiquitinated forms of RIG-I, STING, TRAF3, TBK1, and IRF3 in the STING-TRAF3-TBK1 complex. These results collectively point to a new mechanism used by SARS-CoV through which PLpro negatively regulates IRF3 activation by interaction with STING-TRAF3-TBK1 complex, yielding a SARS-CoV countermeasure against host innate immunity.
Dimerization ; HEK293 Cells ; Humans ; I-kappa B Kinase ; metabolism ; Interferon Regulatory Factor-3 ; metabolism ; Interferon Type I ; antagonists & inhibitors ; metabolism ; Membrane Proteins ; chemistry ; genetics ; metabolism ; Papain ; metabolism ; Peptide Hydrolases ; chemistry ; metabolism ; Phosphorylation ; Protein Binding ; Protein Structure, Tertiary ; Protein-Serine-Threonine Kinases ; metabolism ; SARS Virus ; enzymology ; Signal Transduction ; TNF Receptor-Associated Factor 3 ; metabolism ; Ubiquitination

To study the impact of the enterovirus 71(EV71) on the nuclear transport mechanism,The pGFP-NLS vector with nuclear location signal(NLS) was constructed, RD cells transfected by the pGFP-NLS vector were inoculated with the EV71 or cotransfected by EV71-2A vector. The results showed that GFP protein with NLS was expressed in the cytoplasm due to the inhibition of nuclear transport. In order to further study the mechanism of the EV71 to prevent nuclear transport,Nup62 was detected by Western blotting after RD cells were infected with EV71 or transfected by EV71-2A vector. The results showed that decreased expression of Nup62 could be detected after infection with EV71 and transfection by EV71-2A vector. This study demonstrates that the cleavage of Nup62 by EV71 2A protease may be the mechanism of nuclear transport inhibition.
Active Transport, Cell Nucleus ; Cell Line, Tumor ; Cell Nucleus ; metabolism ; Enterovirus A, Human ; enzymology ; genetics ; metabolism ; Enterovirus Infections ; virology ; Gene Expression Regulation, Viral ; Genetic Vectors ; Green Fluorescent Proteins ; metabolism ; Humans ; Membrane Glycoproteins ; metabolism ; Nuclear Localization Signals ; metabolism ; Nuclear Pore Complex Proteins ; metabolism ; Peptide Hydrolases ; metabolism ; Recombinant Fusion Proteins ; metabolism ; Transfection

OBJECTIVE: To discuss the expression and the significance of Jab1 p27kip1 in laryngeal squamous cell carcinoma and Hep-2 cells. METHOD: Immunohistochemical method was used to examine the expressions of Jab1 and p27kip1 proteins in 50 cases laryngeal squamous cell carcinomas and 10 cases normal laryngeal tissues adjacent to laryngeal squamous cell carcinoma. Hep-2 cells were transfected with synthetic Jab1 siRNA by Lipofectamine 2000. RT-PCR method was adopted to examine the mRNA expression of the Jab1 and p27kip1 gene in Hep-2 cells which was treated with Jab1 siRNA II. RESULT: Clearly brown staining restricted to nucleus was considered as positive expression of Jab1 and p27kip1 protein. The expression rate of Jab1 protein in laryngeal squamous cell carcinoma was significantly higher than that of normal laryngeal mucosa, and the expression rate of protein p27kip1 in laryngeal squamous cell carcinoma was significantly lower than that of normal laryngeal mucosa. There was a negative relationship between Jab1 and p27kip1 protein in laryngeal squamous cell carcinoma. The expression of Jab1 mRNA was suppressed markedly after transfected by Jab1 siRNA II. As the reaction time increased, the expression of Jab1 mRNA of Hep-2 cells decreased significantly, and the expression of p27kip1 mRNA remained unchanged. CONCLUSION The expression rate of Jab1 protein in laryngeal squamous cell carcinoma is significantly higher than that of normal laryngeal mucosa. There is a negative relationship between Jab1 and p27kiPl protein in laryngeal squamous cell carcinoma. After transfected by Jab1 siRNA II in the Hep-2 cells, the expression of Jab1 mRNA is suppressed markedly. Jab1 siRNA would be a good methodology for the further study.
Adult ; Aged ; Aged, 80 and over ; COP9 Signalosome Complex ; Carcinoma, Squamous Cell ; genetics ; metabolism ; pathology ; Cell Line, Tumor ; Cyclin-Dependent Kinase Inhibitor p27 ; genetics ; metabolism ; Female ; Humans ; Intracellular Signaling Peptides and Proteins ; genetics ; metabolism ; Laryngeal Neoplasms ; genetics ; metabolism ; pathology ; Male ; Middle Aged ; Neoplasm Staging ; Peptide Hydrolases ; genetics ; metabolism ; RNA, Messenger ; genetics ; RNA, Small Interfering ; genetics

Human enterovirus 71 (EV71) is one of the major etiological agents for the hand, foot, and month disease (HFMD) and is causing frequent, widespread occurrence in the mainland of China. The single positive-stranded RNA genome of EV71 is translated into a single polyprotein which is autocleavaged into structural and nonstructural proteins. The functions of many nonstructural proteins characterized in the life cycle of virus are potential targets for blocking viral replication. This article reviews the studies of the structures and functions of nonstructural proteins of EV71 and the anti-enterovirus 71 drugs targeting on these nonstructural proteins.
Antiviral Agents ; pharmacology ; Enterovirus A, Human ; enzymology ; genetics ; isolation & purification ; Hand, Foot and Mouth Disease ; drug therapy ; virology ; Humans ; Molecular Targeted Therapy ; Peptide Hydrolases ; chemistry ; metabolism ; physiology ; Protein Kinase Inhibitors ; pharmacology ; RNA, Viral ; genetics ; Viral Nonstructural Proteins ; chemistry ; metabolism ; physiology ; Virus Replication ; drug effects

The inherent evolvability of promiscuous enzymes endows them with great potential to be artificially evolved for novel functions. Previously, we succeeded in transforming a promiscuous acylaminoacyl peptidase (apAAP) from the hyperthermophilic archaeon Aeropyrum pernix K1 into a specific carboxylesterase by making a single mutation. In order to fulfill the urgent requirement of thermostable lipolytic enzymes, in this paper we describe how the substrate preference of apAAP can be further changed from p-nitrophenyl caprylate (pNP-C8) to p-nitrophenyl laurate (pNP-C12) by protein and solvent engineering. After one round of directed evolution and subsequent saturation mutagenesis at selected residues in the active site, three variants with enhanced activity towards pNP-C12 were identified. Additionally, a combined mutant W474V/F488G/R526V/T560W was generated, which had the highest catalytic efficiency (k (cat)/K (m)) for pNP-C12, about 71-fold higher than the wild type. Its activity was further increased by solvent engineering, resulting in an activity enhancement of 280-fold compared with the wild type in the presence of 30% DMSO. The structural basis for the improved activity was studied by substrate docking and molecular dynamics simulation. It was revealed that W474V and F488G mutations caused a significant change in the geometry of the active center, which may facilitate binding and subsequent hydrolysis of bulky substrates. In conclusion, the combination of protein and solvent engineering may be an effective approach to improve the activities of promiscuous enzymes and could be used to create naturally rare hyperthermophilic enzymes.
Aeropyrum ; chemistry ; enzymology ; Archaeal Proteins ; genetics ; metabolism ; Binding Sites ; Biocatalysis ; Caprylates ; metabolism ; Cloning, Molecular ; Dimethyl Sulfoxide ; chemistry ; Escherichia coli ; Hot Temperature ; Industrial Microbiology ; methods ; Kinetics ; Laurates ; metabolism ; Molecular Dynamics Simulation ; Mutagenesis, Site-Directed ; methods ; Peptide Hydrolases ; genetics ; metabolism ; Protein Binding ; Protein Conformation ; Recombinant Proteins ; genetics ; metabolism ; Solvents ; chemistry ; Substrate Specificity