Mutational analysis of the zinc metalloprotease EmpA of Vibrio anguillarum

The extracellular zinc metalloprotease, EmpA, is a putative virulence factor involved in pathogenicity of the fish pathogen Vibrio anguillarum. The 611-amino acid precursor of this enzyme is encoded by the empA gene. The residues His346, His350, Glu370, Glu347, His429, Tyr361 and Asp417 are highly conserved and putatively function together at the active site of the enzyme. In this study, empA was inserted into pET24d(+) and expressed in Escherichia coli strain BL21(DE3) as a 6 x His tagged protein (r-EmpA). All the conserved residues of EmpA mentioned above were individually mutated by site-directed mutagenesis and the mutants were also expressed (m-r-EmpAs). r-EmpA and m-r-EmpAs were purified, and assayed for their proteolytic activities with azocasein as the substrate and cytotoxicities on a flounder gill cell line. m-r-EmpAs that had been mutated at His346, His350, Glu370 and Glu347 almost completely lost their proteolytic activity and cytotoxicity, pointing towards the essential roles played by these residues. In contrast, those mutated at Tyr361, His429 and Asp417 still retained a partial proteolytic activity and cytotoxicity. Our results indicate that these conserved residues play important roles in enzymatic activity and that the proteolytic activity of the enzyme is involved in the pathogenesis of V. anguillarum     

Retinoids induce integrin-independent lymphocyte adhesion through RAR-α nuclear receptor activity

Oxidative metabolites of vitamin A, in particular all-trans-retinoic acid (atRA), have emerged as key factors in immunity by specifying the localization of immune cells to the gut. Although it is appreciated that isomers of retinoic acid activate the retinoic acid receptor (RAR) and retinoid X receptor (RXR) family of nuclear receptors to elicit cellular changes, the molecular details of retinoic acid action remain poorly defined in immune processes. Here we employ a battery of agonists and antagonists to delineate the specific nuclear receptors utilized by retinoids to evoke lymphocyte cell adhesion to ADAM (adisintegrin and metalloprotease) protein family members. We report that RAR agonism is sufficient to promote immune cell adhesion in both immortal and primary immune cells. Interestingly, adhesion occurs independent of integrin function, and mutant studies demonstrate that atRA-induced adhesion to ADAM members required a distinct binding interface(s) as compared to integrin recognition. Anti-inflammatory corticosteroids as well as 1,25-(OH)₂D₃, a vitamin D metabolite that prompts immune cell trafficking to the skin, potently inhibited the observed adhesion. Finally, our data establish that induced adhesion was specifically attributable to the RAR-α receptor isotype. The current study provides novel molecular resolution as to which nuclear receptors transduce retinoid exposure into immune cell adhesion.     

Role of host cellular proteases in the pathogenesis of influenza and influenza-induced multiple organ failure

Influenza A virus (IAV) is one of the most common infectious pathogens in humans. Since the IVA genome does not have the processing protease for the viral hemagglutinin (HA) envelope glycoprotein precursors, entry of this virus into cells and infectious organ tropism of IAV are primarily determined by host cellular trypsin-type HA processing proteases. Several secretion-type HA processing proteases for seasonal IAV in the airway, and ubiquitously expressed furin and pro-protein convertases for highly pathogenic avian influenza (HPAI) virus, have been reported. Recently, other HA-processing proteases for seasonal IAV and HPAI have been identified in the membrane fraction. These proteases proteolytically activate viral multiplication at the time of viral entry and budding. In addition to the role of host cellular proteases in IAV pathogenicity, IAV infection results in marked upregulation of cellular trypsins and matrix metalloproteinase-9 in various organs and cells, particularly endothelial cells, through induced pro-inflammatory cytokines. These host cellular factors interact with each other as the influenza virus-cytokine-protease cycle, which is the major mechanism that induces vascular hyperpermeability and multiorgan failure in severe influenza. This mini-review discusses the roles of cellular proteases in the pathogenesis of IAV and highlights the molecular mechanisms of upregulation of trypsins as effective targets for the control of IAV infection. This article is part of a Special Issue entitled: Proteolysis 50 years after the discovery of lysosome.     

Human CaaX protease ZMPSTE24 expressed in yeast: Structure and inhibition by HIV protease inhibitors

The function and localization of proteins and peptides containing C‐terminal “CaaX” (Cys‐aliphatic‐aliphatic‐anything) sequence motifs are modulated by post‐translational attachment of isoprenyl groups to the cysteine sulfhydryl, followed by proteolytic cleavage of the aaX amino acids. The zinc metalloprotease ZMPSTE24 is one of two enzymes known to catalyze this cleavage. The only identified target of mammalian ZMPSTE24 is prelamin A, the precursor to the nuclear scaffold protein lamin A. ZMPSTE24 also cleaves prelamin A at a second site 15 residues upstream from the CaaX site. Mutations in ZMPSTE24 result in premature‐aging diseases and inhibition of ZMPSTE24 activity has been reported to be an off‐target effect of HIV protease inhibitors. We report here the expression (in yeast), purification, and crystallization of human ZMPSTE24 allowing determination of the structure to 2.0 Å resolution. Compared to previous lower resolution structures, the enhanced resolution provides: (1) a detailed view of the active site of ZMPSTE24, including water coordinating the catalytic zinc; (2) enhanced visualization of fenestrations providing access from the exterior to the interior cavity of the protein; (3) a view of the C‐terminus extending away from the main body of the protein; (4) localization of ordered lipid and detergent molecules at internal and external surfaces and also projecting through fenestrations; (5) identification of water molecules associated with the surface of the internal cavity. We also used a fluorogenic assay of the activity of purified ZMPSTE24 to demonstrate that HIV protease inhibitors directly inhibit the human enzyme in a manner indicative of a competitive mechanism.     

Cloning and characterization of the gene for the metalloprotease enterotoxin of Bacteroides fragilis

The Bacteroides fragilis enterotoxin is an extracellular zinc metalloprotease that has been implicated in diarrheal disease of humans and animals. This toxin causes fluid accumulation in intestinal loops and is cytotoxic for HT-29 cells, an intestinal carcinoma cell line. Here we report the cloning and sequencing of the toxin gene (bftP). bftP is 1191 nucleotides coding for a 397 amino acid protein of 44.4 kDa. The toxin has a signal peptide of 18 amino acids that is typical of many lipoproteins followed by a 379 amino acid protoxin. The portion of the protoxin found in culture filtrates and stools begins at amino acid 212. An additional open reading frame located immediately upstream shows some sequence identity with cobra cytotoxins. If expressed, the ORF protein product could also play a role in the virulence of B. fragilis.     

Identification of a Proteolytic Bacterium,HW08, and Characterization of Its Extracellular Cold-Active Alkaline Metalloprotease Ps5

A psychrophilic protease-producing bacterium, HW08, was isolated from sediment of the Yellow Sea in eastern China. On the basis of 16S rDNA sequence analysis and physiological properties, the isolate was identified as Pseudomonas lundensis. The secreted protease, named Ps5, was purified from the culture supernatant as a monomer with an apparent molecular mass of 46 kDa on SDS–PAGE. As a metalloprotease (inhibited by EDTA), the enzyme showed maximum activity at 30 °C at pH 10.4. It had no activity loss exposed at 4 °C for 60 d or under repeated freezing and thawing. Broad temperature (25–40 °C) and pH (7.0–11.0) stability was observed in the presence of 5 mm Ca²⁺. Furthermore, the enzyme was resistant to detergent additives such as non-ionic surfactants and bleaches. It showed considerable potential for industry that requires alkaline-protease.     

Structural analysis of Mycobacterium tuberculosis M13 metalloprotease Zmp1 open states

1. Download : Download high-res image (301KB)
2. Download : Download full-size image

     

TspanC8 Tetraspanins and A Disintegrin and Metalloprotease 10 (ADAM10) Interact via Their Extracellular Regions: EVIDENCE FOR DISTINCT BINDING MECHANISMS FOR DIFFERENT TspanC8 PROTEINS*

A disintegrin and metalloprotease 10 (ADAM10) is a ubiquitously expressed transmembrane metalloprotease that cleaves the extracellular regions from its transmembrane substrates. ADAM10 is essential for embryonic development and is implicated in cancer, Alzheimer, and inflammatory diseases. The tetraspanins are a superfamily of 33 four-transmembrane proteins in mammals, of which the TspanC8 subgroup (Tspan5, 10, 14, 15, 17, and 33) promote ADAM10 intracellular trafficking and enzymatic maturation. However, the interaction between TspanC8s and ADAM10 has only been demonstrated in overexpression systems and the interaction mechanism remains undefined. To address these issues, an antibody was developed to Tspan14, which was used to show co-immunoprecipitation of Tspan14 with ADAM10 in primary human cells. Chimeric Tspan14 constructs demonstrated that the large extracellular loop of Tspan14 mediated its co-immunoprecipitation with ADAM10, and promoted ADAM10 maturation and trafficking to the cell surface. Chimeric ADAM10 constructs showed that membrane-proximal stalk, cysteine-rich, and disintegrin domains of ADAM10 mediated its co-immunoprecipitation with Tspan14 and other TspanC8s. This TspanC8-interacting region was required for ADAM10 exit from the endoplasmic reticulum. Truncated ADAM10 constructs revealed differential TspanC8 binding requirements for the stalk, cysteine-rich, and disintegrin domains. Moreover, Tspan15was the only TspanC8 to promote cleavage of the ADAM10 substrate N-cadherin, whereas Tspan14 was unique in reducing cleavage of the platelet collagen receptor GPVI. These findings suggest that ADAM10 may adopt distinct conformations in complex with different TspanC8s, which could impact on substrate selectivity. Furthermore, this study identifies regions of TspanC8s and ADAM10 for potential interaction-disrupting therapeutic targeting.     

A recombinant metalloprotease antigen of Vibrio vulnificus elicits protective antibodies in a murine model

Aims: To investigate whether Vibrio vulnificus metalloprotease (VvpE) can induce the production of specific anti‐VvpE antibody to confer effective protection against Vibrio vulnificus infection and to evaluate the possibility of VvpE as a potential vaccine candidate against disease caused by V. vulnificus. Methods and Results: The gene encoding the 65‐kDa VvpE of V. vulnificus was amplified by PCR and cloned into the expression vector pET21(b). The recombinant VvpE of V. vulnificus was expressed in Escherichia coli BL21(DE3). This His₆‐tagged VvpE was purified and injected intramuscularly into mice to evaluate its ability to stimulate immune response. Specific antibody levels were measured by ELISA. The 75% protective efficacy of recombinant VvpE was evaluated by active immunization and intraperitoneal challenge with V. vulnificus in mice. Conclusions: The recombinant His₆‐tagged VvpE of V. vulnificus is capable of inducing high antibody response in mice to confer effective protection against lethal challenge with V. vulnificus. VvpE might be a potential vaccine candidate to against V. vulnificus infection. Significance and Impact of the Study: This study uses His₆‐tagged VvpE to act as vaccine that successfully induces effective and specific anti‐VvpE antibody and offers an option for the potential vaccine candidate against V. vulnificus infection.