Characterisation of the Aspergillus niger dapB gene, which encodes a novel fungal type IV dipeptidyl aminopeptidase

Functional expression and characterization of a novel aminopeptidase B from Aspergillus niger in Pichia pastoris

A novel aminopeptidase B (APB-AN) was identified from Aspergillus niger CGMCC 3.1454 for the first time and was cloned and expressed in Pichia pastoris. The mature enzyme of approximately 100 kDa was purified for characterization. The optimum pH and temperature of the recombinant APB-AN were determined to be 7.0 and 40 °C, respectively. The enzyme was stable below 40 °C and at pH values from 5.0 to 8.0. The K _m and V _max values were determined to be 0.61 mmol/L and 11.45 mmol/L/min, respectively, using Arg-pNA as the substrate. APB-AN was inhibited by Cu²⁺ and Fe²⁺ and activated by Co²⁺ and Na⁺. Most metal chelators (Ca²⁺, Mg²⁺ and Mn²⁺) and aminopeptidase inhibitors (bestatin and puromycin) suppressed its activity. APB-AN was found to be active towards 13 kinds of amino acid p-nitroanilide (pNA) substrates:Arg-pNA, Lys-pNA, Tyr- pNA, Trp-pNA, Phe-pNA, His-pNA, Ala-pNA, Met-pNA, Leu-pNA, Glu-pNA, Val-pNA, Pro-pNA and Ile-pNA, and the most preferred N-terminal amino acids were arginine and lysine. APB-AN also hydrolyzed 4 natural proteins: casein, bovine serum albumin, soy protein isolate and water-soluble wheat protein. It is expected that APB-AN has potential food processing applications.

Bioinformatic mapping of a more precise Aspergillus niger degradome

Aspergillus niger has the ability to produce a large variety of proteases, which are of particular importance for protein digestion, intracellular protein turnover, cell signaling, flavour development, extracellular matrix remodeling and microbial defense. However, the A. niger degradome (the full repertoire of peptidases encoded by the A. niger genome) available is not accurate and comprehensive. Herein, we have utilized annotations of A. niger proteases in AspGD, JGI, and version 12.2 MEROPS database to compile an index of at least 232 putative proteases that are distributed into the 71 families/subfamilies and 26 clans of the 6 known catalytic classes, which represents ~ 1.64% of the 14,165 putative A. niger protein content. The composition of the A. niger degradome comprises ~ 7.3% aspartic, ~ 2.2% glutamic, ~ 6.0% threonine, ~ 17.7% cysteine, ~ 31.0% serine, and ~ 35.8% metallopeptidases. One hundred and two proteases have been reassigned into the above six classes, while the active sites and/or metal-binding residues of 110 proteases were recharacterized. The probable physiological functions and active site architectures of these peptidases were also investigated. This work provides a more precise overview of the complete degradome of A. niger, which will no doubt constitute a valuable resource and starting point for further experimental studies on the biochemical characterization and physiological roles of these proteases.

Dipeptidyl peptidase IV is involved in the cellulose-responsive induction of cellulose biomass-degrading enzyme genes in Aspergillus aculeatus

We screened for factors involved in the cellulose-responsive induction of cellulose biomass-degrading enzyme genes from approximately 12,000 Aspergillus aculeatus T-DNA insertion mutants harboring a transcriptional fusion between the FIII-avicelase gene (cbhI) promoter and the orotidine 5'-monophosphate decarboxylase gene. Analysis of 5-fluoroorodic acid (5-FOA) sensitivity, cellulose utilization, and cbhI expression of the mutants revealed that a mutant harboring T-DNA at the dipeptidyl peptidase IV (dppIV) locus had acquired 5-FOA resistance and was deficient in cellulose utilization and cbhI expression. The deletion of dppIV resulted in a significant reduction in the cellulose-responsive expression of both cbhI as well as genes controlled by XlnR-independent and XlnR-dependent signaling pathways at an early phase in A. aculeatus. In contrast, the dppIV deletion did not affect the xylose-responsive expression of genes under the control of XlnR. These results demonstrate that DppIV participates in cellulose-responsive induction in A. aculeatus.

Plant-based biopharming of recombinant human lactoferrin

Recombinant proteins are currently recognized as pharmaceuticals, enzymes, food constituents, nutritional additives, antibodies and other valuable products for industry, healthcare, research, and everyday life. Lactoferrin (Lf), one of the promising human milk proteins, occupies the expanding biotechnological food market niche due to its important versatile properties. Lf shows antiviral, antimicrobial, antiprotozoal and antioxidant activities, modulates cell growth rate, binds glycosaminoglycans and lipopolysaccharides, and also inputs into the innate/specific immune responses. Development of highly efficient human recombinant Lf expression systems employing yeasts, filamentous fungi and undoubtedly higher plants as bioreactors for the large-scale Lf production is a biotechnological challenge. This review highlights the advantages and disadvantages of the existing non-animal Lf expression systems from the standpoint of protein yield and its biological activity. Special emphasis is put on the benefits of monocot plant system for Lf expression and the biosafety aspects of the transgenic Lf-expressing plants.

Monitoring of the effects of transfection with baculovirus on Sf9 cell line and expression of human dipeptidyl peptidase IV

Human dipeptidylpeptidase IV (hDPPIV) is an enzyme that is in hydrolase class and has various roles in different parts of human body. Its deficiency may cause some disorders in the gastrointestinal, neurologic, endocrinological and immunological systems of humans. In the present study, hDPPIV enzyme was expressed on Spodoptera frugiperda (Sf9) cell lines as a host cell, and the expression of hDPPIV was obtained by a baculoviral expression system. The enzyme production, optimum multiplicity of infection, optimum transfection time, infected and uninfected cell size and cell behavior during transfection were also determined. For maximum hDPPIV (269 mU mL(-1)) enzyme, optimum multiplicity of infection (MOI) and time were 0.1 and 72 h, respectively. The size of infected cells increased significantly (P < 0.001) after 24 h post infection. The results indicated that Sf9 cell line was applicable to the large scale for hDPPIV expression by using optimized parameters (infection time and MOI) because of its high productivity (4.03 mU m L(-1) h(-1)).

Fungal proteases and their pathophysiological effects

Proteolytic enzymes play an important role in fungal physiology and development. External digestion of protein substrates by secreted proteases is required for survival and growth of both saprophytic and pathogenic species. Extracellular serine, aspartic, and metalloproteases are considered virulence factors of many pathogenic species. New findings focus on novel membrane-associated proteases such as yapsins and ADAMs and their role in pathology. Proteases from fungi induce inflammatory responses by altering the permeability of epithelial barrier and by induction of proinflammatory cytokines through protease-activated receptors. Many fungal allergens possess proteolytic activity that appears to be essential in eliciting Th2 responses. Allergenic fungal proteases can act as adjuvants, potentiating responses to other allergens. Proteolytic enzymes from fungi contribute to inflammation through interactions with the kinin system as well as the coagulation and fibrinolytic cascades. Their effect on the host protease-antiprotease balance results from activation of endogenous proteases and degradation of protease inhibitors. Recent studies of the role of fungi in human health point to the growing importance of proteases not only as pathogenic agents in fungal infections but also in asthma, allergy, and damp building related illnesses. Proteolytic enzymes from fungi are widely used in biotechnology, mainly in food, leather, and detergent industries, in ecological bioremediation processes and to produce therapeutic peptides. The involvement of fungal proteases in diverse pathological mechanisms makes them potential targets of therapeutic intervention and candidates for biomarkers of disease and exposure.

Secreted dipeptidyl peptidase IV activity in the dimorphic fungal pathogen Histoplasma capsulatum

Dipeptidyl peptidase type IV (DppIV) enzymes are broadly distributed phylogenetically and display diverse functions, including intercellular signaling, immunomodulation, protein maturation and processing, metabolism, and nutrient acquisition. We identified a secreted proteolytic activity in Histoplasma capsulatum effective toward DppIV-specific substrates. In order to determine the gene(s) that encodes this activity, we identified two putative DPPIV homologs (HcDPPIVA and HcDPPIVB) in H. capsulatum based on a homology search with Aspergillus fumigatus DppIV. Comparative sequence analysis revealed that HcDppIVA is similar to secreted DppIV enzymes, while HcDppIVB clusters with intracellular DapB-like enzymes. Unexpectedly, silencing of HcDPPIVA by RNA interference (RNAi) had no effect on secreted DppIV activity and an HcDPPIVA-null deletion mutant also showed no abrogation of secreted DppIV activity. In contrast, RNAi silencing of HcDPPIVB significantly reduced the level of secreted DppIV activity. RNAi silencing of HcDPPIVB in the HcDPPIVA-null mutant had no additional effect on secreted DppIV activity, indicating that HcDPPIVA does not contribute to secreted activity. RNAi silencing of HcDPPIVB did not affect the ability to kill a murine macrophage-like cell line, RAW 264.7, indicating that this gene is not required for infection of macrophages.

Secreted dipeptidyl peptidases as potential virulence factors for Microsporum canis

Dermatophytoses caused by Microsporum canis are frequently encountered in cats and dogs; they are highly contagious and readily transmissible to humans. In this study, two single genes, respectively coding for dipeptidyl peptidases IV and V (DppIV and DppV), were isolated and characterized. Both proteins share homology with serine proteases of the S9 family, some of which display properties compatible with implication in pathogenic processes. Both genes are expressed in vivo in experimentally infected guinea-pigs and in naturally infected cats, and when the fungus is grown on extracellular matrix proteins as the sole nitrogen and carbon source. DppIV and V were produced as active recombinant proteases in the yeast Pichia pastoris; the apparent molecular weight of rDppV is 83 kDa, whereas rDppIV appears as a doublet of 95 and 98 kDa. Like other members of its enzymatic subfamily, rDppIV has an unusual ability to cleave Pro-X bonds. This activity does not enhance the solubilization of keratin by fungal secreted endoproteases, and the protease probably acts solely on small soluble peptides. RDppV showed no ability to induce delayed-type hypersensitivity (DTH) skin reactions in guinea-pigs, despite the known immunogenic properties of homologous proteins.