Search

Redox signaling and homeostasis are essential for cell survival and the immune response. Peroxiredoxin (Prx) modulates the level of H2O2 as a redox signal through H2O2 decomposition. The redox activity of thioredoxin (Trx) is required as a reducing equivalent to regenerate Prx. Edwardsiella piscicida is an opportunistic Gram-negative enteric pathogen that secretes a novel Trx-like effector protein, ETAE_2186 (Trxlp). Trxlp has unique structural properties compared with other Trx proteins. In enzymatic and binding assays, we confirmed Trxlp to be redox-inactive due to the low reactivity and flexibility of the resolving cysteine residue, C35, at the active site motif “31WCXXC35”. We identified key residues near the active site that are critical for reactivity and flexibility of C35 by site-directed mutagenesis analysis. NMR titration experiment demonstrated prolong inhibitory interaction of Trxlp with Prx1 resulting in the repression of Prx1–mediated H2O2 decomposition leading to increased ROS accumulation in infected host cells. Increased ROS in turn prevented nuclear translocation of NF-κB and inhibition of NF-κB target genes, leading to bacterial survival and enhanced replication inside host cells. Targeting Trxlp-mediated virulence promises to attenuate E. piscicida infection.

Tripartite motif (TRIM) E3 ligases target specific substrates, including viral proteins, for proteasomal degradation, and are thus essential regulators of the innate antiviral response. TRIM69 ubiquitinates the non-structural NS3 protein of Dengue virus for its degradation by the host machinery. This antiviral strategy abrogates the immunosuppression mediated by the NS2B-NS3 protease complex. To understand how this host-driven antiviral response against Dengue virus, we sought to define the mode of interaction between human TRIM69 and Dengue NS2B-NS3 and the subsequent polyubiquitination of the protease by the E3 ligase. We show that NS2B-NS3Δpro is sufficient as a substrate for ubiquitination by TRIM69 using ELISA and in vitro assays. Using hydrogen-deuterium exchange mass spectrometry (HDXMS), we mapped the interface of the interaction between TRIM69 and NS2B-NS3Δpro, and propose a rationale for the binding and subsequent ubiquitination process. Furthermore, through sequence analysis, we showed that the regions targeted by TRIM69 on the DENV-2 NS3 protease (NS3Δpro) are well conserved across DENV serotypes and other flaviviruses, including Zika virus, West Nile virus, and Japanese encephalitis virus. Our results show the direct interactions of TRIM69 with viral proteins, provide mechanistic insights at a molecular level, and highlight the functional relevance of TRIM69 interacting with the Dengue viral protein. Collectively, our findings suggest that TRIM69 may act as a pan-antiflaviviral restriction factor.

Dengue viruses (DENV) are expanding global pathogens that are transmitted through the bite of mosquitoes, mostly Aedes aegypti. As RNA viruses, DENV rely on RNA-binding proteins (RBPs) to complete their life cycle. Alternatively, RBPs can act as restriction factors that prevent DENV multiplication. While the importance of RBPs is well-supported in humans, there is a dearth of information about their influence on DENV transmission by mosquitoes. Such knowledge could be harnessed to design novel, effective interventions against DENV. Here, we successfully adapted RNA-affinity chromatography coupled with mass spectrometry-a technique initially developed in mammalian cells-to identify RBPs in Ae. aegypti cells. We identified fourteen RBPs interacting with DENV serotype 2 3'UTR, which is involved in the viral multiplication and produces subgenomic flaviviral RNA (sfRNA). We validated the RNA affinity results for two RBPs by confirming that AePur binds the 3'UTR, whereas AeStaufen interacts with both 3'UTR and sfRNA. Using in vivo functional evaluation, we determined that RBPs like AeRan, AeExoRNase, and AeRNase have pro-viral functions, whereas AeGTPase, AeAtu, and AePur have anti-viral functions in mosquitoes. Furthermore, we showed that human and mosquito Pur homologs have a shared affinity to DENV2 RNA, although the anti-viral effect is specific to the mosquito protein. Importantly, we revealed that AeStaufen mediates a reduction of gRNA and sfRNA copies in several mosquito tissues, including the salivary glands and that AeStaufen-mediated sfRNA reduction diminishes the concentration of transmission-enhancing sfRNA in saliva, thereby revealing AeStaufen's role in DENV transmission. By characterizing the first RBPs that associate with DENV2 3'UTR in mosquitoes, our study unravels new pro- and anti-viral targets for the design of novel therapeutic interventions as well as provides foundation for studying the role of RBPs in virus-vector interactions.

microRNAs (miRNAs), a class of small and endogenous molecules that control gene expression, are broadly involved in biological processes. Although a number of cofactors that assist or antagonize let-7 miRNA biogenesis are well-established, more auxiliary factors remain to be investigated. Here, we identified SYNCRIP (Synaptotagmin Binding Cytoplasmic RNA Interacting Protein) as a new player for let-7a miRNA. SYNCRIP interacts with pri-let-7a both in vivo and in vitro. Knockdown of SYNCRIP impairs, while overexpression of SYNCRIP promotes, the expression of let-7a miRNA. A broad miRNA profiling analysis revealed that silencing of SYNCRIP regulates the expression of a set of mature miRNAs positively or negatively. In addition, SYNCRIP is associated with microprocessor complex and promotes the processing of pri-let-7a. Strikingly, the terminal loop of pri-let-7a was shown to be the main contributor for its interaction with SYNCRIP. Functional studies demonstrated that the SYNCRIP RRM2–3 domain can promote the processing of pri-let-7a. Structure-based alignment of RRM2–3 with other RNA binding proteins identified the residues likely to participate in protein–RNA interactions. Taken together, these findings suggest the promising role that SYNCRIP plays in miRNA regulation, thus providing insights into the function of SYNCRIP in eukaryotic development.

Background Skin desquamation is facilitated by serine proteases KLK5 and KLK7, which are tightly regulated by lympho-epithelial Kazal-type related inhibitor (LEKTI). LEKTI itself is controlled through degraded by mesotrypsin. Here, we sought to determine whether LEKTI exonic mutations associated with atopic dermatitis (AD) affect the protease inhibitory activity of LEKTI or its susceptibility to mesotrypsin degradation. Methods The inhibitory activities of the LEKTI domain 4 (D4) and D6 WT and AD-associated mutants on the enzyme activities of KLK5 and KLK7 were compared using fluorogenic substrates. A keratinocyte cell culture system using HaCat cells was established to assess the role of D6 WT and D386N on triggering inflammation via the induction of thymic stromal lymphopoietin (TSLP). A degradation assay was used to assess the susceptibility of D4 and D6 mutants to mesotrypsin degradation. Results Enzymatic assays revealed that the D6 D386N mutation affected the inhibitory activity of LEKTI on KLK5 but not KLK7. Other exonic mutations on D6 (N368S, V395M, and E420K) and D4 (R267Q) did not alter LEKTI inhibition. The D386N mutation disrupted the role of D6 in suppressing TSLP induction by KLK5 in HaCat cells. Although WT D4 is more susceptible to mesotrypsin degradation than WT D6, the D4 R267Q mutant was more resistant to mesotrypsin degradation, whereas the D6 E420K mutant showed enhanced mesotrypsin-mediated degradation. Conclusion Exonic mutations in D6, which previously have been associated with AD, may cause a disruption of inhibitory activity on KLK5 or enhance the degradation by mesotrypsin.

Mosquito saliva proteins modulate the human immune and hemostatic systems and control mosquito-borne pathogenic infections. One mechanism through which mosquito proteins may influence host immunity and hemostasis is their interactions with key human receptor proteins that may act as receptors for or coordinate attacks against invading pathogens. Here, using pull-down assays and proteomics-based mass spectrometry, we identified 11Ae.aegyptisalivary gland proteins (SGPs) (e.g., apyrase,Ae.aegyptivenom allergen-1 [AaVA-1], neutrophil stimulating protein 1 [NeSt1], and D7 proteins), that interact with one or more of five human receptor proteins (cluster of differentiation 4 [CD4], CD14, CD86, dendritic cell-specific intercellular adhesion molecule-3-grabbing non-integrin [DC-SIGN], and Toll-like receptor 4 [TLR4]). We focused on CD4- and DC-SIGN-interacting proteins and confirmed that CD4 directly interacts with AaVA-1, D7, and NeST1 recombinant proteins and that AaVA-1 showed a moderate interaction with DC-SIGN using ELISA. Bacteria responsive protein 1 (AgBR1), anAe.aegyptisaliva protein reported to enhance ZIKV infection in humans but that was not identified in our pull-down assay moderately interacts with CD4 in the ELISA assay. Functionally, we showed that AaVA-1 and NeST1 proteins promoted activation of CD4+T cells. We propose the possible impact of these interactions and effects on mosquito-borne viral infections such as dengue, Zika, and chikungunya viruses. Overall, this study provides key insight into the vector-host (protein-protein) interaction network and suggests roles for these interactions in mosquito-borne viral infections.

Human dermcidin (DCD) is an antimicrobial peptide secreted constitutively by sweat glands. The anionic derivative, DCD-1L, comprises of the N-terminal 47 residues of DCD and one additional leucine residue. A previous NMR structure of DCD-1L in 50% TFE showed a partial helical conformation, and its crystal structure in the presence of Zn2+ outlined a hexameric linear α-helical bundle. Three different models to describe membrane insertion were proposed but no conclusion was drawn. In the current study, the NMR structure of DCD-1L in SDS micelles showed an “L-shaped” molecule with three fully formed α-helices connected by flexible turns. Formation of these helices in DCD-1L in the presence of POPG vesicles suggests that the acidic C-terminal region of DCD-1L can suppress the binding of DCD-1L to POPG vesicles at basic but not acidic pH. Mutation of charged residues on the N-terminal and C-terminal regions of DCD-1L cause differences in POPG binding, suggesting distinct functional roles for these two regions. Charged residues from these two regions are also found to differentially affect Zn2+ coordination and aggregation of DCD-1L in the absence or presence of SDS, as monitored by 1D NMR. Our data agrees with one of the three models proposed.

Drug target identification is a critical step toward understanding the mechanism of action of a drug, which can help one improve the drug's current therapeutic regime and expand the drug's therapeutic potential. However, current in vitro affinity-chromatography-based and in vivo activity-based protein profiling approaches generally face difficulties in discriminating specific drug targets from nonspecific ones. Here we describe a novel approach combining isobaric tags for relative and absolute quantitation with clickable activity-based protein profiling to specifically and comprehensively identify the protein targets of andrographolide (Andro), a natural product with known anti-inflammation and anti-cancer effects, in live cancer cells. We identified a spectrum of specific targets of Andro, which furthered our understanding of the mechanism of action of the drug. Our findings, validated through cell migration and invasion assays, showed that Andro has a potential novel application as a tumor metastasis inhibitor. Moreover, we have unveiled the target binding mechanism of Andro with a combination of drug analog synthesis, protein engineering, and mass-spectrometry-based approaches and determined the drug-binding sites of two protein targets, NF-κB and actin.

Human Edwardsiella tarda infections often manifest as gastroenteritis, but can become systemic and potentially lethal. E. tarda uses virulence factors that include type III and type VI secretion systems, quorum sensing, two-component systems, and exoenzymes to gain entry into and survive within the host. Better understanding of interactions between these factors will lead to the development of novel antimicrobials against E. tarda and other enterics.

In up to one-third of patients with acute myeloid leukemia, a C-terminal frame-shift mutation results in abnormal and abundant cytoplasmic accumulation of the usually nucleoli-bound protein nucleophosmin (NPM), and this is thought to function in cancer pathogenesis. Here, we demonstrate a gain-of-function role for cytoplasmic NPM in the inhibition of caspase signaling. The NPM mutant specifically inhibits the activities of the cell-death proteases, caspase-6 and -8, through direct interaction with their cleaved, active forms, but not the immature procaspases. The cytoplasmic NPM mutant not only affords protection from death ligand-induced cell death but also suppresses caspase-6/-8–mediated myeloid differentiation. Our data hence provide a potential explanation for the myeloid-specific involvement of cytoplasmic NPM in the leukemogenesis of a large subset of acute myeloid leukemia.

Despite being initially identified in the blood filtrate, LEKTI is a 15-domain Kazal-type inhibitor mostly known in the regulation of skin desquamation. In the current study, screening of serine proteases in blood coagulation cascade showed that LEKTI domain 4 has inhibitory activity toward only FXIa, whereas LEKTI domain 6 inhibits both FXIa and FXaB (bovine FXa). Nuclear magnetic resonance structural and dynamic experiments plus molecular dynamics simulation revealed that LEKTI domain 4 has enhanced backbone flexibility at the reactive-site loop. A model of the LEKTI-protease complex revealed that FXaB has a narrower S4 pocket compared with FXIa and hence prefers only small side-chain residues at the P4 position, such as Ala in LEKTI domain 6. Mutational studies combined with a molecular complex model suggest that both a more flexible reactive-site loop and a bulky residue at the P4 position make LEKTI domain 4 a weaker but highly selective inhibitor of FXIa. ASTAR (Agency for Sci., Tech. and Research, S’pore) MOE (Min. of Education, S’pore) NMRC (Natl Medical Research Council, S’pore)

Human chitinases (EC.3.2.1.14) are classified into family 18 of glycosyl hydrolase (GH18) superfamily based on their amino acid sequence similarities. Active chitinase hydrolyzes chitin, a beta-1,4-linked N-acetyl-D-glucosamine oligosaccharide. Chitin is a major structural component of the insect exoskeletons and fungal cell walls, but is not found in vertebrates. In human, eight GH18 chitinases have been identified including active chitotriosidase and acidic mammalian chitinase. Most of the human chitinases lack chitinolytic activity due to mutation of an essential glutamic acid residue at the catalytic domain, and they are termed chitolectin. This review highlights some characteristics of human chitinases, compares structural differences among some human GH18 members, and discusses their cellular regulation and function. Finally, we summarize current views on the role of human chitinases in a variety of human diseases.

Asthma is a chronic inflammatory disease characterized by airway inflammation, mucus hypersecretion and airway hyperresponsiveness. Mechanisms underlying the pathogenesis of asthma are not fully understood. In recent years, there are mounting evidences demonstrating that mammalian chitinases may play a key role in mediating the T-helper 2 cell-driven inflammatory response that is commonly associated with asthma. Chitinases (e.g., chitotriosidase and acidic mammalian chitinase) are enzymes that degrade chitin, the second most abundant biopolymer that can be found in the cell walls of fungi, microfilarial sheaths of helminths, and exoskeletons of insects and crustaceans. There are also chitinase-like proteins (e.g., YKL-40, Ym1 and Ym2) that lack chitinolytic activity but retain chitin-binding ability. Therefore, chitinases were originally believed to function in host defense against parasitic infections, but the first discovery of their role in inflammatory airway diseases came as a surprise. There is ample evidence to support an association of acidic mammalian chitinase and YKL-40 with allergic bronchial asthma in patients. Our recent studies in a mouse asthma model revealed that anti-inflammatory drugs like corticosteroid and cysteinyl leukotriene receptor antagonist were able to suppress elevated pulmonary levels of mammalian chitinases. Taken together, mammalian chitinases may be useful as biomarkers for asthma. Notwithstanding, large-scale multi-center association studies are required to confirm this hypothesis. Besides, substantially more works using knockout mice, recombinant chitinases and siRNA technology are required to investigate a potential role of chitinases in the pathogenesis of asthma.

Lung fibroblast plays a pivotal role in lung repair and remodeling, and also contributes to lung inflammation. The present study investigated differential protein profiling of normal human lung fibroblasts stimulated with tumor necrosis factor (TNF)-alpha. Total proteins from lung fibroblasts were separated by 2-DE, and differentially expressed proteins were identified by MALDI-TOF MS. TNF-alpha was found for the first time to alter the expression levels of myxovirus resistance protein A, interferon-stimulated gene 15, plasminogen activator inhibitor-2, lysyl hydroxylase 2 (isoform a), and prolyl 4-hydroxylase (alpha subunit) in human lung fibroblasts. In particular, dendritic cell-derived interferon-gamma-induced protein (DCIP) was upregulated by TNF-alpha in lung fibroblasts and its biological function is at present unknown. We found that TNF-alpha-induced DCIP expression was dependent on the transcription factor interferon regulatory factor-1. DCIP-selective antisense oligodeoxynucleotide inhibited the expression of TNF-alpha-responsive gene targets including vascular cell adhesion molecule-1, intercellular adhesion molecule-1, IL-6, IL-8, IP-10, and thymic stromal lymphopoietin. In a lipopolysaccharide-induced acute lung injury mouse model, DCIP mRNA level was elevated together with that of TNF-alpha. We have demonstrated for the first time that DCIP is upregulated by TNF-alpha and also mediates TNF-alpha stimulation of human lung fibroblasts. Further studies on the role of DCIP in airway inflammation and remodeling are warranted.

The ratio of the levels of pro-survival and pro-apoptotic members of the Bcl-2 protein family is thought to be an important regulatory factor for determining the sensitivity of the mammalian cells to apoptotic stimuli. High levels of expression of pro-survival members such as Bcl(XL) in human cancers were frequently found to be a good prognostic indicator predicting poor response to chemotherapy. The pro-survival members of the Bcl-2 family mediate their effects through heterodimerization with the BH3 region of the pro-apoptotic members. Structural analyses of the binding complex of the BH3 peptide and Bcl(XL) showed that a hydrophobic groove termed the BH3 binding cleft is the docking site for the BH3 region. Chemical mimetics of the BH3 region such as BH3I-1 that target the BH3 binding cleft indeed exhibit pro-apoptotic activities. Chelerythrine (CHE) and sanguinarine (SAN) are natural benzophenanthridine alkaloids that are structurally homologous to each other. CHE was previously identified as an inhibitor of Bcl(XL) function from a high-throughput screen of natural products, but its mode of interaction with Bcl(XL) is not known. By determining the effect of site-directed mutagenesis on ligand binding and using saturation transfer difference (STD) NMR experiments, we have verified locations of these docked ligands. Surprisingly, CHE and SAN bind separately at the BH groove and BH1 region of Bcl(XL) respectively, different from the BH3 binding cleft where other known inhibitors of Bcl(XL) target. Interestingly, certain residues on the flexible loop between helices alpha1 and alpha2 of Bcl(XL) are also perturbed upon CHE, but not SAN or BH3I-1 binding. Although CHE and SAN are similarly effective as BH3I-1 in displacing bound BH3 peptide, they are much more effective in inducing apoptosis, raising the possibility that CHE and SAN might be able to antagonize other pro-survival mechanisms in addition to the one that involves BH3 region binding.

Edwardsiella tarda is a Gram-negative enteric pathogen that causes hemorrhagic septicemia in fish and both gastrointestinal and extraintestinal infections in humans. A type III secretion system (T3SS) was recently shown to contribute to pathogenesis, since deletions of various T3SS genes increased the 50% lethal dose (LD 50 ) by about 1 log unit in the blue gourami infection model. In this study, we report EseG as the first identified effector protein of T3SS. EseG shares partial homology with two Salmonella T3SS effectors (SseG and SseF) over a conserved domain (amino acid residues 142 to 192). The secretion of EseG is dependent on a functional T3SS and, in particular, requires the chaperone EscB. Experiments using TEM-1 β-lactamase as a fluorescence-based reporter showed that EseG was translocated into HeLa cells at 35°C. Fractionation of infected HeLa cells demonstrated that EseG was localized to the host membrane fraction after translocation. EseG is able to disassemble microtubule structures when overexpressed in mammalian cells. This phenotype may require a conserved motif of EseG (EseG 142-192 ), since truncated versions of EseG devoid of this motif lose their ability to cause microtubule destabilization. By demonstrating the function of EseG, our study contributes to the understanding of E. tarda pathogenesis. Moreover, the approach established in this study to identify type III effectors can be used to identify and characterize more type III and possible type VI effectors in Edwardsiella .

Pathogens use type VI secretion systems (T6SSs) to transport proteins into the environment or host cells in response to external stimuli. T6SSs are tightly regulated together with other virulence determinants such as type III secretion systems, quorum sensing (QS), and flagella synthesis. Five pathogens (Salmonella enterica, Edwardsiella tarda, Aeromonas hydrophila, Vibrio cholerae, and Pseudomonas aeruginosa) are examined for crosstalk proteins (global regulators) that connect T6SSs to other virulence determinants. Common transcriptional regulators (TRs) include two component systems (i.e. PhoPQ), σ(54) and σ(54)-dependent TRs (i.e. VasH), and QS regulators. Greater understanding of this integral communication network will define what is essential for bacterial pathogenesis.

Background Nuclear Magnetic Resonance (NMR) spectroscopy offers a variety of experiments to study protein-ligand interactions at atomic resolution. Among these experiments, 15N Heteronuclear Single Quantum Correlation (HSQC)experiment is simple, less time consuming and highly informative in mapping the binding site of the ligand. The interpretation of 15N HSQC becomes ambiguous when the chemical shift perturbations are caused by non-specific interactions like allosteric changes and local structural rearrangement. Under such cases, detailed chemical exchange analysis based on chemical shift perturbation will assist in locating the binding site accurately. Methodology/principal findings We have automated the mapping of binding sites for fast chemical exchange systems using information obtained from 15N HSQC spectra of protein serially titrated with ligand of increasing concentrations. The automated program Auto-FACE (Auto-FAst Chemical Exchange analyzer) determines the parameters, e.g. rate of change of perturbation, binding equilibrium constant and magnitude of chemical shift perturbation to map the binding site residues.Interestingly, the rate of change of perturbation at lower ligand concentration is highly sensitive in differentiating the binding site residues from the non-binding site residues. To validate this program, the interaction between the protein hBcl(XL) and the ligand BH3I-1 was studied. Residues in the hydrophobic BH3 binding groove of hBcl(XL) were easily identified to be crucial for interaction with BH3I-1 from other residues that also exhibited perturbation. The geometrically averaged equilibrium constant (3.0 x 10(4)) calculated for the residues present at the identified binding site is consistent with the values obtained by other techniques like isothermal calorimetry and fluorescence polarization assays (12.8 x 10(4)). Adjacent to the primary site, an additional binding site was identified which had an affinity of 3.8 times weaker than the former one. Further NMR based model fitting for individual residues suggest single site model for residues present at these binding sites and two site model for residues present between these sites. This implies that chemical shift perturbation can represent the local binding event much more accurately than the global binding event. Conclusion/significance Detail NMR chemical shift perturbation analysis enabled binding site residues to be distinguished from non-binding site residues for accurate mapping of interaction site in complex fast exchange system between small molecule and protein. The methodology is automated and implemented in a program called "Auto-FACE", which also allowed quantitative information of each interaction site and elucidation of binding mechanism.

A high incidence of sensitization to Blomia tropicalis, the predominant house dust mite species in tropical regions, is strongly associated with allergic diseases in Singapore, Malaysia, and Brazil. IgE binding to the group 5 allergen, Blo t 5, is found to be the most prevalent among all B. tropicalis allergens. The NMR structure of Blo t 5 determined represents a novel helical bundle structure consisting of three antiparallel α-helices. Based on the structure and sequence alignment with other known group 5 dust mite allergens, surface-exposed charged residues have been identified for site-directed mutagenesis and IgE binding assays. Four charged residues, Glu76, Asp81, Glu86, and Glu91 at around the turn region connecting helices α2 and α3 have been identified to be involved in the IgE binding. Using overlapping peptides, we have confirmed that these charged residues are located on a major putative linear IgE epitope of Blo t 5 from residues 76–91 comprising the sequence ELKRTDLNILERFNYE. Triple and quadruple mutants have been generated and found to exhibit significantly lower IgE binding and reduced responses in skin prick tests. The mutants induced similar PBMC proliferation as the wild-type protein but with reduced Th2:Th1 cytokines ratio. Mass screening on a quadruple mutant showed a 40% reduction in IgE binding in 35 of 42 sera of atopic individuals. Findings in this study further stressed the importance of surface-charged residues on IgE binding and have implications in the cross-reactivity and use of Blo t 5 mutants as a hypoallergen for immunotherapy.

IgE-mediated allergic response involves cross-linking of IgE bound on mast cells by specific surface epitopes of allergens. Structural studies on IgE epitopes of allergens are essential in understanding the characteristics of an allergen and for development of specific allergen immunotherapy. We have determined the structure of a group 13 dust mite allergen from Dermatophagoides farinae, Der f 13, using nuclear magnetic resonance. Sequence comparison of Der f 13 with homologous human fatty acid-binding proteins revealed unique surface charged residues on Der f 13 that may be involved in IgE binding and allergenicity. Site-directed mutagenesis and IgE binding assays have confirmed four surface charged residues on opposite sides of the protein that are involved in IgE binding. A triple mutant of Der f 13 (E41A_K63A_K91A) has been generated and found to have significantly reduced IgE binding and histamine release in skin prick tests on patients allergenic to group 13 dust mite allergens. The triple mutant is also able to induce PBMC proliferation in allergic patients with indices similar to those of wild-type Der f 13 and shift the secretion of cytokines from a Th2 to a Th1 pattern. Mouse IgG serum raised using the triple mutant is capable to block the binding of IgE from allergic patients to wild-type Der f 13, indicating potential for the triple mutant as a hypoallergen for specific immunotherapy. Findings in this study imply the importance of surface charged residues on IgE binding and allergenicity of an allergen, as was also demonstrated in other major allergens studied.