Optimization of secretion and surface localization of heterologous OVA protein in mycobacteria by using LipY as a carrier.

BACKGROUND: Mycobacterium bovis Bacille Calmette-Guérin (BCG) is not only used as a vaccine against tuberculosis but also protects against leprosy and is used as part of bladder cancer treatment to induce a protective immune response. However, protection by BCG vaccination is not optimal. To improve vaccine efficacy, recombinant BCG expressing heterologous antigens has been put forward to elicit antigen-specific cellular and humoral responses. Cell surface localized or secreted antigens induce better immune responses than their cytosolic counterparts. Optimizing secretion of heterologous proteins or protein fragments holds therefore unexplored potential for improving the efficacy of recombinant BCG vaccine candidates. Secretion of heterologous antigens requires crossing the mycobacterial inner and outer membrane. Mycobacteria have specialized ESX or type VII secretion systems that enable translocation of proteins across both membranes. Probing this secretion system could therefore be a valid approach to surface localize heterologous antigens. RESULTS: We show that ESX-5 substrate LipY, a lipase, can be used as a carrier for heterologous secretion of an ovalbumin fragment (OVA). LipY contains a PE domain and a lipase domain, separated by a linker region. This linker domain is processed upon secretion. Fusion of the PE and linker domains of LipY to OVA enabled ESX-5-dependent secretion of the fusion construct LipY-OVA in M. marinum, albeit with low efficiency. Subsequent random mutagenesis of LipY-OVA and screening for increased secretion resulted in mutants with improved heterologous secretion. Detailed analysis identified two mutations in OVA that improved secretion, i.e. an L280P mutation and a protein-extending frameshift mutation. Finally, deletion of the linker domain of LipY enhanced secretion of LipY-OVA, although this mutation also reduced surface association. Further analysis in wild type LipY showed that the linker domain is required for surface association. CONCLUSION: We show that the ESX-5 system can be used for heterologous secretion. Furthermore, minor mutations in the substrate can enhance secretion. Especially the C-terminal region seems to be important for this. The linker domain of LipY is involved in surface association. These findings show that non-biased screening approaches aid in optimization of heterologous secretion, which can contribute to heterologous vaccine development.

NLRP3 rs35829419 polymorphism is associated with increased susceptibility to multiple diseases in humans.

Using a meta-analysis framework, we investigated the association between the NLRP3 rs35829419 polymorphism and increased susceptibility to diverse diseases in humans. Relevant published studies were identified through a comprehensive and systematic electronic search, using the following scientific literature databases: Science Citation Index, the Cochrane Library, PubMed, Embase, CINAHL, Current Contents Index, Chinese Biomedical, the Chinese Journal Full-Text, and the Weipu Journal. Statistical analysis of data extracted from the selected high quality studies was performed using the Version 12.0 STATA software. A total of 13 case-control studies met our stringent inclusion and exclusion criteria for the present meta-analysis. These 13 high quality studies contained relevant information on 7719 patients with various diseases and 7094 healthy controls. Our meta-analysis results showed that the NLRP3 gene rs35829419 C>A polymorphism was associated with a significantly increased risk of developing multiple diseases in humans under 5 genetic models (all P < 0.05). Data stratification and subgroup analysis based on the disease type revealed that rs35829419 C>A carriers displayed a markedly increase susceptibility to leprosy, colorectal cancer, HIV-1 infection, rheumatoid arthritis, abdominal aortic aneurysms, inflammatory bowel disease, ulcerative colitis, and atopic dermatitis. In summary, our meta-analysis results revealed the first identified strong correlation between the NLRP3 rs35829419 polymorphism and increased susceptibility to various diseases in humans.

The thalidomide-binding domain of cereblon defines the CULT domain family and is a new member of the ß-tent fold.

Despite having caused one of the greatest medical catastrophies of the last century through its teratogenic side-effects, thalidomide continues to be an important agent in the treatment of leprosy and cancer. The protein cereblon, which forms an E3 ubiquitin ligase compex together with damaged DNA-binding protein 1 (DDB1) and cullin 4A, has been recently indentified as a primary target of thalidomide and its C-terminal part as responsible for binding thalidomide within a domain carrying several invariant cysteine and tryptophan residues. This domain, which we name CULT (cereblon domain of unknown activity, binding cellular ligands and thalidomide), is also found in a family of secreted proteins from animals and in a family of bacterial proteins occurring primarily in δ-proteobacteria. Its nearest relatives are yippee, a highly conserved eukaryotic protein of unknown function, and Mis18, a protein involved in the priming of centromeres for recruitment of CENP-A. Searches for distant homologs point to an evolutionary relationship of CULT, yippee, and Mis18 to proteins sharing a common fold, which consists of two four-stranded ß-meanders packing at a roughly right angle and coordinating a zinc ion at their apex. A ß-hairpin inserted into the first ß-meander extends across the bottom of the structure towards the C-terminal edge of the second ß-meander, with which it forms a cradle-shaped binding site that is topologically conserved in all members of this fold. We name this the ß-tent fold for the striking arrangement of its constituent ß-sheets. The fold has internal pseudosymmetry, raising the possibility that it arose by duplication of a subdomain-sized fragment.

CUBN and NEBL common variants in the chromosome 10p13 linkage region are associated with multibacillary leprosy in Vietnam.

Leprosy is caused by infection with Mycobacterium leprae and is classified clinically into paucibacillary (PB) or multibacillary (MB) subtypes based on the number of skin lesions and the bacillary index detected in skin smears. We previously identified a major PB susceptibility locus on chromosome region 10p13 in Vietnamese families by linkage analysis. In the current study, we conducted high-density association mapping of the 9.5 Mb linkage peak on chromosome region 10p13 covering 39 genes. Using leprosy per se and leprosy subtypes as phenotypes, we employed 294 nuclear families (303 leprosy cases, 63 % MB, 37 % PB) as a discovery sample and 192 nuclear families (192 cases, 55 % MB, 45 % PB) as a replication sample. Replicated significant association signals were revealed in the genes for cubilin (CUBN) and nebulette (NEBL). In the combined sample, the C allele (frequency 0.26) at CUBN SNP rs10904831 showed association [p = 1 × 10(-5); OR 0.52 (0.38-0.7)] with MB leprosy only. Likewise, allele T (frequency 0.42) at NEBL SNP rs11012461 showed association [p = 4.2 × 10(-5); OR 2.51 (1.6-4)] with MB leprosy only. These associations remained valid for the CUBN signal when taking into account the effective number of tests performed (type I error significance threshold = 2.4 × 10(-5)). We used the results of our analyses to propose a new model for the genetic control of polarization of clinical leprosy.

Mycobacterial laminin-binding histone-like protein mediates collagen-dependent cytoadherence

When grown in the presence of exogenous collagen I, Mycobacterium bovis BCG was shown to form clumps. Scanning electron microscopy examination of these clumps revealed the presence of collagen fibres cross-linking the bacilli. Since collagen is a major constituent of the eukaryotic extracellular matrices, we assayed BCG cytoadherence in the presence of exogenous collagen I. Collagen increased the interaction of the bacilli with A549 type II pneumocytes or U937 macrophages, suggesting that BCG is able to recruit collagen to facilitate its attachment to host cells. Using an affinity chromatography approach, we have isolated a BCG collagen-binding protein corresponding to the previously described mycobacterial laminin-binding histone-like protein (LBP/Hlp), a highly conserved protein associated with the mycobacterial cell wall. Moreover, Mycobacterium leprae LBP/Hlp, a well-characterized adhesin, was also able to bind collagen I. Finally, using recombinant fragments of M. leprae LBP/Hlp, we mapped the collagen-binding activity within the C-terminal domain of the adhesin. Since this protein was already shown to be involved in the recognition of laminin and heparan sulphate-containing proteoglycans, the present observations reinforce the adhesive activities of LBP/Hlp, which can be therefore considered as a multifaceted mycobacterial adhesin, playing an important role in both leprosy and tuberculosis pathogenesis.

Evaluation of the combination of BP180-NC16a enzyme-linked immunosorbent assay and BP230 enzyme-linked immunosorbent assay in the diagnosis of bullous pemphigoid.

BACKGROUND: Bullous pemphigoid (BP) is an acquired autoimmune subepidermal blistering disease characterized by circulating IgG autoantibodies directed against BP180 and BP230 hemidesmosomal proteins. Previous studies have demonstrated that antibodies against the NC16a domain of BP180 mediate BP pathogenesis, while antibodies against BP230 enhance the inflammatory response. Recently, commercial BP180-NC16a enzyme-linked immunosorbent assay (ELISA) and BP230 ELISA kits were developed to detect anti-BP180 and anti-BP230 autoantibodies in human BP sera. AIMS: To evaluate the efficacy of BP180-NC16a ELISA and BP230 ELISA in the initial diagnosis of BP. METHODS: Sera from 62 BP patients and 62 control subjects were tested by BP180-NC16a ELISA and BP230 ELISA and compared with findings from indirect immunofluorescence (IIF) and immunoblotting (IB) to determine the sensitivity and specificity of these assays. RESULTS: The sensitivities of BP180-NC16a ELISA and BP230 ELISA were 87.1% (54/62) and 56.5% (35/62), respectively, and the specificities of both were 100% (62/62). Using both ELISAs for diagnosis increased the sensitivity to 95.2% (59/62) and was statistically comparable with IB sensitivity. CONCLUSIONS: ELISA is a convenient, effective, and reliable method for serodiagnosis of BP, and combined use of BP180-NC16a ELISA and BP230 ELISA can increase the sensitivity of this diagnostic approach.

A novel sarcoidosis risk locus for Europeans on chromosome 11q13.1.

RATIONALE: Sarcoidosis is a complex inflammatory disease with a heterogeneous clinical picture. Among others, an acute and chronic clinical course can be distinguished, for which specific genetic risk factors are known. OBJECTIVES: To identify additional risk loci for sarcoidosis and its acute and chronic subforms, we analyzed imputed data from a genome-wide association scan for these phenotypes. METHODS: After quality control, the genome-wide association scan comprised nearly 1.3 million imputed single-nucleotide polymorphisms based on an Affymetrix 6.0 Gene Chip dataset of 564 German sarcoidosis cases, including 176 acute and 354 chronic cases and 1,575 control subjects. MEASUREMENTS AND MAIN RESULTS: We identified chromosome 11q13.1 (rs479777) as a novel locus influencing susceptibility to sarcoidosis with genome-wide significance. The marker was significantly associated in three distinct German case-control populations and in an additional German family sample with odds ratios ranging from 0.67 to 0.77. This finding was further replicated in two independent European case-control populations from the Czech Republic (odds ratio, 0.75) and from Sweden (odds ratio, 0.79). In a meta-analysis of the included European case-control samples the marker yielded a P value of 2.68 × 10(-18). The locus was previously reported to be associated with Crohn disease, psoriasis, alopecia areata, and leprosy. For sarcoidosis, fine-mapping and expression analysis suggest KCNK4, PRDX5, PCLB3, and most promising CCDC88B as candidates for the underlying risk gene in the associated region. CONCLUSIONS: This study provides striking evidence for association of chromosome 11q13.1 with sarcoidosis in Europeans, and thus identified a further genetic risk locus shared by sarcoidosis, Crohn disease and psoriasis.

Mycobacterial laminin-binding histone-like protein mediates collagen-dependent cytoadherence.

When grown in the presence of exogenous collagen I, Mycobacterium bovis BCG was shown to form clumps. Scanning electron microscopy examination of these clumps revealed the presence of collagen fibres cross-linking the bacilli. Since collagen is a major constituent of the eukaryotic extracellular matrices, we assayed BCG cytoadherence in the presence of exogenous collagen I. Collagen increased the interaction of the bacilli with A549 type II pneumocytes or U937 macrophages, suggesting that BCG is able to recruit collagen to facilitate its attachment to host cells. Using an affinity chromatography approach, we have isolated a BCG collagen-binding protein corresponding to the previously described mycobacterial laminin-binding histone-like protein (LBP/Hlp), a highly conserved protein associated with the mycobacterial cell wall. Moreover, Mycobacterium leprae LBP/Hlp, a well-characterized adhesin, was also able to bind collagen I. Finally, using recombinant fragments of M. leprae LBP/Hlp, we mapped the collagen-binding activity within the C-terminal domain of the adhesin. Since this protein was already shown to be involved in the recognition of laminin and heparan sulphate-containing proteoglycans, the present observations reinforce the adhesive activities of LBP/Hlp, which can be therefore considered as a multifaceted mycobacterial adhesin, playing an important role in both leprosy and tuberculosis pathogenesis.

Comparative analyses of transport proteins encoded within the genomes of Mycobacterium tuberculosis and Mycobacterium leprae.

The co-emergence of multidrug resistant pathogenic bacterial strains and the Human Immunodeficiency Virus pandemic has made tuberculosis a leading public health threat. The causative agent is Mycobacterium tuberculosis (Mtu), a facultative intracellular parasite. Mycobacterium leprae (Mle), a related organism that causes leprosy, is an obligate intracellular parasite. Given that different transporters are required for bacterial growth and persistence under a variety of growth conditions, we conducted comparative analyses of transport proteins encoded within the genomes of these two organisms. A minimal set of genes required for intracellular and extracellular life was identified. Drug efflux systems utilizing primary active transport mechanisms have been preferentially retained in Mle and still others preferentially lost. Transporters associated with environmental adaptation found in Mtu were mostly lost in Mle. These findings provide starting points for experimental studies that may elucidate the dependencies of pathogenesis on transport for these two pathogenic mycobacteria. They also lead to suggestions regarding transporters that function in intra- versus extra-cellular growth.

Functional survey for heterologous sugar transport proteins, using Saccharomyces cerevisiae as a host.

Molecular transport is a key process in cellular metabolism. This step is often limiting when using a nonnative carbon source, as exemplified by xylose catabolism in Saccharomyces cerevisiae. As a step toward addressing this limitation, this study seeks to characterize monosaccharide transport preference and efficiency. A group of 26 known and putative monosaccharide transport proteins was expressed in a recombinant Saccharomyces cerevisiae host unable to transport several monosaccharides. A growth-based assay was used to detect transport capacity across six different carbon sources (glucose, xylose, galactose, fructose, mannose, and ribose). A mixed glucose-and-xylose cofermentation was performed to determine substrate preference. These experiments identified 10 transporter proteins that function as transporters of one or more of these sugars. Most of these proteins exhibited broad substrate ranges, and glucose was preferred in all cases. The broadest transporters confer the highest growth rates and strongly prefer glucose. This study reports the first molecular characterization of the annotated XUT genes of Scheffersomyces stipitis and open reading frames from the yeasts Yarrowia lipolytica and Debaryomyces hansenii. Finally, a phylogenetic analysis demonstrates that transporter function clusters into three distinct groups. One particular group comprised of D. hansenii XylHP and S. stipitis XUT1 and XUT3 demonstrated moderate transport efficiency and higher xylose preferences.

Identification of a primary target of thalidomide teratogenicity.

Half a century ago, thalidomide was widely prescribed to pregnant women as a sedative but was found to be teratogenic, causing multiple birth defects. Today, thalidomide is still used in the treatment of leprosy and multiple myeloma, although how it causes limb malformation and other developmental defects is unknown. Here, we identified cereblon (CRBN) as a thalidomide-binding protein. CRBN forms an E3 ubiquitin ligase complex with damaged DNA binding protein 1 (DDB1) and Cul4A that is important for limb outgrowth and expression of the fibroblast growth factor Fgf8 in zebrafish and chicks. Thalidomide initiates its teratogenic effects by binding to CRBN and inhibiting the associated ubiquitin ligase activity. This study reveals a basis for thalidomide teratogenicity and may contribute to the development of new thalidomide derivatives without teratogenic activity.

Evidence for leptin receptor isoforms heteromerization at the cell surface.

Leptin mediates its metabolic effects through several leptin receptor (LEP-R) isoforms. In humans, long (LEPRb) and short (LEPRa,c,d) isoforms are generated by alternative splicing. Most of leptin's effects are believed to be mediated by the OB-Rb isoform. However, the role of short LEPR isoforms and the possible existence of heteromers between different isoforms are poorly understood. Using BRET1 and optimized co-immunoprecipitation, we observed LEPRa/b and LEPRb/c heteromers located at the plasma membrane and stabilized by leptin. Given the widespread coexpression of LEPRa and LEPRb, our results suggest that LEPRa/b heteromers may represent a major receptor species in most tissues.

Expression of adipose differentiation-related protein (ADRP) and perilipin in macrophages infected with Mycobacterium leprae.

Mycobacterium leprae survives and replicates within a lipid droplet stored in the enlarged phagosome of histiocytes, a typical feature of lepromatous leprosy that is thought to be an important nutrient source for the bacillus. However, the underlying mechanisms by which lipids accumulate within phagosomes remain unclear. Recently, it was revealed that the lipid droplet-associated proteins, including ADRP and perilipin, play essential roles in lipid accumulation in adipocytes or macrophages. Therefore, we attempted to examine the role of these proteins in leprosy pathogenesis. ADRP and perilipin localized to the phagosomal membrane, which contains M. leprae in skin biopsy specimens of lepromatous leprosy. ADRP expression was transiently increased after phagocytosis in THP-1 cells. However, high levels of ADRP expression persisted only when live M. leprae, but not dead bacilli or latex beads, was added. Furthermore, although peptidoglycan, a Toll-like receptor 2 ligand, suppressed the expression levels of ADRP and perilipin, M. leprae infection inhibited this suppression. These results suggest that live M. leprae has the ability to actively induce and support ADRP/perilipin expression to facilitate the accumulation of lipids within the phagosome and to further maintain a suitable environment for the intracellular survival within the macrophage.

Structural characterization of agonist and antagonist-bound acetylcholine-binding protein from Aplysia californica.

Nicotinic acetylcholine receptors (nAChRs) are well-characterized allosteric transmembrane proteins involved in the rapid gating of ions elicited by ACh. These receptors belong to the Cys-loop superfamily of ligand-gated ion channels, which also includes GABAA and GABAC, 5-HT3, and glycine receptors. The nAChRs are homo- or heteromeric pentamers of structurally related subunits that encompass an extracellular N-terminal ligand-binding domain, four transmembrane-spanning regions that form the ion channel, and an extended intracellular region between spans 3 and 4. Ligand binding triggers conformational changes that are transmitted to the transmembrane-spanning region, leading to gating and changes in membrane potential. The four transmembrane spans on each of the five subunits create a substantial region of hydrophobicity that precludes facile crystallization of this protein. However the freshwater snail, Lymnaea stagnalis, produces a soluble homopentameric protein, termed the ACh-binding protein (AChBP), which binds ACh (Smit et al., 2001). Its structure was determined recently (Brejc et al., 2001) at high resolution, revealing the structural scaffold for nAChR, and has become a functional and structural surrogate of the nAChR ligand-binding domain. We have characterized an AChBP from Aplysia californica and determined distinct ligand-binding properties when compared to those of L. stagnalis, including ligand specificity for the nAChR alpha7 subtype-specific alpha-conotoxin ImI (Hansen et al., 2004).

Emergence of species-specific transporters during evolution of the hemiascomycete phylum.

We have traced the evolution patterns of 2480 transmembrane transporters from five complete genome sequences spanning the entire Hemiascomycete phylum: Saccharomyces cerevisiae, Candida glabrata, Kluyveromyces lactis, Debaryomyces hansenii, and Yarrowia lipolytica. The use of nonambiguous functional and phylogenetic criteria derived from the TCDB classification system has allowed the identification within the Hemiascomycete phylum of 97 small phylogenetic transporter subfamilies comprising a total of 355 transporters submitted to four distinct evolution patterns named "ubiquitous," "species specific," "phylum gains and losses," or "homoplasic." This analysis identifies the transporters that contribute to the emergence of species during the evolution of the Hemiascomycete phylum and may aid in establishing novel phylogenetic criteria for species classification.

The Escherichia coli biotin regulatory system: a transcriptional switch.

The ability of any organism to survive depends, in part, on mechanisms that enable it to modify its patterns of gene expression in response to extra- and intracellular signals. In the classical response mechanisms, a small molecule signal impinges on either an extra- or intracellular receptor, and through a series of events the signal is ultimately transmitted to transcription regulatory proteins. An alternative to this classical mechanism is provided by multi-functional transcription factors. These proteins function directly in transcription as well as in at least one additional cellular process. An example of this class of proteins includes the dimerization cofactor of hepatocyte nuclear factor (DcoH), which serves as an enzyme involved in regeneration of the tetra-hydrobiopterin cofactor and as a factor that stabilizes the dimerization of the hepatocyte nuclear transcription factor (Mendel DB, Khavari PA, Conley PB, Graves MK, Hansen LP, Admon A, et al. Characterization of a cofactor that regulates dimerization of a mammalian homeodomain protein. Science 1991;254:1762-7; Citron BA, Davis MD, Milstien S, Gutierrez J, Mendel DB, Crabtree GR. Identity of 4a-carbinolamine dehydratase, a component of the phenylalanine hydroxylation system, and DCoH, a transregulator of homeodomain proteins. Proc Natl Acad Sci U S A 1992;89:11891-4). Another example is the protein PutA, a redox enzyme involved in proline utilization and a regulator of transcription of the genes involved in proline utilization (Ostrovsky de Spicer P, Maloy S. Puta protein, a membrane-associated flavin dehydrogenase, acts as a redox-dependent transcriptional regulator. Proc Natl Acad Sci U S A 1993;90:4295-8). While several proteins of this class have been identified, their mechanisms of functional switching remain to be elucidated.

Activation of signaling lymphocytic activation molecule triggers a signaling cascade that enhances Th1 responses in human intracellular infection.

T cell production of IFN-gamma contributes to host defense against infection by intracellular pathogens, including mycobacteria. Lepromatous leprosy, the disseminated form of infection caused by Mycobacterium leprae, is characterized by loss of cellular response against the pathogen and diminished Th1 cytokine production. Relieving bacterial burden in Ag-unresponsive patients might be achieved through alternative receptors that stimulate IFN-gamma production. We have previously shown that ligation of signaling lymphocytic activation molecule (SLAM) enhances IFN-gamma in mycobacterial infection; therefore, we investigated molecular pathways leading from SLAM activation to IFN-gamma production in human leprosy. The expression of the SLAM-associated protein (an inhibitory factor for IFN-gamma induction) on M. leprae-stimulated cells from leprosy patients was inversely correlated to IFN-gamma production. However, SLAM ligation or exposure of cells from lepromatous patients to a proinflammatory microenvironment down-regulated SLAM-associated protein expression. Moreover, SLAM activation induced a sequence of signaling proteins, including activation of the NF-kappaB complex, phosphorylation of Stat1, and induction of T-bet expression, resulting in the promotion of IFN-gamma production, a pathway that remains quiescent in response to Ag in lepromatous patients. Therefore, our findings reveal a cascade of molecular events during signaling through SLAM in leprosy that cooperate to induce IFN-gamma production and strongly suggest that SLAM might be a focal point for therapeutic modulation of T cell cytokine responses in diseases characterized by dysfunctional Th2 responses.

Oxidative-stress-induced T lymphocyte hyporesponsiveness is caused by structural modification rather than proteasomal degradation of crucial TCR signaling molecules.

In several human pathologies (e.g. cancer, rheumatoid arthritis, AIDS and leprosy) oxidative stress induces T cell hyporesponsiveness. Hyporesponsive T cells often appear to display impaired expression of some (e.g. TCR-zeta, p56(lck) and LAT) but not all (e.g. TCR-alphabeta and CD3-epsilon) crucial TCR-proximal signaling molecules but the underlying mechanisms have as yet not been identified. Using an in vitro system for oxidative-stress-induced T cell hyporesponsiveness we here report two sequential effects of oxidative stress on TCR signaling molecules: protein alterations and proteasomal degradation. We have identified the C-terminal part of TCR-zeta and the membrane-proximal domain of p56(lck) as potential targets for modifications induced by reactive oxygen species. Oxidative-stress-exposed proteins were differentially susceptible to proteasomal degradation: whereas modified TCR-zeta was relatively resistant, reactive oxygen species (ROS)-altered LAT and p56(lck) were much more susceptible. Importantly, we found that T cell hyporesponsiveness best correlated with ROS-dependent protein alteration since inhibition of proteasomal degradation did not restore function. Finally, our data provide an explanation for the paradox of reduced TCR-zeta signals combined with unaltered TCR-alphabeta and CD3-epsilon expression levels: the TCR-zeta chain in hyporesponsive T cells is still expressed but no longer detectable by certain mAb recognizing ROS-sensitive epitopes.