scholarly journals SppI Forms a Membrane Protein Complex with SppA and Inhibits Its Protease Activity in Bacillus subtilis

mSphere ◽  
2020 ◽  
Vol 5 (5) ◽  
Author(s):  
Gabriela Henriques ◽  
Stephen McGovern ◽  
Jolanda Neef ◽  
Minia Antelo-Varela ◽  
Friedrich Götz ◽  
...  
Keyword(s):  
Bacillus Subtilis ◽  
Membrane Protein ◽  
Antimicrobial Peptides ◽  
Protease Activity ◽  
Cationic Antimicrobial Peptide ◽  
Content Type ◽  
Terminal Domain ◽  
Increased Sensitivity

ABSTRACT The membrane protease SppA of Bacillus subtilis was first described as a signal peptide peptidase and later shown to confer resistance to lantibiotics. Here, we report that SppA forms octameric complexes with YteJ, a membrane protein of thus-far-unknown function. Interestingly, sppA and yteJ deletion mutants exhibited no protein secretion defects. However, these mutant strains differed significantly in their resistance to antimicrobial peptides. In particular, sppA mutant cells displayed increased sensitivity to the lantibiotics nisin and subtilin and the human lysozyme-derived cationic antimicrobial peptide LP9. Importantly, YteJ was shown to antagonize SppA activity both in vivo and in vitro, and this SppA-inhibitory activity involved the C-terminal domain of YteJ, which was therefore renamed SppI. Most likely, SppI-mediated control is needed to protect B. subtilis against the potentially detrimental protease activity of SppA since a mutant overexpressing sppA by itself displayed defects in cell division. Altogether, we conclude that the SppA-SppI complex of B. subtilis has a major role in protection against antimicrobial peptides. IMPORTANCE Our study presents new insights into the molecular mechanism that regulates the activity of SppA, a widely conserved bacterial membrane protease. We show that the membrane proteins SppA and SppI form a complex in the Gram-positive model bacterium B. subtilis and that SppI inhibits SppA protease activity in vitro and in vivo. Furthermore, we demonstrate that the C-terminal domain of SppI is involved in SppA inhibition. Since SppA, through its protease activity, contributes directly to resistance to lantibiotic peptides and cationic antibacterial peptides, we propose that the conserved SppA-SppI complex could play a major role in the evasion of bactericidal peptides, including those produced as part of human innate immune defenses.

scholarly journals Evidence that Autophosphorylation of the Major Sporulation Kinase in Bacillus subtilis Is Able To Occur in trans

2015 ◽  
Vol 197 (16) ◽  
pp. 2675-2684 ◽  
Author(s):  
Seram Nganbiton Devi ◽  
Brittany Kiehler ◽  
Lindsey Haggett ◽  
Masaya Fujita
Keyword(s):  
Bacillus Subtilis ◽  
Mutant Protein ◽  
Phosphoryl Group ◽  
Atp Binding ◽  
Histidine Kinases ◽  
Content Type ◽  
Point Mutant ◽  
Terminal Domain

ABSTRACTEntry into sporulation inBacillus subtilisis governed by a multicomponent phosphorelay, a complex version of a two-component system which includes at least three histidine kinases (KinA to KinC), two phosphotransferases (Spo0F and Spo0B), and a response regulator (Spo0A). Among the three histidine kinases, KinA is known as the major sporulation kinase; it is autophosphorylated with ATP upon starvation and then transfers a phosphoryl group to the downstream components in a His-Asp-His-Asp signaling pathway. Our recent study demonstrated that KinA forms a homotetramer, not a dimer, mediated by the N-terminal domain, as a functional unit. Furthermore, when the N-terminal domain was overexpressed in the starving wild-type strain, sporulation was impaired. We hypothesized that this impairment of sporulation could be explained by the formation of a nonfunctional heterotetramer of KinA, resulting in the reduced level of phosphorylated Spo0A (Spo0A∼P), and thus, autophosphorylation of KinA could occur intrans. To test this hypothesis, we generated a series ofB. subtilisstrains expressing homo- or heterogeneous KinA protein complexes consisting of various combinations of the phosphoryl-accepting histidine point mutant protein and the catalytic ATP-binding domain point mutant protein. We found that the ATP-binding-deficient protein was phosphorylated when the phosphorylation-deficient protein was present in a 1:1 stoichiometry in the tetramer complex, while each of the mutant homocomplexes was not phosphorylated. These results suggest that ATP initially binds to one protomer within the tetramer complex and then the γ-phosphoryl group is transmitted to another in atransfashion. We further found that the sporulation defect of each of the mutant proteins is complemented when the proteins are coexpressedin vivo. Taken together, thesein vitroandin vivoresults reinforce the evidence that KinA autophosphorylation is able to occur in atransfashion.IMPORTANCEAutophosphorylation of histidine kinases is known to occur by either thecis(one subunit of kinase phosphorylating itself within the multimer) or thetrans(one subunit of the multimer phosphorylates the other subunit) mechanism. The present study provided directin vivoandin vitroevidence that autophosphorylation of the major sporulation histidine kinase (KinA) is able to occur intranswithin the homotetramer complex. While the physiological and mechanistic significance of thetransautophosphorylation reaction remains obscure, understanding the detailed reaction mechanism of the sporulation kinase is the first step toward gaining insight into the molecular mechanisms of the initiation of sporulation, which is believed to be triggered by unknown factors produced under conditions of nutrient depletion.

scholarly journals Identification of Synthetic Host Defense Peptide Mimics That Exert Dual Antimicrobial and Anti-Inflammatory Activities

2012 ◽  
Vol 19 (11) ◽  
pp. 1784-1791 ◽  
Author(s):  
Abhigyan Som ◽  
Nicolás Navasa ◽  
Avital Percher ◽  
Richard W. Scott ◽  
Gregory N. Tew ◽  
...  
Keyword(s):  
Antimicrobial Peptides ◽  
Lipoteichoic Acid ◽  
Antibacterial Activities ◽  
Innate Immune Responses ◽  
Content Type ◽  
Host Defense Peptide ◽  
Anti Inflammatory ◽  
Molecular Patterns

ABSTRACTA group of synthetic antimicrobial oligomers, inspired by naturally occurring antimicrobial peptides, were analyzed for the ability to modulate innate immune responses to Toll-like receptor (TLR) ligands. These synthetic mimics of antimicrobial peptides (SMAMPs) specifically reduced cytokine production in response toStaphylococcus aureusand theS. aureuscomponent lipoteichoic acid (LTA), a TLR2 agonist. Anti-inflammatory SMAMPs prevented the induction of tumor necrosis factor (TNF), interleukin 6 (IL-6), and IL-10 in response toS. aureusor LTA, but no other TLR2 ligands. We show that these SMAMPs bind specifically to LTAin vitroand prevent its interaction with TLR2. Importantly, the SMAMP greatly reduced the induction of TNF and IL-6in vivoin mice acutely infected withS. aureuswhile simultaneously reducing bacterial loads dramatically (4 log10). Thus, these SMAMPs can eliminate the damage induced by pathogen-associated molecular patterns (PAMPs) while simultaneously eliminating infectionin vivo. They are the first known SMAMPs to demonstrate anti-inflammatory and antibacterial activitiesin vivo.

scholarly journals ModifiedmarinerTransposons for Random Inducible-Expression Insertions and Transcriptional Reporter Fusion Insertions in Bacillus subtilis

2011 ◽  
Vol 78 (3) ◽  
pp. 778-785 ◽  
Author(s):  
Eric R. Pozsgai ◽  
Kris M. Blair ◽  
Daniel B. Kearns
Keyword(s):  
Bacillus Subtilis ◽  
Insertional Mutagenesis ◽  
Inducible Promoter ◽  
Insertion Sequences ◽  
Content Type ◽  
Transcriptional Reporter ◽  
Species Specific ◽  
Genetically Manipulated

ABSTRACTTransposons are mobile genetic elements bounded by insertion sequences that are recognized by a specific mobilizing transposase enzyme. The transposase may mobilize not only the insertion sequences but also intervening DNA.marineris a particularly efficient transposon for the random chromosomal integration of genes and insertional mutagenesis. Here, we modify an existingmarinertransposon, TnYLB, such that it can easily be genetically manipulated and introduced intoBacillus subtilis. We generate a series of three newmarinerderivatives that mobilize spectinomycin, chloramphenicol, and kanamycin antibiotic resistance cassettes. Furthermore, we generate a series of transposons with a strong, outward-oriented, optionally isopropyl-β-d-thiogalactopyranoside (IPTG)-inducible promoter for the random overexpression of neighboring genes and a series of transposons with a promoterlesslacZgene for the random generation of transcriptional reporter fusions. We note that the modification of the base transposon is not restricted toB. subtilisand should be applicable to anymariner-compatible host organism, provided thatin vitromutagenesis or anin vivospecies-specific delivery vector is employed.

scholarly journals Abbreviated Pathway for Biosynthesis of 2-Thiouridine in Bacillus subtilis

2015 ◽  
Vol 197 (11) ◽  
pp. 1952-1962 ◽  
Author(s):  
Katherine A. Black ◽  
Patricia C. Dos Santos
Keyword(s):  
Escherichia Coli ◽  
Bacillus Subtilis ◽  
Cysteine Desulfurase ◽  
Content Type ◽  
E Coli ◽  
Wobble Position ◽  
Lysine Trna ◽  
Domains Of Life

ABSTRACTThe 2-thiouridine (s2U) modification of the wobble position in glutamate, glutamine, and lysine tRNA molecules serves to stabilize the anticodon structure, improving ribosomal binding and overall efficiency of the translational process. Biosynthesis of s2U inEscherichia colirequires a cysteine desulfurase (IscS), a thiouridylase (MnmA), and five intermediate sulfur-relay enzymes (TusABCDE). TheE. coliMnmA adenylates and subsequently thiolates tRNA to form the s2U modification.Bacillus subtilislacks IscS and the intermediate sulfur relay proteins, yet its genome contains a cysteine desulfurase gene,yrvO, directly adjacent tomnmA. The genomic synteny ofyrvOandmnmAcombined with the absence of the Tus proteins indicated a potential functionality of these proteins in s2U formation. Here, we provide evidence that theB. subtilisYrvO and MnmA are sufficient for s2U biosynthesis. A conditionalB. subtilisknockout strain showed that s2U abundance correlates with MnmA expression, andin vivocomplementation studies inE. coliIscS- or MnmA-deficient strains revealed the competency of these proteins in s2U biosynthesis.In vitroexperiments demonstrated s2U formation by YrvO and MnmA, and kinetic analysis established a partnership between theB. subtilisproteins that is contingent upon the presence of ATP. Furthermore, we observed that the slow-growth phenotype ofE. coliΔiscSand ΔmnmAstrains associated with s2U depletion is recovered byB. subtilis yrvOandmnmA. These results support the proposal that the involvement of a devoted cysteine desulfurase, YrvO, in s2U synthesis bypasses the need for a complex biosynthetic pathway by direct sulfur transfer to MnmA.IMPORTANCEThe 2-thiouridine (s2U) modification of the wobble position in glutamate, glutamine, and lysine tRNA is conserved in all three domains of life and stabilizes the anticodon structure, thus guaranteeing fidelity in translation. The biosynthesis of s2U inEscherichia colirequires seven proteins: the cysteine desulfurase IscS, the thiouridylase MnmA, and five intermediate sulfur-relay enzymes (TusABCDE).Bacillus subtilisand most Gram-positive bacteria lack a complete set of biosynthetic components. Interestingly, themnmAcoding sequence is located adjacent toyrvO, encoding a cysteine desulfurase. In this work, we provide evidence that theB. subtilisYrvO is able to transfer sulfur directly to MnmA. Both proteins are sufficient for s2U biosynthesis in a pathway independent of the one used inE. coli.

scholarly journals The Major Chromosome Condensation Factors Smc, HBsu, and Gyrase in Bacillus subtilis Operate via Strikingly Different Patterns of Motion

mSphere ◽  
2020 ◽  
Vol 5 (5) ◽  
Author(s):  
Sonja Schibany ◽  
Rebecca Hinrichs ◽  
Rogelio Hernández-Tamayo ◽  
Peter L. Graumann
Keyword(s):  
Bacillus Subtilis ◽  
Dna Binding ◽  
Single Molecule ◽  
High Mobility ◽  
Single Molecule Tracking ◽  
Content Type ◽  
Dna Compaction ◽  
Transient Interactions

ABSTRACT Although DNA-compacting proteins have been extensively characterized in vitro, knowledge of their DNA binding dynamics in vivo is greatly lacking. We have employed single-molecule tracking to characterize the motion of the three major chromosome compaction factors in Bacillus subtilis, Smc (structural maintenance of chromosomes) proteins, topoisomerase DNA gyrase, and histone-like protein HBsu. We show that these three proteins display strikingly different patterns of interaction with DNA; while Smc displays two mobility fractions, one static and one moving through the chromosome in a constrained manner, gyrase operates as a single slow-mobility fraction, suggesting that all gyrase molecules are catalytically actively engaged in DNA binding. Conversely, bacterial histone-like protein HBsu moves through the nucleoid as a larger, slow-mobility fraction and a smaller, high-mobility fraction, with both fractions having relatively short dwell times. Turnover within the SMC complex that makes up the static fraction is shown to be important for its function in chromosome compaction. Our report reveals that chromosome compaction in bacteria can occur via fast, transient interactions in vivo, avoiding clashes with RNA and DNA polymerases. IMPORTANCE All types of cells need to compact their chromosomes containing their genomic information several-thousand-fold in order to fit into the cell. In eukaryotes, histones achieve a major degree of compaction and bind very tightly to DNA such that they need to be actively removed to allow access of polymerases to the DNA. Bacteria have evolved a basic, highly dynamic system of DNA compaction, accommodating rapid adaptability to changes in environmental conditions. We show that the Bacillus subtilis histone-like protein HBsu exchanges on DNA on a millisecond scale and moves through the entire nucleoid containing the genome as a slow-mobility fraction and a dynamic fraction, both having short dwell times. Thus, HBsu achieves compaction via short and transient DNA binding, thereby allowing rapid access of DNA replication or transcription factors to DNA. Topoisomerase gyrase and B. subtilis Smc show different interactions with DNA in vivo, displaying continuous loading or unloading from DNA, or using two fractions, one moving through the genome and one statically bound on a time scale of minutes, respectively, revealing three different modes of DNA compaction in vivo.

scholarly journals Bifunctional Malic/Malolactic Enzyme Provides a Novel Mechanism for NADPH-Balancing in Bacillus subtilis

mBio ◽  
2021 ◽  
Vol 12 (2) ◽  
Author(s):  
Manuel Hörl ◽  
Tobias Fuhrer ◽  
Nicola Zamboni
Keyword(s):  
Bacillus Subtilis ◽  
Metabolic Flux ◽  
Central Carbon Metabolism ◽  
Flux Analysis ◽  
Content Type ◽  
Malolactic Enzyme ◽  
First Time

ABSTRACT The redox cofactor NADPH is required as a reducing equivalent in about 100 anabolic reactions throughout metabolism. To ensure fitness under all conditions, the demand is fulfilled by a few dehydrogenases in central carbon metabolism that reduce NADP+ with electrons derived from the catabolism of nutrients. In the case of Bacillus subtilis growing on glucose, quantitative flux analyses indicate that NADPH production largely exceeds biosynthetic needs, suggesting a hitherto unknown mechanism for NADPH balancing. We investigated the role of the four malic enzymes present in B. subtilis that could bring about a metabolic cycle for transhydrogenation of NADPH into NADH. Using quantitative 13C metabolic flux analysis, we found that isoform YtsJ alone contributes to NADPH balancing in vivo and demonstrated relevant NADPH-oxidizing activity by YtsJ in vitro. To our surprise, we discovered that depending on NADPH, YtsJ switches activity from a pyruvate-producing malic enzyme to a lactate-generating malolactic enzyme. This switch in activity allows YtsJ to adaptively compensate for cellular NADPH over- and underproduction upon demand. Finally, NADPH-dependent bifunctional activity was also detected in the YtsJ homolog in Escherichia coli MaeB. Overall, our study extends the known redox cofactor balancing mechanisms by providing first-time evidence that the type of catalyzed reaction by an enzyme depends on metabolite abundance. IMPORTANCE A new mechanism for NADPH balancing was discovered in Bacillus subtilis. It pivots on the bifunctional enzyme YtsJ, which is known to catalyze NADP-dependent malate decarboxylation. We found that in the presence of excessive NADPH, the same enzyme switches to malolactic activity and creates a transhydrogenation cycle that ultimately converts NADPH to NADH. This provides a regulated mechanism to immediately adjust NADPH/NADP+ in response to instantaneous needs.

scholarly journals Functional Analysis of Bacillus subtilis Genes Involved in the Biosynthesis of 4-Thiouridine in tRNA

2012 ◽  
Vol 194 (18) ◽  
pp. 4933-4940 ◽  
Author(s):  
Lauren J. Rajakovich ◽  
John Tomlinson ◽  
Patricia C. Dos Santos
Keyword(s):  
Functional Analysis ◽  
Bacillus Subtilis ◽  
Gene Encoding ◽  
Cysteine Desulfurase ◽  
Content Type ◽  
Sulfur Transfer ◽  
Essential Enzyme ◽  
Sulfur Trafficking

ABSTRACTThiI has been identified as an essential enzyme involved in the biosynthesis of thiamine and the tRNA thionucleoside modification, 4-thiouridine. InEscherichia coliandSalmonella enterica, ThiI acts as a sulfurtransferase, receiving the sulfur donated from the cysteine desulfurase IscS and transferring it to the target molecule or additional sulfur carrier proteins. However, inBacillus subtilisand most species from theFirmicutesphylum, ThiI lacks the rhodanese domain that contains the site responsible for the sulfurtransferase activity. The lack of the gene encoding for a canonical IscS cysteine desulfurase and the presence of a short sequence of ThiI in these bacteria pointed to mechanistic differences involving sulfur trafficking reactions in both biosynthetic pathways. Here, we have carried out functional analysis ofB. subtilisthiIand the adjacent gene,nifZ, encoding for a cysteine desulfurase. Gene inactivation experiments inB. subtilisindicate the requirement of ThiI and NifZ for the biosynthesis of 4-thiouridine, but not thiamine.In vitrosynthesis of 4-thiouridine by ThiI and NifZ, along with labeling experiments, suggests the occurrence of an alternate transient site for sulfur transfer, thus obviating the need for a rhodanese domain.In vivocomplementation studies inE. coliIscS- or ThiI-deficient strains provide further support for specific interactions between NifZ and ThiI. These results are compatible with the proposal thatB. subtilisNifZ and ThiI utilize mechanistically distinct and mutually specific sulfur transfer reactions.

scholarly journals Aag Hypoxanthine-DNA Glycosylase Is Synthesized in the Forespore Compartment and Involved in Counteracting the Genotoxic and Mutagenic Effects of Hypoxanthine and Alkylated Bases in DNA during Bacillus subtilis Sporulation

2016 ◽  
Vol 198 (24) ◽  
pp. 3345-3354 ◽  
Author(s):  
Víctor M. Ayala-García ◽  
Luz I. Valenzuela-García ◽  
Peter Setlow ◽  
Mario Pedraza-Reyes
Keyword(s):  
Bacillus Subtilis ◽  
Developmental Process ◽  
Specific Pattern ◽  
Dna Glycosylase ◽  
Regulatory Sequences ◽  
Regulation Of Expression ◽  
Content Type ◽  
Mutagenic Effects

ABSTRACTAag fromBacillus subtilishas been implicated inin vitroremoval of hypoxanthine and alkylated bases from DNA. The regulation of expression ofaaginB. subtilisand the resistance to genotoxic agents and mutagenic properties of an Aag-deficient strain were studied here. A strain with a transcriptionalaag-lacZfusion expressed low levels of β-galactosidase during growth and early sporulation but exhibited increased transcription during late stages of this developmental process. Notably,aag-lacZexpression was higher inside the forespore than in the mother cell compartment, and this expression was abolished in asigG-deficient background, suggesting a forespore-specific mechanism ofaagtranscription. Two additional findings supported this suggestion: (i) expression of anaag-yfpfusion was observed in the forespore, and (ii)in vivomapping of theaagtranscription start site revealed the existence of upstream regulatory sequences possessing homology to σG-dependent promoters. In comparison with the wild-type strain, disruption ofaagsignificantly reduced survival of sporulatingB. subtiliscells following nitrous acid or methyl methanesulfonate treatments, and the Rifrmutation frequency was significantly increased in anaagstrain. These results suggest that Aag protects the genome of developingB. subtilissporangia from the cytotoxic and genotoxic effects of base deamination and alkylation.IMPORTANCEIn this study, evidence is presented revealing thataag, encoding a DNA glycosylase implicated in processing of hypoxanthine and alkylated DNA bases, exhibits a forespore-specific pattern of gene expression duringB. subtilissporulation. Consistent with this spatiotemporal mode of expression, Aag was found to protect the sporulating cells of this microorganism from the noxious and mutagenic effects of base deamination and alkylation.

scholarly journals Regulation of therhaEWRBMAOperon Involved in l-Rhamnose Catabolism through Two Transcriptional Factors, RhaR and CcpA, in Bacillus subtilis

2015 ◽  
Vol 198 (5) ◽  
pp. 830-845 ◽  
Author(s):  
Kazutake Hirooka ◽  
Yusuke Kodoi ◽  
Takenori Satomura ◽  
Yasutaro Fujita
Keyword(s):  
Bacillus Subtilis ◽  
Plant Pathogens ◽  
Bacterial Species ◽  
Regulatory Region ◽  
Regulatory System ◽  
Direct Repeat ◽  
Plant Interactions ◽  
Content Type

ABSTRACTTheBacillus subtilisrhaEWRBMA(formerlyyuxG-yulBCDE) operon consists of four genes encoding enzymes forl-rhamnose catabolism and therhaRgene encoding a DeoR-type transcriptional regulator. DNase I footprinting analysis showed that the RhaR protein specifically binds to the regulatory region upstream of therhaEWgene, in which two imperfect direct repeats are included. Gel retardation analysis revealed that the direct repeat farther upstream is essential for the high-affinity binding of RhaR and that the DNA binding of RhaR was effectively inhibited byl-rhamnulose-1-phosphate, an intermediate ofl-rhamnose catabolism. Moreover, it was demonstrated that the CcpA/P-Ser-HPr complex, primarily governing the carbon catabolite control inB. subtilis, binds to the catabolite-responsive element, which overlaps the RhaR binding site.In vivoanalysis of therhaEWpromoter-lacZfusion in the background ofccpAdeletion showed that thel-rhamnose-responsive induction of therhaEWpromoter was negated by the disruption ofrhaAorrhaBbut notrhaEWorrhaM, whereasrhaRdisruption resulted in constitutiverhaEWpromoter activity. Thesein vitroandin vivoresults clearly indicate that RhaR represses the operon by binding to the operator site, which is detached byl-rhamnulose-1-phosphate formed froml-rhamnose through a sequence of isomerization by RhaA and phosphorylation by RhaB, leading to the derepression of the operon. In addition, thelacZreporter analysis using the strains with or without theccpAdeletion under the background ofrhaRdisruption supported the involvement of CcpA in the carbon catabolite repression of the operon.IMPORTANCESincel-rhamnose is a component of various plant-derived compounds, it is a potential carbon source for plant-associating bacteria. Moreover, it is suggested thatl-rhamnose catabolism plays a significant role in some bacteria-plant interactions, e.g., invasion of plant pathogens and nodulation of rhizobia. Despite the physiological importance ofl-rhamnose catabolism for various bacterial species, the transcriptional regulation of the relevant genes has been poorly understood, except for the regulatory system ofEscherichia coli. In this study, we show that, inBacillus subtilis, one of the plant growth-promoting rhizobacteria, therhaEWRBMAoperon forl-rhamnose catabolism is controlled by RhaR and CcpA. This regulatory system can be another standard model for better understanding the regulatory mechanisms ofl-rhamnose catabolism in other bacterial species.

scholarly journals Characterization of a Mutant Escherichia coli Heat-Labile Toxin, LT(R192G/L211A), as a Safe and Effective Oral Adjuvant

2011 ◽  
Vol 18 (4) ◽  
pp. 546-551 ◽  
Author(s):  
Elizabeth B. Norton ◽  
Louise B. Lawson ◽  
Lucy C. Freytag ◽  
John D. Clements
Keyword(s):  
Escherichia Coli ◽  
Mammalian Cells ◽  
Oral Vaccines ◽  
Content Type ◽  
Intracellular Degradation ◽  
Heat Labile ◽  
Increased Sensitivity

ABSTRACTDespite the fact that the adjuvant properties of the heat-labile enterotoxins ofEscherichia coli(LT) andVibrio cholerae(CT) have been known for more than 20 years, there are no available oral vaccines containing these molecules as adjuvants, primarily because they are both very potent enterotoxins. A number of attempts with various degrees of success have been made to reduce or eliminate the enterotoxicity of LT and CT so they can safely be used as oral adjuvants or immunogens. In this report we characterize the structural, enzymatic, enterotoxic, and adjuvant properties of a novel mutant of LT, designated LT(R192G/L211A), or dmLT. dmLT was not sensitive to trypsin activation, had reduced enzymatic activity for induction of cyclic AMP in Caco-2 cells, and exhibited no enterotoxicity in the patent mouse assay. Importantly, dmLT retained the ability to function as an oral adjuvant for a coadministered antigen (tetanus toxoid) and to elicit anti-LT antibodies.In vitroandin vivodata suggest that the reduced enterotoxicity of this molecule compared to native LT or the single mutant, LT(R192G), is a consequence of increased sensitivity to proteolysis and rapid intracellular degradation in mammalian cells. In conclusion, dmLT is a safe and powerful detoxified enterotoxin with the potential to function as a mucosal adjuvant for coadministered antigens and to elicit anti-LT antibodies without undesirable side effects.

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