Adaptation of the binding domain of Lactobacillus acidophilus S-layer protein as a molecular tag for affinity chromatography development

Introduction

The S-layer proteins are a class of self-assembling proteins that form bi-dimensional lattices named S-Layer on the cell surface of bacteria and archaea. The protein SlpA, which is the major constituent of the Lactobacillus acidophilus S-layer, contains in its C-terminus region (SlpA^{284 - 444}), a protein domain (named here as SLAP_TAG) responsible for the association of SlpA to the bacterial surface. SLAP_TAG was adapted for the development of a novel affinity chromatography method: the SLAP_TAG-based affinity chromatography (SAC).

Methods

Proteins with different molecular weights or biochemical functions were fused in-frame to the SLAP_TAG and efficiently purified by a Bacillus subtilis-derived affinity matrix (named Bio-Matrix or BM). Different binding and elution conditions were evaluated to establish an optimized protocol.

Results

The binding equilibrium between SLAP_TAG and BM was reached after a few minutes of incubation at 4°C, with an apparent dissociation constant (K_D) of 4.3μM. A reporter protein (H6-GFP-SLAP_TAG) was used to compare SAC protein purification efficiency against commercial immobilized metal affinity chromatography. No differences in protein purification performance were observed between the two methods. The stability and reusability of the BM were evaluated, and it was found that the matrix remained stable for more than a year. BM could be reused up to five times without a significant loss in performance. Additionally, the recovery of bound SLAP-tagged proteins was explored using proteolysis with a SLAP-tagged version of the HRV-3c protease (SLAP_ASE). This released the untagged GFP while the cut SLAP_TAG and the SLAP_ASE were retained in the BM. As an alternative, iron nanoparticles were linked to the BM, resulting in BM_mag. The BM_mag was successfully adapted for a magnetic SAC, a technique with potential applications in high-throughput protein production and purification.

Discussion

The SAC protocol can be adapted as a universal tool for the purification of recombinant proteins. Furthermore, the SAC protocol utilizes simple and low-cost reagents, making it suitable for in-house protein purification systems in laboratories worldwide. This enables the production of pure recombinant proteins for research, diagnosis, and the food industry.

Biochemical and functional characterization of Brucella abortus cyclophilins: So similar, yet so different

Brucella spp. are the etiological agent of animal and human brucellosis. We have reported previously that cyclophilins of Brucella (CypA and CypB) are upregulated within the intraphagosomal replicative niche and required for stress adaptation and host intracellular survival and virulence. Here, we characterize B. abortus cyclophilins, CypA, and CypB from a biochemical standpoint by studying their PPIase activity, chaperone activity, and oligomer formation. Even though CypA and CypB are very similar in sequence and share identical chaperone and PPIase activities, we were able to identify outstanding differential features between them. A series of differential peptide loops were predicted when comparing CypA and CypB, differences that might explain why specific antibodies (anti-CypA or anti-CypB) were able to discriminate between both cyclophilins without cross-reactivity. In addition, we identified the presence of critical amino acids in CypB, such as the Trp134 which is responsible for the cyclosporin A inhibition, and the Cys128 that leads to CypB homodimer formation by establishing a disulfide bond. Here, we demonstrated that CypB dimer formation was fully required for stress adaptation, survival within HeLa cells, and mouse infection in B. abortus. The presence of Trp134 and the Cys128 in CypB, which are not present in CypA, suggested that two different kinds of cyclophilins have evolved in Brucella, one with eukaryotic features (CypB), another (CypA) with similar features to Gram-negative cyclophilins.

Development of an Antigen Delivery Platform Using Lactobacillus acidophilus Decorated With Heterologous Proteins: A Sheep in Wolf's Clothing Story

S-layers are bacterial structures present on the surface of several Gram-positive and Gram-negative bacteria that play a role in bacterial protection. In Lactobacillus acidophilus (L. acidophilus ATCC 4356), the S-layer is mainly composed of the protein SlpA. A tandem of two copies of the protein domain SLP-A (pfam: 03217) was identified at the C-terminal of SlpA, being this double SLP-A protein domain (in short dSLP-A) necessary and sufficient for the association of the protein to the L. acidophilus cell wall. A variety of proteins fused to the dSLP-A domain were able to spontaneously associate with high affinity to the cell wall of L. acidophilus and Bacillus subtilis var. natto, in a process that we termed decoration. Binding of dSLP-A-containing-proteins to L. acidophilus was stable at conditions that mimic the gastrointestinal transit in terms of pH, proteases, and bile salts. To evaluate if protein decoration of L. acidophilus can be adapted to generate an oral vaccine platform, a chimeric antigen derived from the bacterial pathogen Shiga-toxin-producing Escherichia coli (STEC) was constructed by fusing the sequences encoding the polypeptides EspA^36–192, Intimin^653–953, Tir^240–378, and H7 flagellin^352–374 (EITH7) to the dSLP-A domain (EITH7-dSLP-A). Recombinantly expressed EITH7-dSLP-A protein was affinity purified and combined with L. acidophilus cultures to allow the association of the chimeric antigen to the bacterial surface. EITH7-decorated L. acidophilus was orally administered to BALB/c mice and the induction of anti-EITH7 specific antibodies in sera and feces determined by ELISA. Mice presenting significantly higher anti-EITH7 antibodies titers were able to control more efficiently an experimental STEC infection than mice that received the non-decorated L. acidophilus carrier, indicating that antigen-decorated L. acidophilus can be adapted as a mucosal immunization delivery platform to elicit a protective immune response for vaccine purposes.

Two Rieske Fe/S Proteins and TAT System in Mesorhizobium loti MAFF303099: Differential Regulation and Roles on Nodulation

Mesorhizobium loti MAFF303099 is a rhizobial strain that nodulates Lotus spp. A M. loti MAFF303099 mutant strain affected in the tatC gene was generated. This strain presented an altered protein secretion level to the culture supernatant and also a higher sensitivity to SDS. Its nodulation phenotype on Lotus showed the induction of small and colorless nodules, and in a larger number than those induced by the wild-type strain. In addition, these nodules presented defects in the degree of occupation by rhizobia. Two Rieske Fe/S proteins, encoded by the mll2707 and mlr0970 genes, were predicted as potential Tat substrates in M. loti MAFF303099. The transcriptional expression of mll2707 and mlr0970 genes was analyzed under different oxygen growth conditions. The mll2707 gene was expressed constitutively, while the expression of the mlr0970 gene was only detected under anaerobic and microaerophilic in vitro conditions. Both genes were down-regulated in the tatC mutant strain. mll2707 and mlr0970 mRNAs from the wild-type strain were detected in nodules. Using a translational reporter peptide fusion, we found that the Mll2707 protein was only detectable in the wild-type strain. On the other hand, although Mlr0970 protein was detected in wild-type and tatC mutant strains, its association with the membrane was favored in the wild-type strain. The tatC and the mll2707 mutant strains were affected in the cytochrome c oxidase activity. These results confirm that Mll2707 is required for cytochrome c-dependent respiration and that Tat functionality is required for the correct activity of Mll2707. The mll2707 mutant strain showed a nodulation phenotype similar to the tatC mutant strain, although it presented only a slight difference in comparison with wild-type strain in terms of nodule occupation. No defective phenotype was observed in the nodulation with the mlr0970 mutant strain. These results indicate that, of the two Rieske Fe/S proteins coded by M. loti MAFF303099, only Mll2707 expression is required for the induction of effective nodules, and that the functionality of the Tat system is necessary not only for the correct function of this protein, but also for some other protein required in an earlier stage of the nodulation process.

Iron-dependent reconfiguration of the proteome underlies the intracellular lifestyle of Brucella abortus

Brucella ssp. is a facultative intracellular pathogen that causes brucellosis, a worldwide zoonosis that affects a wide range of mammals including humans. A critical step for the establishment of a successful Brucella infection is its ability to survive within macrophages. To further understand the mechanisms that Brucella utilizes to adapt to an intracellular lifestyle, a differential proteomic study was performed for the identification of intracellular modulated proteins. Our results demonstrated that at 48 hours post-infection Brucella adjusts its metabolism in order to survive intracellularly by modulating central carbon metabolism. Remarkably, low iron concentration is likely the dominant trigger for reprogramming the protein expression profile. Up-regulation of proteins dedicated to reduce the concentration of reactive oxygen species, protein chaperones that prevent misfolding of proteins, and proteases that degrade toxic protein aggregates, suggest that Brucella protects itself from damage likely due to oxidative burst. This proteomic analysis of B. abortus provides novel insights into the mechanisms utilized by Brucella to establish an intracellular persistent infection and will aid in the development of new control strategies and novel targets for antimicrobial therapy.

U-Omp19 from Brucella abortus Is a Useful Adjuvant for Vaccine Formulations against Salmonella Infection in Mice

Most pathogens infect through mucosal surfaces, and parenteral immunization typically fails to induce effective immune responses at these sites. Development of oral-administered vaccines capable of inducing mucosal as well as systemic immunity while bypassing the issues of antigen degradation and immune tolerance could be crucial for the control of enteropathogens. This study demonstrates that U-Omp19, a bacterial protease inhibitor with immunostimulatory features, coadministered with Salmonella antigens by the oral route, enhances mucosal and systemic immune responses in mice. U-Omp19 was able to increase antigen-specific production of IFN-γ and IL-17 and mucosal (IgA) antibody response. Finally, oral vaccination with U-Omp19 plus Salmonella antigens conferred protection against virulent challenge with Salmonella Typhimurium, with a significant reduction in bacterial loads. These findings prove the efficacy of this novel adjuvant in the Salmonella infection model and support the potential of U-Omp19 as a suitable adjuvant in oral vaccine formulations against mucosal pathogens requiring T helper (Th)1-Th17 protective immune responses.

A bacterial protease inhibitor protects antigens delivered in oral vaccines from digestion while triggering specific mucosal immune responses

We report here that a bacterial protease inhibitor from Brucella spp. called U-Omp19 behaves as an ideal constituent for a vaccine formulation against infectious diseases. When co-administered orally with an antigen (Ag), U-Omp19: i) can bypass the harsh environment of the gastrointestinal tract by inhibiting stomach and intestine proteases and consequently increases the half-life of the co-administered Ag at immune inductive sites: Peyer's patches and mesenteric lymph nodes while ii) it induces the recruitment and activation of antigen presenting cells (APCs) and increases the amount of intracellular Ag inside APCs. Therefore, mucosal as well as systemic Ag-specific immune responses, antibodies, Th1, Th17 and CD8(+) T cells are enhanced when U-Omp19 is co-administered with the Ag orally. Finally, this bacterial protease inhibitor in an oral vaccine formulation confers mucosal protection and reduces parasite loads after oral challenge with virulent Toxoplasma gondii.

Brucella cyclic β-1,2-glucan plays a critical role in the induction of splenomegaly in mice

Brucella, the etiological agent of animal and human brucellosis, is a bacterium with the capacity to modulate the inflammatory response. Cyclic β-1,2-glucan (CβG) is a virulence factor key for the pathogenesis of Brucella as it is involved in the intracellular life cycle of the bacteria. Using comparative studies with different CβG mutants of Brucella, cgs (CβG synthase), cgt (CβG transporter) and cgm (CβG modifier), we have identified different roles for this polysaccharide in Brucella. While anionic CβG is required for bacterial growth in low osmolarity conditions, the sole requirement for a successful Brucella interaction with mammalian host is its transport to periplasmic space. Our results uncover a new role for CβG in promoting splenomegaly in mice. We showed that CβG-dependent spleen inflammation is the consequence of massive cell recruitment (monocytes, dendritics cells and neutrophils) due to the induction of pro-inflammatory cytokines such as IL-12 and TNF-α and also that the reduced splenomegaly response observed with the cgs mutant is not the consequence of changes in expression levels of the characterized Brucella PAMPs LPS, flagellin or OMP16/19. Complementation of cgs mutant with purified CβG increased significantly spleen inflammation response suggesting a direct role for this polysaccharide.

[Prognostic role of perineural invasion in prostate biopsy]

INTRODUCTION

Despite tumour cell dissemination through the intraprostatic nervous system being considered as a prostate cancer progression mechanism, the significance of perineural invasion in prostate biopsies to predict extraprostatic extension and its use as a potential prognosis factor is controversial.

MATERIALS AND METHODS

Retrospective study carried out at an institution on 208 patients treated with radical prostatectomy (January 2007 - July 2010) in which the presence of perineural invasion and the Gleason score in the preoperative biopsy were determined, as well as the clinical stage and the pre-surgery PSA. We classified the patients in risk groups in accordance with the D'Amico classification. We performed bivariate and multivariate statistical analyses to establish the correlations between the different variables.

RESULTS

We objectified PNI in 18.3% of the prostate biopsies. 71% of the prostatectomy specimens with perineural invasion presented extraprostatic extension in the previous biopsy against 23.1% when this was not found (p<0.0001) and 47% of the cases showed positive margins with PNI, against 18.3% without perineural invasion (p<0.0001). In fact, in the multivariate analysis, perineural invasion proved to be an independent risk factor in the presentation of extraprostatic extension and positive margins in the prostatectomy specimen.

CONCLUSIONS

The presence of perineural invasion is a useful prognostic factor for predicting extraprostatic extension and the involvement of surgical margin in the radical prostatectomy specimen. We believe that determining it may be a useful tool for improving preoperative diagnosis and planning treatment.

Regulatory mimicry in Listeria monocytogenes actin-based motility

The actin-based motility of the intracellular pathogen Listeria monocytogenes relies on ActA, a bacterial factor with a structural domain allowing it to mimic the actin nucleation-promoting activity of host cell proteins of the WASP/WAVE family. Here, we used an RNAi-based genetic approach in combination with computer-assisted image analysis to investigate the role of host factors in L. monocytogenes cell-to-cell spread. We showed that the host cell serine/threonine kinase CK2 is required for efficient actin tail formation by L. monocytogenes. Furthermore, CK2-mediated phosphorylation of ActA regulated its affinity for the actin-nucleating ARP2/3 complex, as is the case for CK2-mediated phosphorylation of WASP and WAVE. Thus, ActA not only displays structural mimicry of WASP/WAVE family members, but also regulatory mimicry, having precisely co-opted the host machinery regulating these proteins. Comparisons based on ActA amino acid sequence suggest that unrelated pathogens that display actin-based motility may have evolved a similar strategy of regulatory mimicry.

Optimization of the delivery of heterologous proteins by the Salmonella enterica serovar Typhimurium type III secretion system for vaccine development

Type III protein secretion systems, which are organelles with the capacity to deliver bacterial proteins into host cells, have been adapted to deliver heterologous antigens for vaccine development. A limitation of these antigen delivery systems is that some proteins are not amenable to secretion through this pathway. We show here that proteins from the simian and human immunodeficiency viruses that are not permissive for secretion through a Salmonella enterica serovar Typhimurium type III secretion system can be modified to travel this secretion pathway by introduction of discrete mutations. Proteins optimized for secretion were presented more efficiently via the major histocompatibility complex class I pathway and were able to induce a better immune response.

In vivo antigen delivery by a Salmonella typhimurium type III secretion system for therapeutic cancer vaccines

Bacterial vectors may offer many advantages over other antigen delivery systems for cancer vaccines. We engineered a Salmonella typhimurium vaccine strain to deliver the NY-ESO-1 tumor antigen (S. typhimurium-NY-ESO-1) through a type III protein secretion system. The S. typhimurium-NY-ESO-1 construct elicited NY-ESO-1-specific CD8+ and CD4+ T cells from peripheral blood lymphocytes of cancer patients in vitro. Oral administration of S. typhimurium-NY-ESO-1 to mice resulted in the regression of established NY-ESO-1-expressing tumors. Intratumoral inoculation of S. typhimurium-NY-ESO-1 to NY-ESO-1-negative tumors resulted in delivery of antigen in vivo and led to tumor regression in the presence of preexisting NY-ESO-1-specific CD8+ T cells. Specific T cell responses against at least 2 unrelated tumor antigens not contained in the vaccine were observed, demonstrating epitope spreading. We propose that antigen delivery through the S. typhimurium type III secretion system is a promising novel strategy for cancer vaccine development.

Identification of active site residues of the inverting glycosyltransferase Cgs required for the synthesis of cyclic beta-1,2-glucan, a Brucella abortus virulence factor

Brucella abortus cyclic glucan synthase (Cgs) is a 320-kDa (2868-amino acid) polytopic integral inner membrane protein responsible for the synthesis of the virulence factor cyclic beta-1,2-glucan by a novel mechanism in which the enzyme itself acts as a protein intermediate. Cgs functions as an inverting processive beta-1,2-autoglucosyltransferase and has the three enzymatic activities required for the synthesis of the cyclic glucan: initiation, elongation, and cyclization. To gain further insight into the protein domains that are essential for the enzymatic activity, we have compared the Cgs sequence with other glycosyltransferases (GTs). This procedure allowed us to identify in the Cgs region (475-818) the widely spaced D, DxD, E/D, (Q/R)xxRW motif that is highly conserved in the active site of numerous GTs. By site-directed mutagenesis and in vitro and in vivo activity assays, we have demonstrated that most of the amino acid residues of this motif are essential for Cgs activity. These sequence and site-directed mutagenesis analyses also indicate that Cgs should be considered a bi-functional modular GT, with an N-terminal GT domain belonging to a new GT family related to GT-2 (GT-84) followed by a GH-94 glycoside hydrolase C-terminal domain. Furthermore, over-expression of inactive mutants results in wild-type (WT) production of cyclic glucan when bacteria co-express the mutant and the WT form, indicating that Cgs may function in the membrane as a monomeric enzyme. Together, these results are compatible with a single addition model by which Cgs acts in the membrane as a monomer and uses the identified motif to form a single center for substrate binding and glycosyl-transfer reaction.

Cre reporter system to monitor the translocation of type III secreted proteins into host cells

Central to the study of type III secretion systems is the availability of reporter systems to monitor bacterial protein translocation into host cells. We report here the development of a bacteriophage P1 Cre recombinase-based system to monitor the translocation of bacterial proteins into mammalian cells. Bacteriophage P1 Cre recombinase fused to the secretion and translocation signals of Salmonella enterica serovar Typhimurium of the type III secreted protein SopE was secreted in a type III secretion system-dependent fashion. More importantly, the SopE-Cre chimera was translocated into host cells via the type III secretion system and activated the expression of luciferase and green fluorescent protein reporters of Cre recombinase activity.

Cyclic beta-1,2-glucan is a Brucella virulence factor required for intracellular survival

Pathogenic brucella bacteria have developed strategies to persist for prolonged periods of time in host cells, avoiding innate immune responses. Here we show that the cyclic beta-1,2-glucans (CbetaG) synthesized by brucella is important for circumventing host cell defenses. CbetaG acted in lipid rafts found on host cell membranes. CbetaG-deficient mutants failed to prevent phagosome-lysosome fusion and could not replicate. However, when treated with purified CbetaG or synthetic methyl-beta-cyclodextrin, the mutants were able to control vacuole maturation by avoiding lysosome fusion, and this allowed intracellular brucella to survive and reach the endoplasmic reticulum. Fusion between the endoplasmic reticulum and the brucella-containing vacuole depended on the brucella virulence type IV secretion system but not on CbetaG. Brucella CbetaG is thus a virulence factor that interacts with lipid rafts and contributes to pathogen survival.

Influence of laparoscopic live donor nephrectomy in ischemia-reperfusion syndrome and renal function after kidney transplantation: an experimental study

The increase of intra-abdominal pressure during laparoscopic techniques provokes oliguria and reduction of the renal blood flow (RBF). The aim of this study is to evaluate this effect during living donor nephrectomy and its influence in the ischemia-reperfusion syndrome and renal function after kidney transplantation. Autotransplantation was performed using 22 pigs (15 after conventional open nephrectomy and 7 after laparoscopic nephrectomy). During donor nephrectomy a significant reduction in RBF was observed in the laparoscopic group (70 mL/min) vs the open group (260 mL/min) (P<.05). After a cold ischemia period of 24 hours an autotransplantation was performed. During the first hour after revascularization RBF was lower for the laparoscopic than for the open group: 60 vs 180 mL/s at 1 minute and 160 vs 400 mL/s at 60 minutes (P<.05). The decrease of creatinine was slower for the laparoscopic than for the open group during the first posttransplant week (2 vs 1.3 mg/dL on the first day and 1.4 vs 0.8 mg/dL on the seventh day posttransplant, respectively) (P<.05).

[Non classical subtypes of diabetes mellitus]

BACKGROUND

Some adult, obese and diabetic patients, initiate their disease with a severe diabetic ketoacidosis without a precipitating factor and do not require insulin thereafter. These patients are classified as having a "non classical" diabetes mellitus.

AIM

To study the clinical, immunological, genetic and metabolic features of patients with non classical diabetes mellitus.

PATIENTS AND METHODS

Ten patients (9 men, aged 45 +/- 12 years old) with non classical diabetes mellitus were studied. Anti islet and anti glutamic acid decarboxylase antibodies (ICA and anti GAD), HLA DQ alpha arginine 52 and non aspartic beta 57 were measured. Insulin secretion was measured by C peptide after glucagon injection and with the minimal model of Bergman. The latter model was also used to determine insulin sensitivity.

RESULTS

Three patients were immunologically classified as type 1, since they had positive ICA or antiGAD antibodies and type 1 genetics (neutral or susceptible HLA DQ alpha and beta). They had insulin secretion after glucagon stimulus (C peptide ranging from 2.2 to 7.5 pmol/ml), but an almost absent response to a glucose load. They were also insulin resistant (a sensitivity index ranging from 0.05 to 1.67 x 10(-4) min/microU x ml). These three cases could be categorized as latent type 1. The other seven patients were ICA negative and antiGAD negative. Five had a susceptible HLA genotype for type 1 diabetes and two were neutral. All had insulin secretion after glucagon stimulation and a variable response to glucose. Six were insulin resistant (sensitivity index ranging from 0.32 to 1.29 x 10(-4) min/microU x ml). One patient was insulin sensitive (sensitivity index of 3.83 x 10(-4) min/microU x ml). Therefore all these patients were classified as type two diabetics with an atypical debut.

CONCLUSIONS

Not all diabetics presenting with a severe diabetic ketoacidosis are type I. Among these, there are subjects with a latent type 1 diabetes or with an atypical type 2 diabetes.

Brucella abortus cyclic beta-1,2-glucan mutants have reduced virulence in mice and are defective in intracellular replication in HeLa cells

Null cyclic beta-1,2-glucan synthetase mutants (cgs mutants) were obtained from Brucella abortus virulent strain 2308 and from B. abortus attenuated vaccinal strain S19. Both mutants show greater sensitivity to surfactants like deoxycholic acid, sodium dodecyl sulfate, and Zwittergent than the parental strains, suggesting cell surface alterations. Although not to the same extent, both mutants display reduced virulence in mice and defective intracellular multiplication in HeLa cells. The B. abortus S19 cgs mutant was completely cleared from the spleens of mice after 4 weeks, while the 2308 mutant showed a 1.5-log reduction of the number of brucellae isolated from the spleens after 12 weeks. These results suggest that cyclic beta-1,2-glucan plays an important role in the residual virulence of the attenuated B. abortus S19 strain. Although the cgs mutant was cleared from the spleens earlier than the wild-type parental strain (B. abortus S19) and produced less inflammatory response, its ability to confer protection against the virulent strain B. abortus 2308 was fully retained. Equivalent levels of induction of spleen gamma interferon mRNA and anti-lipopolysaccharide (LPS) of immunoglobulin G2a (IgG2a) subtype antibodies were observed in mice injected with B. abortus S19 or the cgs mutant. However, the titer of anti-LPS antibodies of the IgG1 subtype induced by the cgs mutant was lower than that observed with the parental S19 strain, thus suggesting that the cgs mutant induces a relatively exclusive Th1 response.

Evaluation of primary binding assays for presumptive serodiagnosis of swine brucellosis in Argentina

An indirect enzyme-linked immunosorbent assay (IELISA), a competitive ELISA (CELISA), and a fluorescence polarization assay (FPA) for the presumptive serological diagnosis of swine brucellosis were evaluated using two populations of swine sera: sera from brucellosis-free Canadian herds and sera from Argentina selected based on positive reactions in the buffered antigen plate agglutination test (BPAT) and the 2-mercaptoethanol (2-ME) test. In addition, sera from adult swine from which Brucella suis was isolated at least once for each farm of origin were evaluated. The IELISA, CELISA, and FPA specificity values were 99.9, 99.5, and 98. 3%, respectively, and the IELISA, CELISA, and FPA sensitivity values relative to the BPAT and the 2-ME test were 98.9, 96.6, and 93.8%, respectively. Actual sensitivity was assessed by using 37 sera from individual pigs from which B. suis was cultured, and the values obtained were as follows: BPAT, 86.5%; 2-ME test, 81.1%; IELISA, 86.5%; CELISA, 78.5%; and FPA, 80.0%.

Osmotic regulation of cyclic 1,2-beta-glucan synthesis

In contrast to what happens in AGROBACTERIUM: tumefaciens and RHIZOBIUM: meliloti, synthesis of periplasmic cyclic 1,2-beta-glucan in BRUCELLA: spp. was not inhibited when bacteria were grown in media of high osmolarity. Studies performed with crude membrane preparations showed that cyclic 1,2-beta-glucan synthetase of BRUCELLA: spp. was not inhibited by 0.5 M KCl or potassium glutamate; concentrations that completely inhibit the osmosensitive enzymes of A. tumefaciens A348 or R. meliloti 102F34, respectively encoded by the chvB or ndvB genes. The BRUCELLA: abortus cyclic 1, 2-beta-glucan synthetase gene (cgs) was introduced into A. tumefaciens A1011 chvB and R. meliloti GRT21s ndvB mutants. Synthesis of cyclic 1,2-beta-glucan by the recombinant strains was not inhibited when grown in media of high osmolarity (0.25 M NaCl or 0.5 M mannitol). On the other hand, when the A. tumefaciens cyclic 1, 2-beta-glucan synthetase gene was introduced into the R. meliloti GRT21s ndvB mutant, the recombinant strain displayed marked inhibition of cyclic 1,2-beta-glucan synthesis when grown in high-osmolarity media. However, the same gene introduced into a B. abortus cgs mutant background resulted in no inhibition of glucan synthesis at high osmolarity. In vitro studies with crude membranes isolated from recombinant strains revealed that BRUCELLA: cyclic 1, 2-beta-glucan synthetase was not inhibited by high concentrations of KCl or potassium glutamate even when expressed in AGROBACTERIUM: or RHIZOBIUM: backgrounds. It was concluded that the lack of effect of high osmolarity on 1,2-beta-glucan synthesis in BRUCELLA: is due to two convergent mechanisms: a) the presence of a cyclic 1, 2-beta-glucan synthetase that is not affected by concentrations of solutes such as KCl or potassium glutamate and b) either the possible accumulation of compatible solutes that might protect the enzyme from the inhibition by potassium glutamate or the accumulation of other osmolytes that do not affect the 1, 2-beta-glucan synthetase.

Molecular cloning and characterization of cgs, the Brucella abortus cyclic beta(1-2) glucan synthetase gene: genetic complementation of Rhizobium meliloti ndvB and Agrobacterium tumefaciens chvB mutants

The animal pathogen Brucella abortus contains a gene, cgs, that complemented a Rhizobium meliloti nodule development (ndvB) mutant and an Agrobacterium tumefaciens chromosomal virulence (chvB) mutant. The complemented strains recovered the synthesis of cyclic beta(1-2) glucan, motility, virulence in A. tumefaciens, and nitrogen fixation in R. meliloti; all traits were strictly associated with the presence of an active cyclic beta(1-2) glucan synthetase protein in the membranes. Nucleotide sequencing revealed the presence in B. abortus of an 8.49-kb open reading frame coding for a predicted membrane protein of 2,831 amino acids (316.2 kDa) and with 51% identity to R. meliloti NdvB. Four regions of the B. abortus protein spanning amino acids 520 to 800, 1025 to 1124, 1284 to 1526, and 2400 to 2660 displayed similarities of higher than 80% with R. meliloti NdvB. Tn3-HoHo1 mutagenesis showed that the C-terminal 825 amino acids of the Brucella protein, although highly conserved in Rhizobium, are not necessary for cyclic beta(1-2) glucan synthesis. Confirmation of the identity of this protein as B. abortus cyclic beta(1-2) glucan synthetase was done by the construction of a B. abortus Tn3-HoHo1 insertion mutant that does not form cyclic beta(1-2) glucan and lacks the 316.2-kDa membrane protein. The recovery of this mutant from the spleens of inoculated mice was decreased by 3 orders of magnitude compared with that of the parental strain; this result suggests that cyclic beta(1-2) glucan may be a virulence factor in Brucella infection.

Periplasmic cyclic 1,2-beta-glucan in Brucella spp. is not osmoregulated

Biosynthesis of periplasmic cyclic 1,2-beta-glucans in Brucella ovis strain REO198 and B. abortus strain 519 was found to be carried out by membrane-bound enzymes that use UDP-glucose (UDP-Glc) as donor substrate. Contrary to what happens in species of the genera Agrobacterium and Rhizobium, the accumulation of the reaction products in Brucella appeared not to be osmotically regulated. Incubation of permeabilized cells with UDP-[14C]Glc led to the formation of soluble neutral cyclic 1,2-beta-glucans and [14C]glucose-labelled glucoproteins. PAGE of pulse-chase experiments carried out with permeabilized cells showed that the molecular mass of the labelled protein was indistinguishable from Agrobacterium tumefaciens A348 and Rhizobium fredii USDA191 glucoproteins known to be intermediates in the synthesis of cyclic glucans. Brucella total membrane preparations were less efficient than permeabilized cells in the formation of cyclic glucan; this was attributed to defective cyclization. Accumulation of protein intermediates having oligosaccharides of high molecular mass that were not released from the protein was observed after chase with 2 mM UDP-Glc. This defect was not observed when permeabilized cells were used as enzyme preparation, thus suggesting that in Brucella a factor(s) that was lost or inactivated upon the preparation of membranes was required for the effective regulation between elongation and cyclization reactions.

Characterization of the biosynthesis of beta(1-2) cyclic glucan in R. Fredii. Beta(1-2) glucan has no apparent role in nodule invasion of Mc Call and Peking soybean cultivars

Three wild type strains of Rhizobium fredii, USDA 191, USDA 257 and HH 303, do not synthesize in vivo or in vitro beta(1-3), beta(1-6) cyclic glucans, all strains form in vitro and in vivo cyclic beta(1-2) glucans. Approximately 80% of the recovered R. fredii cellular cyclic beta(1-2) glucans were anionic and the substituent was identified as phosphoglycerol. Inner membranes prepared from these R. fredii strains have a beta(1-2) glucan-intermediate-protein with apparent molecular mass undistinguishable from Agrobacterium tumefaciens beta(1-2) glucan intermediate protein. Studies of the degree of polymerization of the oligosaccharides recovered from the protein-intermediate after short pulse incubations with UDP-14C-glucose suggested that the rate limiting step in the biosynthesis of cyclic glucan is cyclization. Kinetic studies revealed that the K(m) for UDP-glucose was 0.33 mM. No difference was detected between the K(m) for initiation/elongation and cyclization reactions. Nodulation studies of a ndvB R. fredii mutant with Mc Call and Peking soybean cultivars, revealed that beta(1-2) glucans do not seem to be required for normal nodule invasion of these soybean cultivars.

Successful Pneumocystis carinii pneumonia prophylaxis using aerosolized pentamidine in children with acute leukemia

PURPOSE

We report our experience replacing trimethoprim-sulfamethoxazole (TMP/SMX) with aerosolized pentamidine (AP) in 22 children with acute leukemia who could not tolerate TMP/SMX.

PATIENTS AND METHODS

Children (age 1 to 15 years) with acute leukemia during maintenance chemotherapy or post-bone marrow transplantation (BMT) receiving prophylaxis for Pneumocystis carinii pneumonia (PCP) with TMP/SMX received AP following prolonged neutropenia or allergy to TMP/SMX. Patients received 300 mg of AP monthly (children < 4 years received 150 mg) dissolved in 5 mL of distilled water over 20 to 30 minutes.

RESULTS

Over a 3-year period, 358 courses of AP were administered over 10,124 observable days. AP was adequately tolerated on a monthly basis for prophylaxis against PCP in 22 children with acute leukemia. AP was demonstrated to be effective in preventing PCP. There were minimal side effects observed during this trial. The majority of children with acute lymphoblastic leukemia (ALL; 12 of 14 [86%]) undergoing maintenance chemotherapy were able to resume full-dose therapy.

CONCLUSION

AP in children is well tolerated and shows high efficacy for PCP prophylaxis in children with leukemia. We conclude that AP should be considered as second-line PCP prophylactic therapy for children with acute leukemia in instances in which TMP/SMX cannot be tolerated. Phase III trials are required to determine its effect on dose intensification and event-free survival.