Purification and Characterization of Type 1 Fimbriae of Salmonella typhi

Type 1 fimbriae have been purified from a Salmonella typhi strain of clinical origin. Purified fimbriae retained their ability to bind to erythrocytes in a mannose-inhibitable fashion and, in doing so, behaved preferentially as a monovalent adhesin. SDS-PAGE analysis of the fimbrial preparation showed the presence of a 20-kDa major polypeptide component (fimbrillin) and of additional larger polypeptides present in smaller amounts. The amino-terminal sequence of fimbrillin was determined and turned out to be very similar but not identical to that of type 1 fimbrillins of other Salmonella serovars. A Western blot analysis of the purified fimbrial preparation using an antiserum raised against native fimbriae suggested that fimbrial proteins did not carry any major sequential epitope and that, in native fimbriae, conformational epitopes, possibly generated between different subunits, might provide for the major immunogenic epitopes. Analysis of different S. typhi clinical isolates using the anti-fimbrial antiserum showed an overall immunological similarity of these structures within this serovar.     

衣原体主要外膜蛋白的研究进展

衣原体感染与多种慢性疾病密切相关,其主要外膜蛋白(MOMP)是一种多功能蛋白,分别与外膜结构的稳定性、生长代谢调节、抗原性和毒力密切相关。随着沙眼衣原体和肺炎衣原体基因组测序的完成,人们得以揭示其重要的生物合成、代谢途径,确定调控机制及其与致病的相关性。利用分子生物学技术在分子水平分析衣原体主要外膜蛋白的结构、抗原表位,对于免疫防御、免疫病理和免疫诊断均有重要意义。本文综述了衣原体主要外膜蛋白的分子结构、基因特性、抗原表位与应用前景。     

沙门菌外膜蛋白D的原核表达及多克隆抗体制备

目的:在大肠杆菌中表达沙门菌外膜蛋白(OMP)D,纯化后制备兔抗OMPD抗体。方法:用PCR方法从鼠伤寒沙门菌中扩增出ompD基因,并插入融合表达载体pET-28a(+)的多克隆位点,构建重组表达质粒pET28a(+)-ompD;以重组质粒转化大肠杆菌BL21(DE3),筛选阳性重组菌株,经IPTG诱导目的蛋白表达,在变性条件下对目的蛋白进行亲和层析纯化;以表达的OMPD蛋白免疫家兔,制备抗OMPD的多克隆抗体并进行鉴定。结果:扩增了ompD基因,测序证实正确后亚克隆于表达载体pET-28a(+)中,经PCR筛选和酶切鉴定获得阳性克隆,经诱导在大肠杆菌中表达出相对分子质量为40×103的目的蛋白并进行纯化;纯化的OMPD免疫家兔后,能有效地刺激特异性抗体的产生,抗血清的效价达到1∶10000以上,且具有良好的特异性。结论:构建ompD基因的原核表达载体,并在大肠杆菌中获得高效表达;制备出兔抗OMPD抗体,效价及特异性均良好,为进一步制备肠黏膜高亲和力疫苗奠定了基础。     

Isolation and Characterization of an Outer Membrane Protein of Chlorobium tepidum

A protein was isolated from membranes of the green sulfur bacterium Chlorobium tepidum. This protein was characterized by gel electrophoresis, gel filtration, analytical ultracentrifugation and amino acid sequencing. The molecular weight of the purified protein was shown to be 26 kDa by SDS-PAGE. HPLC gelfiltration, SDS-PAGE and analytical ultracentrifugation are consistent with the presence of a homogenous protein in the preparations. Amino acid analysis was obtained from the isolated protein after fragmentation with Lys-C, trypsin and cyanogen bromide. The cleavage pattern resulting from these treatments combined with Edman sequencing yield a sequence allowing the identification of an integral membrane agglutinin in Chl. tepidum.     

Lymphocytic Proliferative Response to Outer-Membrane Proteins Isolated from Salmonella

Porins isolated from Salmonella typhi have been demonstrated to protect against the challenge with this bacteria in mice. The mechanism has not been clarified, but could be associated with activation of both humoral and cellular immunity. In order to evaluate the induction of specific T cell responses, the lymphocytic proliferation to porins isolated from Salmonella typhimurium, Salmonella typhi and Escherichia coli was examined by ³H-thymidine incorporation assay in mice immunized with three different antigens: acetone-killed S. typhimurium, its porins, or outer-membrane proteins (OMPs) isolated from S. typhi. Higher proliferative responses were observed in mice immunized with porins and OMPs compared with those which received the acetone-killed bacteria. Although cross-reactivity was observed between porins, they were not mitogenic. Moreover, porins were able to activate T lymphocytes isolated from mice immunized with S. typhi OMPs. These results suggest that T cell activation, through the release of lymphokines, may play a role in the induction of protective immunity with porins.     

Protective efficacy and immunogenicity of Vi-porin conjugate against Salmonella typhi.

A conjugate vaccine against Salmonella typhi was prepared by covalently binding capsular polysaccharide (Vi) with porin, both isolated from S. typhi. First, Vi and porins were extracted. The Vi was purified from S. typhi Ty2. The purified Vi conformed to the requirements of the World Health Organization. Porins were purified from S. typhi 0901. The Vi was bound to the porins by a heterobifunctional cross-linking reagent, N-succinimidyl-3-(2-pyridyl dithio)-propionate (SPDP). After preparing the Vi-porin conjugate, its protective ability and immunogenicity were studied in mice following systemic immunization. The results showed that the conjugate is 6.5-fold more protective than Vi alone against S. typhi. The mice immunized with conjugate elicited higher anti-Vi antibody (IgG) levels (P < 0.01) than the mice immunized with Vi alone. Anti-porin antibodies were also induced by the conjugate. To study the mucosal immune responses, secretory IgA (sIgA) in the intestinal fluid was measured. Conjugate-immunized mice showed the induction of sIgA as compared to Vi alone. The results showed that when Vi is bound to porins, both isolated from same organism, the resultant conjugate induced both systemic and mucosal immune responses and provided better protection against S. typhi than Vi alone.     

Migration of Salmonella typhi through Intestinal Epithelial Monolayers: An In Vitro Study

This study characterizes the transmigration of enteroinvasive Salmonella typhi in vitro, using a human intestinal epithelial cell line as a model of small intestinal epithelium. C2BBe cells, a subclone of CACO-2 with a highly differentiated enterocytic phenotype, were grown to maturity on Transwell filters. S. typhi Ty2 and the vaccine strain, Ty21a, the S. typhi mutant X7344 and parent strain SB130, and S. typhimurium 5771 in logarithmic phase were introduced to the upper chamber of the filter units. Numbers of bacteria in the lower chamber, TER and permeability of the monolayer to mannitol were measured over time. Monolayers were examined by light, electron and confocal microscopy to determine the pathway of bacterial transmigration, and intracellular bacteria were estimated by gentamicin assay. Epithelial cell injury was quantified by light microscopy. S. typhi transmigrated earlier and in larger numbers than S. typhimurium, inducing marked changes in electrical resistance and permeability. Unlike S. typhimurium, S. typhi selected epithelial cells in small number and caused their death and extrusion from the monolayers leaving holes through which S. typhi transmigrated. Ty2 consistently transmigrated in larger numbers and with more injury to monolayers than Ty21a. S. typhi crosses the monolayers of C2BBe cells by a paracellular route in contrast to the transcellular pathway described for other Salmonellae. This may be related to the unique pathophysiology of S. typhi infection and the restricted host specificity of this pathogen. In these assays the vaccine strain, Ty21a, is slightly less invasive than its parent, though more invasive than S. typhimurium.     

重组土拉弗朗西斯菌外膜蛋白FopA的融合表达及抗原性分析

目的:探索一种大量表达功能性土拉弗朗西斯菌外膜蛋白FopA的方法。方法:采用SignalP 3.0 Server进行信号肽预测,将土拉弗朗西斯菌外膜蛋白FopA信号肽的基因序列(75bp)去除,将1107bp的核心序列克隆至原核表达载体pET32a,并在大肠杆菌BL21(DE3)中诱导表达。结果:构建了pET32a-fopA载体,重组蛋白FopA表达量约占菌体总蛋白量60%,Western blot分析显示重组FopA蛋白有较好的抗原性。结论:获得了高效表达FopA的pET32a-fopA表达载体,为下一步土拉弗朗西斯菌外膜蛋白FopA应用研究奠定了基础。     

Demonstration of a Ferric Vibrioferrin-Binding Protein in the Outer Membrane of Vibrio parahaemolyticus

Under iron-restricted conditions, Vibrio parahaemolyticus produces a siderophore, vibrioferrin, accompanying expression of two major outer membrane proteins of 78 and 83 kDa. Autoradiographic analysis of nondenaturing polyacrylamide gel electrophoregrams of outer membrane preparations previously incubated with [⁵⁵Fe]ferric vibrioferrin revealed a single radiolabeled band, in which the 78-kDa protein was detected predominantly by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The antiserum against the purified 78-kDa protein partially inhibited Fe-VF binding to isolated OMPs. The 78-kDa protein was cleaved by the treatment of whole cells with proteinase K, indicating that a portion of this protein is exposed on the surface of the outer membrane. The treated cells lost most of their iron uptake activity mediated by vibrioferrin. These results suggest that the ferric vibrioferrin-binding protein of 78 kDa may function as the receptor for ferric vibrioferrin involved in the initial step of vibrioferrin-mediated iron uptake. Immunoblot analysis using the antiserum against the 78-kDa protein demonstrated that the molecular mass and antigenic properties of the protein were highly conserved among V. parahaemolyticus strains examined. The antiserum also recognized an iron-repressible outer membrane protein of 78 kDa from iron-restricted V. alginolyticus strains, some of which appeared to produce vibrioferrin.     

Complete Amino Acid Sequence and Location of Omp-28, an Important Immunogenic Protein from Salmonella enterica serovar typhi

Omp-28 isolated from Salmonella enterica serovar typhi presented a subunit molecular mass of 9,632 Da by MALDI-TOF MS. It was denatured, S-alkylated, and 1) directly submitted to Edman sequencing, 2) cleaved with CNBr, and 3) hydrolyzed either with endoproteinase Glu-C or Asp-N. The major CNBr peptide containing the C-terminal portion of Omp-28 was isolated by tricine-SDS-PAGE and electroblotted whereas Omp-28 enzymatic peptides were isolated by C18-RP-HPLC. All peptides were sequenced. This approach allowed the elucidation of the complete primary structure of Omp-28. Its amino acid sequence is identical to that deduced from part of the DNA of the "putative periplasmic transport protein" of either S. enterica serovar typhimurium and a multiple drug resistant S. enterica serovar typhi. Omp-28 homologous protein sequences were also deduced from Escherichia coli and Yersinia pestis genomic DNA. All proteins had their secondary structures predicted. Immunogold cytochemistry indicated that Omp-28 is found on the bacterium outer membrane.     

Release of Prostaglandin E2 by Human Mononuclear Cells Exposed to Heat-Killed Salmonella typhi

Human mononuclear cells pre-labeled with [³H]arachidonic acid were shown to release metabolites following in vitro addition of heat-killed Salmonella typhi (HKST). The amount of label released was significantly higher than that seen with live S. typhi (LST). Addition of increasing amounts of HKST resulted in an increased release of metabolites. Enzyme immunoassay of the culture supernatants revealed that the bulk of the metabolite released was prostaglandin E₂ (PGE₂). Leukotriene B₄ (LTB₄) and leukotriene C₄ (LTC₄) were not detectable in the culture supernatants. The significance and implications of these results are discussed.     

Evaluation of a Recombinant 27-kDa Outer Membrane Protein of Coxiella burnetii as an Immunodiagnostic Reagent

The 27-kDa outer membrane protein from eight strains of Coxiella burnetii was expressed in the pET-21c protein expression system. Two fusion proteins with molecular masses of 30 and 32 kDa were evident in all eight of the recombinants by SDS-PAGE and immunoblotting. A protein having an approximate size of 30 kDa was purified from the Escherichia coli lysates by one-step affinity purification. The utility of the purified recombinant protein in ELISA was also evaluated by testing its reactivity with human sera and comparing this reactivity with that of Nine Mile phase II antigen. All of the 40 IF-positive serum samples were ELISA-positive for both the Nine Mile phase II and recombinant antigens, and negative serum controls were negative for both antigens. These results suggest that ELISA with the 27-kDa recombinant antigen is a sensitive and specific method for detecting anti-C. burnetii antibodies in human sera.     

A Peptidomimetic Antibiotic Targets Outer Membrane Proteins and Disrupts Selectively the Outer Membrane in Escherichia coli

Increasing antibacterial resistance presents a major challenge in antibiotic discovery. One attractive target in Gram-negative bacteria is the unique asymmetric outer membrane (OM), which acts as a permeability barrier that protects the cell from external stresses, such as the presence of antibiotics. We describe a novel β-hairpin macrocyclic peptide JB-95 with potent antimicrobial activity against Escherichia coli. This peptide exhibits no cellular lytic activity, but electron microscopy and fluorescence studies reveal an ability to selectively disrupt the OM but not the inner membrane of E. coli. The selective targeting of the OM probably occurs through interactions of JB-95 with selected β-barrel OM proteins, including BamA and LptD as shown by photolabeling experiments. Membrane proteomic studies reveal rapid depletion of many β-barrel OM proteins from JB-95-treated E. coli, consistent with induction of a membrane stress response and/or direct inhibition of the Bam folding machine. The results suggest that lethal disruption of the OM by JB-95 occurs through a novel mechanism of action at key interaction sites within clusters of β-barrel proteins in the OM. These findings open new avenues for developing antibiotics that specifically target β-barrel proteins and the integrity of the Gram-negative OM.     

伤寒沙门菌和甲型副伤寒沙门菌分离株的外膜蛋白谱比较

目的:比较伤寒沙门菌和甲型副伤寒沙门菌流行菌株的外膜蛋白谱差异。方法:运用二维蛋白电泳方法,对我国伤寒沙门菌株XJ90和甲型副伤寒沙门菌株JX2005-92在实验室通用营养条件下培养提取的外膜蛋白进行分离,比对其差异,对差异蛋白点进行质谱鉴定,对鉴定蛋白点的基因序列也进行比较。结果:菌株XJ90中发现20个特异蛋白点,质谱鉴定出16个;菌株JX2005-92中发现29个特异蛋白点,鉴定出18个。在这些蛋白中,OmpA是数目最多的同种差异蛋白。这些差异蛋白点中的大部分编码基因在2种细菌中序列高度相似或相同。结论:伤寒沙门菌和甲型副伤寒沙门菌基因序列高度相似的外膜蛋白具有不同的修饰形式,提示其不同遗传背景在相同的环境条件下表现出精细的功能差异。     

Vi-Suppressed wild strain Salmonella typhi cultured in high osmolarity is hyperinvasive toward epithelial cells and destructive of Peyer's patches

Salmonella typhi GIFU10007-3 which lost a viaB locus on its chromosome became highly invasive in our previous study. To investigate the phenomenon, we controlled Vi expression in wild strain S. typhi GIFU10007, and studied the invasive phenotype both in vitro and in vivo. When the wild strain of S. typhi was cultured in 300 mM NaCl containing Luria-Bertani broth (LBH), the expression of Vi antigen was suppressed, but secretion of invasion proteins (SipC, SipB and SipA) was increased. In this condition, wild strain S. typhi became highly invasive toward both epithelial cells and M cells of rat Peyer's patches. When GIFU10007 was cultured under conditions of high osmolarity, the bacteria disrupted Peyer's patches and induced massive bleeding in these structures only 20 min after inoculation into the ileal loop. In contrast, Vi-encapsulated wild strain GIFU10007 cultured under low osmolarity was not destructive, even after 60 min. To understand the role of the type III secretion system under conditions of high osmolarity, we knocked out the invA and sipC genes of both GIFU10007 and GIFU10007-3. Neither invA nor sipC mutants could invade epithelial cells or M cells in a high osmolarity environment. Our data show that the highly invasive phenotype was only expressed when the wild strain S. typhi was cultured under high osmolarity, which induced a state of Vi suppression, and in the presence of the type III secretion system.     

鼠伤寒杆菌主要外膜蛋白作为保护性抗原的研究

采用超声破碎,ＴｒｉｔｏｎＸ─１００处理和Ｓｅｐｈａｃｒａｌ超细Ｓ─３００凝胶过滤技术提取了鼠伤寒杆菌的主要外膜蛋白（ＭＯＭＰｓ）。ＭＯＭＰｓ的脂多糖（ＬＰＳ）含量约为０．２％。经ＳＤＳ─ＰＡＧＥ图谱显示蛋白在３６─４１ＫＤ之间。ＭＯＭＰｓ能使小鼠产生典型的足垫肿胀（ＤＴＨ）及高水平的ＩＬ─２;可保护５００ＬＤ５０鼠伤寒杆菌及伤寒杆菌的攻击,其免疫保护率分别为９０％和３３．３％,用５０ｕｇＭＯＭＰｓ免疫的小鼠的Ｔ淋巴细胞经尾静脉注射给非免疫小鼠,可使后者得到被动免疫保护,其保护率为４２．９％。基于上述实验结果,本文认为鼠伤寒杆菌的ＭＯＭＰｓ是一良好的保护性抗原。     

The Fluidity of the Bacterial Outer Membrane Is Species Specific

The outer membrane (OM) is an essential barrier that guards Gram-negative bacteria from diverse environmental insults. Besides functioning as a chemical gatekeeper, the OM also contributes towards the strength and stiffness of cells and allows them to sustain mechanical stress. Largely influenced by studies of Escherichia coli, the OM is viewed as a rigid barrier where OM proteins and lipopolysaccharides display restricted mobility. Here the discussion is extended to other bacterial species, with a focus on Myxococcus xanthus. In contrast to the rigid OM paradigm, myxobacteria possess a relatively fluid OM. It is concluded that the fluidity of the OM varies across environmental species, which is likely linked to their evolution and adaptation to specific ecological niches. Importantly, a fluid OM can endow bacteria with distinct functions for cell-cell and cell-environment interactions.