Basic Membrane Protein Research Articles

Borrelia burgdorferi Basic Membrane Protein A Initiates Arthritis in Tree Shrews

Borrelia burgdorferi Basic membrane protein A (BmpA) plays a crucial role in mediating immune responses to Lyme arthritis. The aim of this study was to describe manifestations and the main evaluation method on recombinant BmpA (rBmpA) - induced arthritis in tree shrews. We used rBmpA to stimulate knee joint in vivo in tree shrew animals. Arthritis was evaluated by Arthritis index, pathology, expression of proinflammation cytokines. Results showed that the joints of tree shrews appeared swelling, both the scores of arthritis and the number of swelling joints were enhanced The levels of TNF-α and CXCR4 increased in Peripheral blood. Day 7-15 after BmpA injection, the inflammation reached its peak. Histopathology examination showed that the synovium was hyperplasia, arranged irregularly. Our data indicated that the rBmpA-induced tree shrew arthritis may be used as a candidate model for Lyme arthritis pathogenesis and treatment.

Isoforskolin and Cucurbitacin IIa promote the expression of anti-inflammatory regulatory factor SIGIRR in human macrophages stimulated with Borrelia burgdorferi basic membrane protein A

Certain natural products, derived from medicinal plants, exhibit anti-inflammatory properties, but the mechanism of action of many remains unclear. Borrelia burgdorferi spirochetes are responsible for causing Lyme arthritis through activation of the Toll-like receptor (TLR) signaling pathway. In this study, we investigated the mechanisms by which Isoforskolin (ISOF) and Cucurbitacin IIa (CuIIa), compounds derived from Chinese herbs, can exert anti-inflammatory effects by modulating single immunoglobulin interleukin-1 receptor-related receptor (SIGIRR; also known as Toll/interleukin-1 receptor 8, TIR8) and thereby inhibiting B. burgdorferi basic membrane protein A (BmpA)-induced TLR signaling in human macrophages, specifically the THP-1 human monocytic cell line. After THP-1 cells were exposed in vitro to: i) recombinant (r)BmpA, ii) rBmpA and ISOF or iii) rBmpA and CuIIa, Cytotoxicity assay (Cell Counting Kit-8, CCK-8) are used to measure the effects of ISOF and CuIIa on cell viability. Meanwhile, real-time polymerase chain reaction and Western blotting were used to quantify SIGIRR mRNA and protein levels, respectively, at 6, 12, 24 and 48 h time points post-stimulation. In addition, proinflammatory cytokine tumor necrosis factor-α (TNF-α) was determined by ELISA analysis. Our study showed that rBmpA stimulation of THP-1 cells resulted in a drop in SIGIRR levels in THP-1 cells. More importantly, SIGIRR levels increased significantly in rBmpA-stimulated THP-1 cells following ISOF or CuIIa administration, and the results of ELISA analysis suggested that ISOF or CuIIa reduced the secretion of the proinflammatory cytokine TNF-α. In conclusion, These results reveal new possibilities for the treatment of Lyme arthritis.

Structural and Biomolecular Analyses of Borrelia burgdorferi BmpD Reveal a Substrate-Binding Protein of an ABC-Type Nucleoside Transporter Family

Borrelia burgdorferi sensu lato, the causative agent of tick-borne Lyme borreliosis (LB), has a limited metabolic capacity and needs to acquire nutrients, such as amino acids, fatty acids, and nucleic acids, from the host environment. Using X-ray crystallography, liquid chromatography-mass spectrometry, microscale thermophoresis, and cellular localization studies, we show that basic membrane protein D (BmpD) is a periplasmic substrate-binding protein of an ABC transporter system binding to purine nucleosides. Nucleosides are essential for bacterial survival in the host organism, and these studies suggest a key role for BmpD in the purine salvage pathway of B. burgdorferi sensu lato Because B. burgdorferi sensu lato lacks the enzymes required for de novo purine synthesis, BmpD may play a vital role in ensuring access to the purines needed to sustain an infection in the host. Furthermore, we show that, although human LB patients develop anti-BmpD antibodies, immunization of mice with BmpD does not confer protection against B. burgdorferi sensu lato infection.

Immunization with the basic membrane protein (BMP) family ABC transporter elicits protection against Enterococcus faecium in a murine infection model

Enterococcus faecium is evolving as a multi-resistant pathogen causing infections with high morbidity and mortality. A protective vaccine against E. faecium is lacking up till now. ATP-binding cassette (ABC) transporter proteins have important functions in bacteria to maintain survival and homeostasis. In the present study, we evaluated the basic membrane protein (BMP) family ABC transporter substrate-binding protein, designated herein as BMP, as a potential vaccine candidate against E. faecium. Recombinant BMP of E. faecium was expressed in Escherichia coli, and purified by metal affinity chromatography. Swiss albino mice were immunized with the recombinant BMP combined with Bacillus Calmette–Guérin (BCG) and/or alum as adjuvants. Mice immunized with BMP combined with alternating BCG and alum developed BMP-specific IgG and were protected against E. faecium challenge as evidenced from organ bioburden and histopathological examination. Furthermore, serum from immunized mice showed enhanced opsonophagocytic activity and protected mice against E. faecium challenge by passive immunization. Bioinformatic analysis revealed appreciable degrees of homology between E. faecium BMP and proteins from other pathogens which suggests BMP could be a useful vaccine against multiple pathogens. To our knowledge, this is the first report of in-vivo evaluation of BMP as a potential vaccine candidate against E. faecium.

Selection of Biophysical Methods for Characterisation of Membrane Proteins.

Over the years, there have been many developments and advances in the field of integral membrane protein research. As important pharmaceutical targets, it is paramount to understand the mechanisms of action that govern their structure–function relationships. However, the study of integral membrane proteins is still incredibly challenging, mostly due to their low expression and instability once extracted from the native biological membrane. Nevertheless, milligrams of pure, stable, and functional protein are always required for biochemical and structural studies. Many modern biophysical tools are available today that provide critical information regarding to the characterisation and behaviour of integral membrane proteins in solution. These biophysical approaches play an important role in both basic research and in early-stage drug discovery processes. In this review, it is not our objective to present a comprehensive list of all existing biophysical methods, but a selection of the most useful and easily applied to basic integral membrane protein research.

Borrelia burgdorferi basic membrane protein A initiates proinflammatory chemokine storm in THP 1-derived macrophages via the receptors TLR1 and TLR2

Lyme disease, reffered to as Lyme borreliosis, is a tick-borne zoonotic disease caused by Borrelia burgdorferi spirochetes. Lyme arthritis, the most common, serious and harmful manifestation during the late stages of Lyme disease, is closely associated with the Borrelia burgdorferi basic membrane protein A (BmpA). Chemokines are also reported to have an important role in Lyme arthritis. Toll-like receptors (TLRs) recognize and bind to pathogen-associated molecules which are structurally conserved among microbes, to activate transcriptional events, including cytokine production, inflammation, and tissue damage. We speculated that BmpA could induce a storm of proinflammatory chemokines via TLRs and downstream moleculars, and that TLR1, TLR2, TLR5, TLR6 and the adaptor protein, MyD88, may be involved in this process. We explored this hypothesis using the human monocytic leukemia cell line, THP-1, and recombinant BmpA (rBmpA). Cell surface TLR1 and TLR2 were neutralized using specific antibodies before stimulation with rBmpA and analysis of chemokine secretion using a chemokine chip. Further, the expressions level of the four TLRs and MyD88 were analyzed following stimulation with rBmpA. Stimulation with rBmpA resulted in elevated levels of seven cytokines. Further, TLR1 and TLR2 antibody treated cells exhibited an overall reduction in rBmpA-induced chemokine expression. TLR1, TLR2, and MyD88 expression levels (both mRNA and protein) increased after stimulation with rBmpA. Our data confirm that TLR1, TLR2, and MyD88 are involved in BmpA-induced proinflammatory chemokines, which may be closely involved in Lyme arthritis pathogenesis.

Engineering recombinant Lactococcus lactis as a delivery vehicle for BPC-157 peptide with antioxidant activities

Lactic acid bacteria (LAB) are attractive hosts for the expression of heterologous proteins and can be engineered to deliver therapeutic proteins or peptides to mucosal surfaces. The gastric stable pentadecapeptide BPC-157 is able to prevent and treat gastrointestinal inflammation by reducing the production of reactive oxygen species (ROS). In this study, we used LAB Lactococcus lactis as a vector to deliver BPC-157 by surface display and trypsin shedding or by secretion to the growth medium. Surface display of BPC-157 was achieved by fusing it with basic membrane protein A (BmpA) or with the peptidoglycan binding domain of AcmA and Usp45 secretion signal. While the expression of BmpA-fusion proteins was higher than that of AcmA/Usp45-fusion protein, the surface display ability of BPC-157 was approximately 14-fold higher with AcmA/Usp45-fusion protein. Release of BPC-157 from the bacterial surface or from isolated fusion proteins by trypsinization was demonstrated with anti-BPC-157 antibodies or by mass spectrometry. The concentration of BPC-157 delivered by surface display via AcmA/Usp45-fusion was 30ng/ml. This increased to 117ng/ml by Usp45 signal-mediated secretion, making the latter the most effective lactococcal delivery approach for BPC-157. Secreted BPC-157 significantly decreased ROS production in 149BR fibroblast cell model, suggesting its potential benefit in the treatment of intestinal inflammations. Additionally, a comparison of different modes of small peptide delivery by L. lactis, performed in the present study, will facilitate the future use of L. lactis as peptide delivery vehicle.

HtrA of Borrelia burgdorferi Leads to Decreased Swarm Motility and Decreased Production of Pyruvate.

ABSTRACTBorrelia burgdorferi HtrA (HtrABb) is a serine protease that targets damaged or improperly folded proteins. In our previous studies, HtrABb specifically degraded basic membrane protein BmpD, chemotaxis phosphatase CheX, and outer membrane protein P66. In addition, HtrABb degrades virulence factor BB0323 and components of the extracellular matrix fibronectin and aggrecan. A proteomics-based analysis (two-dimensional difference gel electrophoresis [2-D DIGE], liquid chromatography-mass spectrometry [LC-MS]) of an HtrABb-overexpressing strain of B. burgdorferi (A3HtrAOE) revealed that protein levels of P66 were reduced in comparison to wild-type B. burgdorferi, confirming its status as an HtrABb substrate. Hbb, a P66-DNA-binding transcription factor, was specifically degraded by HtrABb, providing supportive evidence for a role for both in the regulation of P66. A3HtrAOE exhibited reduced motility in swarm assays, a possible link between overabundance of HtrABb and its enzymatic specificity for P66. However, the ΔP66 strain did not have reduced motility in the swarm assays, negating a role for this protein. The proteomics analyses also identified three enzymes of the glycolytic pathway, glyceraldehyde-3-phosphate dehydrogenase (GAPDH), glycerol-3-phosphate dehydrogenase (GPDH), and glycerol kinase (GK), and one enzyme involved in carbohydrate metabolism, diphosphate-fructose-6-phosphate 1-phosphotransferase, which were reduced in A3HtrAOE. Consistent with its reduced protein levels of these glycolytic enzymes, A3HtrAOE was also deficient in production of pyruvate. We propose a model for a role for HtrABb in contributing to a decrease in metabolic activity of B. burgdorferi.

NF‑κB is a key modulator in the signaling pathway of Borreliaburgdorferi BmpA‑induced inflammatory chemokines in murine microglia BV2 cells.

Lyme disease, caused by the bacterial spirochete Borrelia burgdorferi, is a tick-borne zoonosis. Lyme neuroborreliosis is a principal manifestation of Lyme disease and its pathogenesis remains incompletely understood. Recent studies have demonstrated that Borrelia burgdorferi lipoproteins caused similar inflammatory effects as exhibited in Lyme neuroborreliosis. Basic membrane protein A (BmpA) is one of the dominant lipoproteins in the Borrelia burgdorferi membrane. In addition, nuclear factor κ-B (NF-κB) modulates the regulation of gene transcription associated with immunity and inflammation; however, in unstimulated cells, NF-κB is combined with the inhibitor of NF-κB (IκB-β). Therefore, it was hypothesized that NF-κB may be associated with BmpA-induced inflammation and the occurrence of Lyme neuroborreliosis. Therefore, the aim of the present study was to investigate the role that NF-κB serves in the signaling pathway of rBmpA-induced inflammatory chemokines. The present study measured the expression levels of NF-κB, IκB-β and inflammatory chemokines following recombinant BmpA (rBmpA) stimulation of murine microglia BV2 cells. Following stimulation with rBmpA, concentrations of pro-inflammatory cytokines including C-X-C motif chemokine 2, C-C motif chemokine (CCL) 5 and CCL22 were determined by ELISA analysis. Reverse transcription-quantitative polymerase chain reaction and western blotting were used to detect the expression levels of NF-κB p65 and IκB-β. The data demonstrated that concentrations of these chemokines in cell supernatants increased significantly following rBmpA stimulation. NF-κB was overexpressed, but IκB-β expression was significantly decreased. In conclusion, these results suggested that NF-κB serves an important stimulatory role in the signaling pathway of rBmpA-induced inflammatory chemokines in BV2 cells.

Borrelia burgdorferi basic membrane protein A stimulates murine macrophage to secrete specific chemokines.

In this study, we investigated the mechanisms that lead to the production of proinflammatory mediators by the murine macrophage cell line, RAW264.7, when these cells are exposed in vitro to recombinant Borrelia burgdorferi basic membrane protein A (rBmpA). Using antibody protein microarray technology with high-throughput detection ability for detecting 25 chemokines in culture supernatant the RAW264.7 cell culture supernatants at 12 and 24 h post-stimulation with rBmpA, we identified two chemokines, a monocyte chemoattractant protein-5 (MCP-5/CCL12) and a macrophage inflammatory protein-2 (MIP-2/CXCL2), both of which increased significantly after stimulation. We then chose these two chemokines for further study. Enzyme-linked immunosorbent assay and real-time polymerase chain reaction revealed that with the increase of rBmpA concentration, MCP-5/CCL12 and MIP-2/CXCL2 showed concentration-dependent increases (p <0.01).Our results indicate that the rBmpA could stimulate the secretion of several specific chemokines and induce Lyme arthritis.

Isoforskolin downregulates proinflammatory responses induced by Borrelia burgdorferi basic membrane protein A.

The plant Coleus forskohlii is distributed primarily in India, Thailand, China, Egypt and Brazil and has a history of use in the treatment of multiple diseases. Isoforskolin (ISOF) is the principle active component of C. forskohlii native to China and has previously been studied for its biological effects. The aim of the present study was to evaluate the effect of ISOF on the proinflammatory responses induced by recombinant Borrelia burgdorferi basic membrane protein A (rBmpA). In in vitro experiments, the proinflammatory effects of rBmpA and the anti-inflammatory function of ISOF were evaluated in murine macrophages, human macrophages and dendritic cells by detecting the transcription and expression of tumor necrosis factor (TNF)-α and interleukin (IL)-6. In in vivo experiments, mean arthritis index and X-ray and histopathological examinations were used to verify the role of ISOF in experimental Lyme arthritis in mice. The results indicated that rBmpA, which induced the transcription and expression of TNF-α and IL-6, activated proinflammatory responses in murine macrophages, human macrophages and dendritic cells. In turn, ISOF downregulated the transcription and expression of TNF-α and IL-6 induced by rBmpA. Additionally, the in vivo experiments demonstrated that ISOF could also inhibit the symptoms of experimental Lyme arthritis. These results suggest that ISOF may have a potential application as an anti-inflammatory agent for the treatment of Lyme arthritis.

Development and Evaluation of a Loop-Mediated Isothermal Amplification Assay for the Detection of Treponema pallidum DNA in the Peripheral Blood of Secondary Syphilis Patients.

Secondary syphilis (SS) has always been puzzling for the clinicians because of the similarity of the appearance of skin rashes with other dermatoses. Serological assays are useful, but less sensitive at an early stage of SS or when patients are immunodeficient. Therefore, there is an urgent need to develop a rapid and effective tool for the diagnosis of SS, which may play an important role in the control of epidemic syphilis outbreaks. In this study, we evaluated a loop-mediated isothermal amplification (LAMP) assay, targeting gene encoding the basic membrane protein of Treponema pallidum, to detect the presence of circulating T. pallidum DNA in the blood of SS patients. The specificity of LAMP was validated using three strains of Spirochaetales and six common clinical bacteria. The clinical applicability of LAMP assay was assessed using 642 blood samples from clinically suspected SS patients and 80 samples from healthy blood donors, showing a sensitivity of 82.1% and a specificity of 100.0% in the diagnosis of SS. Thus, our results indicate that the LAMP can be used as a supplementary method for the diagnosis of SS.

Borrelia burgdorferi basic membrane protein A could induce chemokine production in murine microglia cell line BV2

Lyme neuroborreliosis is a nervous system infectious disease caused by Borrelia burgdorferi (B. burgdorferi). It has been demonstrated that cytokines induced by B. burgdorferi are related to Lyme neuroborreliosis. Microglia is known as a key player in the immune responses that occur within the central nervous system. In response to inflammation, it will be activated and generate cytokines and chemokines. Experiments in vitro cells have showed that B. Burgdorferi membrane protein A (BmpA), a major immunogen of B. Burgdorferi, could induce Lyme arthritis and stimulate human and murine lymphocytes to produce inflammatory cytokines. In our study, the murine microglia BV2 cell line was used as a cell model to explore the stimulating effects of recombinant BmpA (rBmpA); Chemokine chip, ELISA and QPCR technology were used to measure the production of chemokines from microglial cells stimulated by rBmpA. Compared with the negative control group, CXCL2, CCL22, and CCL5 concentrations in the cell supernatant increased significantly after the rBmpA stimulation; the concentration of these chemokines increased with rBmpA concentration increasing; the mRNA expression levels of chemokines (CXCL2, CCL22, and CCL5) in murine BV2 cells increased significantly with 10 μg/mL and 20 μg/mL rBmpA stimulation; CXCL13 was not change after the rBmpA stimulation. Our study shows that chemokines, such as CXCL2, CCL22, and CCL5 were up-regulated by the rBmpA in the BV2 cells. The production of chemokines in Lyme neuroborreliosis may be mainly from microglia cells and the rBmpA may be closely related with the development of Lyme neuroborreliosis.

TLR4‑dependent signaling pathway modulation: A novel mechanism by which pioglitazone protects against nutritional fibrotic steatohepatitis in mice.

Activation of the innate immune system is involved in the development of chronic liver diseases, including nonalcoholic steatohepatitis. Toll‑like receptor 4 (TLR4) is one of the sensors of the innate immune system. The aim of the present study was to elucidate the role of the TLR4‑dependent signaling pathway, and examine the effect of pioglitazone on hepatic fibrosis, through modulation of the TLR4 pathway in a mouse model of nutritional fibrotic steatohepatitis. Male C57BL/6J mice were fed a methionine‑choline deficient (MCD) diet for 8 weeks to induce nonalcoholic fibrotic steatohepatitis. The PPARγ agonist, pioglitazone, and PPARγ inhibitor, GW9662, were administered to the mice, respectively. The effects of the induction of PPARγ on liver biochemistry and histology, the modulation of TLR4 and its downstream pathway, and the expression levels of inflammatory and fibrogenic genes were assessed using reverse transcription‑quantitative polymerase chain reaction and Western blot analyses. The MCD‑fed mice exhibited progressive hepatic steatosis, necrotic inflammation and fibrosis, along with increase levels of serum alanine aminotransferase and aspartate aminotransferase, accompanied by the upregulation of TLR4, the TLR4‑myeloid differentiation primary response gene 88‑dependent pathway and downstream genes, and proinflammatory and profibrotic genes; and downregulation of basic membrane protein and activin membrane‑bound inhibitor. The administration of pioglitazone was found to reverse hepatic nutritional fibrosis via restoration of the expression levels of proinflammatory and profibrotic genes in the MCD‑fed mice. The results of the present study provide novel evidence supporting the protective role of pioglitazone in ameliorating nutritional fibrotic steatohepatitis, through modulation of the TLR4‑mediated signaling pathway.

PGE2 MEDIATES OENOCYTOID CELL LYSIS VIA A SODIUM-POTASSIUM-CHLORIDE COTRANSPORTER.

Prostaglandin E2 (PGE2 ) mediates immune responses of the beet armyworm, Spodoptera exigua, including oenocytoid cell lysis (a class of lepidopteran hemocytes: OCL) via its specific membrane receptor to release inactive prophenoloxidase (PPO) into hemolymph. PPO is activated into phenoloxidase in the plasma to play crucial roles in the immune responses of S. exigua. The mechanism of OCL has not been elucidated, however we posed the hypothesis that a rapid accumulation of sodium ions within the oenocytoids allows a massive influx of water by the ion gradient, which leads to the cell lysis. It remains unclear which sodium channel is responsible for the OCL in response to PGE2 . This study identified a specific sodium channel called sodium-potassium-chloride cotransporter 1 (Se-NKCC1) expressed in hemocytes of S. exigua and analyzed its function in the OCL in response to PGE2 . Se-NKCC1 encodes a basic membrane protein (pI value = 8.445) of 1,066 amino acid residues, which contains 12 putative transmembrane domains. Se-NKCC1 was expressed in all developmental stages and tissues. qPCR showed that bacterial challenge significantly induced its expression. A specific inhibitor of NKCC, bumetanide, prevented the OCL in a dose-dependent manner. When RNA interference (RNAi) using double-stranded RNA specific to Se-NKCC1 suppressed its expression, the OCL and PPO activation were significantly inhibited in response to PGE2 . The RNAi treatment also reduced nodule formation to bacterial challenge. These results suggest that Se-NKCC1 is associated with OCL by facilitating inward transport of ions in response to PGE2 .

Engineering BmpA as a carrier for surface display of IgG-binding domain on Lactococcus lactis

Basic membrane protein A (BmpA) is a potential carrier protein for surface display of the IgG-binding domain on Lactococcus lactis. We have shown that it can increase the adhesion of bacteria to the intestinal cell model by 1.3-fold and have improved BmpA-based surface display by engineering the BmpA molecule. The bulk of the BmpA molecule was shown to be important in surface display; however, limited shortening (variant Bmp1) resulted in a large increase in the surface display ability. The closeness of the N- and the C-terminals in the Bmp1 model and the inefficiency of the spacer suggest that the distance of the passenger from the membrane is not of prime importance in surface display.

The HtrA protease of Borrelia burgdorferi degrades outer membrane protein BmpD and chemotaxis phosphatase CheX

Borrelia burgdorferi, the spirochaetal agent of Lyme disease, codes for a single HtrA protein, HtrABb (BB0104) that is homologous to DegP of Escherichia coli (41% amino acid identity). HtrABb shows physical and biochemical similarities to DegP in that it has the trimer as its fundamental unit and can degrade casein via its catalytic serine. Recombinant HtrABb exhibits proteolytic activity in vitro, while a mutant (HtrABbS198A) does not. However, HtrABb and DegP have some important differences as well. Native HtrABb occurs in both membrane-bound and soluble forms. Despite its homology to DegP, HtrABb could not complement an E. coli DegP deletion mutant. Late stage Lyme disease patients, as well as infected mice and rabbits developed a robust antibody response to HtrABb, indicating that it is a B-cell antigen. In co-immunoprecipitation studies, a number of potential binding partners for HtrABb were identified, as well as two specific proteolytic substrates, basic membrane protein D (BmpD/BB0385) and chemotaxis signal transduction phosphatase CheX (BB0671). HtrABb may function in regulating outer membrane lipoproteins and in modulating the chemotactic response of B. burgdorferi.

A host-restricted viral vector for antigen-specific immunization against Lyme disease pathogen

Newcastle disease virus (NDV) is an avian virus that is attenuated in primates and is a potential vaccine vector for human use. We evaluated NDV as a vector for expressing selected antigens of the Lyme disease pathogen Borrelia burgdorferi. A series of recombinant NDVs were generated that expressed intracellular or extracellular forms of two B. burgdorferi antigens: namely, the basic membrane protein A (BmpA) and the outer surface protein C (OspC). Expression of the intracellular and extracellular forms of these antigens was confirmed in cultured chicken cells. C3H or Balb/C mice that were immunized intranasally with the NDV vectors mounted vigorous serum antibody responses against the NDV vector, but failed to mount a robust response against either the intracellular or extracellular forms of BmpA or OspC. By contrast, a single immunization of hamsters with the NDV vectors via the intranasal, intramuscular, or intraperitoneal route resulted in rapid and rigorous antibody responses against the intracellular or extracellular forms of BmpA and OspC. When groups of hamsters were separately inoculated with various NDV vectors and challenged with B. burgdorferi (108cells/animal), immunization with vector expressing either intracellular or extracellular BmpA was associated with a significant reduction of the pathogen load in the joints. Taken together, our studies highlighted the importance of NDV as vaccine vector that can be used for simple yet effective immunization of hosts against bacterial infections including Lyme disease.

Identification of Candidate Carrier Proteins for Surface Display on Lactococcus lactis by Theoretical and Experimental Analyses of the Surface Proteome

Lactococcus lactis is a lactic acid bacterium of proven safety for use in human oral applications. For this purpose, surface display of recombinant proteins is important, and new approaches for it are being sought. Analysis of the bacterial surface proteome is essential in identifying new candidate carrier proteins for surface display. We have made two different predictions of surface-associated proteins of L. lactis MG1363 by using Augur and LocateP software, which yielded 666 and 648 proteins, respectively. Surface proteins of L. lactis NZ9000, a derivative of MG1363, were identified by using a proteomics approach. The surface proteins were cleaved from intact bacteria, and the resulting peptides were identified by mass spectrometry. The latter approach yielded 80 proteins, 34 of which were not predicted by either software. Of the 80 proteins, 7 were selected for further study. These were cloned in frame with a C-terminal hexahistidine tag and overexpressed in L. lactis NZ9000 using nisin-controlled expression. Proteins of correct molecular weight carrying a hexahistidine tag were detected. Their surface localization was confirmed with flow cytometry. Basic membrane protein A (BmpA) was exposed at the highest level. To test BmpA as a candidate carrier protein, the hexahistidine tag was replaced by the B domain of staphylococcal protein A in the genetic construct. The B domain was displayed on the surface with BmpA as a carrier. The advantage of covalent BmpA binding was demonstrated. BmpA was thus shown to be a suitable candidate for a carrier protein in lactococcal surface display.

Borrelia burgdorferi lipoprotein BmpA activates pro-inflammatory responses in human synovial cells through a protein moiety

Borrelia burgdorferi invasion of mammalian joints results in genesis of Lyme arthritis. Other than spirochete lipids, existence of protein antigens, which are abundant in joints and participate in B. burgdorferi-induced host inflammatory response, is unknown. Here, we report that major products of the B. burgdorferi basic membrane protein (bmp) A/B operon that are induced in murine and human joints, possess inflammatory properties. Compared to the wild type B. burgdorferi, an isogenic bmpA/B mutant induced significantly lower levels of pro-inflammatory cytokines TNF-α and IL-1β in cultured human synovial cells, which could be restored using bmpA/B-complemented mutants, and more directly, upon addition of recombinant BmpA, but not BmpB or control spirochete proteins. Non-lipidated and lipidated versions of BmpA induced similar levels of cytokines, and remained unaffected by treatment with lipopolysaccharide inhibitor, polymyxin B. The bmpA/B mutant was also impaired in the induction of NF-κB and p38 MAP kinase signaling pathways in synovial cells, which were activated by non-lipidated BmpA. These results show that a protein moiety of BmpA can induce cytokine responses in synovial cells via activation of the NF-κB and p38 MAP kinase pathways and thus, could potentially contribute to the genesis of Lyme arthritis.