Assessment of vaccine potential of the Neisseria-specific protein NMB0938

The surface lipoproteins of gram-negative bacteria: Protectors and foragers in harsh environments

Gram-negative pathogens are enveloped by an outer membrane that serves as a double-edged sword: On the one hand, it provides a layer of protection for the bacterium from environmental insults, including other bacteria and the host immune system. On the other hand, it restricts movement of vital nutrients into the cell and provides a plethora of antigens that can be detected by host immune systems. One strategy used to overcome these limitations is the decoration of the outer surface of gram-negative bacteria with proteins tethered to the outer membrane through a lipid anchor. These surface lipoproteins (SLPs) fulfill critical roles in immune evasion and nutrient acquisition, but as more bacterial genomes are sequenced, we are beginning to discover their prevalence and their different roles and mechanisms and importantly how we can exploit them as antimicrobial targets. This review will focus on representative SLPs that gram-negative bacteria use to overcome host innate immunity, specifically the areas of nutritional immunity and complement system evasion. We elaborate on the structures of some notable SLPs required for binding target molecules in hosts and how this information can be used alongside bioinformatics to understand mechanisms of binding and in the discovery of new SLPs. This information provides a foundation for the development of therapeutics and the design of vaccine antigens.

Proteome-scale identification of Leishmania infantum for novel vaccine candidates: A hierarchical subtractive approach

Vaccines are one of the most significant achievements in medical science. However, vaccine design is still challenging at all stages. The selection of antigenic peptides as vaccine candidates is the first and most important step for vaccine design. Experimental selection of antigenic peptides for the design of vaccines is a time-consuming, labor-intensive and expensive procedure. More recently, in the light of computer-aided biotechnology and reverse vaccinology, the precise selection of antigenic peptides and rational vaccine design against many pathogens have developed. In this study, the whole proteome of Leishmania infantum was analyzed using a pipeline of algorithms. From the set of 8045 proteins of L. infantum, sixteen novel antigenic proteins were derived using a hierarchical proteome subtractive analysis. These novel vaccine targets can be utilized as top candidates for designing the new prophylactic or therapeutic vaccines against visceral leishmaniasis. Significantly, all the sixteen novel vaccine candidates are non-allergen antigenic proteins that have not been used for the design of vaccines against visceral leishmaniasis until now.

Excavating the surface-associated and secretory proteome of Mycobacterium leprae for identifying vaccines and diagnostic markers relevant immunodominant epitopes

For centuries, Mycobacterium leprae, etiological agent of leprosy, has been afflicting mankind regardless of extensive use of live-attenuated vaccines and antibiotics. Surface-associated and secretory proteins (SASPs) are attractive targets against bacteria. We have integrated biological knowledge with computational approaches and present a proteome-wide identification of SASPs. We also performed computational assignment of immunodominant epitopes as coordinates of prospective antigenic candidates in most important class of SASPs, the outer membrane proteins (OMPs). Exploiting the known protein sequence and structural characteristics shared by the SASPs from bacteria, 17 lipoproteins, 11 secretory and 19 novel OMPs (including 4 essential proteins) were identified in M. leprae As OMPs represent the most exposed antigens on the cell surface, their immunoinformatics analysis showed that the identified 19 OMPs harbor T-cell MHC class I epitopes and class II epitopes against HLA-DR alleles (54), while 15 OMPs present potential T-cell class II epitopes against HLA-DQ alleles (6) and 7 OMPs possess T-cell class II epitopes against HLA-DP alleles (5) of humans. Additionally, 11 M. leprae OMPs were found to have B-cell epitopes and these may be considered as prime candidates for the development of new immunotherapeutics against M. leprae.

The Journey of Lipoproteins Through the Cell: One Birthplace, Multiple Destinations

Bacterial lipoproteins are a very diverse group of proteins characterized by the presence of an N-terminal lipid moiety that serves as a membrane anchor. Lipoproteins have a wide variety of crucial functions, ranging from envelope biogenesis to stress response. In Gram-negative bacteria, lipoproteins can be targeted to various destinations in the cell, including the periplasmic side of the cytoplasmic or outer membrane, the cell surface or the external milieu. The sorting mechanisms have been studied in detail in Escherichia coli, but exceptions to the rules established in this model bacterium exist in other bacteria. In this chapter, we will present the current knowledge on lipoprotein sorting in the cell. Our particular focus will be on the surface-exposed lipoproteins that appear to be much more common than previously assumed. We will discuss the different targeting strategies, provide numerous examples of surface-exposed lipoproteins and discuss the techniques used to assess their surface exposure.

Immunoproteomic identification of MbovP579, a promising diagnostic biomarker for serological detection of Mycoplasma bovis infection

A lack of knowledge regarding the antigenic properties of Mycoplasma bovis proteins prevents the effective control of bovine infections using immunological approaches. In this study, we detected and characterized a specific and sensitive M. bovis diagnostic biomarker. After M. bovis total proteins and membrane fractions were separated with two dimensional gel electrophoresis, proteins reacting with antiserawere detected using MALDI-TOF MS. Thirty-nine proteins were identified, 32 of which were previously unreported. Among them, immunoinformatics predicted eight antigens, encoded by Mbov_0106, 0116, 0126, 0212, 0275, 0579, 0739, and 0789, to have high immunological value. These genes were expressed in E. coli after mutagenesis of UGA to UGG using overlap extension PCR. A lipoprotein, MbovP579, encoded by a functionally unknown gene, was a sensitive and specific antigen for detection of antibodies in sera from both M. bovis-infected and vaccinated cattle. The specificity of MbovP579 was confirmed by its lack of cross-reactivity with other mycoplasmas, including Mycoplasma agalactiae. An iELISA based on rMbovP579 detected seroconversion 7 days post-infection (dpi). The ELISA had sensitivity of 90.2% (95% CI: 83.7%, 94.3%) and a specificity of 97.8% (95% CI: 88.7%, 99.6%) with clinical samples. Additional comparative studies showed that both diagnostic and analytic sensitivities of the ELISA were higher than those of a commercially available kit (p<0.01). We have thus detected and characterized the novel antigen, MbovP579, and established an rMbovP579-based ELISA as a highly sensitive and specific method for the early diagnosis of M. bovis infection.

Surface-Exposed Lipoproteins: An Emerging Secretion Phenomenon in Gram-Negative Bacteria

Bacterial lipoproteins are hydrophilic proteins that are anchored to a cell membrane by N-terminally linked fatty acids. It is widely believed that nearly all lipoproteins produced by Gram-negative bacteria are either retained in the inner membrane (IM) or transferred to the inner leaflet of the outer membrane (OM). Lipoproteins that are exposed on the cell surface have also been reported but are generally considered to be rare. Results from a variety of recent studies, however, now suggest that the prevalence of surface-exposed lipoproteins has been underestimated. In this review we describe the evidence that the surface exposure of lipoproteins in Gram-negative bacteria is a widespread phenomenon and discuss possible mechanisms by which these proteins might be transported across the OM.

Proteome-wide B and T cell epitope repertoires in outer membrane proteins of Mycobacterium avium subsp. paratuberculosis have vaccine and diagnostic relevance: a holistic approach

Mycobacterium avium subsp. paratuberculosis (MAP) is an etiological agent of chronic inflammation of the intestine among ruminants and humans. Currently, there are no effective vaccines and sensitive diagnostic tests available for its control and detection. For this, it is of paramount importance to identify the MAP antigens, which may be immunologically recognized by the host immune system. To address this challenge, we performed identification of the immunogenic epitopes in the MAP outer membrane proteins (OMPs). We have previously identified 57 MAP proteins as OMPs [Rana A, Rub A, Akhter Y. 2014. Molecular BioSystems, 10:2329-2337] and have evaluated them for the epitope selection and analysis employing a computational approach. Thirty-five MAP OMPs are reported with nine-mer peptides showing high binding affinity to major histocompatibility complex (MHC) class I molecules and 28 MAP OMPs with 15-mer peptides of high binding affinity for MHC class II molecules. The presence of MHC binding epitopes indicates the potential cell-mediated immune response inducing capacity of these MAP OMPs in infected host. To further investigate the humoral response inducing properties of OMPs of MAP, we report potential B cell epitopes based on the sequences of peptide antigens and their molecular structures. We also report 10 proteins having epitopes for both B and T cells representing potential candidates which may invoke both humoral and cellular immune responses in the host. These findings will greatly accelerate and expedite the formulation of effective and cost-efficient vaccines and diagnostic tests against MAP infection.

Inhibition of the alternative pathway of nonhuman infant complement by porin B2 contributes to virulence of Neisseria meningitidis in the infant rat model

Neisseria meningitidis utilizes capsular polysaccharide, lipooligosaccharide (LOS) sialic acid, factor H binding protein (fHbp), and neisserial surface protein A (NspA) to regulate the alternative pathway (AP) of complement. Using meningococcal mutants that lacked all four of the above-mentioned molecules (quadruple mutants), we recently identified a role for PorB2 in attenuating the human AP; inhibition was mediated by human fH, a key downregulatory protein of the AP. Previous studies showed that fH downregulation of the AP via fHbp or NspA is specific for human fH. Here, we report that PorB2-expressing quadruple mutants also regulate the AP of baby rabbit and infant rat complement. Blocking a human fH binding region on PorB2 of the quadruple mutant of strain 4243 with a chimeric protein that comprised human fH domains 6 and 7 fused to murine IgG Fc enhanced AP-mediated baby rabbit C3 deposition, which provided evidence for an fH-dependent mechanism of nonhuman AP regulation by PorB2. Using isogenic mutants of strain H44/76 that differed only in their PorB molecules, we confirmed a role for PorB2 in resistance to killing by infant rat serum. The PorB2-expressing strain also caused higher levels of bacteremia in infant rats than its isogenic PorB3-expressing counterpart, thus providing a molecular basis for increased survival of PorB2 isolates in this model. These studies link PorB2 expression with infection of infant rats, which could inform the choice of meningococcal strains for use in animal models, and reveals, for the first time, that PorB2-expressing strains of N. meningitidis regulate the AP of baby rabbits and rats.

Immunization with recombinant Chaperonin60 (Chp60) outer membrane protein induces a bactericidal antibody response against Neisseria meningitidis

Sera from individuals colonized with Neisseria meningitidis and from patients with meningococcal disease contain antibodies specific for the neisserial heat-shock/chaperonin (Chp)60 protein. In this study, immunization of mice with recombinant (r)Chp60 in saline; adsorbed to aluminium hydroxide; in liposomes and detergent micelles, with and without the adjuvant MonoPhosphoryl Lipid A (MPLA), induced high and similar (p>0.05) levels of antibodies that recognized Chp60 in outer membranes (OM). FACS analysis and immuno-fluorescence experiments demonstrated that Chp60 was surface-expressed on meningococci. By western blotting, murine anti-rChp60 sera recognized a protein of Mr 60kDa in meningococcal cell lysates. However, cross-reactivity with human HSP60 protein was also observed. By comparing translated protein sequences of strains, 40 different alleles were found in meningococci in the Bacterial Isolate Genome Sequence database with an additional 5 new alleles found in our selection of 13 other strains from colonized individuals and patients. Comparison of the non-redundant translated amino acid sequences from all the strains revealed ≥97% identity between meningococcal Chp60 proteins, and in our 13 strains the protein was expressed to high and similar levels. Bactericidal antibodies (median reciprocal titres of 32-64) against the homologous strain MC58 were induced by immunization with rChp60 in liposomes, detergent micelles and on Al(OH)3. Bactericidal activity was influenced by the addition of MPLA and the delivery formulation used. Moreover, the biological activity of anti-Chp60 antisera did not extend significantly to heterologous meningococcal strains. Thus, in order to provide broad coverage, vaccines based on Chp60 would require multiple proteins and specific bactericidal epitope identification.

In silico identification of epitopes in Mycobacterium avium subsp. paratuberculosis proteins that were upregulated under stress conditions

Johne's disease in ruminants is caused by Mycobacterium avium subsp. paratuberculosis. Diagnosis of M. avium subsp. paratuberculosis infection is difficult, especially in the early stages. To date, ideal antigen candidates are not available for efficient immunization or immunodiagnosis. This study reports the in silico selection and subsequent analysis of epitopes of M. avium subsp. paratuberculosis proteins that were found to be upregulated under stress conditions as a means to identify immunogenic candidate proteins. Previous studies have reported differential regulation of proteins when M. avium subsp. paratuberculosis is exposed to stressors which induce a response similar to dormancy. Dormancy may be involved in evading host defense mechanisms, and the host may also mount an immune response against these proteins. Twenty-five M. avium subsp. paratuberculosis proteins that were previously identified as being upregulated under in vitro stress conditions were analyzed for B and T cell epitopes by use of the prediction tools at the Immune Epitope Database and Analysis Resource. Major histocompatibility complex class I T cell epitopes were predicted using an artificial neural network method, and class II T cell epitopes were predicted using the consensus method. Conformational B cell epitopes were predicted from the relevant three-dimensional structure template for each protein. Based on the greatest number of predicted epitopes, eight proteins (MAP2698c [encoded by desA2], MAP2312c [encoded by fadE19], MAP3651c [encoded by fadE3_2], MAP2872c [encoded by fabG5_2], MAP3523c [encoded by oxcA], MAP0187c [encoded by sodA], and the hypothetical proteins MAP3567 and MAP1168c) were identified as potential candidates for study of antibody- and cell-mediated immune responses within infected hosts.

Lipoproteins of bacterial pathogens

Bacterial lipoproteins are a set of membrane proteins with many different functions. Due to this broad-ranging functionality, these proteins have a considerable significance in many phenomena, from cellular physiology through cell division and virulence. Here we give a general overview of lipoprotein biogenesis and highlight examples of the roles of lipoproteins in bacterial disease caused by a selection of medically relevant Gram-negative and Gram-positive pathogens: Mycobacterium tuberculosis, Streptococcus pneumoniae, Borrelia burgdorferi, and Neisseria meningitidis. Lipoproteins have been shown to play key roles in adhesion to host cells, modulation of inflammatory processes, and translocation of virulence factors into host cells. As such, a number of lipoproteins have been shown to be potential vaccines. This review provides a summary of some of the reported roles of lipoproteins and of how this knowledge has been exploited in some cases for the generation of novel countermeasures to bacterial diseases.