Protective immunity of pneumococcal glycoconjugates

Elucidating the Structural and Minimal Protective Epitope of the Serogroup X Meningococcal Capsular Polysaccharide

Despite the considerable progress toward the eradication of meningococcal disease with the introduction of glycoconjugate vaccines, previously unremarkable serogroup X has emerged in recent years, recording several outbreaks throughout the African continent. Different serogroup X polysaccharide-based vaccines have been tested in preclinical trials, establishing the principles for further improvement. To elucidate the antigenic determinants of the MenX capsular polysaccharide, we generated a monoclonal antibody, and its bactericidal nature was confirmed using the rabbit serum bactericidal assay. The antibody was tested by the inhibition enzyme-linked immunosorbent assay and surface plasmon resonance against a set of oligosaccharide fragments of different lengths. The epitope was shown to be contained within five to six α-(1–4) phosphodiester mannosamine repeating units. The molecular interactions between the protective monoclonal antibody and the MenX capsular polysaccharide fragment were further detailed at the atomic level by saturation transfer difference nuclear magnetic resonance (NMR) spectroscopy. The NMR results were used for validation of the in silico docking analysis between the X-ray crystal structure of the antibody (Fab fragment) and the modeled hexamer oligosaccharide. The antibody recognizes the MenX fragment by binding all six repeating units of the oligosaccharide via hydrogen bonding, salt bridges, and hydrophobic interactions. In vivo studies demonstrated that conjugates containing five to six repeating units can produce high functional antibody levels. These results provide an insight into the molecular basis of MenX vaccine-induced protection and highlight the requirements for the epitope-based vaccine design.

Straightforward synthesis of the pentasaccharide repeating unit of the cell wall O-antigen of Escherichia coli O43 strain

A concise synthetic strategy has been developed for the synthesis of the pentasaccharide repeating unit of the cell wall O-antigen of Escherichia coli O43 strain involving stereoselective β-D-mannosylation and α-L-fucosylation using corresponding trichloroacetimidate intermediates and perchloric acid supported over silica (HClO₄-SiO₂) as glycosylation promoter. The yield and stereoselectivity of the glycosylations were very good.

Protection against Streptococcus suis Serotype 2 Infection Using a Capsular Polysaccharide Glycoconjugate Vaccine

Streptococcus suis serotype 2 is an encapsulated bacterium and one of the most important bacterial pathogens in the porcine industry. Despite decades of research for an efficient vaccine, none is currently available. Based on the success achieved with other encapsulated pathogens, a glycoconjugate vaccine strategy was selected to elicit opsonizing anti-capsular polysaccharide (anti-CPS) IgG antibodies. In this work, glycoconjugate prototypes were prepared by coupling S. suis type 2 CPS to tetanus toxoid, and the immunological features of the postconjugation preparations were evaluated in vivo In mice, experiments evaluating three different adjuvants showed that CpG oligodeoxyribonucleotide (ODN) induces very low levels of anti-CPS IgM antibodies, while the emulsifying adjuvants Stimune and TiterMax Gold both induced high levels of IgGs and IgM. Dose-response trials comparing free CPS with the conjugate vaccine showed that free CPS is nonimmunogenic independently of the dose used, while 25 μg of the conjugate preparation was optimal in inducing high levels of anti-CPS IgGs postboost. With an opsonophagocytosis assay using murine whole blood, sera from immunized mice showed functional activity. Finally, the conjugate vaccine showed immunogenicity and induced protection in a swine challenge model. When conjugated and administered with emulsifying adjuvants, S. suis type 2 CPS is able to induce potent IgM and isotype-switched IgGs in mice and pigs, yielding functional activity in vitro and protection against a lethal challenge in vivo, all features of a T cell-dependent response. This study represents a proof of concept for the potential of glycoconjugate vaccines in veterinary medicine applications against invasive bacterial infections.

Effect of abatacept on the immunogenicity of 23-valent pneumococcal polysaccharide vaccination (PPSV23) in rheumatoid arthritis patients

Introduction

Patients with rheumatoid arthritis (RA) treated with abatacept (ABT) are at increased risk for vaccine-preventable infections. The aim of the present study is to evaluate the humoral response to 23-valent pneumococcal polysaccharide (PPSV23) vaccination in RA patients receiving ABT.

Methods

The immunogenicity study was nested within a randomized, double-blind placebo-controlled study, designed to evaluate the efficacy of the PPSV23. PPSV23 was given to 111 RA patients, who were classified into three groups: RA control (n = 35), methotrexate (MTX) alone (n = 55), and ABT (n = 21). Before and 4–6 weeks after vaccination, we measured the patients’ concentrations of antibodies against pneumococcal serotypes 6B and 23F using an enzyme-linked immunosorbent assay and determined their antibody functionality using a multiplexed opsonophagocytic killing assay, reported as the opsonization index (OI).

Results

The pneumococcal serotype-specific IgG concentrations and OIs were both significantly increased in all treatment groups in response to PPSV23 vaccination. In the ABT group, the IgG responses for the 6B serotype were lower compared with those in the MTX alone or control groups, whereas the OI responses were similar to those in the other two groups. In a subgroup analysis, the pneumococcal serotype-specific IgG responses were significantly lower in both serotypes (6B and 23F) in the ABT/MTX group; however, the OI responses in the ABT group were not different from the control group. There was no association between the pneumococcal serotype-specific IgG and OI responses for the 6B serotype in patients receiving ABT in contrast to the control or MTX alone patients. No severe adverse effects were observed in any of the treatment groups.

Conclusions

OI responses indicate antibody functionality rather than simply their amount, so the similarity of these measurements between all three groups suggests that RA patients receiving ABT still benefit from receiving the PPSV23 vaccination, even though they produce less IgG in response to it. The results suggest an influence of ABT on the humoral response to PPSV23 vaccination under MTX treatment; however, preserved opsonin responses are expected in RA patients treated with ABT plus MTX.

Trial registration

University Hospital Medical Information Network Clinical Trials Registry: UMIN000009566. Registered 12 December 2012.

Opsonic and Antibody Responses to Pneumococcal Polysaccharide in Rheumatoid Arthritis Patients Receiving Golimumab Plus Methotrexate

Vaccination against Streptococcus pneumoniae is recommended for rheumatoid arthritis (RA) patients receiving immunosuppressive treatments. The objective of this study was to evaluate the humoral response to 23-valent pneumococcal polysaccharide vaccination (PPSV23) in RA patients receiving methotrexate (MTX) alone or in combination with a tumor necrosis factor inhibitor, golimumab (GOM).PPSV23 was given to 114 RA patients, who were classified into three groups: RA control (n = 35), MTX alone (n = 55), and GOM + MTX (n = 24). Before and 4 to 6 weeks after vaccination, concentrations of antibodies against pneumococcal serotypes 6B and 23F were measured using an enzyme-linked immunosorbent assay and antibody functionality was determined using a multiplexed opsonophagocytic killing assay, reported as the opsonization index (OI).The IgG concentrations and OIs were both significantly increased in all treatment groups in response to PPSV23 vaccination. In the GOM + MTX group, the IgG responses were lower than those in the MTX alone or control groups, whereas the OI responses were similar to those in the other 2 groups. Furthermore, discrepancies between the IgG and OI responses were found in GOM + MTX group. No severe adverse effect was observed in any treatment groups.OI responses indicate that antibody functionality rather than antibody quantity is important. The similarity of these measurements between all 3 groups suggests that RA patients receiving MTX + GOM still benefit from receiving the PPSV23 vaccination, even though they produce less IgG in response to it. These results can help clinicians to better schedule and evaluate pneumococcal vaccination for RA patients.

Sequence variability is correlated with weak immunogenicity in Streptococcus pyogenes M protein

The M protein of Streptococcus pyogenes, a major bacterial virulence factor, has an amino-terminal hypervariable region (HVR) that is a target for type-specific protective antibodies. Intriguingly, the HVR elicits a weak antibody response, indicating that it escapes host immunity by two mechanisms, sequence variability and weak immunogenicity. However, the properties influencing the immunogenicity of regions in an M protein remain poorly understood. Here, we studied the antibody response to different regions of the classical M1 and M5 proteins, in which not only the HVR but also the adjacent fibrinogen-binding B repeat region exhibits extensive sequence divergence. Analysis of antisera from S. pyogenes-infected patients, infected mice, and immunized mice showed that both the HVR and the B repeat region elicited weak antibody responses, while the conserved carboxy-terminal part was immunodominant. Thus, we identified a correlation between sequence variability and weak immunogenicity for M protein regions. A potential explanation for the weak immunogenicity was provided by the demonstration that protease digestion selectively eliminated the HVR-B part from whole M protein-expressing bacteria. These data support a coherent model, in which the entire variable HVR-B part evades antibody attack, not only by sequence variability but also by weak immunogenicity resulting from protease attack.

Pneumococcal polysaccharide vaccination in rheumatoid arthritis patients receiving tacrolimus

Introduction

In rheumatoid arthritis (RA) patients receiving immunosuppressive treatments, vaccination against Streptococcus pneumoniae is recommended. The objective of the study was to evaluate the effects of tacrolimus (TAC) on immune response following administration of a 23-valent pneumococcal polysaccharide vaccine (PPSV23) in patients with established RA.

Methods

Patients with RA (n = 133) were vaccinated with PPSV23. Patients were classified into TAC (n = 29), methotrexate (MTX) (n = 55), control (n = 35), and TAC/MTX (n = 14) treatment groups. We measured the concentrations of pneumococcal serotypes 6B and 23F by using an enzyme-linked immunosorbent assay and determined antibody functionality by using a multiplexed opsonophagocytic killing assay, reported as the opsonization index (OI), before and 4 to 6 weeks after vaccination. A positive antibody response was defined as at least a twofold increase in the IgG concentration or as at least a 10-fold increase in the OI.

Results

IgG concentrations and OIs were significantly increased in all treatment groups after PPSV23 vaccination. The TAC treatment group appears to respond in a manner similar to that of the RA control group in terms of 6B and 23F serotype concentration and function. In contrast, the MTX group had the lowest immune response. Patients who received a combination of TAC and MTX (TAC/MTX) also had a diminished immune response compared with those who received TAC alone.

Conclusions

TAC monotherapy does not appear to impair PPSV23 immunogenicity in patients with RA, whereas antibody production and function may be reduced when TAC is used with MTX. Thus, PPSV23 administration during ongoing TAC treatment should be encouraged for infection-prone TAC-treated patients with rheumatic diseases.

Trial registration

University Hospital Medical Information Network Clinical Trials Registry: UMIN000009566. Registered 12 December 2012.

Electronic supplementary material

The online version of this article (doi:10.1186/s13075-015-0662-x) contains supplementary material, which is available to authorized users.

Combination of adjuvants: the future of vaccine design

It is thought that the development of vaccines for the treatment of infectious diseases and cancer is likely to be achieved in the coming decades. This is partially due to a better understanding of the regulatory networks connecting innate with adaptive immune responses. The innate immune response is triggered by the recognition of conserved pathogen-associated molecular patterns by germ line-coded pattern recognition receptors. Several families of pattern recognition receptors have been characterized, including Toll-like receptors and nucleotide-binding domain receptors. The identification of their ligands has driven the development of novel adjuvants many of which have been tested in vaccine clinical trials. Here, the authors review recent preclinical data and clinical trial results supporting the view that combinations of adjuvants are the way forward in vaccine design. Multiadjuvanted vaccines can stimulate the broad and robust protective immune responses required to fight chronic infectious diseases and cancer.

The ABCs (Antibody, B Cells, and Carbohydrate Epitopes) of Cholera Immunity: Considerations for an Improved Vaccine

Cholera, a diarrheal disease, is known for explosive epidemics that can quickly kill thousands. Endemic cholera is a seasonal torment that also has a significant mortality. Not all nations with extensive rural communities can achieve the required infrastructure or behavioral changes to prevent epidemic or endemic cholera. For some communities, a single-dose cholera vaccine that protects those at risk is the most efficacious means to reduce morbidity and mortality. It is clear that our understanding of what a protective cholera immune response is has not progressed at the rate our understanding of the pathogenesis and molecular biology of cholera infection has. This review addresses V. cholerae lipopolysaccharide (LPS)-based immunogens because LPS is the only immunogen proven to induce protective antibody in humans. We discuss the role of anti-LPS antibodies in protection from cholera, the importance and the potential role of B cell subsets in protection that is based on their anatomical location and the intrinsic antigen-receptor specificity of various subsets is introduced.

The wciN gene encodes an α-1,3-galactosyltransferase involved in the biosynthesis of the capsule repeating unit of Streptococcus pneumoniae serotype 6B

Almost all Streptococcus pneumoniae (pneumococcus) capsule serotypes employ the Wzy-dependent pathway for their capsular polysaccharide (CPS) biosynthesis. The assembly of the CPS repeating unit (RU) is the first committed step in this pathway. The wciN gene was predicted to encode a galactosyltransferase involved in the RU assembly of pneumococcus type 6B CPS. Herein, we provide the unambiguous in vitro biochemical evidence that wciN encodes an α-1,3-galactosyltransferase catalyzing the transfer of galactosyl from UDP-Gal onto the Glcα-pyrophosphate-lipid (Glcα-PP-lipid) acceptor to form Galα(1-3)Glcα-PP-lipid. A chemically synthesized acceptor (Glcα-PP-O(CH(2))(10)CH(3)) was used to characterize the WciN activity. The disaccharide product, i.e., Galα(1-3)Glcα-PP-O(CH(2))(10)CH(3), was characterized by mass and NMR spectroscopy. Substrate specificity study indicated that the acceptor structural region composed of pyrophosphate and lipid moieties may play an important role in the enzyme-acceptor recognition. Furthermore, divalent metal cations were found indispensable to the WciN activity, suggesting that this glycosyltransferase (GT) belongs to the GT-A superfamily. By analyzing the activities of six WciN mutants, a DXD motif involved in the coordination of a divalent metal cation was identified. This work provides a chemical biology approach to characterize the activities of pneumococcal CPS GTs in vitro and will help to better understand the pneumococcal CPS biosynthetic pathway.

Pneumococcal vaccines for children and adults with bronchiectasis

BACKGROUND

Bronchiectasis is increasingly recognized as a major cause of respiratory morbidity especially in developing countries. Even in affluent countries, bronchiectasis is increasingly seen in some community subsections (e.g. Aboriginal communities) and occurs as a comorbidity and disease modifier in respiratory diseases such as chronic obstructive pulmonary disease (COPD). Respiratory exacerbations in people with bronchiectasis are associated with reduced quality of life, accelerated pulmonary decline, hospitalisation and even death. Conjugate pneumococcal vaccine is part of the routine infant immunisation schedule in many countries. Current recommendations for additional pneumococcal vaccination include children and adults with chronic suppurative disease.

OBJECTIVES

To evaluate the effectiveness of pneumococcal vaccine as routine management in children and adults with bronchiectasis in (a) reducing the severity and frequency of respiratory exacerbations and (b) pulmonary decline.

SEARCH STRATEGY

The Cochrane Register of Controlled Trials (CENTRAL), the Cochrane Airways Group Specialised Register, MEDLINE and EMBASE databases were searched by the Cochrane Airways Group. Pharmaceutical manufacturers of pneumococcal vaccines were also contacted. The latest searches were performed in November 2008.

SELECTION CRITERIA

All randomised controlled trials that utilised pneumococcal vaccine on children and adults with bronchiectasis. All types of pneumococcal vaccines were included.

DATA COLLECTION AND ANALYSIS

Results of searches were reviewed against pre-determined criteria for inclusion. No eligible trials were identified and thus no data was available for analysis. One small non-randomised controlled trial in children was reported.

MAIN RESULTS

One randomised controlled open label study in 167 adults with chronic lung disease (bronchiectasis and other diseases associated with bronchiectasis) compared 23-valent pneumococcal (PV) and influenza vaccine with influenza vaccine alone (control group). The study found a significant reduction in acute infective respiratory exacerbations in the PV group compared to the control group, OR=0.48 (95%CI 0.26, 0.88); number needed to treat to benefit = 6 (95%CI 4, 32) over 2-years. There was however no difference in episodes of pneumonia between groups and no data on pulmonary decline was available. In another study, a benefit in elimination of Strep. pneumoniae in the sputum was found in a non-randomised trial in children but no clinical effect was described.

AUTHORS' CONCLUSIONS

Current but limited evidence support the use of 23-valent pneumococcal vaccine as routine management in adults with bronchiectasis. Circumstantial evidence also support the use of routine 23-valent pneumococcal vaccination in children with bronchiectasis. Further randomised controlled trials examining the efficacy of this intervention using various vaccine types in different age groups are needed. There is no data on the efficacy of pneumococcal vaccine on pulmonary decline. With the lack of evidence in how often the vaccine should be given, it is recommended that health providers adhere to national guidelines.

Mouse models for the study of mucosal vaccination against otitis media

Otitis media (OM) is one of the most common infectious diseases in humans. The pathogenesis of OM involves nasopharyngeal (NP) colonization and retrograde ascension of the pathogen up the Eustachian tube into the middle ear (ME). Due to increasing rates of antibiotic resistance, there is an urgent need for vaccines to prevent infections caused by the most common causes of bacterial OM, including nontypeable Haemophilus influenzae, Streptococcus pneumoniae and Moraxella catarrhalis. Current vaccine strategies aim to diminish bacterial NP carriage, thereby reducing the likelihood of developing acute OM. To be effective, vaccination should induce local mucosal immunity both in the ME and in the NP. Studies in animal models have demonstrated that the intranasal route of vaccination is particularly effective at inducing immune responses in the nasal passage and ME for protection against OM. The mouse is increasingly used in these models, because of the availability of murine reagents and the existence of technology to manipulate murine models of disease immunologically and genetically. Previous studies confirmed the suitability of the mouse as a model for inflammatory processes in acute OM. Here, we discuss various murine models of OM and review the applicability of these models to assess the efficacy of mucosal vaccination and the mechanisms responsible for protection. In addition, we discuss various mucosal vaccine antigens, mucosal adjuvants and mucosal delivery systems.

Bacterial Infections

In Osier’s time, bacterial pneumonia was a dreaded event, so important that he borrowed John Bunyan’s characterization of tuberculosis and anointed the pneumococcus, as the prime pathogen, “Captain of the men of death.”1 One hundred years later much has changed, but much remains the same. Pneumonia is now the sixth most common cause of death and the most common lethal infection in the United States. Hospital-acquired pneumonia is now the second most common nosocomial infection.2 It was documented as a complication in 0.6% of patients in a national surveillance study,3 and has been reported in as many as 20% of patients in critical care units.4 Furthermore, it is the leading cause of death among nosocomial infections.5 Leu and colleagues6 were able to associate one third of the mortality in patients with nosocomial pneumonia to the infection itself. The increase in hospital stay, which averaged 7 days, was statistically significant. It has been estimated that nosocomial pneumonia produces costs in excess of $500 million each year in the United States, largely related to the increased length of hospital stay.

The role of complement in the success of vaccination with conjugated vs. unconjugated polysaccharide antigen

The complement system, a well-characterised arm of the innate immune system, significantly influences the adaptive immune response via direct cell-cell interaction and maintenance of lymphoid organ architecture. Development of vaccines is a major advance in modern health care. In this review, we highlight the importance of the marginal zone in response to both, polysaccharide and conjugated vaccines, and discuss the relevance of complement herein, based on findings obtained from animal models with specific deletions of certain complement components and from vaccination reports of complement-deficient individuals. We conclude that both, intactness of the complement system and maturity of expression of its components, are relatively more important to aid in the immune response to polysaccharide vaccine than to conjugated vaccines.

Pneumococcal vaccines for children and adults with bronchiectasis

BACKGROUND

Bronchiectasis is increasingly recognized as a major cause of respiratory morbidity especially in developing countries. Even in affluent countries, bronchiectasis is increasingly seen in some community subsections (e.g. Aboriginal communities) and occurs as a comorbidity and disease modifier in respiratory diseases such as chronic obstructive pulmonary disease (COPD). Respiratory exacerbations in people with bronchiectasis is associated with reduced quality of life, accelerated pulmonary decline, hospitalisation and even death. Conjugate pneumococcal vaccine is part of the routine infant immunisation schedule in many countries. Current recommendations for additional pneumococcal vaccination include children and adults with chronic suppurative disease.

OBJECTIVES

To evaluate the effectiveness of pneumococcal vaccine as routine management in children and adults with bronchiectasis in (a) reducing the severity and frequency of respiratory exacerbations and (b) pulmonary decline.

SEARCH STRATEGY

The Cochrane Register of Controlled Trials (CENTRAL), the Cochrane Airways Group Specialised Register, MEDLINE and EMBASE databases were searched by the Cochrane Airways Group. Pharmaceutical manufacturers of pneumococcal vaccines were also contacted. The latest searches were performed in October 2006.

SELECTION CRITERIA

All randomised controlled trials that utilised pneumococcal vaccine on children and adults with bronchiectasis. All types of pneumococcal vaccines were included.

DATA COLLECTION AND ANALYSIS

Results of searches were reviewed against pre-determined criteria for inclusion. No eligible trials were identified and thus no data was available for analysis. One small non-randomised controlled trial in children was reported.

MAIN RESULTS

No randomised controlled trials pertaining effectiveness of pneumococcal vaccine as routine management in children and adults with bronchiectasis were found. A benefit in elimination of Strep. pneumoniae in the sputum was found in a non-randomised trial in children but no clinical effect was described.

AUTHORS' CONCLUSIONS

At present, there is a lack of reliable evidence to support or refute the routine use of pneumococcal vaccine as routine management in children and adults with bronchiectasis. Randomised controlled trials examining the efficacy of this intervention using various vaccine types in different age groups are needed. Until further evidence is available, it is recommended that health providers adhere to national guidelines.

Advances in combating fungal diseases: vaccines on the threshold

The dramatic increase in fungal diseases in recent years can be attributed to the increased aggressiveness of medical therapy and other human activities. Immunosuppressed patients are at risk of contracting fungal diseases in healthcare settings and from natural environments. Increased prescribing of antifungals has led to the emergence of resistant fungi, resulting in treatment challenges. These concerns, together with the elucidation of the mechanisms of protective immunity against fungal diseases, have renewed interest in the development of vaccines against the mycoses. Most research has used murine models of human disease and, as we review in this article, the knowledge gained from these studies has advanced to the point where the development of vaccines targeting human fungal pathogens is now a realistic and achievable goal.

Experimental infection of rhesus macaques with Streptococcus pneumoniae: a possible model for vaccine assessment

BACKGROUND

We explored the possibility of using normal adult rhesus macaques for the preclinical assessment of safety, immunogenicity, and efficacy of newly developed vaccines against Streptococcus pneumoniae infection of the lung.

METHODS

Our primary objective was to determine whether an intra-bronchial inoculum of at least 10(6)S. pneumoniae colony-forming units, or one as high as 10(8)-10(9) organisms, could detectably survive in rhesus macaques for a period longer than 1-2 weeks. If so, we hypothesized, it would be possible to observe signs of pneumonia commonly observed in humans, and discriminate between vaccinated/protected animals and controls. Infection was detectable in bronchoalveolar lavage fluids 3-5 weeks post-inoculation.

RESULTS

The clinical course of disease mimicked aspects of that of human pneumococcal pneumonia. Signs of inflammation typical of the disease in humans, such as elevated concentrations of neutrophils and of pro-inflammatory cytokines in bronchoalveolar lavage fluids were also observed.

CONCLUSIONS

These findings underscore the utility of this model to assess the safety, immunogenicity, and efficacy of newly developed S. pneumoniae vaccines.

A novel Staphylococcus aureus vaccine: iron surface determinant B induces rapid antibody responses in rhesus macaques and specific increased survival in a murine S. aureus sepsis model

Staphylococcus aureus is a major cause of nosocomial infections worldwide, and the rate of resistance to clinically relevant antibiotics, such as methicillin, is increasing; furthermore, there has been an increase in the number of methicillin-resistant S. aureus community-acquired infections. Effective treatment and prevention strategies are urgently needed. We investigated the potential of the S. aureus surface protein iron surface determinant B (IsdB) as a prophylactic vaccine against S. aureus infection. IsdB is an iron-sequestering protein that is conserved in diverse S. aureus clinical isolates, both methicillin resistant and methicillin sensitive, and it is expressed on the surface of all isolates tested. The vaccine was highly immunogenic in mice when it was formulated with amorphous aluminum hydroxyphosphate sulfate adjuvant, and the resulting antibody responses were associated with reproducible and significant protection in animal models of infection. The specificity of the protective immune responses in mice was demonstrated by using an S. aureus strain deficient for IsdB and HarA, a protein with a high level of identity to IsdB. We also demonstrated that IsdB is highly immunogenic in rhesus macaques, inducing a more-than-fivefold increase in antibody titers after a single immunization. Based on the data presented here, IsdB has excellent prospects for use as a vaccine against S. aureus disease in humans.

The capsular polysaccharide biosynthesis of Streptococcus pneumoniae serotype 8: functional identification of the glycosyltransferase WciS (Cap8H)

CPS (capsular polysaccharide) is a major virulence factor in Streptococcus pneumoniae. Biosynthesis of CPS RU (repeat unit) proceeds by sequential transfer of sugar residues from the appropriate sugar donor to an activated lipid carrier by committed GTs (glycosyltransferases). While the nucleotide sequence of many cps loci is already known, the real substrate specificity of the hypothetical GTs, as well as the sequence of sugar addition is unclear. In the present paper, we report the biochemical characterization of one alpha-galactosyltransferase, WciS (Cap8H), a member of GT family 4. This enzyme is implicated in the tetrasaccharide RU biosynthetic pathway of Strep. pneumoniae CPS 8 ([-->4)-alpha-D-Glcp-(1-->4)-alpha-D-Galp-(1-->4)-beta-D-GlcAp-(1-->4)-beta-D-Glcp-(1-->]n). Expression of WciS-His6 in Escherichia coli BL21 (DE3) strains or BL21 (DE3)/DeltagalU strain resulted in synthesis of a 39 kDa membrane-associated protein identified by N-terminal sequencing and recognized by anti-His6-tag antibody. This protein was capable of adding a galactose residue cellobiuronic acid [beta-D-GlcAp-(1-->4)-D-Glcp]-pyrophosphate-polyprenol from UDP-Gal. The newly added galactose residue is removed by alpha-galactosidase, indicating that WciS is a retaining GT. Our results suggest that WciS catalyses the addition of the third sugar residue of the CPS 8 RU. The recombinant WciS-His6 was solubilized and purified as a soluble multimer, opening the way for structural studies.