Determination of the disulfide bond arrangement of human respiratory syncytial virus attachment (G) protein by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

Mutation in the CX3C Motif of G Protein Disrupts Its Interaction with Heparan Sulfate: A Calorimetric, Spectroscopic, and Molecular Docking Study

Respiratory syncytial virus (RSV) is the leading cause of lower respiratory tract infection in children and infants. To date, there is no effective vaccine available against RSV. Heparan sulfate is a type of glycosaminoglycan that aids in the attachment of the RSV to the host cell membrane via the G protein. In the present study, the effect of amino acid substitution on the structure and stability of the ectodomain G protein was studied. Further, it was investigated whether mutation (K117A) in the CX3C motif of G protein alters the binding with heparan sulfate. The point mutation significantly affects the conformational stability of the G protein. The mutant protein showed a low binding affinity with heparan sulfate as compared to the wild-type G protein, as determined by fluorescence quenching, isothermal titration calorimetry (ITC), and molecular docking studies. The low binding affinity and decreased stability suggested that this mutation may play an important role in prevention of attachment of virion to the host cell receptors. Collectively, this investigation suggests that mutation in the CX3C motif of G protein may likely improve the efficacy and safety of the RSV vaccine.

Respiratory syncytial virus: from pathogenesis to potential therapeutic strategies

Respiratory syncytial virus (RSV) is one of the most important viral pathogens causing respiratory tract infection in infants, the elderly and people with poor immune function, which causes a huge disease burden worldwide every year. It has been more than 60 years since RSV was discovered, and the palivizumab monoclonal antibody, the only approved specific treatment, is limited to use for passive immunoprophylaxis in high-risk infants; no other intervention has been approved to date. However, in the past decade, substantial progress has been made in characterizing the structure and function of RSV components, their interactions with host surface molecules, and the host innate and adaptive immune response to infection. In addition, basic and important findings have also piqued widespread interest among researchers and pharmaceutical companies searching for effective interventions for RSV infection. A large number of promising monoclonal antibodies and inhibitors have been screened, and new vaccine candidates have been designed for clinical evaluation. In this review, we first briefly introduce the structural composition, host cell surface receptors and life cycle of RSV virions. Then, we discuss the latest findings related to the pathogenesis of RSV. We also focus on the latest clinical progress in the prevention and treatment of RSV infection through the development of monoclonal antibodies, vaccines and small-molecule inhibitors. Finally, we look forward to the prospects and challenges of future RSV research and clinical intervention.

Structural Characterization and Binding Studies of the Ectodomain G Protein of Respiratory Syncytial Virus Reveal the Crucial Role of pH with Possible Implications in Host-Pathogen Interactions

Respiratory syncytial virus (RSV) is a leading viral pathogen causing acute lower respiratory tract infection in children. The G protein of RSV is involved in attachment with the host cell. It is a neutralizing antigen and thus a vaccine candidate. Heparan sulfate is a type of glycosaminoglycan (GAG) present on the host cell membrane that is involved in attachment with the G protein of RSV. We describe a novel approach for efficient expression and purification of the ectodomain G protein in the prokaryotic system and its biophysical characterization. The native ectodomain G protein was purified using a two-step process by Ni-NTA and DEAE weak anion-exchange chromatography through the supernatant obtained after cell lysis. In addition, the denatured form of the protein was also purified from the solubilized inclusion bodies (IBs) by Ni-NTA affinity chromatography with a higher yield. Dynamic light scattering (DLS) was performed to confirm the homogeneity of the purified protein. The effect of pH on the stability and structure of the purified protein was studied by circular dichroism (CD), fluorescence, and absorbance spectroscopy techniques. Isothermal titration calorimetry (ITC) and microscale thermophoresis (MST) were exploited to demonstrate the interaction of heparan sulfate with the ectodomain G protein. The dynamic light scattering results showed that the purified protein was homogenic and had a well-folded native conformation. Biophysical characterization of the protein revealed that it was stable and had intact secondary and tertiary structures at pH 7.5. CD analysis revealed that the protein showed a loss in the secondary structure at pH values 5.5 and 3.5, while absorbance spectroscopy suggested a stable tertiary structure at pH values 7.5 and 5.5 with a probable aggregation pattern at pH 3.5. This loss in the structure of the ectodomain G protein at low pH can be correlated with its physiological activity. A slight change in pH might play a crucial role in host-pathogen interactions. The fluorescence intensity of the protein decreased on moving toward a lower pH with no spectral shift in emission maxima. In addition, isothermal titration calorimetry and microscale thermophoresis results showed strong binding affinity of the ectodomain G protein with heparan sulfate. The binding of heparan sulfate with protein was probably due to the electrostatic interaction of positively charged amino acid residues of the heparin-binding domain of the protein and the negatively charged group of GAGs. Future studies may involve the development of possible therapeutic agents interacting with the G protein and affecting the overall charge and pH that might hinder the host-pathogen interaction.

Impact of Respiratory Syncytial Virus Infection on Host Functions: Implications for Antiviral Strategies

Respiratory syncytial virus (RSV) is one of the leading causes of viral respiratory tract infection in infants, the elderly, and the immunocompromised worldwide, causing more deaths each year than influenza. Years of research into RSV since its discovery over 60 yr ago have elucidated detailed mechanisms of the host-pathogen interface. RSV infection elicits widespread transcriptomic and proteomic changes, which both mediate the host innate and adaptive immune responses to infection, and reflect RSV's ability to circumvent the host stress responses, including stress granule formation, endoplasmic reticulum stress, oxidative stress, and programmed cell death. The combination of these events can severely impact on human lungs, resulting in airway remodeling and pathophysiology. The RSV membrane envelope glycoproteins (fusion F and attachment G), matrix (M) and nonstructural (NS) 1 and 2 proteins play key roles in modulating host cell functions to promote the infectious cycle. This review presents a comprehensive overview of how RSV impacts the host response to infection and how detailed knowledge of the mechanisms thereof can inform the development of new approaches to develop RSV vaccines and therapeutics.

Respiratory syncytial virus entry and how to block it

Respiratory syncytial virus (RSV) is a leading cause of lower respiratory tract disease in young children and elderly people. Although the virus was isolated in 1955, an effective RSV vaccine has not been developed, and the only licensed intervention is passive immunoprophylaxis of high-risk infants with a humanized monoclonal antibody. During the past 5 years, however, there has been substantial progress in our understanding of the structure and function of the RSV glycoproteins and their interactions with host cell factors that mediate entry. This period has coincided with renewed interest in developing effective interventions, including the isolation of potent monoclonal antibodies and small molecules and the design of novel vaccine candidates. In this Review, we summarize the recent findings that have begun to elucidate RSV entry mechanisms, describe progress on the development of new interventions and conclude with a perspective on gaps in our knowledge that require further investigation.

Respiratory syncytial virus (RSV) is a leading cause of lower respiratory tract disease in young children and elderly people. In this Review, Battles and McLellan summarize our current understanding of RSV entry, describe progress on the development of new interventions and conclude with a perspective on gaps in our knowledge that require further investigation.

Importance of Virus Characteristics in Respiratory Syncytial Virus-Induced Disease

Severe lower respiratory tract infection in infants and young children is most frequently caused by respiratory syncytial virus (RSV). RSV infects the smallest airways, making breathing difficult and in some infants requiring medical support. Severity is affected by viral dose, infant age, virus genotype, and effectiveness of the innate/adaptive immune responses. Severe disease correlates with later wheezing and asthma in some children. The adaptive immune response is protective but wanes after each infection, likely due to the ability of the RSV NS1/NS2 proteins to inhibit the innate immune response. Several vaccine approaches and candidates are currently in clinical trials.

Biophysical and flavonoid-binding studies of the G protein ectodomain of group A human respiratory syncytial virus

The human Respiratory Syncytial Virus (hRSV) is the major causative agent of lower respiratory tract diseases in infants, young children and elderly. The membrane protein G is embedded in the viral lipid envelope and plays an adhesion function of the virus to host cells. The present study reports the production of the group A hRSV recombinant G protein ectodomain (edG) and its characterization of secondary structure and thermal unfolding by circular dichroism (CD), as well as the binding investigation of flavonoids quercetin and morin to this protein by fluorescent quenching. CD data reveal that edG is composed mostly of β-structure and its melting temperature is of 325 K. Fluorescence quenching experiments of hRSV edG show that the dissociation constants for the flavonoids binding are micromolar and the binding affinity for the edG/quercetin complex is inversely dependent on rising temperature while is directly dependent for the edG/morin interaction. The thermodynamic parameters suggest that hydrophobic contacts are important for the edG/morin association while van der Waals forces and hydrogen bonds contribute to the stabilization of the edG/quercetin complex. Thus, data reported herein may contribute to the development of new treatment strategies that prevent the viral infection by hRSV.

Structural basis for recognition of the central conserved region of RSV G by neutralizing human antibodies

Respiratory syncytial virus (RSV) is a major cause of severe lower respiratory tract infections in infants and the elderly, and yet there remains no effective treatment or vaccine. The surface of the virion is decorated with the fusion glycoprotein (RSV F) and the attachment glycoprotein (RSV G), which binds to CX3CR1 on human airway epithelial cells to mediate viral attachment and subsequent infection. RSV G is a major target of the humoral immune response, and antibodies that target the central conserved region of G have been shown to neutralize both subtypes of RSV and to protect against severe RSV disease in animal models. However, the molecular underpinnings for antibody recognition of this region have remained unknown. Therefore, we isolated two human antibodies directed against the central conserved region of RSV G and demonstrated that they neutralize RSV infection of human bronchial epithelial cell cultures in the absence of complement. Moreover, the antibodies protected cotton rats from severe RSV disease. Both antibodies bound with high affinity to a secreted form of RSV G as well as to a peptide corresponding to the unglycosylated central conserved region. High-resolution crystal structures of each antibody in complex with the G peptide revealed two distinct conformational epitopes that require proper folding of the cystine noose located in the C-terminal part of the central conserved region. Comparison of these structures with the structure of fractalkine (CX3CL1) alone or in complex with a viral homolog of CX3CR1 (US28) suggests that RSV G would bind to CX3CR1 in a mode that is distinct from that of fractalkine. Collectively, these results build on recent studies demonstrating the importance of RSV G in antibody-mediated protection from severe RSV disease, and the structural information presented here should guide the development of new vaccines and antibody-based therapies for RSV.

Functional correlations of respiratory syncytial virus proteins to intrinsic disorder

Protein intrinsic disorder is an important characteristic demonstrated by the absence of higher order structure, and is commonly detected in multifunctional proteins encoded by RNA viruses. Intrinsically disordered regions (IDRs) of proteins exhibit high flexibility and solvent accessibility, which permit several distinct protein functions, including but not limited to binding of multiple partners and accessibility for post-translational modifications. IDR-containing viral proteins can therefore execute various functional roles to enable productive viral replication. Respiratory syncytial virus (RSV) is a globally circulating, non-segmented, negative sense (NNS) RNA virus that causes severe lower respiratory infections. In this study, we performed a comprehensive evaluation of predicted intrinsic disorder of the RSV proteome to better understand the functional role of RSV protein IDRs. We included 27 RSV strains to sample major RSV subtypes and genotypes, as well as geographic and temporal isolate differences. Several types of disorder predictions were applied to the RSV proteome, including per-residue (PONDR®-FIT and PONDR® VL-XT), binary (CH, CDF, CH-CDF), and disorder-based interactions (ANCHOR and MoRFpred). We classified RSV IDRs by size, frequency and function. Finally, we determined the functional implications of RSV IDRs by mapping predicted IDRs to known functional domains of each protein. Identification of RSV IDRs within functional domains improves our understanding of RSV pathogenesis in addition to providing potential therapeutic targets. Furthermore, this approach can be applied to other NNS viruses that encode essential multifunctional proteins for the elucidation of viral protein regions that can be manipulated for attenuation of viral replication.

The Central Conserved Region (CCR) of Respiratory Syncytial Virus (RSV) G Protein Modulates Host miRNA Expression and Alters the Cellular Response to Infection

Respiratory Syncytial Virus (RSV) infects respiratory epithelial cells and deregulates host gene expression by many mechanisms including expression of RSV G protein (RSV G). RSV G protein encodes a central conserved region (CCR) containing a CX3C motif that functions as a fractalkine mimic. Disruption of the CX3C motif (a.a. 182-186) located in the CCR of the G protein has been shown to affect G protein function in vitro and the severity of RSV disease pathogenesis in vivo. We show that infection of polarized Calu3 respiratory cells with recombinant RSV having point mutations in Cys173 and 176 (C173/176S) (rA2-GC12), or Cys186 (C186S) (rA2-GC4) is associated with a decline in the integrity of polarized Calu-3 cultures and decreased virus production. This is accompanied with downregulation of miRNAs let-7f and miR-24 and upregulation of interferon lambda (IFNλ), a primary antiviral cytokine for RSV in rA2-GC12/rA2-GC4 infected cells. These results suggest that residues in the cysteine noose region of RSV G protein can modulate IFN λ expression accompanied by downregulation of miRNAs, and are important for RSV G protein function and targeting.

Expression and antigenicity of recombinant human respiratory syncytial virus glycoproteins having different affinity tags

Human respiratory syncytial virus (HRSV) is a main cause of lower respiratory tract infections in infants and the elderly. Glycoprotein (G) is major antigen on the viral surface, and plays a key role for virus entry. Therefore, purification of the glycoprotein of HRSV is critical for the development of HRSV vaccine and serological diagnosis. In this study, we report the design and characterization of glycoprotein engineered rationally to enhance the protein solubility and to facilitate efficient purification. We permuted HRSV glycoproteins with two tags: (i) an immunoglobulin (Ig) M signal peptide and a protein A B domain tag to render HRSV glycoprotein secret into the culture media and (ii) a foldon and 6 × histidine tag with or without transmembrane domain. Three recombinant baculoviruses were constructed: (i) transmembrane-truncated HRSV glycoprotein (amino acid positions 66-298) inserted with the N-terminal IgM signal peptide and protein A B domain (MG-GΔTM), (ii) truncated HRSV glycoprotein (amino acid positions 66-298) fused with a C-terminal foldon and 6 × histidine tag (GΔTM-FH), and (iii) full-length HRSV glycoprotein (amino acid positions 1-298) fused with a C-terminal foldon and 6 × histidine tag (G-FH). Highly soluble recombinant MG-GΔTM protein was clearly purified using one-step affinity chromatography with IgG-sepharose resin, whereas the recombinant G-FH protein and truncated GΔTM-FH were purified partially using nickel-resin. Although, the antigenicity of GΔTM-FH was stronger than highly mannose-rich MG-GΔTM protein, MG-GΔTM induced neutralizing antibodies efficiently in the mice to protect from infectious HRSV.

Respiratory Syncytial Virus Uses CX3CR1 as a Receptor on Primary Human Airway Epithelial Cultures

Respiratory syncytial virus (RSV) is the most frequent cause of lower respiratory disease in infants, but no vaccine or effective therapy is available. The initiation of RSV infection of immortalized cells is largely dependent on cell surface heparan sulfate (HS), a receptor for the RSV attachment (G) glycoprotein in immortalized cells. However, RSV infects the ciliated cells in primary well differentiated human airway epithelial (HAE) cultures via the apical surface, but HS is not detectable on this surface. Here we show that soluble HS inhibits infection of immortalized cells, but not HAE cultures, confirming that HS is not the receptor on HAE cultures. Conversely, a “non-neutralizing” monoclonal antibody against the G protein that does not block RSV infection of immortalized cells, does inhibit infection of HAE cultures. This antibody was previously shown to block the interaction between the G protein and the chemokine receptor CX3CR1 and we have mapped the binding site for this antibody to the CX3C motif and its surrounding region in the G protein. We show that CX3CR1 is present on the apical surface of ciliated cells in HAE cultures and especially on the cilia. RSV infection of HAE cultures is reduced by an antibody against CX3CR1 and by mutations in the G protein CX3C motif. Additionally, mice lacking CX3CR1 are less susceptible to RSV infection. These findings demonstrate that RSV uses CX3CR1 as a cellular receptor on HAE cultures and highlight the importance of using a physiologically relevant model to study virus entry and antibody neutralization.

Respiratory syncytial virus (RSV) is the second most common infectious cause of infant death worldwide. Despite this great clinical impact, no effective antivirals or vaccines against RSV are available. Here we find that the RSV attachment (G) glycoprotein uses CX3CR1 as a receptor on primary human airway epithelial (HAE) cultures, an excellent model of RSV infection of the human lung. The G protein contains a CX3C motif and we find that this region is critical for its role in infection of HAE cultures, but not of immortalized cells. Furthermore, we find that antibodies against the G protein neutralize RSV infection of HAE cultures differently from immortalized cells. These insights suggest that HAE cultures should be used to quantify neutralizing antibodies, including during vaccine development, that the CX3CR1 interaction with the RSV G protein could be a target for antiviral drug development, and that the G protein should be considered for inclusion in vaccines.

A comprehensive proteomic view of responses of A549 type II alveolar epithelial cells to human respiratory syncytial virus infection

Human respiratory syncytial virus is a major respiratory pathogen for which there are no suitable antivirals or vaccines. A better understanding of the host cell response to this virus may redress this problem. The present report concerns analysis of multiple independent biological replicates of control and 24 h infected lysates of A549 cells by two different proteomic workflows. One workflow involved fractionation of lysates by in-solution protein IEF and individual fractions were digested using trypsin prior to capillary HPLC-LTQ-OrbitrapXL-MS/MS. A second workflow involved digestion of whole cell lysates and analysis by nanoUltraHPLC-LTQ-OrbitrapElite-MS/MS. Both workflows resulted in the quantification of viral proteins exclusively in lysates of infected cells in the relative abundances anticipated from previous studies. Unprecedented numbers (3247 - 5010) of host cell protein groups were also quantified and the infection-specific regulation of a large number (191) of these protein groups was evident based on a stringent false discovery rate cut-off (<1%). Bioinformatic analyses revealed that most of the regulated proteins were potentially regulated by type I, II, and III interferon, TNF-α and noncanonical NF-κB2 mediated antiviral response pathways. Regulation of specific protein groups by infection was validated by quantitative Western blotting and the cytokine-/key regulator-specific nature of their regulation was confirmed by comparable analyses of cytokine treated A549 cells. Overall, it is evident that the workflows described herein have produced the most comprehensive proteomic characterization of host cell responses to human respiratory syncytial virus published to date. These workflows will form the basis for analysis of the impacts of specific genes of human respiratory syncytial virus responses of A549 and other cell lines using a gene-deleted version of the virus. They should also prove valuable for the analysis of the impact of other infectious agents on host cells.

Charge detection mass spectrometry of bacteriophage P22 procapsid distributions above 20 MDa

RATIONALE

Charge state resolution is required to determine the masses of ions in electrospray mass spectrometry, a feat which becomes increasingly difficult as the mass increases. Charge detection mass spectrometry (CDMS) circumvents this limitation by simultaneously measuring the charge and the m/z of individual ions. In this work, we have used electrospray CDMS to determine the number of scaffolding proteins associated with bacteriophage P22 procapsids.

METHODS

P22 procapsids containing a native cargo of scaffolding protein were assembled in E. coli and purified via differential centrifugation. Electrospray CDMS was used to measure their mass distribution.

RESULTS

The procapsid peak was centered at 23.60 MDa, which indicates that they contain an average of ~112 scaffolding proteins. The distribution is relatively narrow, less than 31 scaffolding proteins wide. In addition, a peak at 19.84 MDa with a relative abundance of ~15% is attributed to empty capsids. Despite having the same sizes in solution, the empty capsid and the procapsid have significantly different average charges.

CONCLUSIONS

The detection of empty capsids is unexpected and the process that leads to them is unknown. The average charge on the empty capsids is significantly lower than expected from the charge residue model, which probably indicates that the empty capsids have contracted in the gas phase. The scaffolding protein presumably limits the contraction of the procapsids. This work shows that electrospray CDMS can provide valuable information for masses greater than 20 MDa.

Use of proteomics to define targets of T-cell immunity

The mammalian immune system has evolved to display peptides derived from microbial antigens to immune effector cells. Liberated from the intact antigens through distinct proteolytic mechanisms, these peptides are subsequently transported to the cell surface while bound to chaperone-like receptors known as major histocompatibility complex molecules. These complexes are then scrutinized by T-cells that express receptors with specificity for specific major histocompatibility complex-peptide complexes. In normal uninfected cells, this process of antigen processing and presentation occurs continuously, with the resultant array of self-antigen-derived peptides displayed on the surface of these cells. Changes in this cellular peptide array alert the immune system to changes in the intracellular environment that may be associated with infection, oncogenesis or other abnormal cellular processes, resulting in a cascade of events that result in the elimination of the abnormal cell. Since peptides play such an essential role in informing the immune system of infection with viral or microbial pathogens and the transformation of cells in malignancy, the tools of proteomics, in particular mass spectrometry, are ideally suited to study these immune responses at a molecular level. Recent advances in studies of immune responses that have utilized mass spectrometry and associated technologies are reviewed. The authors gaze into the future and look at current challenges and where proteomics will impact in immunology over the next 5 years.

Nanoparticle vaccines encompassing the respiratory syncytial virus (RSV) G protein CX3C chemokine motif induce robust immunity protecting from challenge and disease

Nanoparticle vaccines were produced using layer-by-layer fabrication and incorporating respiratory syncytial virus (RSV) G protein polypeptides comprising the CX3C chemokine motif. BALB/c mice immunized with G protein nanoparticle vaccines produced a neutralizing antibody response that inhibited RSV replication in the lungs following RSV challenge. ELISPOT analysis showed that G nanoparticle vaccinated mice had increased levels of RSV G protein-specific IL-4 and IFN-γ secreting cells compared to controls following RSV challenge. Remarkably, RSV challenge of G protein nanoparticle vaccinated mice resulted in increased RSV M2-specific IL-4 and IFN-γ secreting T cells, and increased M2-specific H-2Kd-tetramer positive CD8⁺ T cells in the lungs compared to controls. Cell type analysis showed vaccination was not associated with increased pulmonary eosinophilia following RSV challenge. These results demonstrate that vaccination of mice with the RSV G protein nanoparticle vaccines induces a potent neutralizing antibody response, increased G protein- and M2- specific T cell responses, and a reduction in RSV disease pathogenesis.

Structure and function of respiratory syncytial virus surface glycoproteins

The two major glycoproteins on the surface of the respiratory syncytial virus (RSV) virion, the attachment glycoprotein (G) and the fusion glycoprotein (F), control the initial phases of infection. G targets the ciliated cells of the airways, and F causes the virion membrane to fuse with the target cell membrane. The F protein is the major target for antiviral drug development, and both G and F glycoproteins are the antigens targeted by neutralizing antibodies induced by infection. In this chapter, we review the structure and function of the RSV surface glycoproteins, including recent X-ray crystallographic data of the F glycoprotein in its pre- and postfusion conformations, and discuss how this information informs antigen selection and vaccine development.

Targeting RSV with vaccines and small molecule drugs

Respiratory syncytial virus (RSV) is the most significant cause of pediatric respiratory infections. Palivizumab (Synagis®), a humanized monoclonal antibody, has been used successfully for a number of years to prevent severe RSV disease in at-risk infants. However, despite intense efforts, there is no approved vaccine or small molecule drug for RSV. As an enveloped virus, RSV must fuse its envelope with the host cell membrane, which is accomplished through the actions of the fusion (F) glycoprotein, with attachment help from the G glycoprotein. Because of their integral role in initiation of infection and their accessibility outside the lipid bilayer, these proteins have been popular targets in the discovery and development of antiviral compounds and vaccines against RSV. This review examines advances in the development of antiviral compounds and vaccine candidates.

Dual role of respiratory syncytial virus glycoprotein fragment as a mucosal immunogen and chemotactic adjuvant

Respiratory syncytial virus (RSV) is a major cause of severe lower respiratory tract disease in infancy and early childhood. Despite its importance as a pathogen, there is no licensed vaccine to prevent RSV infection. The G glycoprotein of RSV, a major attachment protein, is a potentially important target for protective antiviral immune responses and has been shown to exhibit chemotactic activity through CX3C mimicry. Here, we show that sublingual or intranasal immunization of a purified G protein fragment of amino acids from 131 to 230, designated Gcf, induces strong serum IgG and mucosal IgA responses. Interestingly, these antibody responses could be elicited by Gcf even in the absence of any adjuvant, indicating a novel self-adjuvanting property of our vaccine candidate. Gcf exhibited potent chemotactic activity in in vitro cell migration assay and cysteine residues are necessary for chemotactic activity and self-adjuvanticity of Gcf in vivo. Mucosal immunization with Gcf also provides protection against RSV challenge without any significant lung eosinophilia or vaccine-induced weight loss. Together, our data demonstrate that mucosal administration of Gcf vaccine elicits beneficial protective immunity and represents a promising vaccine regimen preventing RSV infection.

Rapid sequencing of a peptide containing a single disulfide bond using high-energy collision-induced dissociation

A peptide containing a single disulfide bond was sequenced using high-energy collision-induced dissociation (HE-CID) in conjunction with a high mass resolution time-of-flight tandem mass spectrometer equipped with a matrix-assisted laser desorption/ionization source. This mass spectrometer, which has spiral ion trajectory, allowed both high mass resolution and high precursor ion selectivity. It is difficult to obtain sufficient product ions from peptides containing disulfide bonds using HE-CID due to the single collision in the gas phase. To compensate for insufficient dissociation, the disulfide bond was cleaved via an in-source reduction process using 1,5-diaminonaphthalene, a reducing matrix. After applying the reduction in the ionization, subsequent sequencing using HE-CID provided the detailed structural information of the peptide containing the single disulfide bond.

Progress in understanding and controlling respiratory syncytial virus: still crazy after all these years

Human respiratory syncytial virus (RSV) is a ubiquitous pathogen that infects everyone worldwide early in life and is a leading cause of severe lower respiratory tract disease in the pediatric population as well as in the elderly and in profoundly immunosuppressed individuals. RSV is an enveloped, nonsegmented negative-sense RNA virus that is classified in Family Paramyxoviridae and is one of its more complex members. Although the replicative cycle of RSV follows the general pattern of the Paramyxoviridae, it encodes additional proteins. Two of these (NS1 and NS2) inhibit the host type I and type III interferon (IFN) responses, among other functions, and another gene encodes two novel RNA synthesis factors (M2-1 and M2-2). The attachment (G) glycoprotein also exhibits unusual features, such as high sequence variability, extensive glycosylation, cytokine mimicry, and a shed form that helps the virus evade neutralizing antibodies. RSV is notable for being able to efficiently infect early in life, with the peak of hospitalization at 2-3 months of age. It also is notable for the ability to reinfect symptomatically throughout life without need for significant antigenic change, although immunity from prior infection reduces disease. It is widely thought that re-infection is due to an ability of RSV to inhibit or subvert the host immune response. Mechanisms of viral pathogenesis remain controversial. RSV is notable for a historic, tragic pediatric vaccine failure involving a formalin-inactivated virus preparation that was evaluated in the 1960s and that was poorly protective and paradoxically primed for enhanced RSV disease. RSV also is notable for the development of a successful strategy for passive immunoprophylaxis of high-risk infants using RSV-neutralizing antibodies. Vaccines and new antiviral drugs are in pre-clinical and clinical development, but controlling RSV remains a formidable challenge.

Induction and identification of disulfide-intact and disulfide-reduced β-subunit of Shiga toxin 2 from Escherichia coli O157:H7 using MALDI-TOF-TOF-MS/MS and top-down proteomics

The disulfide-intact and disulfide-reduced β-subunit of Shiga toxin 2 (β-Stx2) from Escherichia coli O157:H7 (strain EDL933) has been identified by matrix-assisted laser desorption/ionization time-of-flight-time-of-flight tandem mass spectrometry (MALDI-TOF-TOF-MS/MS) and top-down proteomic analysis using software developed in-house. E. coli O157:H7 was induced to express Stx2 by culturing on solid agar media supplemented with 10-50 ng mL(-1) of ciprofloxacin (CP). Bacterial cell lysates at each CP concentration were analyzed by MALDI-TOF-MS. A prominent ion at mass-to-charge (m/z) ~7820 was observed for the CP concentration range: 10-50 ng mL(-1), reaching a maximum signal intensity at 20 ng mL(-1). Complex MS/MS data were obtained of the ion at m/z ~7820 by post-source decay resulting in top-down proteomic identification as the mature, signal peptide-removed, disulfide-intact β-Stx2. Eight fragment ion triplets (each spaced Δm/z ~33 apart) were also observed resulting from backbone cleavage between the two cysteine residues (that form the intra-molecular disulfide bond) and symmetric and asymmetric cleavage of the disulfide bond. The middle fragment ion of each triplet, from symmetric disulfide bond cleavage, was matched to an in silico fragment ion formed from cleavage of the backbone at a site adjacent to an aspartic acid or glutamic acid residue. The flanking fragment ions of each triplet, from asymmetric disulfide bond cleavage, were not matched because their corresponding in silico fragment ions are not represented in the database. Easier to interpret MS/MS data were obtained for the disulfide-reduced β-Stx2 which resulted in an improved top-down identification.

Prophylactic treatment with a G glycoprotein monoclonal antibody reduces pulmonary inflammation in respiratory syncytial virus (RSV)-challenged naive and formalin-inactivated RSV-immunized BALB/c mice

We examined whether prophylactically administered anti-respiratory syncytial virus (anti-RSV) G monoclonal antibody (MAb) would decrease the pulmonary inflammation associated with primary RSV infection and formalin-inactivated RSV (FI-RSV)-enhanced disease in mice. MAb 131-2G administration 1 day prior to primary infection reduced the pulmonary inflammatory response and the level of RSV replication. Further, intact or F(ab')(2) forms of MAb 131-2G administered 1 day prior to infection in FI-RSV-vaccinated mice reduced enhanced inflammation and disease. This study shows that an anti-RSV G protein MAb might provide prophylaxis against both primary infection and FI-RSV-associated enhanced disease. It is possible that antibodies with similar reactivities might prevent enhanced disease and improve the safety of nonlive virus vaccines.

Newcastle disease virus-like particles containing respiratory syncytial virus G protein induced protection in BALB/c mice, with no evidence of immunopathology

Respiratory syncytial virus (RSV) is the leading cause of serious respiratory infections in children as well as a serious cause of disease in elderly and immunosuppressed populations. There are no licensed vaccines available to prevent RSV disease. We have developed a virus-like particle (VLP) vaccine candidate for protection from RSV. The VLP is composed of the NP and M proteins of Newcastle disease virus (NDV) and a chimeric protein containing the cytoplasmic and transmembrane domains of the NDV HN protein and the ectodomain of the human RSV G protein (H/G). Immunization of mice with 10 or 40 microg total VLP-H/G protein by intraperitoneal or intramuscular inoculation stimulated antibody responses to G protein which were as good as or better than those stimulated by comparable amounts of UV-inactivated RSV. Immunization of mice with two doses or even a single dose of these particles resulted in the complete protection of mice from RSV replication in the lungs. Immunization with these particles induced neutralizing antibodies with modest titers. Upon RSV challenge of VLP-H/G-immunized mice, no enhanced pathology in the lungs was observed, although lungs of mice immunized in parallel with formalin-inactivated RSV (FI-RSV) showed the significant pathology that has previously been documented after immunization with FI-RSV. Thus, the VLP-H/G candidate vaccine was immunogenic in BALB/c mice and prevented replication of RSV in murine lungs, with no evidence of immunopathology. These data support further development of virus-like particle vaccine candidates for protection against RSV.

Gas-phase scrambling of disulfide bonds during matrix-assisted laser desorption/ionization mass spectrometry analysis

Evidence for photo-induced radical disulfide bond scrambling in the gas phase during matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) is described. The phenomenon was observed during the analysis of tryptic peptides from insulin and was confirmed in the determination of disulfide bonds in the rhamnose-binding lectin SEL24K from the Chinook salmon Oncorhynchus tshawytscha. A possible mechanism for this surprising scrambling is proposed. Despite this finding, the disulfide bond pattern in SEL24K was assigned unambiguously by a multi-enzyme digestion strategy in combination with MALDI mass spectrometry. The pattern was found to be symmetrical in the tandem repeat sequence of SEL24K. To the best of our knowledge, this is the first report of disulfide bond scrambling in the gas phase during MALDI-MS analysis. This observation has important ramifications for unambiguous assignment of disulfide bonds.

Respiratory syncytial virus grown in Vero cells contains a truncated attachment protein that alters its infectivity and dependence on glycosaminoglycans

Human respiratory syncytial virus (RSV) contains a heavily glycosylated 90-kDa attachment glycoprotein (G). Infection of HEp-2 and Vero cells in culture depends largely on virion G protein binding to cell surface glycosaminoglycans (GAGs). This GAG-dependent phenotype has been described for RSV grown in HEp-2 cells, but we have found that it is greatly reduced by a single passage in Vero cells. Virions produced from Vero cells primarily display a 55-kDa G glycoprotein. This smaller G protein represents a post-Golgi compartment form that is lacking its C terminus, indicating that the C terminus is required for GAG dependency. Vero cell-grown virus infected primary well-differentiated human airway epithelial (HAE) cell cultures 600-fold less efficiently than did HEp-2 cell-grown virus, indicating that the C terminus of the G protein is also required for virus attachment to this model of the in vivo target cells. This reduced infectivity for HAE cell cultures is not likely to be due to the loss of GAG attachment since heparan sulfate, the primary GAG used by RSV for attachment to HEp-2 cells, is not detectable at the apical surface of HAE cell cultures where RSV enters. Growing RSV stocks in Vero cells could dramatically reduce the initial infection of the respiratory tract in animal models or in volunteers receiving attenuated virus vaccines, thereby reducing the efficiency of infection or the efficacy of the vaccine.

Preliminary mechanistic information on disulfide-bond formation and the role of hydrogen bonds by nanoelectrospray mass spectrometry

The formation of disulfide-bonds is vital for the proper folding of most secreted proteins and the stabilization of the final protein structure, including many of medical importance. The determination of disulfide-bonds is an important aspect of gaining a comprehensive understanding of the chemical structure of a protein. A long-term goal of ours is to examine the mechanism of disulfide-bond formation in aqueous solution and the potential role hydrogen bonds play in this process. Here, we report preliminary results from a method that utilizes the oxidizing power of iodine to generate disulfide bonds from synthesized model compounds, which is followed by nanoelectrospray ionization (nanoESI)- mass spectrometry (MS). By continuously monitoring the reaction mixture during disulfide formation, this nanoESI approach provides insight on the sequence of intermediate species formed, and how hydrogen-bonding donor/acceptor pairs may promote disulfide bond formation.

Differential labeling of free and disulfide-bound thiol functions in proteins

A method for the simultaneous determination of the number of free cysteine groups and disulfide-bound cysteine groups in proteins has been developed based on the sequential labeling of free and bound thiol functionalities with two ferrocene-based maleimide reagents. Liquid chromatography/electrochemistry/mass spectrometry was used to assign the N-(2-ferroceneethyl)maleimide (FEM) labeled free cysteine functionalities in a tryptic digest mixture, whereas a precursor ion scan enables the detection of peptides with ferrocenecarboxylic acid-(2-maleimidoyl)ethylamide (FMEA) labeled disulfide-bound cysteine groups after reduction. Fragment spectra of the labeled peptides yield an excellent coverage of b-type and y-type ions. The ferrocene labeled cysteines were fragmented as 412 Da (FEM) and 455 Da (FMEA). These fragment masses are significantly higher than unlabeled amino acids or dipeptides and are easily detected. The position of free and disulfide-bound cysteine may therefore be assigned in an amino acid sequence.

Determination of the disulfide bond arrangement of dengue virus NS1 protein

The 12 half-cystines of NS1 proteins are absolutely conserved among flaviviruses, suggesting their importance to the structure and function of these proteins. In the present study, peptides from recombinant Dengue-2 virus NS1 were produced by tryptic digestion in 100% H(2)(16)O, peptic digestion in 50% H(2)(18)O, thermolytic digestion in 50% H(2)(18)O, or combinations of these digestion conditions. Peptides were separated by size exclusion and/or reverse phase high performance liquid chromatography and examined by matrix-assisted laser desorption ionization-time of flight mass spectrometry, matrix-assisted laser desorption ionization post-source decay, and matrix-assisted laser desorption ionization tandem mass spectrometry. Where digests were performed in 50% H(2)(18)O, isotope profiles of peptide ions aided in the identification and characterization of disulfide-linked peptides. It was possible to produce two-chain peptides containing C1/C2, C3/C4, C5/C6, and C7/C12 linkages as revealed by comparison of the peptide masses before and after reduction and by post-source decay analysis. However, the remaining four half-cystines (C8, C9, C10, and C11) were located in a three-chain peptide of which one chain contained adjacent half-cystines (C9 and C10). The linkages of C8/C10 and C9/C11 were determined by tandem mass spectrometry of an in-source decay fragment ion containing C9, C10, and C11. This disulfide bond arrangement provides the basis for further refinement of flavivirus NS1 protein structural models.

Immunoproteomics: Mass spectrometry-based methods to study the targets of the immune response

The mammalian immune system has evolved to display fragments of protein antigens derived from microbial pathogens to immune effector cells. These fragments are typically peptides liberated from the intact antigens through distinct proteolytic mechanisms that are subsequently transported to the cell surface bound to chaperone-like receptors known as major histocompatibility complex (MHC) molecules. These complexes are then scrutinized by effector T cells that express clonally distributed T cell receptors with specificity for specific MHC-peptide complexes. In normal uninfected cells, this process of antigen processing and presentation occurs continuously, with the resultant array of self-antigen-derived peptides displayed on the surface of these cells. Changes in this peptide landscape of cells act to alert immune effector cells to changes in the intracellular environment that may be associated with infection, malignant transformation, or other abnormal cellular processes, resulting in a cascade of events that result in their elimination. Because peptides play such a crucial role in informing the immune system of infection with viral or microbial pathogens and the transformation of cells in malignancy, the tools of proteomics, in particular mass spectrometry, are ideally suited to study these immune responses at a molecular level. Here we review recent advances in the studies of immune responses that have utilized mass spectrometry and associated technologies, with specific examples from collaboration between our laboratories.

Positions of disulfide bonds and N-glycosylation site in juvenile hormone binding protein

The juvenile hormone binding protein (JHBP) from Galleria mellonella hemolymph is a glycoprotein composed of 225 amino acid residues. It contains four Cys residues forming two disulfide bridges. In this study, the topography of the disulfide bonds as well as the site of glycan attachment in the JHBP molecule from G. mellonella was determined, using electrospray mass spectrometry. The MS analysis was performed on tryptic digests of JHBP. Our results show that the disulfide bridges link Cys10 and Cys17, and Cys151 and Cys195. Of the two potential N-glycosylation sites in JHBP, Asn4, and Asn94, only Asn94 is glycosylated. This site of glycosylation is also found in the fully biologically active recombinant JHBP expressed in the yeast Pichia pastoris.

Complete disulfide bond assignment of a recombinant immunoglobulin G4 monoclonal antibody

Recombinant monoclonal antibodies (mAbs) are an emerging therapeutic area. However, there are few reports on disulfide bond assignment of recombinant mAbs. This work describes the complete disulfide bond assignment of a recombinant immunoglobulin G4 (IgG4) mAb. N-ethylmaleimide (NEM) was used to mask free sulfhydryl groups present in the mAb. Digestion of the mAb with endoproteinase Lys-C without disulfide scrambling was achieved by denaturing the mAb in the presence of NEM in guanidine hydrochloride (GuHCl). The Lys-C digest was subsequently reduced with dithiothreitol (DTT). Native and reduced Lys-C digests were mass analyzed by on-line reversed-phase-high-performance liquid chromatography mass spectrometry (RP-HPLC/MS). Disulfide-containing peptides were sequenced by off-line nanoelectrospray quadrupole time-of-flight mass spectrometry (nanoESI-QTOF MS) and N-terminal Edman sequencing for verifying connectivities. The recombinant IgG4 mAb was found to contain the expected disulfide linkages with the proposed method. The NEM alkylating reagent was critical in minimizing disulfide scrambling during the denaturation and digestion of the mAb. This integrated approach, combining MS and N-terminal Edman sequencing, was capable of assigning the disulfide pattern of the IgG4 mAb rapidly and completely, and should be applicable for disulfide bond assignment and structural analysis of other mAbs and large proteins with multiple disulfide bonds.

The central conserved cystine noose of the attachment G protein of human respiratory syncytial virus is not required for efficient viral infection in vitro or in vivo

The G glycoprotein of human respiratory syncytial virus (RSV) was identified previously as the viral attachment protein. Although we and others recently showed that G is not essential for replication in vitro, it does affect the efficiency of replication in a cell type-dependent fashion and is required for efficient replication in vivo. The ectodomain of G is composed of two heavily glycosylated domains with mucin-like characteristics that are separated by a short central region that is relatively devoid of glycosylation sites. This central region contains a 13-amino acid segment that is conserved in the same form among RSV isolates and is overlapped by a second segment containing four cysteine residues whose spacings are conserved in the same form and which create a cystine noose. The conserved nature of the cystine noose and flanking 13-amino acid segment suggested that this region likely was important for attachment activity. To test this hypothesis, we constructed recombinant RSVs from which the region containing the cysteine residues was deleted together with part or all of the conserved 13-amino acid segment. Surprisingly, each deletion had little or no effect on the intracellular synthesis and processing of the G protein, the kinetics or efficiency of virus replication in vitro, or sensitivity to neutralization by soluble heparin in vitro. In addition, neither deletion had any discernible effect on the ability of RSV to infect the upper respiratory tract of mice and both resulted in a 3- to 10-fold reduction in the lower respiratory tract. Thus, although the G protein is necessary for efficient virus replication in vivo, this activity does not require the central conserved cystine noose region.

Protein disulfide bond determination by mass spectrometry

The determination of disulfide bonds is an important aspect of gaining a comprehensive understanding of the chemical structure of a protein. The basic strategy for obtaining this information involves the identification of disulfide-linked peptides in digests of proteins and the characterization of their half-cystinyl peptide constituents. Tools for disulfide bond analysis have improved dramatically in the past two decades, especially in terms of speed and sensitivity. This improvement is largely due to the development of matrix-assisted laser desorption/ionization (MALDI) and electrospray ionization (ESI), and complementary analyzers with high resolution and accuracy. The process of pairing half-cystinyl peptides is now generally achieved by comparing masses of non-reduced and reduced aliquots of a digest of a protein that was proteolyzed with intact disulfide bonds. Pepsin has favorable properties for generating disulfide-linked peptides, including its acidic pH optimum, at which disulfide bond rearrangement is precluded and protein conformations are likely to be unfolded and accessible to cleavage, and broad substrate specificity. These properties potentiate cleavage between all half-cystine residues of the substrate protein. However, pepsin produces complex digests that contain overlapping peptides due to ragged cleavage. This complexity can produce very complex spectra and/or hamper the ionization of some constituent peptides. It may also be more difficult to compute which half-cystinyl sequences of the protein of interest are disulfide-linked in non-reduced peptic digests. This ambiguity is offset to some extent by sequence tags that may arise from ragged cleavages and aid sequence assignments. Problems associated with pepsin cleavage can be minimized by digestion in solvents that contain 50% H(2) (18)O. Resultant disulfide-linked peptides have distinct isotope profiles (combinations of isotope ratios and average mass increases) compared to the same peptides with only (16)O in their terminal carboxylates. Thus, it is possible to identify disulfide-linked peptides in digests and chromatographic fractions, using these mass-specific markers, and to rationalize mass changes upon reduction in terms of half-cystinyl sequences of the protein of interest. Some peptides may require additional cleavages due to their multiple disulfide bond contents and/or tandem mass spectrometry (MS/MS) to determine linkages. Interpretation of the MS/MS spectra of peptides with multiple disulfides in supplementary digests is also facilitated by the presence of (18)O in their terminal carboxylates.

Identification of disulfide-linked peptides by isotope profiles produced by peptic digestion of proteins in 50% (18)O water

Determination of the disulfide-bond arrangement of a protein by characterization of disulfide-linked peptides in proteolytic digests may be complicated by resistance of the protein to specific proteases, disulfide interchange, and/or production of extremely complex mixtures by less specific proteolysis. In this study, mass spectrometry has been used to show that incorporation of (18)O into peptides during peptic digestion of disulfide-linked proteins in 50% (18)O water resulted in isotope patterns and increases in average masses that facilitated identification and characterization of disulfide-linked peptides even in complex mixtures, without the need for reference digests in 100% (16)O water. This is exemplified by analysis of peptic digests of model proteins lysozyme and ribonuclease A (RNaseA) by matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) and electrospray ionization (ESI) mass spectrometry (MS). Distinct isotope profiles were evident when two peptide chains were linked by disulfide bonds, provided one of the chains did not contain the C terminus of the protein. This latter class of peptide, and single-chain peptides containing an intrachain disulfide bond, could be identified and characterized by mass shifts produced by reduction. Reduction also served to confirm other assignments. Isotope profiling of peptic digests showed that disulfide-linked peptides were often enriched in the high molecular weight fractions produced by size exclusion chromatography (SEC) of the digests. Applicability of these procedures to analysis of a more complex disulfide-bond arrangement was shown with the hemagglutinin/neuraminidase of Newcastle disease virus.

Antiviral activity and structural characteristics of the nonglycosylated central subdomain of human respiratory syncytial virus attachment (G) glycoprotein

Segments of the cystine noose-containing nonglycosylated central subdomain, residues 149-197, of the attachment (G) glycoprotein of human respiratory syncytial virus (HRSV) have been assessed for impact on the cytopathic effect (CPE) of respiratory syncytial virus (RSV). Nalpha-acetyl residues 149-197-amide (G149-197), G149-189, and G149-177 of the A2 strain of HRSV protected 50% of human epithelial HEp-2 cells from the CPE of the A2 strain at concentrations (IC(50)) between 5 and 80 microm. Cystine noose-containing peptides G171-197 and G173-197 did not inhibit the CPE even at concentrations above 150 microm. Systematic C- and N-terminal truncations from G149-189 and G149-177 and alanine substitutions within G154-177 demonstrated that residues 166-170 (EVFNF), within a sequence that is conserved in HRSV strains, were critical for inhibition. Concordantly, G154-177 of bovine RSV and of an antibody escape mutant of HRSV with residues 166-170 of QTLPY and EVSNP, respectively, were not inhibitory. Surprisingly, a variant of G154-177 with an E166A substitution had an IC(50) of 750 nm. NMR analysis demonstrated that G149-177 adopted a well-defined conformation in solution, clustered around F168 and F170. G154-170, particularly EVFNF, may be important in binding of RSV to host cells. These findings constitute a promising platform for the development of antiviral agents for RSV.

Determination of the complete amino acid sequence for the coat protein of brome mosaic virus by time-of-flight mass spectrometry. Evidence for mutations associated with change of propagation host

Time-of-flight mass spectrometry (TOFMS) has been applied to determine the complete coat protein amino acid sequences of a number of distinct brome mosaic virus (BMV) isolates. Ionization was carried out by both electrospray ionization and matrix-assisted laser desorption/ionization (MALDI). After determining overall coat protein masses, the proteins were digested with trypsin or Lys-C proteinases, and the digestion products were analyzed in a MALDI QqTOF mass spectrometer. The N terminus of the coat protein was found to be acetylated in each BMV isolate analyzed. In one isolate (BMV-Valverde), the amino acid sequence was identical to that predicted from the cDNA sequence of the "type" isolate, but deviations from the predicted amino acid sequence were observed for all the other isolates analyzed. When isolates were propagated in different host taxa, modified coat protein sequences were observed in some cases, along with the original sequence. Sequencing by TOFMS may therefore provide a basis for monitoring the effects of host passaging on a virus at the molecular level. Such TOFMS-based analyses assess the complete profiles of coat protein sequences actually present in infected tissues. They are therefore not subject to the selection biases inherent in deducing such sequences from reverse-transcribed viral RNA and cloning the resulting cDNA.

The use of post-source decay in matrix-assisted laser desorption/ionisation mass spectrometry to delineate T cell determinants

The identification of naturally processed peptides presented by molecules of the major histocompatibility complex (MHC) has progressed significantly over the past decade. The elution of peptides from immunoaffinity purified complexes of MHC class I or class II molecules has provided highly specific biochemical information regarding the nature of endogenous peptides capable of binding to and being presented by particular MHC alleles. Whilst Edman chemistry is sufficient for the identification of abundant or homogeneous immunodominant peptides contained in samples of fractionated peptides, mass spectrometry has proved more powerful for sequencing less abundant species present in the typically heterogeneous fractions of eluted peptides. This review focuses on the characterisation of T cell determinants by matrix-assisted laser desorption/ionisation (MALDI)-time-of-flight (TOF) mass spectrometry (MS). We demonstrate, with specific examples, the utility of post-source decay in MALDI-TOF MS for the characterisation of the amino acid sequences of both native and modified T cell determinants. The potential advantages and pitfalls of this technique relative to the more commonly used forms of tandem mass spectrometry in electrospray and ion spray modes of ionisation as well as hybrid quadrupole-quadrupole-TOF instruments are discussed. We highlight the complementarity between these techniques and discuss the advantages in the combined use of both MALDI- and electrospray-based instrumentation in epitope identification strategies.

Immune-mediated disease pathogenesis in respiratory syncytial virus infection

Respiratory syncytial virus (RSV) is an important cause of severe respiratory disease in persons at both extremes of age. Wheezing is a cardinal sign of infection and the illness is associated with an increased incidence of childhood asthma. Data from both humans and animal models have linked severe disease in infants and the syndrome of vaccine-enhanced illness with an aberrant composition of CD4+ T cells, suggestive of an exaggerated Th2 response. Studies in murine models have shown that prior vaccination, coexisting allergic inflammation, or direct modulation of the cytokine milieu can profoundly influence the immune response to RSV and thereby affect the expression of disease. In addition, there are intrinsic antigenic properties of the RSV G glycoprotein that promote Th2 responses and eosinophilia. This paper proposes an integrated working model of how host and virus factors interact to determine the characteristics of RSV-induced illness. This model suggests strategies for the development of new vaccine and immunotherapeutic interventions, and creates a framework for asking additional questions about the immunopathogenesis of RSV.

Determination of the disulfide bond arrangement of Newcastle disease virus hemagglutinin neuraminidase. Correlation with a beta-sheet propeller structural fold predicted for paramyxoviridae attachment proteins

Disulfide bonds stabilize the structure and functions of the hemagglutinin neuraminidase attachment glycoprotein (HN) of Newcastle disease virus. Until this study, the disulfide linkages of this HN and structurally similar attachment proteins of other members of the paramyxoviridae family were undefined. To define these linkages, disulfide-linked peptides were produced by peptic digestion of purified HN ectodomains of the Queensland strain of Newcastle disease virus, isolated by reverse phase high performance liquid chromatography, and analyzed by mass spectrometry. Analysis of peptides containing a single disulfide bond revealed Cys(531)-Cys(542) and Cys(172)-Cys(196) linkages and that HN ectodomains dimerize via Cys(123). Another peptide, with a chain containing Cys(186) linked to a chain containing Cys(238), Cys(247), and Cys(251), was cleaved at Met(249) with cyanogen bromide. Subsequent tandem mass spectrometry established Cys(186)-Cys(247) and Cys(238)-Cys(251) linkages. A glycopeptide with a chain containing Cys(344) linked to a chain containing Cys(455), Cys(461), and Cys(465) was treated sequentially with peptide-N-glycosidase F and trypsin. Further treatment of this peptide by one round of manual Edman degradation or tandem mass spectrometry established Cys(344)-Cys(461) and Cys(455)-Cys(465) linkages. These data, establishing the disulfide linkages of all thirteen cysteines of this protein, are consistent with published predictions that the paramyxoviridae HN forms a beta-propeller structural fold.

Determination of disulfide bonds in highly bridged alpha-dendrotoxin by matrix-assisted laser desorption/ionization mass spectrometry

A methodology which combines tryptic digestions, 1,4-dithiothreitol reduction, and matrix-assisted laser desorption/ionization mass spectrometry (MALDI-TOF-MS) allows verification of the location of the disulfide bridges in alpha-dendrotoxin (C7-C57, C16-C40 and C32-C53). Copyright 2000 John Wiley & Sons, Ltd.

Identification of a linear heparin binding domain for human respiratory syncytial virus attachment glycoprotein G

Respiratory syncytial virus (RSV) is the leading cause of lower respiratory tract disease in infants and young children worldwide. Infection is mediated, in part, by an initial interaction between attachment protein (G) and a highly sulfated heparin-like glycosaminoglycan (Gag) located on the cell surface. Synthetic overlapping peptides derived from consensus sequences of the G protein ectodomain from both RSV subgroups A and B were tested by heparin-agarose affinity chromatography for their abilities to bind heparin. This evaluation identified a single linear heparin binding domain (HBD) for RSV subgroup A (184A-->T198) and B (183K-->K197). The binding of these peptides to Vero cells was inhibited by heparin. Peptide binding to two CHO cell mutants (pgsD-677 and pgsA-745) deficient in heparan sulfate or total Gag synthesis was decreased 50% versus the parental cell line, CHO-K1, and decreased an average of 87% in the presence of heparin. The RSV-G HBD peptides were also able to inhibit homologous and heterologous virus infectivity of Vero cells. These results indicate that the sequence 184A/183K-->198T/K197 for RSV subgroups A and B, respectively, defines an important determinant of RSV-G interactions with heparin.

Determination of the complete covalent structure of the major glycoform of DQH sperm surface protein, a novel trypsin-resistant boar seminal plasma O-glycoprotein related to pB1 protein

The complete covalent structure of a novel boar DQH sperm surface protein resistant to many classical procedures of enzymatic fragmentation was determined. The relative molecular mass of the major form of this protein determined by ESI-MS and MALDI-MS was 13,065.2+/-1.0 and 13,065.1, respectively. However, additional peaks differing by 162 Da (i.e., minus hexose), 365 Da (i.e., minus hexose and N-acetylhexosamine), 146 Da (i.e., plus deoxyhexose), and 291 Da (i.e., plus sialic acid) indicated the heterogeneity due to differences in glycosylation. The complete covalent structure of the protein was determined using automated Edman degradation, MALDI-MS, and post-source decay (PSD) MALDI-MS, and shown to consist of N-terminal O-glycosylated peptide followed by two fibronectin type II repeats. The carbohydrates are O-glycosidically linked to threonine 10, as confirmed by PSD MALDI-MS of the isolated N-terminal glycopeptide. Eight cysteine residues of the protein form four disulfide bridges, the positions of which were assigned from MALDI-MS and Edman degradation data. We conclude that mass spectral techniques provide an indispensable tool for the detailed analysis of the covalent structure of proteins, especially those that are refractory to standard approaches of protein chemistry.