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V A Fischetti

Publications and source records attributed to V A Fischetti.

At least 37 records · Page 2Linked to original sources
PubMed1998

Role of alpha-dystroglycan as a Schwann cell receptor for Mycobacterium leprae.

alpha-Dystroglycan (alpha-DG) is a component of the dystroglycan complex, which is involved in early development and morphogenesis and in the pathogenesis of muscular dystrophies. Here, alpha-DG was shown to serve as a Schwann cell receptor for Mycobacterium leprae, the causative organism of leprosy. Mycobacterium leprae specifically bound to alpha-DG only in the presence of the G domain of the alpha2 chain of laminin-2. Native alpha-DG competitively inhibited the laminin-2-mediated M. leprae binding to primary Schwann cells. Thus, M. leprae may use linkage between the extracellular matrix and cytoskeleton through laminin-2 and alpha-DG for its interaction with Schwann cells.

Animals↗
PubMed1998

alpha-enolase, a novel strong plasmin(ogen) binding protein on the surface of pathogenic streptococci.

The plasmin(ogen) binding property of group A streptococci is incriminated in tissue invasion processes. We have characterized a novel 45-kDa protein displaying strong plasmin(ogen) binding activity from the streptococcal surface. Based on its biochemical properties, we confirmed the identity of this protein as alpha-enolase, a key glycolytic enzyme. Dose-dependent alpha-enolase activity, immune electron microscopy of whole streptococci using specific antibodies, and the opsonic nature of polyclonal and monoclonal antibodies concluded the presence of this protein on the streptococcal surface. We, henceforth, termed the 45-kDa protein, SEN (streptococcal surface enolase). SEN is found ubiquitously on the surface of most streptococcal groups and serotypes and showed significantly greater plasmin(ogen) binding affinity compared with previously reported streptococcal plasminogen binding proteins. Both the C-terminal lysine residue of SEN and a region N-terminal to it play a critical role in plasminogen binding. Results from competitive plasminogen binding inhibition assays and cross-linking studies with intact streptococci indicate that SEN contributes significantly to the overall streptococcal ability to bind plasmin(ogen). Our findings, showing both the protected protease activity of SEN-bound plasmin and SEN-specific immune responses, provide evidence for an important role of SEN in the disease process and post-streptococcal autoimmune diseases.

Amino Acid Sequence↗
PubMed1998

Why have group A streptococci remained susceptible to penicillin? Report on a symposium.

In spite of 50 years of extensive use of penicillin, group A streptococci remain exquisitely susceptible to this antibiotic. This observation that continuing susceptibility has occurred despite the development of resistance to other antimicrobial agents prompted a day-long meeting at Rockefeller University (New York) in October 1996. Among the most likely explanations for this remarkable state of continued susceptibility to penicillin are that beta-lactamase may not be expressed or may be toxic to the organism and/or that low-affinity penicillin-binding proteins either are not expressed or render organisms nonviable. Other potential explanations are that circumstances favorable for the development of resistance have not yet occurred and/or that there are inefficient mechanisms for or barriers to genetic transfer. Recommended future actions include (1) additional laboratory investigations of gene transfer, penicillin-binding proteins, virulence factors, and homeologous recombination and mismatch repair; (2) increased surveillance for the development of penicillin resistance; (3) application of bioinformatics to analyze streptococcal genome sequences; and (4) development of vaccines and novel antimicrobial agents. Thus far the susceptibility of group A streptococci to penicillin has not been a major clinical or epidemiological problem. A similar observation, however, could have been made decades ago about Streptococcus pneumoniae. It is therefore vital for the scientific community to closely examine why penicillin has remained uniformly highly active against group A streptococci in order to maintain this desirable state.

Humans↗
PubMed1998

Immunoglobulins to group A streptococcal surface molecules decrease adherence to and invasion of human pharyngeal cells.

The M protein is one of the most important virulence factors of group A streptococci (Streptococcus pyogenes) and may play an important role in the first steps of streptococcal infection. Since acute pharyngitis is a frequently occurring infectious disease caused by these bacteria, we wished to know whether antibodies to the M protein or other surface components inhibit adherence and internalization of streptococci to pharyngeal cells. We investigated the role of whole human secretory immunoglobulin A (sIgA), M6 protein-specific sIgA, and M6 protein-specific serum IgG in the inhibition of streptococcal adherence and internalization to cultured human pharyngeal cells. S. pyogenes D471, which produces a type 6 M protein (M+), and its isogenic M-negative (M-) derivative JRS75 were tested. Purified whole sIgA, M protein-specific sIgA, and sIgA preabsorbed with M protein were able to decrease significantly the adherence of streptococci to pharyngeal cells. Purified IgG against the M6 protein did not diminish the attachment of streptococci to the pharyngeal cells but did reduce internalization. Thus, our data suggest that secretory IgA may play a key role in preventing streptococcal infection at mucosal surfaces by blocking adherence while affinity-purified anti-M protein-specific IgG blocks epitopes responsible for invasion.

Animals↗
PubMed1998

M protein of the group A Streptococcus binds to the seventh short consensus repeat of human complement factor H.

Streptococcus pyogenes evades complement by binding the complement-regulatory protein factor H (fH) via the central conserved C-repeat region of M protein. However, the corresponding binding region within fH has not previously been precisely localized. fH is composed of 20 conserved modules called short consensus repeats (SCRs), each of which contains approximately 60 amino acids. A series of fH truncated and deletion mutants were prepared, and their interaction with M6 protein was examined. The M protein binding site was initially localized to SCRs 6 to 15 as demonstrated by ligand dot blotting, chemical cross-linking, and enzyme-linked immunosorbent assay. SCR 7 was then shown to contain the M protein binding site, as a construct consisting of the first seven SCRs bound M protein but a construct containing the first six SCRs did not bind. In addition, deletion of SCR 7 from full-length fH abolished binding to M protein. SCR 7 is known to contain a heparin binding domain, and binding of fH to M6 protein was almost totally inhibited in the presence of 400 U of heparin per ml. These results localize the M6 protein binding site of fH to SCR 7 and indicate that it is in close proximity to the heparin binding site.

Animals↗
PubMed1998

The specificity patterns of human immunoglobulin G antibodies in serum differ from those in autologous secretions.

The specificity patterns of immunoglobulin G (IgG) antibodies to streptococcal antigens in serum and autologous secretions were compared in order to determine whether IgG found in human secretions is exclusively of serum origin or can also be locally produced irrespective of the systemic immune system. Surface antigens from a type 6 M-protein strain of Streptococcus pyogenes were extracted by cell wall digestion and subjected to sodium lauryl sulfate-polyacrylamide gel electrophoresis under reducing conditions. After being blotted onto nitrocellulose, the antigens were incubated with purified IgG from various body fluids: saliva, cervicovaginal secretions, seminal fluid, and colostrum. Binding was then revealed with labeled antibodies to human Fcgamma fragments. The antibody specificity patterns obtained by computer-assisted analysis were compared with those of paired sera. Major variations were observed between serum and secretions, as well as between different secretions from the same subject. These results are in favor of IgG-associated local immunity within different tissue compartments. This IgG response to mucosal antigens can complement that of secretory IgA in the defense against pathogens and should be taken into account during topical vaccinations.

Antibodies, Bacterial↗
PubMed1998

Immunological relationship between the class I epitope of streptococcal M protein and myosin.

The class I epitope of streptococcal M protein is an epidemiological marker for acute rheumatic fever (ARF)-associated serotypes of group A streptococci and is recognized by anti-M protein monoclonal antibody (MAb) 10B6. Using MAb 10B6, we determined the relationship between the class I epitope of M protein and the alpha-helical coiled-coil protein myosin. MAb 10B6 reacted by enzyme-linked immunosorbent assay and Western blotting with human cardiac myosin and rabbit skeletal myosin and its heavy meromyosin (HMM) subfragment. Overlapping synthetic peptides of M5 protein were used to identify the region of M5 protein recognized by MAb 10B6. Two C repeat peptides (C2A and C3) containing the amino acid sequence KGLRRDLDASREAK reacted with MAb 10B6. Partial sequence identity, RRDL, was found in the HMM fragment of myosin, which reacted with MAb 10B6. However, not all peptides of M5 protein and myosin containing the RRDL sequence reacted with MAb 10B6. ARF sera and sera from uncomplicated pharyngitis (UNC) reacted with C repeat region peptides of M protein, while acute glomerulonephritis sera were not as reactive. Affinity-purified human antibody to peptide C3 reacted with myosin. The data demonstrate that the class I epitope of M protein is immunologically cross-reactive with myosin and the HMM subfragment, and antibodies to peptide C3 and myosin were present in ARF and UNC sera.

Amino Acid Sequence↗
PubMed1997

Regulation of the phosphorylation of human pharyngeal cell proteins by group A streptococcal surface dehydrogenase: signal transduction between streptococci and pharyngeal cells.

Whether cell-to-cell communication results when group A streptococci interact with their target cells is unknown. Here, we report that upon contact with cultured human pharyngeal cells, both whole streptococci and purified streptococcal surface dehydrogenase (SDH) activate pharyngeal cell protein tyrosine kinase as well as protein kinase C, thus regulating the phosphorylation of cellular proteins. SDH, a major surface protein of group A streptococci, has both glyceraldehyde-3-phosphate dehydrogenase and ADP-ribosylating enzyme activities that may relate to early stages of streptococcal infection. Intact streptococci and purified SDH induce a similar protein phosphorylation pattern with the de novo tyrosine phosphorylation of a 17-kD protein found in the membrane/particulate fraction of the pharyngeal cells. However, this phosphorylation required the presence of cytosolic components. NH2-terminal amino acid sequence analysis identified the 17-kD protein as nuclear core histone H3. Both phosphotyrosine and phosphoserine-specific monoclonal antibodies reacted with the 17-kD protein by Western blot, suggesting that the binding of SDH to these pharyngeal cells elicits a novel signaling pathway that ultimately leads to activation of histone H3-specific kinases. Genistein-inhibitable phosphorylation of histone H3 indicates that tyrosine kinase plays a key role in this event. Treatment of pharyngeal cells with protein kinase inhibitors such as genistein and staurosporine significantly inhibited streptococcal invasion of pharyngeal cells. Therefore, these data indicated that streptococci/SDH-mediated phosphorylation plays a critical role in bacterial entry into the host cell. To identify the membrane receptor that elicits these signaling events, we found that SDH bound specifically to 30- and 32-kD membrane proteins in a direct ligand-binding assay. These findings clearly suggest that SDH plays an important role in cellular communication between streptococci and pharyngeal cells that may be important in host cell gene transcription, and hence in the pathogenesis of streptococcal infection.

Amino Acid Sequence↗
PubMed1997

Antibodies in the sera of acute rheumatic fever patients bind to human cardiac tropomyosin.

Previous work from this laboratory has demonstrated the occurrence of heart reactive antibodies (HRA) in the sera of acute rheumatic fever (ARF) patients which bound primarily to the sarcolemmal sheath of cardiac myofibres. While many investigators have reported the presence of antibodies to myosin in the sera of ARF patients, the question of whether these sera also contain antibodies to other cytoskeletal proteins has not been addressed. In this study, crude human sarcolemmal sheaths were extracted with 3 M KCl and partially purified using a DEAE cellulose column and a step gradient of NaCl. Maximum reactivity with ARF sera was seen with a protein fraction eluted with 0.3 M NaCl. Using FPLC, a single polypeptide of 38 kDa reacted in ELISA preferentially with ARF sera when compared to sera from patients with uncomplicated streptococcal infections and acute post-streptococcal glomerulonephritis (APSGN). A comparison of the N-terminal sequence of the purified protein and competitive inhibition assays indicated that the reactive sarcolemmal antigen was human cardiac tropomyosin.

Amino Acid Sequence↗
PubMed1997

Identification and characterization of a new protein from Streptococcus pyogenes having homology with fibronectin and fibrinogen binding proteins.

Fibronectin and fibrinogen-binding proteins have been described as possible adhesin in streptococci and staphylococci. Recent published data has demonstrated that Protein F, a fibronectin-binding protein from group A streptococci, is important in adherence to respiratory cells (8). Other similar proteins already described (i.e. SOF, Sfb and SfbII) are able to competitively inhibit the binding of fibronectin to S. pyogenes (9,10,5). Similarly, clumping factor from S. aureus, is known to promote adherence to fibrinogen-coated surfaces (7). When the sequence from SFFBP-12 was compared against all the others fibronectin and fibrinogen-binding proteins described in streptococci and staphylococci (1-10), an identity at the amino acid level, ranging from 38 to 69% was found for the C region. For the repeated region (R), the identity ranged between 47 and 75%. Unlike all the other proteins already described in group A streptococci, the protein we describe here, SFFBP-12, shares a high degree homology (67-75%) with the fibronectin-binding protein B from S. dysgalactiae (6), as well as homology with the S. aureus clumping factor (7) and fibronectin-binding protein B (3), making it a new potential fibronectin-fibrinogen binding protein for group A streptococci. These characteristics would also imply that SFFBP-12 contains two different fibronectin-binding domains (regions B and C), thus enhancing its role as a possible major adhesin molecule. RNA transcription assays showed a transcript with the expected molecular size for the intact SFFBP-12 protein, confirming that the protein is actively expressed during bacterial growth. SFFBP-12 is the largest protein of its kind identified from group A streptococci and is comparable in size to the fibronectin binding protein B from S. dysgalactiae (6). If it is shown that SFFBP-12 does in fact bind both fibronectin and fibrinogen, as the sequence data suggest, it would make this molecule a major virulence determinant for the group A streptococcus.

Adhesins, Bacterial↗
PubMed1997

Group A and group B streptococcal vaccine development. A round table presentation.

The data presented above provide a broad overview of ongoing work to develop vaccines against group A and group B streptococcal infections. The encouraging results of human trials with conjugate group B polysaccharide vaccines suggest that this approach will lead to a safe and effective method for preventing these devastating infections in newborn infants. The results of preclinical studies of the various strategies to develop group A streptococcal vaccines are also encouraging. Whether one approach will be more advantageous or efficacious than another will need to await clinical trials. Nevertheless, we predict that in the next decade we will make significant strides in preventing streptococcal infections and their complications.

Adhesins, Bacterial↗
PubMed1997

Immunoglobulins inhibit adherence and internalization of Streptococcus pyogenes to human pharyngeal cells.

Purified human sIgA against group A streptococci inhibited streptococcal adherence to pharyngeal cells whereas rabbit serum raised against the whole M+ strain did not. Of note, inhibition of adherence by sIgA occurred despite a much lower immunreactivity against the M6 protein as compared to the hyperimmune serum against the whole M+ strain. The M protein does probably not mediate the adherence of group A streptococci to respiratory cells, as shown by previous studies. However, since the isogenic M- derivative was less invasive to human pharyngeal cells than the M+ strain, our invasion experiments suggest that the M protein may play a role in internalization of group A streptococci into eukaryotic cells. More importantly, internalization and not adherence could be blocked by rabbit serum immunized with recombinant M6 protein.

Animals↗
PubMed1997

Cell wall anchoring of the Streptococcus pyogenes M6 protein in various lactic acid bacteria.

The M6 protein from Streptococcus pyogenes is the best-characterized member of a family of cell envelope-associated proteins. Based on the observation that the C-terminal sorting signals of these proteins can drive cell wall anchoring of heterologous unanchored proteins, we have cloned and expressed the emm6 structural gene for the M6 protein in various lactic acid bacteria (LAB). The emm6 gene was successfully expressed from lactococcal promoters in several Lactococcus lactis strains, an animal-colonizing Lactobacillus fermentum strain, Lactobacillus sake, and Streptococcus salivarius subsp. thermophilus. The M6 protein was efficiently anchored to the cell wall in all strains tested. In lactobacilli, essentially all detectable M6 protein was cell wall associated. These results suggest the feasibility of using the C-terminal anchor moiety of M6 for protein surface display in LAB.

Antigens, Bacterial↗