Isolation and partial characterization of a type II Fc receptor from a group A streptococcus

Quantitative investigation of the affinity properties of different recombinant forms of protein G by means of high-performance monolithic chromatography

The recombinantly produced different forms of protein G, namely monofunctional immunoglobulin G (IgG) binding, monofunctional serum albumin (SA) binding and bifunctional IgG/SA binding proteins G, are compared with respect to their specific affinities to blood IgG and SA. The affinity mode of the recently developed high-performance monolithic disk chromatography has been used for fast quantitative investigations. Using single affinity disks as well as two discs stacked into one separation unit, one order of magnitude in adsorption capacities for IgG and SA were found both for monofunctional and bifunctional protein G forms used as specific affinity ligands. However, despite the adsorption difference observed, the measured dissociation constants of the affinity complexes seemed to be very close. The analytical procedure developed can be realized within a couple of minutes. Up-scaling of the developed technology was carried out using another type of monolithic materials, i.e. CIM affinity tubes.

Nonimmune interaction of the SfbI protein of Streptococcus pyogenes with the immunoglobulin G F(ab')(2) fragment

Fibronectin-binding protein I (SfbI) of Streptococcus pyogenes binds to mouse immunoglobulin G (IgG) but not to IgA or IgM in a nonimmune fashion. The fibronectin-binding domains of SfbI were responsible for this activity, which was targeted to the IgG F(ab')(2) fragment. SfbI also binds to B cells but not to CD4(+) or CD8(+) lymphocytes.

Purification and characterization of a 52-kilodalton immunoglobulin G-binding protein from Streptococcus suis capsular type 2

We previously reported that group D streptococci exhibited immunoglobulin G (IgG)-binding activity and that a 52-kDa IgG-binding protein was present in all Streptococcus suis strains examined (B. Serhir, R. Higgins, B. Foiry, and M. Jacques, J. Gen. Microbiol. 139:2953-2958, 1993). The objective of the present study was to purify and characterize this protein. Pig IgG were immobilized through their Fab fragments to ECH-Sepharose 4B, and the protein was purified by affinity chromatography. Electron microscopy observations of the purified material showed filamentous structures with a diameter of approximately 4 nm; these structures were not observed when the material was treated with either urea or ethanolamine. Electrophoretic and Western immunoblot analyses showed that the 52-kDa protein constituted the bulk of the recovered material. This protein was stained with either Coomassie brilliant blue or silver nitrate; it reacted with a large variety of mammalian IgG, human IgG (Fc) fragments, human IgA, and other human plasma proteins. The 52-kDa protein exhibited lower IgG-binding affinities than protein A and protein G. However, it was able to compete with protein A and protein G for binding to human IgG. In addition, it bound chicken IgG with high affinity. This last property differentiated the 52-kDa protein of S. suis from the six IgG-binding proteins described to date. The 52-kDa protein displayed similar affinities for untreated and deglycosylated pig IgG. The N-terminal amino acid sequence (SIITDVYAXEVLDSXGNPTLEV) revealed no homology with any bacterial proteins in the Swiss-Prot database. Its isoelectric point of approximately 4.6 and its amino acid composition, rich in aspartic and glutamic acids, showed that it had some similarities with other IgG-binding proteins. In this report, we have purified and characterized a 52-kDa IgG-binding protein from S. suis capsular type 2. Although this protein shares some similarities with other IgG- and/or IgA-binding proteins, it is unique in reacting with chicken IgG.

Analysis of the interaction of group A streptococci with fibrinogen, streptokinase and plasminogen

Group A streptococci demonstrate a number of distinct ways to interact with the human fibrinolytic system to acquire unregulatable cell-surface enzymatic activity. Interactions between bacteria, fibrinogen, streptokinase and plasminogen resulted in acquisition of cell-associated enzymatic activity that can lyse fibrin clots despite the presence of the major physiological plasmin inhibitor, alpha 2-antiplasmin. Western blot analysis of extracted streptococcal surface proteins suggested that binding of fibrinogen to M or M-related proteins mediated the capture of streptokinase-plasminogen complexes to the bacteria. The enzymatic complex formed by reaction of bacteria with fibrinogen, streptokinase and plasminogen was found to be more stable in human plasma than pre-formed plasmin bound directly to the same bacteria strain.

Association of type II immunoglobulin G-binding protein expression and survival of group A streptococci in human blood

Expression of immunoglobulin G (IgG)-binding proteins on group A streptococcus strain 64 was monitored on bacteria subjected to sequential passage in human blood. After approximately 10 cycles through human blood, strain 64 demonstrated enhanced levels of IgG-binding protein, including the expression of a type IIa binding molecule with an M(r) of approximately 47,000 present only at very low levels on the parent isolate. Changes in the expression of IgG-binding proteins after passage in human blood were similar to those observed when the same organism was passaged sequentially intraperitoneally in mice. Strain 64, passaged in human blood 23 times, was found to be more virulent than the parent isolate when used to infect mice either intraperitoneally or in a skin air sac. These findings suggest that the expression of IgG-binding proteins may be a common response of group A organisms to pressures exerted by distinct host defense mechanisms.

Association between expression of immunoglobulin G-binding proteins by group A streptococci and virulence in a mouse skin infection model

In this study, we developed a mouse model of skin infection to test the association between expression of immunoglobulin-binding proteins by and infectivity of group A streptococci. Group A streptococci capable of crossing tissue barriers and establishing a lethal systemic infection in mice showed a higher level of immunoglobulin-binding protein expression. The group A streptococci recovered from the spleen of a mouse that died following a skin infection were found to be more virulent when injected into the skin of naive mice. Together, these results suggest that immunoglobulin-binding protein expression by group A streptococci correlates with their ability to establish invasive skin infections.

Isolation and partial characterization of a type IV bacterial immunoglobulin binding protein

A series of bovine G streptococcal isolates were screened for expression of type IV Fc binding proteins. An isolate expressing high levels of type IV binding proteins was selected and expanded by use of a colony selection technique. A variety of different extraction procedures were compared and the optimal solubilization procedure was found to be hot acid extraction of the bacteria. The extracted protein could be affinity purified on a column of immobilized rabbit IgG. The type IV Fc binding protein was found to be antigenically unrelated to the type I, II or III bacterial Fc binding proteins and displayed the lowest affinity and most limited range of species and subclass reactivity of any bacterial Fc binding protein thus far characterized.

Comparison of albumin receptors expressed on bovine and human group G streptococci

The albumin receptor expressed by bovine group G streptococci was extracted and affinity purified. The protein was characterized for species reactivity, and monospecific antibodies were prepared to the purified receptor. The bovine group G albumin receptor was compared functionally, antigenically, and for DNA homology with the albumin-binding protein expressed by human group G streptococci. In agreement with previous reports, the albumin-binding activity of human strains was mediated by a unique domain of the type III immunoglobulin G-Fc-binding molecule, protein G. The albumin receptor expressed by bovine group G strains was found to lack any immunoglobulin G-binding potential but displayed a wider profile of species albumin reactivity than protein G. Both albumin receptors could inhibit the binding of the other to immobilized human serum albumin, and each displayed similar binding properties. Antigenic comparison of the two albumin receptors demonstrated a low level of cross-reactivity; however comparison at the DNA level, using an oligonucleotide probe specific for the albumin-binding region of protein G, demonstrated that the two albumin receptors expressed by human and bovine group G streptococcal strains do not display significant homology.

Protein D, an immunoglobulin D-binding protein of Haemophilus influenzae: cloning, nucleotide sequence, and expression in Escherichia coli

The gene for protein D, a membrane-associated protein with specific affinity for human immunoglobulin D, was cloned from a nontypeable strain of Haemophilus influenzae. The gene was expressed in Escherichia coli from an endogenous promoter, and the gene product has an apparent molecular weight equal to that of H. influenzae protein D (42,000). The complete nucleotide sequence of the gene for protein D was determined, and the deduced amino acid sequence of 364 residues includes a putative signal sequence of 18 amino acids containing a consensus sequence, Leu-Ala-Gly-Cys, for bacterial lipoproteins. The sequence of protein D shows no similarity to those of other immunoglobulin-binding proteins. Protein D is the first example of immunoglobulin receptors from gram-negative bacteria that has been cloned and sequenced.

Colloidal gold immunolabeling of immunoglobulin-binding sites and beta antigen in group B streptococci

We have characterized the immunoglobulin A (IgA)-Fc-binding properties and beta-antigen expression of several strains of group B streptococci by using ultrastructural immunocytochemistry. Colloidal gold-labeled tracers were used with intact and sectioned bacteria in order to gain information regarding the location and distribution of cell surface and cytoplasmic IgA-Fc-binding molecules and beta antigen. Colloidal gold (5- or 15-nm particles) was conjugated to IgA to characterize IgA-binding properties and to IgG to test for IgG binding. Rabbit anti-beta antiserum was reacted with the bacteria and then with protein G labeled with 15-nm colloidal gold particles. A double-labeling technique was used for simultaneous localization of IgA-Fc- and anti-beta-antibody-binding properties on sectioned bacteria. The data corroborated previous results which indicated that (i) IgA-Fc-binding and IgA-Fc-nonbinding forms of beta antigen can be secreted by strains which do not express beta antigen on the cell surfaces (HG806, VC75); (ii) differences in levels of expression of beta antigen and/or IgA-Fc-binding proteins can be detected among various group B isolates; (iii) group B streptococci do not express human IgG-Fc-binding proteins; and (iv) not all forms of beta antigen are capable of binding human IgA.

Interaction of type II IgG Fc-receptors from streptococci of serological group A with murine IgG

A group A streptococcal strain demonstrated binding activities for 125I-murine IgG3 and 125I-human IgG. This 125I-murine IgG3 binding could be inhibited by unlabelled equine IgG but not by IgG from cattle, chickens and dogs, indicating binding properties of IgG Fc-receptors of type II. In contrast to binding sites of Streptococcus dysgalactiae (serogroup C) carrying type III IgG Fc-receptors, the binding sites of the group A streptococcus appeared to be antigenically different, extremely sensitive to trypsin and did not show any cross reactions with human albumin. The group A and group C streptococcal binding sites could be solubilized by lysozyme treatment of the bacteria and subsequently isolated by affinity chromatography on human IgG-Sepharose. Further analysis of the group A and group C streptococcal binding proteins by SDS-PAGE and Western blotting revealed numerous, almost identical protein bands with binding activities for 125I-murine IgG3.

Mapping of the human plasmin domain recognized by the unique plasmin receptor of group A streptococci

A high-affinity surface receptor for human plasmin has been reported on certain group A streptococci. To map the region of the plasmin molecule that binds to the bacterial receptor, isolated domains of plasmin were tested for their ability to inhibit the binding of intact radiolabeled plasmin to receptor-positive bacteria. Complete inhibition of binding of labeled plasmin to bacteria by isolated heavy chains was achieved, but this inhibition was not as efficient on a molar basis when compared with that of unlabeled plasmin. By contrast, a conformationally altered form of native plasminogen was found to bind to bacteria and was as efficient a competitive inhibitor as intact plasmin was. The results of this study indicate that the selective binding of human plasmin to a group A streptococcus is dependent on structures present in the conformationally altered form of native plasminogen or plasmin that are not found on the native zymogen, the plasminogen with NH2-terminal glutamic acid.

Characterization of the interaction of human plasmin with its specific receptor on a group A streptococcus

Certain Group A beta-hemolytic streptococci express a receptor that is capable of specifically binding the human plasma protease plasmin. Once bound, plasmin remains enzymatically active and is unregulated by its naturally occurring inhibitor alpha-2-antiplasmin (Lottenberg, R., C. C. Broder and M. D. P. Boyle, 1987. Infect. Immun. 55: 1914-1918). In this study certain characteristics of the interaction between plasmin and the receptor expressed on a group A beta-hemolytic streptococcus, strain 64/14, were examined. Binding occurred optimally at physiologic pH and ionic strength. The KD was 5 x 10(-11) M and there were approximately 800 receptors per bacterium. Mouse passage of strain 64 had no significant effect on the KD of the receptor. Binding of plasmin to the bacteria was inhibited by lysine and epsilon-aminocaproic acid in a concentration dependent manner. Similarly these amino acids would displace pre-bound plasmin from the bacteria. These findings suggest a role for plasmin's high affinity lysine binding site in the interaction of plasmin with the bacteria.

Bindings of plasma proteins to streptococci of serological group L with special reference to their immunoglobulin G Fc-receptor activity

Of 33 streptococcal cultures belonging to serological group L, all bound human immunoglobulin (Ig) G, fibrinogen, and fibronectin; 32 bound bovine IgG; 31 bound alpha 2-macroglobulin; 5 bound albumin; and none bound either haptoglobin or IgA. The binding sites for IgG could be isolated from the L streptococci by trypsinization and purified by affinity chromatography on human IgG-Sepharose. The purified Fc receptors reacted with IgG subclasses 1, 2, 3, 4 of humans, 1 and 2 of bovines, ovines, and caprines as well as a, b, c, and T of equines. They had a molecular mass of approximately 49,000 Da. Thus, the Fc receptors from L streptococci corresponded to type III Fc receptors of Streptococcus dysgalactiae.

Structure and evolution of the repetitive gene encoding streptococcal protein G

The complete sequence of the structural gene encoding the immunoglobulin G binding protein from Streptococcus G148 has been determined, as well as its 5' and 3' flanking sequences. The sequence reveals an open reading frame encoding a putative preprotein with a relative molecular mass of 63294. N-Terminal sequencing of the mature protein, spontaneously released from streptococcal cells, demonstrates that the signal peptide consists of 33 amino acids. The DNA sequence reveals extensive internal homologies similar to other cell-wall-bound receptors from gram-positive bacteria. Comparisons with a related gene previously isolated from another strain of streptococci revealed large differences in size, due to variations in the number of internal repeats. The structure of the gene suggests an evolution through multiple duplications.

Identification of a specific receptor for plasmin on a group A streptococcus

Certain group A streptococci demonstrate surface receptors that bind selectively to the key fibrinolytic enzyme, plasmin. These bacteria show no reactivity with the zymogen protein plasminogen or with other serine class proteases, such as trypsin or urokinase. Bacterium-bound plasmin retains its ability to cleave synthetic substrates and its ability to hydrolyze a fibrin clot. The bacterium-bound plasmin is not effectively regulated by its physiological regulator, alpha 2-plasmin inhibitor. This study is the first report of a bacterium-associated receptor for plasmin.

Isolation and characterization of type IIa and type IIb Fc receptors from a group A streptococcus

Certain group A streptococcal strains have been reported to express two distinct type II receptors that bind to the Fc region of human IgG. In this study, we have isolated and characterized these two type II Fc receptors and characterized their reactivity with differing species of IgG. The type IIa receptor was found to be a 56,000 molecular weight protein which binds human IgG1, IgG2 and IgG4, in addition to pig and rabbit IgG. The type IIb receptor was found to be a 38,000 molecular weight protein that bound exclusively to human IgG3. Neither the type IIa nor the type IIb receptor bound to goat, cow, dog, rat, or sheep IgG. Monospecific polyclonal antibodies were prepared against both the type IIa and type IIb Fc receptors. These antibodies demonstrated that the type IIa and type IIb were antigenically closely related and could not be distinguished from each other on the basis of their reactivity with either antibody. The distribution of type IIa and type IIb Fc receptors on a variety of different nephritogenic and non-nephritogenic group A streptococcal strains was documented.

Comparison of type III Fc receptors associated with group C and group G streptococci

The type III Fc receptors present on or secreted by a series of group C and G streptococcal strains were studied. All strains capable of binding radiolabeled human IgG were shown to do so via an antigenically related Fc receptor. Treatment of any of the bacterial strains with papain or trypsin resulted in solubilization of Fc receptor activity. The pattern of Fc receptor activity recovered following enzyme treatment was not uniform. Differences were observed both between group C and G strains as well as within group C and G strains. Analysis of secreted Fc receptors indicated the presence of five molecular forms of Fc receptor. Each form was present at some level in the supernatant of every group C and G strain studied. The relative concn of each form of receptor secreted varied from strain to strain. The Fc receptor activity secreted by each strain demonstrated a similar affinity for the Fc region of human IgG and all were antigenically related. These results suggest that there is a family of closely related Fc receptors associated with group C and G streptococcal strains.