Immunosuppressor role of staphylococcal protein A

The removal of protein A from the surface of staphylococci by means of proteolytic enzymes increases the immunogenic properties of staphylococci. Staphylococci containing protein A are less effective in mediating the immunological memory than those treated with proteolytic enzymes. The conjugation of protein A with staphylococci treated with proteolytic enzymes leads to the decrease of the immunogenic properties of staphylococci. Protein A not bound to staphylococci also suppresses antistaphylococcal immune response. The protective properties of corpuscular staphylococcal antigen are increased after the removal of protein A from the surface of staphylococci by proteolysis.     

Differential IgG-binding characteristics of staphylococcal protein A, streptococcal protein G, and a chimeric protein AG

Various Gram-positive bacteria express different types of IgG-binding receptors, each of which displaying certain unique binding properties. To evaluate specificity and avidity aspects of the differential binding pattern, a set of competitive binding assays was employed, by using staphylococcal protein A (SPA), streptococcal protein G (SPG), and a chimeric protein AG. These receptors were analyzed, in a reciprocal fashion, for binding and inhibition of binding to a selected panel of polyclonal and monoclonal Ig. Results of the study reveal that a majority of the determinants on human and bovine IgG, recognized by SPA and SPG, are either coextensive or closely overlapping. Accordingly, a minor portion of the determinants appear to be unique in the sense that a particular determinant(s) is selectively identified by one of the two receptors. Binding assays involving purified Fc fragments from human IgG, suggest that SPG shows exclusive specificity for an Fab region determinant(s) not recognized by SPA, whereas the Fc determinants for SPA and SPG are identical or overlapping. Furthermore, one of the IgG subclasses of bovine origin appears to be seen by the SPG receptor only. The competition study also demonstrates that the novel chimeric protein AG receptor shows higher or equal avidity for variants of human IgG molecules compared to the best of its parental constituents. It can thus be deduced that chimeric receptors might be useful as optimized tools for immunologic applications.     

Sorting of protein A to the staphylococcal cell wall.

The cell wall of gram-positive bacteria can be thought of as representing a unique cell compartment, which contains anchored surface proteins that require specific sorting signals. Some biologically important products are anchored in this way, including protein A and fibronectin binding protein of Staphylococcus aureus and streptococcal M protein. Studies of staphylococcal protein A and Escherichia coli alkaline phosphatase show that the signal both necessary and sufficient for cell wall anchoring consists of an LPXTGX motif, a C-terminal hydrophobic domain, and a charged tail. These sequence elements are conserved in many surface proteins from different gram-positive bacteria. We propose the existence of a hitherto undescribed sorting mechanism that positions proteins on the surface of gram-positive bacteria.     

Biochemical and genetic heterogeneity of staphylococcal protein A

Abstract We investigated the biochemical and genetic heterogeneity of protein A from Staphylococcus aureus . SpA genes ( spas ) of various strains were heterogeneous when detected as Dra I and Eco RV fragments of chromosomal DNA. Polymerase chain reaction using primers to detect DNA encoding the IgG-binding domains in spa revealed that they numbered between 2 and 5. Protein A from several S. aureus strains showed two types of reactivities to immunoglobulins in normal canine serum according to the number of active domains.     

A structurally novel staphylococcal protein A from the V8 strain

Protein A from the Staphylococcus aureus strain V8 has a molecular mass about 8000 Da less than that of known proteins A. The corresponding gene was cloned and expressed in Escherichia coli. Sequence analysis of this structurally new protein A revealed that it lacked an IgG-binding domain (58 amino acids), and that it also lacked two octapeptide repetitions located in the membrane/wall attaching region. Contrary to what had been proposed previously, the first translated amino acid is probably not a leucine, but very likely a methionine located 12 residues upstream.     

A synthetic IgG-binding domain based on staphylococcal protein A

A synthetic IgG-binding domain based on staphylococcal protein A was designed with the aid of sequence comparisons and computer graphic analysis. A strategy, utilizing non-palindromic restriction sites, was used to overcome the difficulties of introducing site-specific changes into the repetitive gene. A single mutagenized gene fragment was polymerized to different multiplicities, and the different gene products were expressed in Escherichia coli. Using this scheme, protein A-like proteins composed of different numbers of IgG-binding domains were produced. These domains were changed to lack asparagine--glycine dipeptide sequences as well as methionine residues and are thus, in contrast to native protein A, resistant to treatment with hydroxylamine and cyanogen bromide.     

Serologic and immunogenic properties of staphylococcal protein A]

Protein antigen A was isolated from the microbial cells of Cowan I strain of Staphylococcus aureus by hot extraction method. Ion exchange chromatography on DEAE-cellulose-32 and gel-filtration on sephadex F-100 were used for purification of protein A. Microprecipitation in agar test against homologous immune rabbit serum and normal human serum showed purified protein A to be identical by serological specificity to the standard preparation obtained from Prof. Oeding's laboratory. In order to assess the immunogenic properties of protein A by various doses of the preparation (from 2 to 1000 microgram) mixed with A1 (OH)3 albino mice were immunized and then infected with the microbial culture of the homologous strain. As revealed, protein A not only failed to protect the animals from death, but even aggravated the course of infection.     

Gene fusion vectors based on the gene for staphylococcal protein A

Two plasmid vectors, containing the gene coding for staphylococcal protein A and adapted for gene fusion, have been constructed. These vectors will allow fusion of any gene to the protein A gene, thus giving hybrid proteins which can be purified, in a one-step procedure, by IgG affinity chromatography. As an example of the practical use of such vectors, the protein A gene has been fused to the lacZ gene of Escherichia coli. E. coli strains containing such plasmids produce hybrid proteins with both IgG binding and β-galactosidase activities. The hybrid protein(s) can be immobilized on IgG-Sepharose by its protein A moiety with high efficiency without losing its enzymatic activity and they can be eluted from the column by competitive elution with pure protein A. The fused protein(s) also binds to IgG-coated microtiter wells which means that the in vivo product can be used as an enzyme conjugate in ELISA tests.     

Experience in studying protein A in staphylococcal cultures]

Methods of quantitative and qualitative determination of protein A in staphylococcus cultures were studied comparatively. The maximal number of strains positive by protein A were revealed by means of indirect hemagglutination test with cell extracts. Quantitative and qualitative characteristics by protein A can be used in studying the problems of strain and clone heterogeneity of S. aureus. A common antigen was revealed in the reactions with human gamma-globulin in 21 of 38 S. aureus strains, and in 1 of 11 S. epidermidis strains; the presence of this antigen failed to correlate with the quantitative protein A content in the same strains.     

Interactions between staphylococcal protein A and immunoglobulin domains.

The affinity and stoichiometry of interaction between staphylococcal protein A and different domains of immunoglobulins have been studied. Light scattering and tryptophan fluorescence quenching titrations along with direct binding assays were performed. The lack of binding to protein A of pFc′ fragment (corresponding to C_H3 domain of IgG) or of Facb derivative of rabbit IgG (which is devoid of the C_H3) suggests that the locus of protein A binding is at the interface between the C_H2 and C_H3 domains. This assignment is also supported by results of the tryptophan fluorescence quenching and C$\text{1}$ binding experiments.     

Chimeric IgG-binding receptors engineered from staphylococcal protein A and streptococcal protein G

Chimeric Fc receptors, consisting of the IgG-binding domains of both staphylococcal protein A and streptococcal protein G, were constructed. An efficient bacterial expression system was used to produce the recombinant proteins, which vary in size and number of IgG-binding domains. The purified receptors were analyzed by immunodiffusion and a competitive enzyme-linked immunosorbent assay to establish the relative binding strength to various polyclonal and monoclonal immunoglobulins from different species. The results demonstrate that protein A and protein G have complementary binding patterns and that the chimeric receptors retain the binding capacities of both the parental constituents. This suggests that these novel chimeric receptors might be versatile reagents for immunochemical assays.     

Interaction between heat shock protein DnaK and recombinant staphylococcal protein A.

When a protein derived from the immunoglobulin G (IgG)-binding domains of staphylococcal protein A was expressed in Escherichia coli and recovered from cell extract by IgG affinity chromatography, the 69-kilodalton heat shock protein DnaK was found to be copurified. DnaK could be selectively eluted from the IgG column by ATP or by lowering the pH to 4.7. Protein A could subsequently be eluted by lowering the pH to 3.2. Thus, this procedure allows a one-step purification of both DnaK and protein A from cell extract. In vitro experiments with pure DnaK and protein A revealed that DnaK did not interfere with the IgG-binding properties of protein A but associated with its unfolded C-terminal in a salt-resistant manner. In addition, a specific interaction between DnaK and denaturated casein was found.     

Analysis of signals for secretion in the staphylococcal protein A gene.

Different constructs of the gene encoding staphylococcal protein A were introduced in Staphylococcus aureus and S. xylosus as well as Escherichia coli. The product of the gene without the cell wall anchoring domain was efficiently secreted in all three hosts. N-terminal sequencing of the affinity-purified mature protein revealed a common processing site after the alanine residue at position 36. In contrast, when an internal IgG-binding fragment of protein A (region B) was inserted after the protein A signal sequence, the product was poorly secreted and N-terminal sequencing revealed no processing at the normal site. This demonstrates that the structure of the polypeptide chain beyond the signal peptide cleavage site can affect cleavage. Another construct, containing the N-terminal IgG-binding part of the mature protein A (region E) followed by region B, gave correct processing and efficient secretion. Unexpectedly, the gene product, EB, was not only secreted and correctly processed, but was also excreted to the culture medium of E. coli. Secretion vectors containing the protein A signal sequence were constructed to facilitate secretion of foreign gene products. Insertion of the E. coli gene phoA, lacking its own promoter and signal sequence, led to efficient secretion of alkaline phosphatase both in E. coli and S. aureus.     

Heterogencity of human polyclonal IgE reacting with staphylococcal protein A

A small part of polyclonal IgE (6 %) was bound to protein A-Sepharose from the serum of M.P., containing a high concentration of IgE. No monoclonal IgE isolated from the serum of V.L. was bound to this sorbent. This binding of polyclonal IgE appears to be heterogeneous since a multiphasic pattern was observed with discontinuous pH gradient elution from protein A-Sepharose. Also, like IgE from the whole serum, monomeric IgE isolated from the serum of M.P. on Sepharose 6B showed this binding heterogeneity. It is suggested that IgE molecules with different affinities for protein A could belong to different isotypic or allotypic variants.