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

Abstract

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, antigenicaily, 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.

Isolation and molecular characterization of a novel albumin-binding protein from group G streptococci

“…Thus, both the DG12 protein and protein G bound strongly to albumin from humans, rats, mice, guinea pigs, horses, and dogs. However, previous experiments with whole bacteria have demonstrated that bovine group G streptococci, contrary to human isolates, also bind albumin from cows, goats, and rabbits (23,38). This suggests that the specificity of the protein expressed by bovine strains is different from that of protein G. We did not detect binding of these albumins to the purified DG12 protein.…”

“…We did not detect binding of the purified and labeled DG12 protein to bovine serum albumin. In contrast, other authors have reported binding of radiolabeled BSA to group G streptococci (23,38). No binding was seen to IgG from any of the tested species (humans, rabbits, mice, rats, cats, dogs, guinea pigs, goats, cows, horses, or sheep).…”

“…Isolation of the albumin-binding protein of strain DG12. Albumin-binding polypeptides have been isolated from bovine group G streptococci by using various heat extraction methods (23,37). However, these molecules showed considerable size heterogeneity.…”

Binding of native alpha 2-macroglobulin to human group G streptococci

“…However, proteins structurally related to M proteins, the principal virulence factors of group A streptococci (19), have been identified in group G streptococcal strains (5,14). Human group G streptococci also express receptors for plasma proteins like immunoglobulin G (IgG) (7), albumin (35,40), fibronectin (29), plasminogen (49), and ␣ 2macroglobulin (␣ 2 M) (31,32). Among these, the IgG-binding protein, protein G (PG), has been extensively studied because of its practical value for immunochemical applications (9,18).…”

Distinct Immunologic Properties of Soluble Versus Particulate Antigens

“…Thus, glycation alters the conformation and function of albumin ( 42 ). Albumin also binds various serum ligands ( 43 ) and interacts with a variety of host cells ( 44 ) and some bacterial pathogens ( 45 – 47 ). Bacteria can also bind albumin indirectly such as specific binding to heme that contains bound albumin ( 48 ).…”