Surface receptors for serum albumin in group C and G streptococci show three different types of albumin specificity

Abstract

A total of 100 bacterial strains were tested for binding uptake of radiolabeled albumin preparations from 15 mammalian species. Three types of surface structures with specific binding sites for albumin were defined. A previously described receptor for albumin was separated into type a in Streptococcus equisimilis strains and in human group G streptococcal strains and type b in bovine group C streptococci. A new type of albumin receptor, type c, was found in Streptococcus dysgalactiae strains, the only receptor type so far with high affinity for bovine serum albumin. Type of albumin receptor correlated with bacterial species. The three receptor types showed high binding capacities; 2 X 10(8) bacterial organisms bound from 5 to 16 micrograms of albumin. All types of albumin receptors were stable to heat treatment at 80 degrees C for 5 min, but susceptible to both pepsin and trypsin treatment. Bacteria-bound albumin preparations were eluted at various concentrations of KSCN, reflecting differences in affinity. Up to 500 micrograms of human fibrinogen or polyclonal human immunoglobulin G had no inhibitory effect on the uptake of albumin, indicating a separate molecular localization of receptors for these proteins.

Binding of Aggregated Human Serum Albumin to M12 And Some Other Types of Group A Streptococci

“…These authors found group A streptococci to interact with murine serum albumin, and to a lesser degree with HSA. In contrast, various group C and G streptococci displayed a high binding of HSA as well as the albumin of a number of mammalian species (15,24,25). The present results suggest that aggregation of HSA may facilitate detection of reactivity with streptococci.…”

“…On the other hand, the finding that fibrinogen binds to most or all group A streptococci (2) indicates that M-protein epitopes both distinct from and identical with those binding a*HSA may bind fibrinogen. By contrast, in group C and G streptococci no common sites binding HSA and fibrinogen have been found (24). It is unknown at present whether the interaction with a*HSA may in some way be related to streptococcal pathogenicity.…”

“…IgG F(ab')2 or aggregated Fab and/or light chains can bind to intact bacteria (5,19). In addition, a number of interactions between hemolytic streptococci and serum proteins have been detected, including fibrinogen (8,12), P2-microglobulin ( 1 l), a2-macroglobulin (14), fibronectin (16, 22), albumin (15,24) and haptoglobin (9).…”

Further Studies on Immunoglobulin G‐ and Albumin‐Binding Properties of Streptococci of Serological Group L

“…In addition to IgG, some group C and G streptococci also have an affinity for albumin preparations of various origins (WIDEBACK and KRONVALL, 1982). According to and AKERSTROM et al (1987), protein G appears to be a bifunctional receptor molecule capable of binding to both IgG and serum albumin.…”

Isolation of a Specific Albumin Receptor From a Group G Streptococcal Strain

“…These interactions are mediated by binding structures on the bacterial surface. Albumin-specific surface receptors are found on group A, C and G streptococci (13,19,29,30,31). The receptors for albumin are sterically different from all other described receptors on streptococci, e.g., albumin binds to the bacterial cell independently of other proteins.…”