Abstract
Human β2-microglobulin (β2-m) was isolated from urine samples of patients with tubular dysfunctions and aggregated with glutaraldehyde. Four aggregates with molecular weights of 800, 000, 480, 000, 260, 000, and 60, 000 were separated by filtration on Sephacryl S-300. The aggregates and monomeric β2-m (11, 800MW) were subsequently labeled with 125I and tested for binding to streptococci. Group A streptococci bound only aggregated β2-m with a mean binding of 44.5%. Most of the group G streptococci, on the other hand, bound only monomeric β2-m with a mean binding of 58%. Among group B streptococci the serotypes with protein antigens interacted mainly with monomeric β2-m and those without protein antigens preferentially with aggregated β2-m. Nontypable group B streptococcal serotypes did not bind monomeric or aggregated β2-m. Of the streptococci belonging to group C, S. equisimilis reacted with monomeric β2-m and S. dysgalactiae with aggregated β2-m. S. equi did not interact with monomeric β2-m or aggregated β2-m. Bindings of monomeric β2-m and aggregated β2-m were saturable and could be inhibited by the respective unlabeled forms of β2-m. Fibrinogen, fibronectin, α2-macroglobulin, haptoglobin, or immunoglobulin G did not inhibit the binding of either form of β2-m. The binding sites for monomeric β2-m were more susceptible to trypsin than those for aggregated β2-m. Treatment of streptococci with pronase destroyed their binding activities for monomeric and aggregated β2-m. Both monomeric β2-m and aggregated β2-m binding sites were sensitive to heat. The Scatchard plots of monomeric β2-m and aggregated β2-m were linear with Kd of 1.29×10-9M and 1.9×10-9M respectively. The number of binding sites per bacterium were estimated to be 81, 000 for monomeric β2-m and 1, 210 for aggregated β2-m.