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Specific Binding Sites for Monomeric and Aggregated β 2 ‐Microglobulin on Surface of Groups A, B, C, and G Streptococci
Author(s) -
Chhatwal Gursharan S.,
Dutra Iveraldo S.,
Blobel Hans
Publication year - 1986
Publication title -
microbiology and immunology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.664
H-Index - 70
eISSN - 1348-0421
pISSN - 0385-5600
DOI - 10.1111/j.1348-0421.1986.tb00930.x
Subject(s) - monomer , biology , trypsin , beta 2 microglobulin , binding site , group a , biochemistry , microbiology and biotechnology , chemistry , immunology , enzyme , medicine , organic chemistry , polymer
Human β 2 ‐microglobulin (β 2 ‐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 β 2 ‐m (11,800 MW) were subsequently labeled with 125 I and tested for binding to streptococci. Group A streptococci bound only aggregated β 2 ‐m with a mean binding of 44.5%. Most of the group G streptococci, on the other hand, bound only monomeric β 2 ‐m with a mean binding of 58%. Among group B streptococci the serotypes with protein antigens interacted mainly with monomeric β 2 ‐m and those without protein antigens preferentially with aggregated β 2 ‐m. Nontypable group B streptococcal serotypes did not bind monomeric or aggegated β 2 ‐m. Of the streptococci belonging to group C, S. equisimilis reacted with monomeric β 2 ‐m and S. dysgalactiae with aggregated β 2 ‐m. S. equi did not interact with monomeric β 2 ‐m or aggregated β 2 ‐m. Bindings of monomeric β 2 ‐m and aggregated β 2 ‐m were saturable and could be inhibited by the respective unlabeled forms of β 2 ‐m. Fibrinogen, fibronectin, α 2 ‐macroglobulin, haptoglobin, or immunoglobulin G did not inhibit the binding of either form of β 2 ‐m. The binding sites for monomeric β 2 ‐m were more susceptible to trypsin than those for aggregated β 2 ‐m. Treatment of streptococci with pronase destroyed their binding activities for monomeric and aggregated β 2 ‐m. Both monomeric β 2 ‐m and aggregated β 2 ‐m binding sites were sensitive to heat. The Scatchard plots of monomeric β 2 ‐m and aggregated β 2 ‐m were linear with K d of 1.29 × 10 −9 M and >1.9 × 10 −9 M respectively. The number of binding sites per bacterium were estimated to be 81,000 for monomeric β 2 ‐m and 1,210 for aggregated β 2 ‐m.