Resolution of Highly Purified Toxic-Shock Syndrome Toxin 1 into Two Distinct Proteins by Isoelectric Focusing

Highly purified toxic-shock syndrome toxin 1 (TSST-1) was prepared by differential precipitation with ethanol and resolubilization in water followed by successive electrofocusing in pH gradients of 3–10, 6–8, and 6.5-7.5. TSST-1, thus isolated, migrated as two distinct protein bands with isoelectric points of 7.08 (TSST-1a) and 7.22 (TSST-1b). When tested by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, both toxins migrated as homogeneous bands with molecular weights of 22 000. The gel bands were visualized by silver staining. The two toxins have nearly identical amino acid compositions and are immunologically identical as shown by Ouchterlony reactivity against TSST-1 hyperimmune serum. TSST-la and TSST-lb have the same biological activities as TSST-1: the capacity to induce fever, enhancement of host susceptibility to lethal endotoxin shock, nonspecific T lymphocyte mitogenicity, and suppression of immunoglobulin M synthesis against sheep erythrocytes. These two proteins have been isolated from several different TSS-associated Staphylococcus aureus strains. The data suggest that the differences in isoelectric point result either from the presence of a cofactor or from alternative conformations. Since only two bands appear, microheterogeneity as a result of deamination or acetylation is unlikely.