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A putative sirolimus (rapamycin) effector protein
Abstract:
Sirolimus (rapamycin), a new immunosuppressive drug, inhibits proliferation of a wide spectrum of T and B cells. The immunosuppressive mechanism of sirolimus is still unclear. We recently isolated a membrane associated protein with an apparent molecular weight of 210 kDa, p210, from cultured Molt 4 cells and BJAB cells and from normal human T cells using an affinity matrix method. The p210 binds to sirolimus:FKBP12 complex, but only at background levels to FKBP12 alone, to FK506:FKBP12 complex, or sirolimus-biotin alone. Among the sirolimus analogs tested, the binding ability of p210 to drug:FKBP12 complexes correlates with the immunosuppressive activity of the drugs, suggesting that p210 is the sirolimus effector protein.
Insights
Researchers identified a novel protein, p210, that binds to sirolimus (rapamycin) and its FKBP12 complex. This binding correlates with immunosuppressive activity, suggesting p210 is the sirolimus effector protein.
Area of Science:
- Immunology
- Molecular Biology
- Pharmacology
Background:
- Sirolimus (rapamycin) is an immunosuppressive drug that inhibits T and B cell proliferation.
- The precise immunosuppressive mechanism of sirolimus remains incompletely understood.
Purpose of the Study:
- To identify the sirolimus effector protein responsible for its immunosuppressive activity.
Main Methods:
- Isolation of a membrane-associated protein, p210, using affinity matrix methods from human T cells and cell lines (Molt 4, BJAB).
- Binding assays to assess the interaction of p210 with sirolimus:FKBP12 complex, FKBP12 alone, FK506:FKBP12 complex, and sirolimus-biotin.
Main Results:
- p210 specifically binds to the sirolimus:FKBP12 complex.
- Binding to FKBP12 alone, FK506:FKBP12 complex, or sirolimus-biotin was negligible.
- The binding affinity of p210 to various drug:FKBP12 complexes correlated directly with the known immunosuppressive potency of the respective sirolimus analogs.
Conclusions:
- The identified protein, p210, is a strong candidate for the sirolimus effector protein.
- These findings provide crucial insights into the molecular mechanism of sirolimus immunosuppression.