FK506 and rapamycin are immunosuppressants that inhibit signalling cascades required for T-cell activation, yet both are natural products of that live in the soil. FK506 and rapamycin also have potent antimicrobial activity against yeast and pathogenic fungi, suggesting a natural role in inhibiting growth of competing micro-organisms. The immunosuppressive and antimicrobial activities of FK506 and rapamycin are mediated by binding to the FKBP12 prolyl isomerase and the resulting FKBP12/FK506 and FKBP12/rapamycin complexes inhibit conserved protein targets, either the phosphatase calcineurin or the TOR (target of rapamycin) kinases, respectively. sp., ‘ subsp. ’ and , which produce FK506, FK520 (also known as ascomycin, a C21 ethyl derivative of FK506) and rapamycin, respectively, produced toxins that inhibited the growth of competing cells of the yeast and the pathogenic fungus Yeast and fungal mutants lacking FKBP12 or expressing dominant drug-resistant calcineurin or TOR mutants were resistant to FK506 and rapamycin, and to the toxins produced by strains with mutations in the FK506 or rapamycin biosynthetic enzymes were impaired in toxin production. Finally, the toxins secreted by ‘ subsp. ’ and promoted formation of FKBP12/calcineurin and FKBP12/TOR complexes in a two-hybrid assay and mutations that rendered calcineurin or TOR drug-resistant prevented interaction. These observations support the hypothesis that evolved to secrete FK506, FK520 and rapamycin as toxins to inhibit the growth of competing yeast and fungi.


Article metrics loading...

Loading full text...

Full text loading...


Most cited this month Most Cited RSS feed

This is a required field
Please enter a valid email address
Approval was a Success
Invalid data
An Error Occurred
Approval was partially successful, following selected items could not be processed due to error