Mechanistic target of rapamycin kinase (mTOR) FKBP12-rapamycin binding (FRB) domain (mTOR FRB domain)

The FKBP12-rapamycin binding (FRB) domain is a specialized structural motif within the mechanistic target of rapamycin (mTOR) kinase, a master regulator of cellular growth and metabolism [1.1.1, 1.2.2]. This domain is the specific target of the natural product rapamycin (sirolimus) and its synthetic analogs, known as rapalogs [1.3.1, 1.6.1]. Upon entering the cell, rapamycin first binds to the immunophilin FKBP12; this binary complex then docks onto the FRB domain of mTOR, specifically within the mTOR Complex 1 (mTORC1) [1.1.1, 1.3.3]. This interaction allosterically inhibits the kinase activity of mTORC1 by sterically blocking the recruitment of downstream substrates like S6K1 and 4E-BP1, thereby suppressing protein synthesis and cell proliferation [1.3.1, 1.5.3]. Beyond its role as a drug target, the FRB domain also functions as a sensor for phosphatidic acid, which competes with rapamycin for binding and promotes mTORC1 activation [1.2.2, 1.5.3]. Clinically, drugs targeting the FRB domain are utilized as immunosuppressants and in the treatment of various malignancies and genetic disorders like tuberous sclerosis, though their efficacy can be hampered by incomplete inhibition of mTORC1 and the activation of compensatory survival pathways [1.3.2, 1.6.1].

Other names

FKBP12-rapamycin binding domainFRB domainRapamycin-binding domain of mTORFKBP-rapamycin binding domainRAFT1 domainFRAP domain

Allosteric inhibition of mTORC1 via formation of a ternary complex with FKBP12 and rapamycin/rapalogs, which sterically blocks substrate recruitment to the kinase active site.