Interaction between FKBP12-rapamycin and TOR involves a conserved serine residue

Area of Science:

• Molecular Biology
• Biochemistry
• Immunology

Background:

• The yeast TOR1 and TOR2 proteins are targets of the immunosuppressive drug rapamycin.
• Their cellular function remains unknown, but they possess a conserved phosphatidylinositol (PI) kinase-related domain.
• A specific serine residue within this domain is linked to dominant rapamycin resistance.

Purpose of the Study:

• To investigate the physical interaction between FKBP12-rapamycin and TOR proteins.
• To determine if the conserved serine residue is critical for this interaction.
• To provide genetic evidence for the mechanism of rapamycin's action on TOR.

Main Methods:

• Utilized the yeast two-hybrid system for genetic interaction studies.
• Employed a small fragment of yeast TOR2, including the conserved serine residue.
• Tested interactions in the presence and absence of rapamycin and FK506.

Main Results:

• Provided genetic proof of a physical interaction between FKBP12-rapamycin and TOR.
• Demonstrated that this interaction is dependent on the conserved serine residue (Ser1975 in TOR2).
• Showed that a wild-type TOR2 fragment interacts with human FKBP12 in the presence of rapamycin, while a mutant (Arg1975) does not.

Conclusions:

• The conserved serine residue is essential for the physical interaction between TOR and the FKBP12-rapamycin complex.
• This interaction is rapamycin-dependent and can be antagonized by FK506.
• The findings offer genetic validation for the molecular mechanism of rapamycin's immunosuppressive effects via TOR signaling.