InterPro domain: IPR004083

This family consists of Raptor (regulatory associated protein of TOR) and its orthologs which includes Kog1p of Saccharomyces cerevisiae (Baker's yeast), a highly conserved 150kDa TOR-binding protein [ 1 , 2 , 3 ]. The target-of-rapamycin (TOR) proteins are protein kinases that were first identified in S. cerevisiae through mutants that conferred resistance to growth inhibition induced by the immunosuppressive macrolide rapamycin [ 4 ].

All Raptor orthologs contain a unique conserved region in their N-terminal half (raptor N-terminal conserved, also called the RNC domain) followed by three HEAT (huntingtin, elongation factor 3, A subunit of protein phosphatase 2A and TOR1) repeats and seven WD-40 repeats near the C terminus. Research on mammalian Raptor suggests that its association with mTOR promotes the phosphorylation of downstream effectors in nutrient-stimulated cells [ 5 , 5 ]. In concordance with these observations, the binding of TOR to Raptor or to Kog1p [ 5 ] is necessary for TOR signalling in vivo in Caenorhabditis elegans and S. cerevisiae [ 5 , 5 ].

The RNC domain consists of 3 blocks with at least 67 to 79% sequence similarity and is predicted to have a high propensity to form alpha helices. The RNC domain is characterised by the presence of invariant catalytic Cys-His dyad, which is structurally and evolutionarily related to known caspases, suggesting that the raptor proteins may have protease activity [ 5 ].

1. mTOR interacts with raptor to form a nutrient-sensitive complex that signals to the cell growth machinery. Cell 110, 163-75
2. Raptor, a binding partner of target of rapamycin (TOR), mediates TOR action. Cell 110, 177-89
3. Two TOR complexes, only one of which is rapamycin sensitive, have distinct roles in cell growth control. Mol. Cell 10, 457-68
4. Target of rapamycin in yeast, TOR2, is an essential phosphatidylinositol kinase homolog required for G1 progression. Cell 73, 585-96
5. Raptor protein contains a caspase-like domain. Trends Biochem. Sci. 29, 522-4