TORC1 organized in inhibited domains (TOROIDs) regulate TORC1 activity.

Abstract

The Target of Rapamycin (TOR) is a eukaryotic serine/threonine protein kinase that functions in two distinct complexes, TORC1 and TORC2, to regulate growth and metabolism1,2. GTPases, responding to signals generated by abiotic stressors, nutrients, and, in metazoans, growth factors, play an important3, but poorly understood role in TORC1 regulation. Here, we report that, in budding yeast, glucose withdrawal, which leads to an acute loss of TORC1 kinase activity4, triggers a similarly rapid Rag GTPase-dependent redistribution of TORC1 from being semi-uniform around the vacuolar membrane to a single, vacuole-associated cylindrical structure visible by super-resolution optical microscopy. 3D reconstructions of cryo-electron micrograph images of these purified cylinders demonstrate that TORC1 oligomerizes into a higher-level hollow helical assembly which we name a TOROID (TORC1 Organised in Inhibited Domain). Fitting of the recently described mammalian TORC1 structure into our helical map revealed that oligomerisation leads to steric occlusion of the active site. Guided by the implications from our reconstruction, we present a TOR1 allele that prevents both TOROID formation and TORC1 inactivation in response to glucose withdrawal demonstrating that oligomerisation is necessary for TORC1 inactivation. Our results reveal a novel mechanism by which Rag-GTPases regulate TORC1 activity and suggest that the reversible assembly/disassembly of higher-level structure may be a new paradigm for the regulation of protein kinases.