Structural and Mechanistic Insights into the Yeast TORC1-Body

Abstract

The Target of Rapamycin Complex 1 (TORC1) is a critical coordinator of eukaryotic growth. A large amount of work has been done to uncover the specific mechanisms of TORC1 regulation across eukaryotes. In the baker’s yeast Saccharomyces cerevisiae, the key conserved regulators known as SEAC (GATOR in humans) and small GTPases Gtr1/2 (RagA/C in humans) report sufficiency of nutrients such as nitrogen, amino acids, and glucose to TORC1. While some of the crucial TORC1 regulators are highly-conserved between yeast and mammals, there remain many key regulatory steps that have diverged significantly, or have not yet been uncovered, in yeasts. Due to the desire to create a unified model of TORC1 signaling across eukaryotes, it is then highly valuable to learn more about how TORC1 is regulated in organisms missing such components. Here, I will describe two studies that begin to uncover some of the previously unknown regulatory mechanisms of TORC1 signaling in yeast. The first study addresses the formation of a TORC1-body, an aggregate comprised of TORC1-components that forms in response to nutrient starvation, and the specific biochemical pathways involved in their formation. Here we discover a large network of proteins implicated in TORC1 regulation and describe a novel TORC1 regulator, Pib2. Next, to address how TORC1 interacts with other proteins in its regulatory network, we developed methods to purify TORC1 covalently bound to all nearby proteins and assessed their influence on TORC1-body formation. In this study we assemble a TORC1 interactome to begin to analyze the dynamics in protein-protein interaction with TORC1 in various stress/starvation states. In doing so, we identify and characterize an unstudied protein, Ait1, that regulates TORC1 in organisms missing critical regulatory components identified in mammals.