Mechanisms of amino-acid sensing by the GATOR complex

Kacper B. Rogala | NIGMS R35 MIRA-ESI (PAR-20-117) | Project Summary | October 3, 2022 The focus of this project is on the mechanisms of signal transduction by the large macromolecular supercomplex called GATOR, which is made of three individual sub-complexes with distinct roles: GATOR1, GATOR2, and KICSTOR. The GATOR supercomplex was previously shown to be responsible for receiving information from various cellular sensors, and then passing that information down to a large protein kinase called mTORC1, the role of which is to regulate cellular metabolism in response to the environment. One of the key signals that must be relayed to mTORC1 is availability of nutrients in the cell — amino acids and sugars. Monitoring how much of every individual nutrient the cell has at its disposal is critical for making rational decisions that will determine the future activities of the cell — whether it should grow when nutrients are available, or stand-by and maintain itself when nutrients are in short supply. This project will specifically focus on amino acids as signaling molecules. Our goal is to decipher the molecular chain of events that accompany changes in cellular concentration of three critical amino acids — leucine, arginine, and methionine. Indeed, out of twenty different amino acid types, only three of them are directly monitored by the mTORC1 pathway to inform cellular growth decisions. Each one of these amino acids also appears to signal to the GATOR complex — via three distinct mechanisms. Yet, despite extensive research in this field, we still know very little about how these mechanisms propagate amino-acid availability signals to either activate or deactivate mTORC1. Is the presence of leucine, arginine, and methionine equally important, or perhaps one amino acid dominates the rest? Are there any large conformational changes that accompany binding of amino-acid sensors to GATOR proteins? Does the composition and localization of the GATOR supercomplex change upon amino acid supplementation or withdrawal? We built this research project around three main themes that will begin answering these (and many more!) fascinating questions. In Theme #1, we will focus on the GATOR complex itself — in its apo form. Theme #2 will explore the mechanism of leucine and arginine signal transduction to GATOR2. And in Theme #3, we will attempt to decipher the enigmatic methionine-availability effects on GATOR1. Our ambition is to inspire deeper protein-mechanism-centered thinking in this field. And by providing novel protocols, protein complex structures, and a set of validated structure-guided mutants, we will lay the foundation that will enable new research directions, while also contributing to the development of therapeutics against devastating diseases of growth, such as cancer.