Uncovering Ensemble Function Relationships of the Ancient Enzyme Glutamine Synthetase
Authors: Yuly Cruz, Dan Fournier, Emily Hernandez, Markus Tecson
Faculty Supervisor: Eric Greene
Department: Chemistry & Biochemistry
Glutamine synthetase is a key enzyme in the global nitrogen cycle and human glutamine synthetase is essential. However, how human glutamine synthetase is regulated in the body is not fully understood, especially whether this enzyme may be under allosteric control. To address this, we conducted a study that combined cryogenic electron microscopy (cryo-EM), structural bioinformatics, and molecular dynamics (MD) ensemble fitting. Our aim was to map allosteric pathways and conformational consequences on critical residues, such as pKa changes to active site residues and large conformational changes to a loop that gates the active site. We present a putative allosteric network that modulates the conformational state of glutamine synthetase. Importantly, this network links a transiently formed oligomeric state interface to the active site, suggesting that changes to the oligomeric state could significantly disrupt enzyme activity. Furthermore, we found that these structural changes also cause subtle changes in the conformation of the active site, which are responsible for extensive pKa changes, particularly in the ammonia binding pocket. Interestingly, structural changes to the active site loop appear to be conserved, as this element is structurally variable in GS structures from diverse organisms. Our findings provide a detailed view of glutamine synthetase dynamics, offering new insights into allosteric regulation mechanisms and suggesting potential targets for the development of therapies for related disorders.