Enzyme Filamentation: A Focus on Mammalian Glutamate Dehydrogenase

Abstract

Enzyme filamentation is an emerging regulatory mechanism influencing enzymatic activity, stability, and metabolic organization. Chapter one explores the structural and functional significance of enzyme filaments and how higher-order assemblies modulate reaction kinetics and metabolic flux. This chapter provides an overview of known filament-forming enzymes and their physiological roles, including but not limited to, acetyl-CoA carboxylase (ACC), CTP synthase (CTPS) and inosine-5-monophosphate dehydrogenase (IMPDH).Chapter two focuses on glutamate dehydrogenase (GDH), a key enzyme in nitrogen metabolism that catalyzes the reversible conversion of glutamate to α-ketoglutarate and ammonia. GDH serves as a critical metabolic node, linking amino acid catabolism to the tricarboxylic acid (TCA) cycle and responding to cellular energy demands. This chapter examines what is known about the structure, regulation, and function of mammalian GDH in hexameric and filamentous forms. Chapter three is centered on the kinetics of mammalian GDH filamentation and its biochemical and functional implications (with raw data presented in Appendix A). This chapter details the effect of GDH filaments on enzymatic activity, and their regulatory significance. Chapter four reports on two new cryo-EM structures of filamentous bovine GDH and structure-function analysis combining the kinetics data from Chapter three. This study provides new knowledge to the growing field of filament-forming enzymes and enhances our understanding of the biochemical and enzymatic nature of mammalian GDH1 filamentation. Finally, chapter five outlines future directions, proposing the next steps to deepen our understanding of GDH filamentation and its potential for therapeutic applications. These findings provide a foundation for future structural studies that would uncover the functional significance in vitro and in vivo.