2024/12/26 by Melisa Lázaro, Nicolás Chamorro, Jorge P. López‐Alonso +5 · 1 voice
Materials Science · Biochemistry, Genetics and Molecular Biology · Agricultural and Biological Sciences · #Enzyme Structure and Function #Protein Structure and Dynamics #GABA and Rice Research
paper · doi:10.1101/2024.12.26.630402
ABSTRACT Glutamate dehydrogenases (GDHs) catalyze the oxidative deamination of L-glutamate to 2-oxoglutarate using NAD(P) + as a cofactor. The large type of GDHs (L-GDHs) displays a dynamic homotetrameric architecture that alternates between open and closed states. However, the catalytic mechanism and the functional relevance of the large conformational changes in L-GDHs remain poorly understood. Here, we use cryo-EM to investigate the structure and the conformational landscape of the mycobacterial L-GDH composed of 180 kDa subunits (mL-GDH 180 ) when incubated with L-glutamate and NAD + . Classification of the heterogeneous population of tetramers reveals opening-closing motions and sorting of individual subunits resolves the occupancy of the cofactor and substrate binding pockets. Cryo-EM maps show that ligand binding to the glutamate binding pocket is accompanied by structural changes in a region approximately two nanometers away from the active site, leading to the formation of a previously undetected interaction between the catalytic domains of neighboring subunits in mL-GDH 180 closed tetrameric states. Our findings indicate that the occupancy of the substrate binding site of mL-GDH 180 is linked to a remodeling of both the tertiary and quaternary structure of the enzyme. STATEMENT FOR A BROADER AUDIENCE This work reveals how the binding of L-glutamate and NAD + reshapes the architecture of a large glutamate dehydrogenase, linking active site occupancy to long-range structural remodeling. By capturing previously unseen conformational transitions with cryo-electron microscopy, we provide insights into the molecular logic of enzyme function in mycobacteria. These findings establish a framework to understand how structural plasticity supports metabolic control.