A metabolite-bridged complex between SerRS and SIRT2 couples NAD⁺ metabolism to translation control

Cellular homeostasis requires tight coordination between metabolic and translational networks. Here we identify a direct molecular link between these processes through a cryo-EM structure of human cytosolic seryl-tRNA synthetase (SerRS) in complex with the NAD⁺-dependent deacetylase SIRT2. This interaction is promoted by the NAD⁺ metabolite ADP-ribose (ADPR), which acts as a molecular bridge between the two enzymes. Within the SIRT2 active site, ADPR engages SerRS residue K414 located in a flexible catalytic-domain loop. Acetylation of K414 is dispensable for binding. Functionally, complex formation inhibits SIRT2 deacetylase activity by blocking substrate access, while SIRT2 association suppresses SerRS aminoacylation activity by preventing tRNA binding. Thus, SerRS and SIRT2 mutually regulate each other, with ADPR enhancing while tRNA attenuating their interaction. Oxidative stress promotes this interaction via a PARP1-dependent pathway, revealing an ADPR-responsive regulatory module that couples metabolic state to translational output. This regulatory module is likely conserved across vertebrates.