NAD(+) hydrolase SARM1
NAD+ nucleosidase activity
Initial Kinetic Characterization of Sterile Alpha and Toll/Interleukin Receptor Motif-Containing Protein 1.
Sterile alpha and toll/interleukin receptor (TIR) motif-containing protein 1 (SARM1) plays a pivotal role in triggering the neurodegenerative processes that underlie peripheral neuropathies, traumatic brain injury, and neurodegenerative diseases. Importantly, SARM1 knockdown or knockout prevents degeneration, thereby demonstrating that SARM1 is a promising therapeutic target. Recently, SARM1 was shown to promote neurodegeneration via its ability to hydrolyze NAD<sup>+</sup>, forming nicotinamide and ADP ribose (ADPR). Herein, we describe the initial kinetic characterization of full-length SARM1, as well as the truncated constructs corresponding to the SAM<sup>1-2</sup>TIR and TIR domains, highlighting the distinct challenges that have complicated efforts to characterize this enzyme. Moreover, we show that bacterially expressed full-length SARM1 (<i>k</i><sub>cat</sub>/<i>K</i><sub>M</sub> = 6000 ± 2000 M<sup>-1</sup> s<sup>-1</sup>) is at least as active as the TIR domain alone (<i>k</i><sub>cat</sub>/<i>K</i><sub>M</sub> = 1500 ± 300 M<sup>-1</sup> s<sup>-1</sup>). Finally, we show that the SARM1 hydrolyzes NAD<sup>+</sup> via an ordered uni-bi reaction in which nicotinamide is released prior to ADPR.