SARM1-specific motifs in the TIR domain enable NAD+ loss and regulate injury-induced SARM1 activation.
Axon injury in response to trauma or disease stimulates a self-destruction program that promotes the localized clearance of damaged axon segments. Sterile alpha and Toll/interleukin receptor (TIR) motif-containing protein 1 (SARM1) is an evolutionarily conserved executioner of this degeneration cascade, also known as Wallerian degeneration; however, the mechanism of SARM1-dependent neuronal destruction is still obscure. SARM1 possesses a TIR domain that is necessary for SARM1 activity. In other proteins, dimerized TIR domains serve as scaffolds for innate immune signaling. In contrast, dimerization of the SARM1 TIR domain promotes consumption of the essential metabolite NAD+and induces neuronal destruction. This activity is unique to the SARM1 TIR domain, yet the structural elements that enable this activity are unknown. In this study, we identify fundamental properties of the SARM1 TIR domain that promote NAD+loss and axon degeneration. Dimerization of the TIR domain from the Caenorhabditis elegans SARM1 ortholog TIR-1 leads to NAD+loss and neuronal death, indicating these activities are an evolutionarily conserved feature of SARM1 function. Detailed analysis of sequence homology identifies canonical TIR motifs as well as a SARM1-specific (SS) loop that are required for NAD+loss and axon degeneration. Furthermore, we identify a residue in the SARM1 BB loop that is dispensable for TIR activity yet required for injury-induced activation of full-length SARM1, suggesting that SARM1 function requires multidomain interactions. Indeed, we identify a physical interaction between the autoinhibitory N terminus and the TIR domain of SARM1, revealing a previously unrecognized direct connection between these domains that we propose mediates autoinhibition and activation upon injury.
Department of Genetics, Washington University in St. Louis, St. Louis, MO 63110; Department of Developmental Biology, Washington University in St. Louis, St. Louis, MO 63110.
Daniel W
DW
Summers
Department of Developmental Biology, Washington University in St. Louis, St. Louis, MO 63110.
Daniel A
DA
Gibson
Department of Developmental Biology, Washington University in St. Louis, St. Louis, MO 63110; Hope Center for Neurological Disorders, Washington University in St. Louis, St. Louis, MO 63110 jmilbrandt@wustl.edu diantonio@wustl.edu.
Aaron
A
DiAntonio
Department of Genetics, Washington University in St. Louis, St. Louis, MO 63110; Hope Center for Neurological Disorders, Washington University in St. Louis, St. Louis, MO 63110 jmilbrandt@wustl.edu diantonio@wustl.edu.
Jeffrey
J
Milbrandt
D000255:Adenosine Triphosphate / Q000378:metabolism; D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D051186:Armadillo Domain Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001369:Axons / Q000502:physiology; D016923:Cell Death; D002460:Cell Line; D003598:Cytoskeletal Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D005727:Ganglia, Spinal / Q000166:cytology; D015870:Gene Expression; D006801:Humans; D051379:Mice; D018345:Mice, Knockout; D008954:Models, Biological; D008958:Models, Molecular; D009154:Mutation; D009243:NAD / Q000378:metabolism*; D009416:Nerve Regeneration; D009474:Neurons / Q000502:physiology; D061251:Primary Cell Culture; D054730:Protein Interaction Domains and Motifs; D055503:Protein Multimerization; D017433:Protein Structure, Secondary
D051186:Armadillo Domain Proteins; D003598:Cytoskeletal Proteins; C435689:SARM1 protein, human; D009243:NAD; D000255:Adenosine Triphosphate
NAD; SARM; axon degeneration; cell death; sarmoptosis
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