This entry represents a sensor domain consisting of 7 TPR repeats forming a tightly-wound solenoid structure harbouring a deep central pocket. The TPR-S binding pocket is lined with several conserved aromatic and polar residues predicted to bind a NAD+-derived nucleotide in prokaryotic NAD+-derived nucleotide-activated effector conflict systems. It has been acquired at the base of the choanoflagellate-animal lineage as a core component of the ASK signalosome [1].

1: Identification of Uncharacterized Components of Prokaryotic Immune Systems and Their Diverse Eukaryotic Reformulations. Burroughs AM, Aravind L; J Bacteriol. 2020; [Epub ahead of print] PMID:32868406