The function to find (FIIND) was initially discovered in two proteins, NLRP1 (aka NALP1, CARD7, NAC, DEFCAP) and CARD8 (aka TUCAN, Cardinal) [1]. NLRP1 is a member of the Nod-like receptor (NLR) protein superfamily and is involved in apoptosis and inflammation. To date, it is the only NLR protein known to have a FIIND domain. The FIIND domain is also present in the CARD8 protein where, like in NLRP1, it is followed by a C-terminal CARD domain. Both proteins are described to form an "inflammasome", a macro-molecular complex able to process caspase 1 and activate pro-IL1beta [2]. The FIIND domain is present in only a very small subset of the kingdom of life, comprising primates, rodents (mouse, rat), carnivores (dog) and a few more, such as horse. Publications describing the newly discovered NLRP1 protein failed to identify it as a separate domain; for example, it was taken as part of the adjacent leucine rich repeat domain (LRR) [3]. Upon discovery of CARD8 it was noted that the N-terminal region shared significant sequence identity with an undescribed region in NLRP1 [1]. Before getting its final name, FIIND [2], this domain was termed NALP1-associated domain (NAD) [4]. This is a peptidase domain of the ZU5 superfamily that is predicted to be involved in autoproteolytic cleavage [5].

1: TUCAN, an antiapoptotic caspase-associated recruitment domain family protein overexpressed in cancer. Pathan N, Marusawa H, Krajewska M, Matsuzawa S, Kim H, Okada K, Torii S, Kitada S, Krajewski S, Welsh K, Pio F, Godzik A, Reed JC; J Biol Chem. 2001;276:32220-32229. PMID:11408476

2: NALPs: a novel protein family involved in inflammation. Tschopp J, Martinon F, Burns K; Nat Rev Mol Cell Biol. 2003;4:95-104. PMID:12563287

3: Molecular cloning and characterization of DEFCAP-L and -S, two isoforms of a novel member of the mammalian Ced-4 family of apoptosis proteins. Hlaing T, Guo RF, Dilley KA, Loussia JM, Morrish TA, Shi MM, Vincenz C, Ward PA; J Biol Chem. 2001;276:9230-9238. PMID:11076957

4: The Inflammasome: A Molecular Platform Triggering Activation of Inflammatory Caspases and Processing of proIL-beta. Martinon F, Burns K, and Tschopp J Mol Cell. 2002;10:417-26. PMID:12191486

5: Bacterial death and TRADD-N domains help define novel apoptosis and immunity mechanisms shared by prokaryotes and metazoans. Kaur G, Iyer LM, Burroughs AM, Aravind L; Elife. 2021; [Epub ahead of print] PMID:34061031