Meaning of "Domain with function to find" (FIIND)

Question

From NALPs: a novel protein family involved in inflammation.

FIIND - Domain with Function to Find.

What is the meaning of this name? Does it mean "Domain with an unknown function"?

I'm translating an article in which this domain is mentioned, and I found three different translations of the term into Russian: "Domain with an unknown function", "Domain with a search function", "Domain with identification function".

I think the first translation is the most logical one, but I'm asking just in case, because I'm not an expert in this field.

The NALP subfamily. Finally, a large subfamily of the CATERPILLAR proteins is composed of 14 NALPs (also called PANs³⁶ or PYPAFs³⁷; FIG 2.) and is characterized by the presence of an amino-terminal PYD. This modular architecture is found in NALPs 2–14 (short NALPs), whereas NALP1 contains an additional domain — which our group has designated FIIND (function to find) — and a CARD, forming a carboxy-terminal extension. With two notable exceptions (NALP1 and NALP3), the NALP genes are located in two clusters on human chromosomes 11p15 (NALPs 6, 10 and 14) and 19q13.4 (NALPs 2, 4, 5, 7, 8, 9, 11, 12 and 13) (TABLE 1). Interestingly, the 11p15.5 region is an important IMPRINTED region and has been implicated in the imprinting disorder Beckwith-Wiedemann syndrome and in various human cancers, including Wilm's tumour³⁸.

Answer 1

I was pretty certain @David's comment was spot on, that this was some one-use funny acronym from just this paper, but a search of Google Scholar suggests that it has indeed been propagated sufficiently to have meaning beyond this paper, while also originating, as these things do, in some clumsy one-off usage.

One of them gives a clear definition that is consistent with what you supposed:

The acronym FIIND (domain with function to find) was coined several years ago to indicate a highly conserved protein region with unknown function[4]

D'Osualdo, A., Weichenberger, C. X., Wagner, R. N., Godzik, A., Wooley, J., & Reed, J. C. (2011). CARD8 and NLRP1 undergo autoproteolytic processing through a ZU5-like domain. PloS one, 6(11).

The paper they cite (reference 4 in the previous quote) is in fact this one:

Tschopp, J., Martinon, F., & Burns, K. (2003). NALPs: a novel protein family involved in inflammation. Nature reviews Molecular cell biology, 4(2), 95-104.

...which probably looks familiar since it is in fact the paper you started from. Importantly, though, this is not a generic term for a domain with unknown function, it's a specific domain which was known to be highly conserved (and since found in several other proteins) - it's just that it's specific function was at the time unknown.

This paper is a recent review of NLRP1 that may also be useful and has some discussions of what has been found of the functions of the FIIND:

Mitchell, P. S., Sandstrom, A., & Vance, R. E. (2019). The NLRP1 inflammasome: new mechanistic insights and unresolved mysteries. Current opinion in immunology, 60, 37-45.