Functional and structural characterization of zebrafish ASC

Abstract

Structural data are available in the PDB under accession numbers 5GPP and 5GPQ.

Homotypic CARD-CARD interaction is critical for the activation of NLRP1 inflammasome

“…The crystallographic structure of human ASC CARD is composed of six amphipathic α-helices engaging a hydrophobic core, similar to what has been found for other CARD domains 25,33,34 . The structure was refined to 2.0 Å resolution and exhibits excellent agreement with the cryo-EM structure of ASC CARD in filaments with an root mean squared deviation (RMSD) of 0.502 Å 31 (Fig.…”

Zebrafish in Inflammasome Research

“…Nlrp6 is able to form inflammasome complexes in response to Edwarsiella piscicida in vivo, confirming its function as inflammasome sensor [56]. Another predicted protein, referred to as Nlp3 isoform X1, is able to interact with zebrafish Asc in vitro via the interaction of their PYD domains [57]. However, the downstream caspase recruitment and activation dynamics differ to the ones in the mammalian NLRP inflammasomes.…”

“…Upon recruitment, ASC self-assembles into large signalling platforms, named ASC specks or foci, which are considered a hallmark of canonical inflammasome activation [64,65]. Unlike in mammals, zebrafish Asc PYD domain is critical for both auto-assembly and downstream proinflammatory caspase recruitment via PYD-PYD interactions [27,57]. Despite this difference, zebrafish Asc functionality seems to be conserved between zebrafish and mammals, as pyroptosis of zebrafish keratinocytes and macrophages has been recently visualized after Asc speck formation in vivo [27,29].…”

“…This assumption was originally backed by percentage of protein sequence homology and protease substrate preference [41]. Further functional analysis reported that only the Caspa PYD domain, but not the one of Caspb, is able to directly interact with Asc [27,41,57], and therefore promote Asc-dependent pyroptosis [27]. On the other hand, the Caspb PYD prodomain, but not the one in Caspa, is able to bind to LPS when overexpressed in HEK293T cells [42].…”

“…While the abilities of Caspa and Caspb to cleave Gasdermin remains to be studied, they are both able to cleave Il1b, albeit with different specificities [52]. Interestingly, Caspa and Caspb can directly interact in vitro via its PYD domains, thus opening the possibility of Caspa/Caspb oligomerization needed to fully mature Il1b [57]. In contrast, mammalian CASP4/5/11 cleave Gasdermin D but not proinflammatory cytokines during pyroptosis [67].…”