Nematode DAF-12 nuclear receptor reveals conserved and novel coactivator binding mechanisms

Parasitic nematodes inflict significant health and economic burdens globally, with widespread anthelmintic resistance severely compromising current control strategies. A critical juncture in parasite infection is the resumption of development by infective third-stage larvae (iL3) upon host entry, a process tightly regulated by the nuclear receptor DAF-12. Activation of DAF-12 by dafachronic acids drives developmental progression and reproductive maturation, positioning it as an attractive therapeutic target. However, the precise molecular mechanisms governing DAF-12 activation, particularly the recruitment of transcriptional coactivators, have remained poorly understood.

Researchers employed a multifaceted approach, combining biophysical, cellular, structural, and bioinformatic methods to dissect coactivator recognition by DAF-12 from the parasitic nematodes Brugia malayi and Haemonchus contortus. The core of the study involved obtaining crystal structures of ligand-bound DAF-12 ligand-binding domains in complex with coactivator-derived peptides. This structural work was complemented by structure-guided analyses to redefine the interaction motif of the only described parasite-specific coactivator DIP-1 and to identify novel candidate interaction motifs.

Crystal structures of ligand-bound DAF-12 ligand-binding domains in complex with coactivator-derived peptides revealed conserved features of ligand-dependent coactivator recruitment, shared with mammalian nuclear receptors. These structures provided the first atomic-level insights into how DAF-12 engages its transcriptional partners. Importantly, the study uncovered previously unrecognized interaction features, including motif-specific contacts that extend beyond the canonical LXXLL binding mode of coactivators. Distinct patterns of DAF-12 conservation were also identified across various nematode clades, suggesting evolutionary adaptations in its regulatory mechanisms. Structure-guided analyses successfully redefined the interaction motif of DIP-1, the only known parasite-specific coactivator, and proposed novel candidate motifs for other DAF-12-interacting proteins. This comprehensive structural and evolutionary analysis establishes the fundamental basis of coactivator binding to nematode DAF-12.

The findings provide crucial mechanistic insight into the transcriptional regulation underlying parasite development, expanding our understanding of nuclear receptor signaling in these pathogens.