POP2 helix-1 is necessary and sufficient to inhibit NF-κB p65 activity. A, schematic of POP2 deletion mutants showing individual α-helices. B—D, 293T cells were co-transfected with NF-κB luciferase and NF-κB p65 in the presence or absence of WT and POP2 deletion mutants (B), increasing amounts of POP2 Δα1 lacking helix-1 (C), and the indicated POP2 point mutants (D). Alignment of POP2 α1 and the first 19 residues in human NLRP2 with non-conserved residues is shown in box (D). E, NF-κB luciferase assay in 293T cells following TNFα stimulation (open bars) or NF-κB p65 co-transfection (closed bars) in cells expressing WT or mutant versions of POP2 and NLRP2. Results are representative of at least three experiments (error bars, S.D.).