Impact of Poirier-Bienvenu Neurodevelopmental Disease-associated Variants on CK2 Holoenzyme Assembly

Protein kinase CK2 is a constitutively active and highly conserved serine/threonine kinase that is ubiquitously expressed in eukaryotic cells.^[1] It functions as a heterotetrameric holoenzyme composed of two catalytic subunits (α or α′) and two regulatory β subunits.^[2] Mutations in CSNK2B, the gene encoding CK2β, cause Poirier-Bienvenu neurodevelopmental syndrome (POBINDS), a disorder characterized by early-onset epilepsy, variable intellectual disability, language impairment, and, in some cases, physical disabilities and psychiatric manifestations.^{[3] [4]} 

To investigate whether POBINDS-associated mutations affect holoenzyme assembly 12 variants located within regions implicated in α/β or β/β interaction, including the αF helix, hairpin loop and zinc finger domain, were selected for functional characterization. All variants located within regions important for holoenzyme formation exhibited reduced affinity for the α subunit. In addition, kinase activity was reduced for most variants. The α/β interaction was subsequently investigated by determination of dissociation constants (K_D). Dimerization and holoenzyme assembly were assessed by size-exclusion chromatography. Surprisingly, the C137G variant retained the ability to form intact holoenzymes and dimers, which was further confirmed by negative-stain electron microscopy. These findings indicate that POBINDS-associated mutations in structurally important regions of CK2β can impair α/β subunit interaction and CK2 function, while the preserved assembly observed for C137G suggests that individual variants may affect CK2 through distinct molecular mechanisms.

^[1] D. W. Litchfield, G. Dobrowolska et al., Biochem. J., 2003, 369, 1–15.

^[2] K. Niefind, J. Raaf et al., Cell. Mol. Life Sci., 2009, 66, 1800–1816.

^[3] W. Zhang, F. Ye et al., Front. Neurosci., 2022, 16, 892768.

^[4] A. Orsini, A. Santangelo et al., Genes, 2022, 13, 276.