Pathogenic missense variants of CSNK2B associated with Poirier-Bienvenu neurodevelopmental disorder impact differently on CK2 holoenzyme formation

Poirier-Bienvenu neurodevelopmental syndrome is a neurodevelopmental disorder associated with de novo variants of the CSNK2B gene, characterized by intellectual disability, developmental delay, frequent seizures and more. While the majority of variants are nonsense variants leading to abortion of protein translation and no or truncated CK2 beta, many pathogenic missense variants also exist. We investigated the effect of four variants on CK2 holoenzyme formation and activity. We show that variants in the Zinc-finger region leads to reduced protein stability and altered subcellular localization. The instability is partly mediated by proteasomal and lysosomal degradation. We further show that homodimerization of these CK2 beta variants (p.Arg111Pro, p.Cys137Phe), localized within the Zinc-finger domain, is significantly reduced, while CK2 alpha binding appears not affected. Other variants, p.Asp32Asn and p.Arg86Cys, did not affect stability or CK2 beta/alpha binding. For these mutants, the key to understanding the pathological mechanism may depend on external factors, such as altered protein-protein interaction. We conclude that Zinc-finger domain variants appear to destabilize the protein and affect holoenzyme formation, effectively reducing the pool of competent holoCK2. In the context of POBINDS, our findings suggest that Zinc-finger domain variants are likely to affect cells similarly to truncating and splicing variants with reduced translation of full-length CK2 beta.