Unlocking TYK2 Biology: How Deep Mutational Scanning Reveals New Therapeutic Frontiers

Systematic variant analysis illuminates pseudokinase function and guides next-generation autoimmune drug development

Deep mutational scanning has transformed our understanding of Tyrosine Kinase 2 (TYK2), a genetically validated target in autoimmune disease, by systematically interrogating over 23,000 amino acid substitutions across critical protein functions. This high-throughput approachcouples variant library generation with functional selection and next-generation sequencing to create comprehensive sequence-function maps, enabling researchers to identify novel druggable sites and clarify how human genetic variants influence disease susceptibility. The study specifically examined TYK2’s role in IFN-α signaling and protein abundance, revealing that protective human variants associated with reduced autoimmune risk actually decrease TYK2 protein levels rather than merely reducing enzymatic activity. This finding fundamentally challenges conventional therapeutic approaches that focus solely on kinase inhibition.

The pseudokinase domain, also known as the JH2 domain, emerges as a critical regulatory element that allosterically controls the adjacent catalytic kinase domain through extensive interdomain contacts. Unlike traditional ATP-competitive inhibitors that target the conserved active site, allosteric inhibitors binding to the JH2 domain achieve remarkable selectivity for TYK2 over other JAK family members (JAK1, JAK2, JAK3). Recent clinical successes with selective TYK2 pseudokinase inhibitors like deucravacitinib and zasocitinib demonstrate this strategy’s therapeutic potential, with zasocitinib achieving up to 33% complete skin clearance in psoriasis patients after just 12 weeks. The deep mutational scanning data further identified variants that modulate compound potency by coupling DMS with inhibitor treatment, prospectively revealing structure-activity relationships that inform medicinal chemistry optimization.

Beyond inhibition, the observation that naturally occurring protective variants reduce TYK2 abundance suggests protein degradation as an underexplored therapeutic modality. This concept aligns with emerging PROTAC (proteolysis-targeting chimera) technologies that have successfully entered clinical trials for other kinase targets. The comprehensive variant effect mapping enabled by DMS provides unprecedented insights into which protein regions are most sensitive to destabilization, potentially guiding the design of degrader molecules that selectively eliminate TYK2 while sparing related kinases. Additionally, the identification of novel allosteric sites through high-resolution structure-function mapping opens new avenues for drug discovery beyond the well-characterized JH2 pocket.

The integration of deep mutational scanning with computational variant effect prediction tools represents a powerful synergy for interpreting the clinical significance of rare human variants. While TYK2 loss-of-function variants protect against multiple autoimmune conditions including psoriasis, Crohn’s disease, and multiple sclerosis, complete TYK2 deficiency causes severe immunodeficiency with susceptibility to mycobacterial infections. The DMS approach helps define this therapeutic window by quantifying exactly how much functional impairment provides benefit without causing immunosuppression. These findings have direct translational relevance as they inform optimal target engagement levels for clinical inhibitors and help predict which patients carrying specific TYK2 variants might respond differently to therapy. The work establishes a paradigm where prospective functional assessment of all possible mutations informs both precision medicine approaches and structure-based drug design simultaneously.