Investigating the interaction between Fam83G/PAWS1 and Ser/Thr protein kinase CK1α

Abstract

Protein-protein interactions (PPIs) are fundamental to biological processes, and are implicated in diseases, including cancer and neurodegenerative disorders. Targeting PPIs has emerged as a promising yet challenging approach in drug discovery, particularly when addressing “undruggable” proteins. Advances in the development of PPI modulators, such as small molecule degraders, highlight the potential to manipulate these interactions therapeutically.

This thesis focuses on the interaction between Fam83G, also known as Protein Associated with SMAD1 (PAWS1), and Ser/Thr protein kinase CK1α (also known as Casein Kinase 1α). The Fam83G-CK1α interaction drives the activation of canonical Wnt signalling, a pathway often hyperactivated in colorectal cancer. Proteomic analysis has revealed that Fam83G interacts with various proteins, notably CK1α. However, the detailed molecular mechanisms underpinning this interaction has not been fully elucidated. Mutations in Fam83G that are linked to palmoplantar keratoderma (PPK) disrupt CK1α binding and inhibit Wnt signalling. This study set out to investigate the impact of point mutations of Fam83G guided by reported small fragment binding sites on Fam83B and predicted AlphaFold models of FAM83G-CK1α complex on CK1α binding. The study also tested the impact of reported small molecule degraders of CK1α, namely DEG-77 and SJ3149, on Fam83G-CK1α complex stability.

The findings from this study suggest that several residues identified within the small fragment binding pockets are important for Fam83G-CK1α interaction. Similarly, at least one residue on Fam83G predicted by AlphaFold to be on the FAM83G-CK1α interface abolished binding to CK1α. Similarly, for the first time, a point mutant on CK1α was identified that abolished binding to Fam83G. Two small molecule degraders of DEG-77 and SJ3149 that induce degradation of CK1α, through recruitment of Cullin4A-cereblon E3 ligase complex, also degrade wild type Fam83G but not those mutants that do not interact with CK1α, suggesting co-degradation of Fam83G necessitates interaction with CK1α.

Date of Award	2025
Original language	English
Awarding Institution	University of Dundee
Supervisor	Gopal Sapkota (Supervisor)