Cell polarity is an essential property of cells critical for maintaining cellular integrity and it has been linked with cancer development due to cell polarity deregulation by mislocalisation [1]. Scribble, a cell polarity protein, is often mislocalised during cancer progression. Its role as an adaptor protein relies on the PDZ domains which are essential in protein-protein interaction and each domain has a different binding specificity which enables them to interact with several Scribble binding partners [2,6].
Previous studies demonstrated that Scribble has interactions with the planar cell polarity protein Vangl2, utilizing Scribble PDZ2 and PDZ3, [3,4] and tumor-suppressing protein APC, utilizing PDZ1 and PDZ4 [5]. However, the significance of these findings has yet to be elucidated from a structural perspective. Affinity measurements using isothermal titration calorimetry in this study demonstrated however that all PDZ domains except PDZ4 has shown interaction with the binding partners with affinities in the micromolar range. Intriguingly, despite the presence of three functional binding sites amongst the four Scribble PDZ domains, only one binding site is utilized when either binding partners binds a construct comprising all four Scribble PDZ domains, suggesting the role of the Scribble supertertiary structure in regulating protein interactions. To understand the structural basis of Scribble PDZ domain interactions with Vangl2 and APC, the complexes were crystallized, and structures of PDZ1-APC, PDZ2-Vangl2, and PDZ3-Vangl2 complexes were determined.
These findings will serve as a platform to understand the role of Scribble PDZ domains in cell polarity regulation at the atomic level, and inform future mutagenesis experiments to delineate how individual Scribble PDZ domains contribute to these interactions.