NMR investigation of WIP/WASP complexes suggests a structure-based therapeutic approach to Wiskott Aldrich syndrome

Wiskott-Aldrich syndrome (WAS) is an X-linked primary immunodeficiency caused by mutations in the Wiskott-Aldrich syndrome protein (WASP), leading to symptoms including eczema, thrombocytopenia, and immunosuppressive neutropenia. An important regulator of WASP is WASP-Interacting Protein (WIP), a 503-residue intrinsically disordered protein (IDP). The interaction between the WIP C-terminal domain and WASP N-terminal EVH1 domain is essential for the immune response because WIP localizes WASP and protects it from degradation. In our group, co-expression of WASP (20-158) and WIP (442-492) fragments allowed structural determination of a natively folded complex.

Here we present a final structure of the complex deciphered using NMR methods based on NOESY- and RDC-derived constraints. The WIP-derived peptide wraps around the WASP pleckstrin homology domain and interacts with it via four short structural elements, including a newly identified segment that protects WASP from degradation. We then hypothesized that molecular factors causing WAS could be determined by structural characterization of complexes containing a WAS-causing mutation. We have produced and characterized an array of complexes with pathogenic and benign single-residue mutations spanning different regions of WASP. Based upon our new structure, and placing an emphasis on the WIP/WASP interface, we find a direct relationship between the observed spectral changes (reflecting structural changes) and patterns of disease severity. Our results demonstrate the power of NMR to follow the biological consequences of protein-protein interactions in health and disease and lay the groundwork for ongoing efforts in personalized therapeutic approaches to WAS.