Structural recognition mechanisms between human Src homology domain 3 (SH3) and ALG-2-interacting protein X (Alix).

The functions of Src family kinases are tightly regulated through Src homology (SH) domain-mediated protein-protein interactions. We previously reported the biophysical characteristics of the apoptosis-linked gene 2-interacting protein X (Alix) in complex with the haemopoietic cell kinase (Hck) SH3 domain. In the current study, we have combined ITC, NMR, SAXS and molecular modeling to determine a 3D model of the complex. We demonstrate that Hck SH3 recognizes an extended linear proline-rich region of Alix. This particular binding mode enables Hck SH3 to sense a specific non-canonical residue situated in the SH3 RT-loop of the kinase. The resulting model helps clarify the mechanistic insights of Alix-Hck interaction.