Deciphering the unconventional peptide binding to the PDZ domain of MAST2.

Phosphatase and tensin homologue (PTEN) and microtubule-associated serine threonine kinase 2 (MAST2) are key negative regulators of survival pathways in neuronal cells. The two proteins interact via the PDZ (PSD-95, Dlg1, Zo-1) domain of MAST2 (MAST2-PDZ). During infection by rabies virus, the viral glycoprotein competes with PTEN for interaction with MAST2-PDZ and promotes neuronal survival. The C-terminal PDZ-binding motifs (PBMs) of the two proteins bind similarly to MAST2-PDZ through an unconventional network of connectivity involving two anchor points. Combining stopped-flow fluorescence, analytical ultracentrifugation (AUC), microcalorimetry and NMR, we document the kinetics of interaction between endogenous and viral ligands to MAST2-PDZ as well as the dynamic and structural effects of these interactions. Viral and PTEN peptide interactions to MAST2-PDZ occur via a unique kinetic step which involves both canonical C-terminal PBM binding and N-terminal anchoring. Indirect effects induced by the PBM binding include modifications to the structure and dynamics of the PDZ dimerization surface which prevent MAST2-PDZ auto-association. Such an energetic communication between binding sites and distal surfaces in PDZ domains provides interesting clues for protein regulation overall.