Phosphorylation Induced Global Structural Destabilization of a Small Protein Domain

Abstract

Protein phosphorylation at a single or multiple sites is utilized to regulate protein functional outcomes and overall cellular activities through signaling pathways. At a molecular level, the addition of a phosphoryl group may alter the function of a protein through distinct and versatile mechanisms. These include allosteric structural and dynamic changes, direct positive or negative modulation of affinities, masking or unmasking of cofactor binding sites, autoinhibition and local disorder-to-order or order-to-disorder transitions. Here we present evidence from NMR spectroscopy and other biophysical techniques that protein phosphorylation may lead to a global domain destabilization. Upon phosphorylation a small protein domain acquires a molten globule state, where at least two stable folding intermediates exist in equilibrium with a heterogeneous conformational ensemble. This conformational transition modulates in turn the affinity for protein partners but also permits rapid domain refolding upon removal of the phosphoryl group.