Collision-Induced Unfolding of Partially Metalated Metallothionein-2A: Tracking Unfolding Reactions of Gas-Phase Ions

Metallothioneins (MTs) constitute a group of intrinsically disordered proteins that exhibit extreme diversity in structure, biological functionality, and metal ion specificity. Structures of coordinatively saturated metalated MTs have been extensively studied, but very limited structural information for the partially metalated MTs exists. Here, the conformational preferences from partial metalation of rabbit metallothionein-2A (MT) by Cd2+, Zn2+, and Ag+ are studied using nanoelectrospray ionization ion mobility mass spectrometry. We also employ collision-induced unfolding to probe differences in the gas-phase stabilities of these partially metalated MTs. Our results show that despite their similar ion mobility profiles, Cd-4-MT, Zn-4-MT, Ago-MT, and Ag-6-MT differ dramatically in their gas-phase stabilities. Furthermore, the sequential addition of each Cd2+ and Zn2+ ion results in the incremental stabilization of unique unfolding intermediates.