Structural Analysis of human RXR Homotetramer by use of Hydrogen/Deuterium Exchange Mass Spectrometry

摘要

HDX MS analysis of hRXR-LBD apo homotetramer vs. homodimer clearly reflects the tetramer-specific interactions reported in the crystal structure (Figure 3). Dissociation of hRXRα-LBD homotetramer to homodimer occurs upon addition of between a 2:1 and 4:1 ratio of agonist to tetramer (Figure 2, H3 regions). HDX MS analysis of homotetramer in the presence of 1:1 ratio of agonist indicates initial protein-ligand interaction is with H3 and the ligand's polyene tail and would indicate this is where the structural mechanism of homotetramer dissociation begins (Figure 2). Helix 12 destabilizes upon addition of agonist and indicates dissociation of homotetramer into two homodimers (Figure 2). The homodimer interface (H7 and H11) is more stable in an apo homotetramer than in an apo homodimer (Figure 3). GRIP-1 coactivator alone does not bind homotetramer and will only bind after switch to homodimer begins (Figure 4).