The productive dimerization of hMPL, induced by hTPO binding. (A) The optimized configurations of hMPL dimer without hTPO presence. (B) Distance analysis of the D1-D1 domain indicating that the hMPL ECD adopts open configurations when hTPO is absent. Here, the distance between the center of mass of Cα atoms within residues (26-130) was measured across both hMPL D1 domains. (C) The configurations of the TMD-TMD interface under various conditions: hTPO-bound WT hMPL dimer, unbound (apo) WT hMPL dimer, and unbound (apo) S505N mutant hMPL dimer. The formation of an S505 hydrogen bond with its counterpart on the adjacent hMPL leads to the activation of the dimer. (D) Analysis of the hydrogen bonding between TMD-TMD at position 505 in the TPO-bound WT hMPL dimer, the unbound apo WT hMPL, and the unbound hMPL S505N dimers. The distance between oxygen gamma (OG) atoms on S505-S505 interaction and between carbon gamma (CG) atoms on N505-N505 interaction was considered for this analysis. (E) Without hTPO binding, the TMD shifts into nonproductive configurations due to the disruption of the hydrogen bonding between S505-S505, leading to a 170-degree rotation of the TM around its axis.