Indeed, when analyzing the obtained cryo-EM structure of MutSβ bound to mismatch DNA and 4 (PDB: 8R7V), we observed significant changes in the conformation of Leu871-Val878. Whereas the side chain of Asp875 is in a nearly parallel orientation with the piperazine ring in the crystal structure, the cryo-EM structure does not restrict any rearrangement of this loop upon ligand binding. Through its interaction with Asp875, this loop is drawn towards the active site. This observation confirms our hypothesis derived from in silico analysis regarding the crucial role of Asp875 in ligand binding for this series (Figure ).