Opposing structural changes in two symmetrical polypeptides bring about opposing changes to the thermal stability of a complex integral membrane protein

► Structure and stability were studied in a complex integral membrane protein. ► Opposing mutations were introduced at symmetrical positions in the protein. ► The opposing mutations had opposing effects on thermal stability. ► Destabilisation was due to the removal of specific hydrogen bonds. ► Stabilisation was due to the introduction of symmetrical hydrogen bonds.