Essential role of the metal-ion in the IPM-assisted domain closure of 3-isopropylmalate dehydrogenase

► The role of the metal-ion in the catalytic domain closure of IPMDH has been investigated. ► SAXS studies of the Thermus thermophilus enzyme showed no domain closure without the metal. ► Only the metal-IPM complex is efficient in stabilizing the native E. coli enzyme conformation. ► FRET studies with both IPMDHs confirm the importance of the metal. ► A possible atomic level explanation of the metal-effect is given.