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

X-ray structures of 3-isopropylmalate dehydrogenase (IPMDH) do not provide sufficient information on the role of the metal-ion in the metal-IPM assisted domain closure. Here solution studies were carried out to test its importance. Small-angle X-ray scattering (SAXS) experiments with the Thermus thermophilus enzyme (complexes with single substrates) have revealed only a very marginal (0-5%) extent of domain closure in the absence of the metal-ion.