Transferring redox regulation properties from sorghum NADP-malate dehydrogenase to Thermus NAD-malate dehydrogenase

NADP-dependent chloroplastic malate dehydrogenase (E.C.1.1.1.82) is regulated by thiol disulfide-interchange with thioredoxin. It displays two regulatory disulfides per subunit, located in specific sequence extensions respectively at the N- and C-terminal ends of each subunit. In the present study, attempts were made to transfer the regulatory properties of sorghum NADP-malate dehydrogenase to a constitutively active NAD-dependent malate dehydogenase (E.C.1.1.1.37) from the thermophilic bacteria Thermus flavus, by grafting the regulatory extensions of the former to the latter. The results demonstrate that a successful transfer of redox regulation properties requires the grafting of both full-length extensions, but also the introduction of specific hydrophobic residues in the core part of the protein. These residues are very likely involved in the interaction between monomers, and structural changes at the active site.