The isocitrate dehydrogenase kinase/phosphatase from Escherichia coli is highly sensitive to in-vitro oxidative conditions role of cysteine67 and cysteine108 in the formation of a disulfide-bonded homodimer.
Isocitrate dehydrogenase kinase/phosphatase (IDHK/P) is a homodimeric enzyme which controls the oxidative metabolism of Escherichia coli, and exibits a high intrinsic ATPase activity. When subjected to electrophoresis under nonreducing conditions, the purified enzyme migrates partially as a dimer. The proportion of the dimer over the monomer is greatly increased by treatment with cupric 1,10 phenanthrolinate or 5,5'-dithio-bis(2-nitrobenzoic acid), and fully reversed by dithiothreitol, indicating that covalent dimerization is produced by a disulfide bond. To identify the residue(s) involved in this intermolecular disulfide-bond, each of the eight cysteines of the enzyme was individually mutated into a serine. It was found that, under nonreducing conditions, the electrophoretic patterns of all corresponding mutants are identical to that of the wild-type, except for the Cys67-->Ser which migrates exclusively as a monomer and for the Cys108-->Ser which migrates preferentially as a dimer. Furthermore, in contrast to the wild-type enzyme and all the other mutants, the Cys67-->Ser mutant still migrates as a monomer after treatment with cupric 1,10 phenanthrolinate. This result indicates that the intermolecular disulfide bond involves only Cys67 in each IDHK/P wild-type monomer. This was further supported by mass spectrum analysis of the tryptic peptides derived from either the cupric 1,10 phenanthrolinate-treated wild-type enzyme or the native Cys108-->Ser mutant, which show that they both contain a Cys67-Cys67 disulfide bond. Moreover, both the cupric 1,10 phenanthrolinate-treated wild-type enzyme and the native Cys108-->Ser mutant contain another disulfide bond between Cys356 and Cys480. Previous results have shown that this additional Cys356-Cys480 disulfide bond is intramolecular [Oudot, C., Jault, J.-M., Jaquinod, M., Negre, D., Prost, J.-F., Cozzone, A.J. & Cortay, J.-C. (1998) Eur. J. Biochem. 258, 579-585].
Oudot
C
C
Institut de Biologie et Chimie des Protéines, CNRS, Lyon, France.
Jaquinod
M
M
Cortay
J C
JC
Cozzone
A J
AJ
Jault
J M
JM
D001483:Base Sequence; D003545:Cysteine / Q000378:metabolism*; D017931:DNA Primers; D019281:Dimerization; D004220:Disulfides / Q000737:chemistry; D004926:Escherichia coli / Q000201:enzymology*; D010084:Oxidation-Reduction; D010749:Phosphoprotein Phosphatases / Q000737:chemistry / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000737:chemistry / Q000378:metabolism*
D017931:DNA Primers; D004220:Disulfides; D017346:Protein Serine-Threonine Kinases; C042301:isocitrate dehydrogenase kinase; C042300:isocitrate dehydrogenase phosphatase; D010749:Phosphoprotein Phosphatases; D003545:Cysteine