Cooperativity of two active sites in bacterial homodimeric aconitases.
Aconitase catalyzes a reversible isomerization of citrate into isocitrate in the Krebs cycle. Escherichia coli possesses two kinds of aconitases, aconitase A (AcnA) and B (AcnB), whose structural organizations are different. We analyzed the structural state of AcnA by the chemical crosslinking and small-angle X-ray scattering. The protein adopts a homodimer in solution, as AcnB does. The catalytic assay of the two aconitases revealed that the isomerization of isocitrate displayed a negative cooperativity of the two active sites within each homodimer. On the other hand, insignificant cooperativity was observed in the reverse reaction. Therefore, the homodimerization of AcnAB yields a substrate-dependent cooperative effect. In conjunction with the dissociable homodimer of AcnB, the catalytic property could affect the intracellular metabolic process involving the Krebs cycle.
Tsuchiya
Daisuke
D
Institute for Advanced Biosciences, Keio University, 403-1 Nipponkoku, Daihoji, Tsuruoka, Yamagata 9970017, Japan. dsktcy@ybb.ne.jp
Shimizu
Nobutaka
N
Tomita
Masaru
M
D000154:Aconitate Hydratase / Q000737:chemistry*; D000595:Amino Acid Sequence; D002384:Catalysis; D020134:Catalytic Domain; D019281:Dimerization; D004926:Escherichia coli / Q000201:enzymology*; D006801:Humans; D008969:Molecular Sequence Data; D017434:Protein Structure, Tertiary; D053838:Scattering, Small Angle; D014961:X-Ray Diffraction
D000154:Aconitate Hydratase