Primary Citation of Related Structures: 5YZH, 5YZI
PubMed Abstract:
Cadmium (Cd 2+ ) is toxic to living organisms because it causes the malfunction of essential proteins and induces oxidative stress. NADP + -dependent cytosolic isocitrate dehydrogenase (IDH) provides reducing energy to counteract oxidative stress via oxidative decarboxylation of isocitrate ...
Cadmium (Cd 2+ ) is toxic to living organisms because it causes the malfunction of essential proteins and induces oxidative stress. NADP + -dependent cytosolic isocitrate dehydrogenase (IDH) provides reducing energy to counteract oxidative stress via oxidative decarboxylation of isocitrate. Intriguingly, the effects of Cd 2+ on the activity of IDH are both positive and negative, and to understand the molecular basis, we determined the crystal structure of NADP + -dependent cytosolic IDH in the presence of Cd 2+ . The structure includes two Cd 2+ ions, one coordinated by active site residues and another near a cysteine residue. Cd 2+ presumably inactivates IDH due to its high affinity for thiols, leading to a covalent enzyme modification. However, Cd 2+ also activates IDH by providing a divalent cation required for catalytic activity. Inactivation of IDH by Cd 2+ is less effective when the enzyme is activated with Cd 2+ than Mg 2+ . Although reducing agents cannot restore activity following inactivation by Cd 2+ , they can maintain IDH activity by chelating Cd 2+ . Glutathione, a cellular sulphydryl reductant, has a moderate affinity for Cd 2+ , allowing IDH to be activated with residual Cd 2+ , unlike dithiothreitol, which has a much higher affinity. In the presence of Cd 2+ -consuming cellular antioxidants, cells must continually supply reductants to protect against oxidative stress. The ability of IDH to utilise Cd 2+ to generate NADPH could allow cells to protect themselves against Cd 2+ .
Organizational Affiliation:
School of Life Science and Biotechnology, BK21 Plus KNU Creative BioResearch Group, Kyungpook National University, 80 Daehak-ro, Buk-gu, Daegu, 41566, South Korea. bskang2@knu.ac.kr.
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