Chakraborty Subhra, Chakraborty Niranjan, Jain Deepti, Salunke Dinakar M, Datta Asis
National Center for Plant Genome Research, Jawaharlal Nehru University Campus, New Delhi 110067, India.
Protein Sci. 2002 Sep;11(9):2138-47. doi: 10.1110/ps.0206802.
Oxalate decarboxylase (OXDC) from the wood-rotting fungus Flammulina velutipes, which catalyzes the conversion of oxalate to formic acid and CO(2) in a single-step reaction, is a duplicated double-domain germin family enzyme. It has agricultural as well as therapeutic importance. We reported earlier the purification and molecular cloning of OXDC. Knowledge-based modeling of the enzyme reveals a beta-barrel core in each of the two domains organized in the hexameric state. A cluster of three histidines suitably juxtaposed to coordinate a divalent metal ion exists in both the domains. Involvement of the two histidine clusters in the catalytic mechanism of the enzyme, possibly through coordination of a metal cofactor, has been hypothesized because all histidine knockout mutants showed total loss of decarboxylase activity. The atomic absorption spectroscopy analysis showed that OXDC contains Mn(2+) at up to 2.5 atoms per subunit. Docking of the oxalate in the active site indicates a similar electrostatic environment around the substrate-binding site in the two domains. We suggest that the histidine coordinated manganese is critical for substrate recognition and is directly involved in the catalysis of the enzyme.
来自金针菇的草酸脱羧酶（OXDC）是一种重复的双结构域萌发素家族酶，它能在一步反应中催化草酸转化为甲酸和二氧化碳。它具有农业和治疗方面的重要性。我们之前报道过OXDC的纯化和分子克隆。基于知识的该酶模型显示，在以六聚体状态组织的两个结构域中，每个结构域都有一个β桶状核心。两个结构域中都存在一组三个相邻的组氨酸，用于配位二价金属离子。由于所有组氨酸敲除突变体均显示脱羧酶活性完全丧失，因此推测这两个组氨酸簇可能通过配位金属辅因子参与了该酶的催化机制。原子吸收光谱分析表明，OXDC每个亚基最多含有2.5个原子的Mn(2+)。草酸在活性位点的对接表明，两个结构域中底物结合位点周围的静电环境相似。我们认为，组氨酸配位的锰对于底物识别至关重要，并直接参与该酶的催化作用。
