Active site geometry of oxalate decarboxylase from Flammulina velutipes: Role of histidine-coordinated manganese in substrate recognition |
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Authors: | Chakraborty Subhra Chakraborty Niranjan Jain Deepti Salunke Dinakar M Datta Asis |
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Institution: | National Center for Plant Genome Research, Jawaharlal Nehru University Campus, New Delhi 110067, India. |
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Abstract: | 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. |
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Keywords: | Oxalate decarboxylase ECM protein germin motif knowledge-based modeling knockout mutants |
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