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Structure and catalytic mechanism of monodehydroascorbate reductase, MDHAR, from Oryza sativa L. japonica

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Title
Structure and catalytic mechanism of monodehydroascorbate reductase, MDHAR, from Oryza sativa L. japonica
Authors
Park, Ae Kyung
Kim, Il-Sup
Do, Hackwon
Jeon, Byoung Wook
Lee, Chang Woo
Roh, Soo Jung
Shin, Seung Chul
Park, Hyun
Kim, Young-Saeng
Kim, Yul-Ho
Yoon, Ho-Sung
Lee, Jun Hyuck
Kim, Han-Woo
Subject
Science & Technology - Other Topics
Keywords
Crystal structure; Isoascorbic acid; Monodehydroascorbate reductase; Reactive oxygen species
Issue Date
2016
Citation
Park, Ae Kyung., et al. 2016. Structure and catalytic mechanism of monodehydroascorbate reductase, MDHAR, from Oryza sativa L. japonica. Scientific Reports, 6(33903): 1-10.
Abstract
Ascorbic acid (AsA) maintains redox homeostasis by scavenging reactive oxygen species from prokaryotes to eukaryotes, especially plants. The enzyme monodehydroascorbate reductase (MDHAR) regenerates AsA by catalysing the reduction of monodehydroascorbate, using NADH or NADPH as an electron donor. The detailed recycling mechanism of MDHAR remains unclear due to lack of structural information. Here, we present the crystal structures of MDHAR in the presence of cofactors, nicotinamide adenine dinucleotide (NAD+) and nicotinamide adenine dinucleotide phosphate (NADP+), and complexed with AsA as well as its analogue, isoascorbic acid (ISD). The overall structure of MDHAR is similar to other iron-sulphur protein reductases, except for a unique long loop of 63?80 residues, which seems to be essential in forming the active site pocket. From the structural analysis and structure-guided point mutations, we found that the Arg320 residue plays a major substrate binding role, and the Tyr349 residue mediates electron transfer from NAD(P)H to bound substrate via FAD. The enzymatic activity of MDHAR favours NADH as an electron donor over NADPH. Our results show, for the first time, structural insights into this preference. The MDHAR-ISD complex structure revealed an alternative binding conformation of ISD, compared with the MDHAR-AsA complex. This implies a broad substrate (antioxidant) specificity and resulting greater protective ability of MDHAR.
DOI
10.1038/srep33903
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