Publications

• Enzymatic chlorophyll degradation in wheat near-isogenic lines elicited by cereal aphid (Homoptera: Aphididae) feeding.

  Wang T., Quisenberry S.S., Ni X., Tolmay V.

  Chlorophyll degradation enzyme (i.e., chlorophyllase, Mg-dechelatase, and chlorophyll oxidase) activities of aphid-infested and uninfested 'Tugela' and Tugela near-isogenic wheat lines (i.e., Tugela-Dn1, Tugela-Dn2, and Tugela-Dn5) were assayed. Chlorophyllase activity was higher in bird cherry-oa ... >> More

  Chlorophyll degradation enzyme (i.e., chlorophyllase, Mg-dechelatase, and chlorophyll oxidase) activities of aphid-infested and uninfested 'Tugela' and Tugela near-isogenic wheat lines (i.e., Tugela-Dn1, Tugela-Dn2, and Tugela-Dn5) were assayed. Chlorophyllase activity was higher in bird cherry-oat aphid, Rhopalosiphum padi (L.) (Homoptera: Aphididae),-infested wheat lines compared with Russian wheat aphid, Diuraphis noxia (Mordvilko) (Homoptera: Aphididae)]-infested and uninfested plants. Mg-dechelatase activity was higher in D. noxia-infested wheat lines than in R. padi-infested and uninfested plants. Also, Mg-dechelatase activity was lower in Tugela wheat infested with D. noxia than in Tugela near-isogenic lines with Dn genes. Based on the in vitro assays of chlorophyll degradation enzyme (i.e., chlorophyllase and Mg-dechelatase) activities, we proposed that the chlorotic symptoms observed on D. noxia-infested Tugela wheat were most likely to be elicited by unbalanced chlorophyll biosynthesis and degradation. << Less

  J Econ Entomol 97:661-667(2004) [PubMed] [EuropePMC]

  This publication is cited by 1 other entry.

• Crystal structure and reaction mechanism of a bacterial Mg-dechelatase homolog from the Chloroflexi Anaerolineae.

  Dey D., Nishijima M., Tanaka R., Kurisu G., Tanaka H., Ito H.

  Chlorophyll degradation plays a myriad of physiological roles in photosynthetic organisms, including acclimation to light environment and nutrient remobilization during senescence. Mg extraction from chlorophyll a is the first and committed step of the chlorophyll degradation pathway. This reactio ... >> More

  Chlorophyll degradation plays a myriad of physiological roles in photosynthetic organisms, including acclimation to light environment and nutrient remobilization during senescence. Mg extraction from chlorophyll a is the first and committed step of the chlorophyll degradation pathway. This reaction is catalyzed by the Mg-dechelatase enzyme encoded by Stay-Green (SGR). The reaction mechanism of SGR protein remains elusive since metal ion extraction from organic molecules is not a common enzymatic reaction. Additionally, experimentally derived structural information about SGR or its homologs has not yet been reported. In this study, the crystal structure of the SGR homolog from Anaerolineae bacterium was determined using the molecular replacement method at 1.85 Å resolution. Our previous study showed that three residues-H32, D34, and D62 are essential for the catalytic activity of the enzyme. Biochemical analysis involving mutants of D34 residue further strengthened its importance in the functioning of the dechelatase. Docking simulation also revealed the interaction between the D34 side chain and central Mg ion of chlorophyll a. Structural analysis showed the arrangement of D34/H32/D62 in the form of a catalytic triad that is generally found in hydrolases. The probable reaction mechanism suggests that deprotonated D34 side chain coordinates and destabilizes Mg, resulting in Mg extraction. Besides, H32 possibly acts as a general base catalyst and D62 facilitates H32 to be a better proton acceptor. Taken together, the reaction mechanism of SGR partially mirrors the one observed in hydrolases. << Less

  Protein Sci 31:e4430-e4430(2022) [PubMed] [EuropePMC]

• Removal of magnesium by Mg-dechelatase is a major step in the chlorophyll-degrading pathway in Ginkgo biloba in the process of autumnal tints.

  Tang L., Okazawa A., Fukusaki E., Kobayashi A.

  Autumnal tints are one of the most manifest and fascinating natural phenomena, but the mechanism of chlorophyll (Chl)-breakdown in deciduous trees has not been fully elucidated. In this study, we analyzed the composition of Chl-related compounds and determined the activities of initial Chl-degradi ... >> More

  Autumnal tints are one of the most manifest and fascinating natural phenomena, but the mechanism of chlorophyll (Chl)-breakdown in deciduous trees has not been fully elucidated. In this study, we analyzed the composition of Chl-related compounds and determined the activities of initial Chl-degrading enzymes in Ginkgo leaves at various stages in the process of autumnal coloring. Only pheophytin a (Pheo a, Mg-free Chl a) was detected in yellow leaves by HPLC analysis, and the activity of Mg-dechelatase in yellow leaves was found to be higher than in green leaves. These findings showed that the removal of magnesium from Chl a occurred in advance of dephytylation in the Ginkgo. << Less

  Z Naturforsch C J Biosci 55:923-926(2000) [PubMed] [EuropePMC]

  This publication is cited by 1 other entry.

• Mg-dechelation activity in radish cotyledons with artificial and native substrates, Mg-chlorophyllin a and chlorophyllide a.

  Suzuki T., Kunieda T., Murai F., Morioka S., Shioi Y.

  The Mg-dechelation activity in extracts from radish (Raphanus sativus L.) cotyledons was investigated using an artificial substrate, Mg-chlorophyllin a (Chlin) and the native substrate, chlorophyllide a (Chlide). In addition to a known a small molecular weight metal-chelating substance (MCS), Mg-r ... >> More

  The Mg-dechelation activity in extracts from radish (Raphanus sativus L.) cotyledons was investigated using an artificial substrate, Mg-chlorophyllin a (Chlin) and the native substrate, chlorophyllide a (Chlide). In addition to a known a small molecular weight metal-chelating substance (MCS), Mg-releasing protein (MRP) was present when Chlin was used as the substrate. However, only MCS had Mg-dechelation activity with the native substrate. To examine the possibility of the dissociation of MRP into a protein moiety and a small molecular mass compound with an activity like MCS, extraction with low and high ionic strength buffers was carried out. No evidence was obtained that MCS is a moiety of MRP, however. Inhibitor studies showed that MCS and MRP had different susceptibilities to the inhibitors, especially to the chelators tiron and EDTA when Chlin was used as the substrate. Tiron had no effect on MRP, but it severely reduced MCS activity in both substrates. The activity of MRP increased during senescence, indicating the induction of MRP, while the activity of MCS was almost unchanged. These results suggest different reaction mechanisms by independent compounds. These findings suggest that MRP and MCS are present independently, and MCS is postulated to be a substance that catalyzes the Mg-dechelation reaction in the breakdown pathway of Chl, although MCS was not induced during senescence. The properties of MRP and MCS in relation to the small molecular mass substance obtained from strawberry fruit are also discussed. << Less

  Plant Physiol Biochem 43:459-464(2005) [PubMed] [EuropePMC]

  This publication is cited by 1 other entry.

• Arabidopsis STAY-GREEN, Mendel's green cotyledon gene, encodes magnesium-dechelatase.

  Shimoda Y., Ito H., Tanaka A.

  Pheophytin <i>a</i> is an essential component of oxygenic photosynthetic organisms because the primary charge separation between chlorophyll <i>a</i> and pheophytin <i>a</i> is the first step in the conversion of light energy. In addition, conversion of chlorophyll <i>a</i> to pheophytin <i>a</i> ... >> More

  Pheophytin <i>a</i> is an essential component of oxygenic photosynthetic organisms because the primary charge separation between chlorophyll <i>a</i> and pheophytin <i>a</i> is the first step in the conversion of light energy. In addition, conversion of chlorophyll <i>a</i> to pheophytin <i>a</i> is the first step of chlorophyll degradation. Pheophytin is synthesized by extracting magnesium (Mg) from chlorophyll; the enzyme Mg-dechelatase catalyzes this reaction. In this study, we report that Mendel's green cotyledon gene, <i>STAY-GREEN</i> (<i>SGR</i>), encodes Mg-dechelatase. The <i>Arabidopsis thaliana</i> genome has three <i>SGR</i> genes, <i>SGR1</i>, <i>SGR2</i>, and <i>STAY-GREEN LIKE</i> (<i>SGRL</i>). Recombinant SGR1/2 extracted Mg from chlorophyll <i>a</i> but had very low or no activity against chlorophyllide <i>a</i>; by contrast, SGRL had higher dechelating activity against chlorophyllide <i>a</i> compared with chlorophyll <i>a</i> All SGRs could not extract Mg from chlorophyll <i>b</i> Enzymatic experiments using the photosystem and light-harvesting complexes showed that SGR extracts Mg not only from free chlorophyll but also from chlorophyll in the chlorophyll-protein complexes. Furthermore, most of the chlorophyll and chlorophyll binding proteins disappeared when SGR was transiently expressed by a chemical induction system. Thus, SGR is not only involved in chlorophyll degradation but also contributes to photosystem degradation. << Less

  Plant Cell 28:2147-2160(2016) [PubMed] [EuropePMC]

  This publication is cited by 1 other entry.

• Insights into the structure and function of the rate-limiting enzyme of chlorophyll degradation through analysis of a bacterial Mg-dechelatase homolog.

  Dey D., Dhar D., Fortunato H., Obata D., Tanaka A., Tanaka R., Basu S., Ito H.

  The Mg-dechelatase enzyme encoded by the <i>Stay-Green</i> (<i>SGR</i>) gene catalyzes Mg²⁺ dechelation from chlorophyll <i>a.</i> This reaction is the first committed step of chlorophyll degradation pathway in plants and is thus indispensable for the process of leaf senescence. There i ... >> More

  The Mg-dechelatase enzyme encoded by the <i>Stay-Green</i> (<i>SGR</i>) gene catalyzes Mg²⁺ dechelation from chlorophyll <i>a.</i> This reaction is the first committed step of chlorophyll degradation pathway in plants and is thus indispensable for the process of leaf senescence. There is no structural information available for this or its related enzymes. This study aims to provide insights into the structure and reaction mechanism of the enzyme through biochemical and computational analysis of an SGR homolog from the Chloroflexi <i>Anaerolineae</i> (AbSGR-h). Recombinant AbSGR-h with its intact sequence and those with mutations were overexpressed in <i>Escherichia coli</i> and their Mg-dechelatase activity were compared. Two aspartates - D34 and D62 were found to be essential for catalysis, while R26, Y28, T29 and D114 were responsible for structural maintenance. Gel filtration analysis of the recombinant AbSGR-h indicates that it forms a homo-oligomer. The three-dimensional structure of AbSGR-h was predicted by a deep learning-based method, which was evaluated by protein structure quality evaluation programs while structural stability of wild-type and mutant forms were investigated through molecular dynamics simulations. Furthermore, in concordance with the results of enzyme assay, molecular docking concluded the significance of D34 in ligand interaction. By combining biochemical analysis and computational prediction, this study unveils the detailed structural characteristics of the enzyme, including the probable pocket of interaction and the residues of structural and functional importance. It also serves as a basis for further studies on Mg-dechelatase such as elucidation of its reaction mechanism or inhibitor screening. << Less

  Comput Struct Biotechnol J 19:5333-5347(2021) [PubMed] [EuropePMC]

• Activity examination of plant Mg-dechelatase and its bacterial homolog in plants and in vitro.

  Ando S., Tanaka R., Ito H.

  Chlorophyll a serves as a photosynthetic pigment in plants. Its degradation is initiated by the extraction of the central Mg by the Mg-dechelatase enzyme, which is encoded by Stay-Green (SGR). Plant SGR is believed to be derived from bacterial SGR homolog obtained through horizontal gene transfer ... >> More

  Chlorophyll a serves as a photosynthetic pigment in plants. Its degradation is initiated by the extraction of the central Mg by the Mg-dechelatase enzyme, which is encoded by Stay-Green (SGR). Plant SGR is believed to be derived from bacterial SGR homolog obtained through horizontal gene transfer into photosynthetic eukaryotes. However, it is not known how the bacterial SGR homolog was modified to function in plants. To assess its adaptation mechanism in plants, a bacterial SGR homolog derived from the Anaerolineae bacterium SM23_63 was introduced into plants. It was found that the bacterial SGR homolog metabolized chlorophyll in plants. However, its chlorophyll catabolic activity was lower than that of plant SGR. Recombinant proteins of the bacterial SGR homolog exhibited higher activity than those of the plant SGR. The reduced chlorophyll catabolic activity of bacterial SGR homologs in plants may be associated with low hydrophobicity of the entrance to the catalytic site compared to that of plant SGR. This hinders the enzyme access to chlorophyll, which is localized in hydrophobic environments. This study offers insights into the molecular changes underlying the optimization of enzyme function. << Less

  Plant Physiol Biochem 215:109073-109073(2024) [PubMed] [EuropePMC]