Demonstration that the BchH protein of <i>Rhodobacter capsulatus</i> activates <i>S</i>‐adenosyl‐<scp>l</scp>‐methionine:magnesium protoporphyrin IX methyltransferase

Hinchigeri, S.B.; Hundle, Bhupinder S.; Richards, William R.

doi:10.1016/s0014-5793(97)00371-2

Cited by 54 publications

(43 citation statements)

References 41 publications

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“…Indeed, a tight channeling of substrate between the magnesium chelatase and the methyltransferase has been suspected for a long time due to the absence of detectable magnesium protoporphyrin intermediates in standard conditions (39). More recently, the physical interaction between CHLM and CHLH has been shown (40,7). During diurnal growth, the magnesium chelatase activity peaks during the transfer from dark to light, whereas the methyltransferase activity maximum follows only a few hours later.…”

Section: Discussionmentioning

confidence: 99%

Knock-out of the Magnesium Protoporphyrin IX Methyltransferase Gene in Arabidopsis

Pontier

Albrieux

Joyard

et al. 2007

Journal of Biological Chemistry

124

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Protoporphyrin IX is the last common intermediate between the heme and chlorophyll biosynthesis pathways. The addition of magnesium directs this molecule toward chlorophyll biosynthesis. The first step downstream from the branchpoint is catalyzed by the magnesium chelatase and is a highly regulated process. The corresponding product, magnesium protoporphyrin IX, has been proposed to play an important role as a signaling molecule implicated in plastid-to-nucleus communication. To get more information on the chlorophyll biosynthesis pathway and on magnesium protoporphyrin IX derivative functions, we have identified an magnesium protoporphyrin IX methyltransferase (CHLM) knock-out mutant in Arabidopsis in which the mutation induces a blockage downstream from magnesium protoporphyrin IX and an accumulation of this chlorophyll biosynthesis intermediate. Our results demonstrate that the CHLM gene is essential for the formation of chlorophyll and subsequently for the formation of photosystems I and II and cytochrome b6f complexes. Analysis of gene expression in the chlm mutant provides an independent indication that magnesium protoporphyrin IX is a negative effector of nuclear photosynthetic gene expression, as previously reported. Moreover, it suggests the possible implication of magnesium protoporphyrin IX methyl ester, the product of CHLM, in chloroplast-to-nucleus signaling. Finally, post-transcriptional up-regulation of the level of the CHLH subunit of the magnesium chelatase has been detected in the chlm mutant and most likely corresponds to specific accumulation of this protein inside plastids. This result suggests that the CHLH subunit might play an important regulatory role when the chlorophyll biosynthetic pathway is disrupted at this particular step.Chloroplast development depends on the coordinated synthesis of chlorophylls and cognate proteins and on their specific integration into photosynthetic complexes (for review, see Ref. 1). Chlorophylls are magnesium tetrapyrrole molecules resulting from condensation of ALA.2 Insertion of magnesium into protoporphyrin IX, the last common intermediate of hemes and chlorophylls, is catalyzed by magnesium chelatase, a membrane-interacting multisubunit enzyme containing 3 different soluble proteins: CHLH, CHLI, and CHLD (2-5). In the next step, magnesium protoporphyrin IX is methylated by a membrane Ado-Met-dependent methyltransferase. In Arabidopsis the gene At4g25080 or CHLM has been identified as encoding the methyltransferase enzyme, and the product of this single gene has been reported to be present in the two chloroplast membrane systems; that is, the envelope and the thylakoids (6). Whereas a sequence homologous to CHLM has been identified in tobacco (7), the existence in plants of an additional and quite dissimilar gene for magnesium protoporphyrin IX methylation has not been totally excluded. Expression analysis of tobacco CHLM revealed posttranslational activation of methyltransferase activity during greening and direct interaction of CHLM with the CHLH subun...

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Section: Discussionmentioning

confidence: 99%

Knock-out of the Magnesium Protoporphyrin IX Methyltransferase Gene in Arabidopsis

Pontier

Albrieux

Joyard

et al. 2007

Journal of Biological Chemistry

124

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“…This porphyrin forms a very tight (possibly covalent) attachment to the H subunit and renders it inactive ; this may be an additional mechanism for the inhibition of Bchl biosynthesis by high oxygen tension and light [69]. Additionally, it has been observed that, in itro, the presence of the H subunit increases the activity of the next enzyme in the pathway, namely the methyltransferase [70]. Interestingly, in whole Rhodobacter cells, it was found that Mgchelatase activity was only measurable if S-adenosylmethionine was included to allow the methyltransferase to operate [12].…”

Section: Regulation Of Bacterial Gene Transcriptionmentioning

confidence: 99%

Mechanism and regulation of Mg-chelatase

Walker

Willows

1997

Biochemical Journal

229

173

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Mg-chelatase catalyses the insertion of Mg into protoporphyrin IX (Proto). This seemingly simple reaction also is potentially one of the most interesting and crucial steps in the (bacterio)chlorophyll (Bchl/Chl)-synthesis pathway, owing to its position at the branch-point between haem and Bchl/Chl synthesis. Up until the level of Proto, haem and Bchl/Chl synthesis share a common pathway. However, at the point of metal-ion insertion there are two choices: Mg2+ insertion to make Bchl/Chl (catalysed by Mg-chelatase) or Fe2+ insertion to make haem (catalysed by ferrochelatase). Thus the relative activities of Mg-chelatase and ferrochelatase must be regulated with respect to the organism's requirements for these end products . How is this regulation achieved? For Mg-chelatase, the recent design of an in vitro assay combined with the identification of Bchl-biosynthetic enzyme genes has now made it possible to address this question. In all photosynthetic organisms studied to date, Mg-chelatase is a three-component enzyme, and in several species these proteins have been cloned and expressed in an active form. The reaction takes place in two steps, with an ATP-dependent activation followed by an ATP-dependent chelation step. The activation step may be the key to regulation, although variations in subunit levels during diurnal growth may also play a role in determining the flux through the Bchl/Chl and haem branches of the pathway.

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“…It is proposed that GBP subdivides a small portion of GluTR for ALA synthesis, which is not controlled by the FLU-mediated repression of ALA synthesis in darkness (Czarnecki et al, 2011). Mutual interaction of enzymes, such as the Mg chelatase subunit CHLH and MgP methyltransferase, have been reported to stimulate the enzymatic activities (Hinchigeri et al, 1997;Alawady et al, 2005;Shepherd et al, 2005). Apart from these regulatory interactions of proteins, attachments of chemical-modifying groups and the posttranslational processing of amino acid side chains control the functions of proteins.…”

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confidence: 99%

Posttranslational Influence of NADPH-Dependent Thioredoxin Reductase C on Enzymes in Tetrapyrrole Synthesis

Richter

Peter²,

Rothbart³

et al. 2013

Plant Physiology

117

112

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The NADPH-dependent thioredoxin reductase C (NTRC) is involved in redox-related regulatory processes in chloroplasts and nonphotosynthetic active plastids. Together with 2-cysteine peroxiredoxin, it forms a two-component peroxide-detoxifying system that acts as a reductant under stress conditions. NTRC stimulates in vitro activity of magnesium protoporphyrin IX monomethylester (MgPMME) cyclase, most likely by scavenging peroxides. Reexamination of tetrapyrrole intermediate levels of the Arabidopsis (Arabidopsis thaliana) knockout ntrc reveals lower magnesium protoporphyrin IX (MgP) and MgPMME steadystate levels, the substrate and the product of MgP methyltransferase (CHLM) preceding MgPMME cyclase, while MgP strongly accumulates in mutant leaves after 5-aminolevulinic acid feeding. The ntrc mutant has a reduced capacity to synthesize 5-aminolevulinic acid and reduced CHLM activity compared with the wild type. Although transcript levels of genes involved in chlorophyll biosynthesis are not significantly altered in 2-week-old ntrc seedlings, the contents of glutamyl-transfer RNA reductase1 (GluTR1) and CHLM are reduced. Bimolecular fluorescence complementation assay confirms a physical interaction of NTRC with GluTR1 and CHLM. While ntrc contains partly oxidized CHLM, the wild type has only reduced CHLM. As NTRC also stimulates CHLM activity in vitro, it is proposed that NTRC has a regulatory impact on the redox status of conserved cysteine residues of CHLM. It is hypothesized that a deficiency of NTRC leads to a lower capacity to reduce cysteine residues of GluTR1 and CHLM, affecting the stability and, thereby, altering the activity in the entire tetrapyrrole synthesis pathway.During the last decades, almost all enzymes of tetrapyrrole biosynthesis and their complex network of transcriptional regulation have been comprehensively studied (Tanaka et al., 2011). These studies revealed a complex control of the expression of genes encoding enzymes in the light-regulated chlorophyll (Chl)-synthesizing branch of tetrapyrrole metabolism. In brief, 5-aminolevulinic acid (ALA) is synthesized in a transfer RNA (tRNA) GLU -mediated pathway, and eight molecules of ALA are ultimately converted in a series of enzymatic steps to protoporphyrin IX. The polymeric magnesium (Mg) chelatase complex consisting of the three different subunits CHLH, CHLI, and CHLD directs protoporphyrin IX into the Mg branch of tetrapyrrole biosynthesis. Methylation of magnesium protoporphyrin (MgP) by MgP methyltransferase (CHLM) at the C13 of pyrrole ring C initiates the formation of the typical fifth ring. The product of this step, magnesium protoporphyrin monomethylester (MgPMME), is then converted to divinyl protochlorophyllide (PChlide) by an oxidative cyclase complex. NADPH:protochlorophyllide oxidoreductase (POR) synthesizes chlorophyllide (Chlide). PChlide and Chlide are most likely the main substrates of a divinyl reductase that reduces the C7-C8 double bond, forming a monovinyl product. The two final steps of Chl a and b synthesis are likely ...

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Demonstration that the BchH protein of Rhodobacter capsulatus activates S‐adenosyl‐l‐methionine:magnesium protoporphyrin IX methyltransferase

Cited by 54 publications

References 41 publications

Knock-out of the Magnesium Protoporphyrin IX Methyltransferase Gene in Arabidopsis

Knock-out of the Magnesium Protoporphyrin IX Methyltransferase Gene in Arabidopsis

Mechanism and regulation of Mg-chelatase

Posttranslational Influence of NADPH-Dependent Thioredoxin Reductase C on Enzymes in Tetrapyrrole Synthesis

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