Structure of the Cyanobacterial Magnesium Chelatase H Subunit Determined by Single Particle Reconstruction and Small-angle X-ray Scattering

Qian, Pu; Marklew, Christopher J.; Viney, Joanne L.; Davison, Paul A.; Brindley, Amanda A.; Söderberg, Christopher; Al-Karadaghi, Salam; Bullough, Per A.; Großmann, Joachim; Hunter, C. Neil

doi:10.1074/jbc.m111.308239

Cited by 20 publications

(34 citation statements)

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“…CHLH protein sequences are well conserved from photosynthetic bacteria to land plants. In addition, the protein structure of CHLH has been studied using single-particle reconstruction and small-angle X-ray scattering (Qian et al, 2012), and the crystal structure of Synechocystis PCC6803 CHLH (SynCHLH) was recently solved at 2.5 Å resolution (Chen et al, 2015). SynCHLH is thought to consist of six domains (I–VI, Supplementary Figures 1, 14), with small amino (N)-terminal domains (domains I and II) that form a “head” and “neck” structure, followed by a cage-like assembly (domains III-VI).…”

Section: Introductionmentioning

confidence: 99%

“…SynCHLH is thought to consist of six domains (I–VI, Supplementary Figures 1, 14), with small amino (N)-terminal domains (domains I and II) that form a “head” and “neck” structure, followed by a cage-like assembly (domains III-VI). It was reported that CHLH predominantly exists as a monomer in solution (Qian et al, 2012), whereas a loosely bound CHLH dimer was observed in the crystal. The dimerization interface are domains I and V, which is consistent with a previous study that removal of the N-terminal 159 residues of T. elongates ChlH facilitates a monomeric state (Adams et al, 2014).…”

Section: Introductionmentioning

confidence: 99%

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CHLH/GUN5 Function in Tetrapyrrole Metabolism Is Correlated with Plastid Signaling but not ABA Responses in Guard Cells

2016

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Expression of Photosynthesis-Associated Nuclear Genes (PhANGs) is controlled by environmental stimuli and plastid-derived signals (“plastid signals”) transmitting the developmental and functional status of plastids to the nucleus. Arabidopsis genomes uncoupled (gun) mutants exhibit defects in plastid signaling, leading to ectopic expression of PhANGs in the absence of chloroplast development. GUN5 encodes the plastid-localized Mg-chelatase enzyme subunit (CHLH), and recent studies suggest that CHLH is a multifunctional protein involved in tetrapyrrole biosynthesis, plastid signaling and ABA responses in guard cells. To understand the basis of CHLH multifunctionality, we investigated 15 gun5 missense mutant alleles and transgenic lines expressing a series of truncated CHLH proteins in a severe gun5 allele (cch) background (tCHLHs, 10 different versions). Here, we show that Mg-chelatase function and plastid signaling are generally correlated; in contrast, based on the analysis of the gun5 missense mutant alleles, ABA-regulated stomatal control is distinct from these two other functions. We found that none of the tCHLHs could restore plastid-signaling or Mg-chelatase functions. Additionally, we found that both the C-terminal half and N-terminal half of CHLH function in ABA-induced stomatal movement.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

CHLH/GUN5 Function in Tetrapyrrole Metabolism Is Correlated with Plastid Signaling but not ABA Responses in Guard Cells

2016

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“…Rather less is known about the H subunit, although a low-resolution structural model of BchH from Rba. capsulatus has been obtained through 3D reconstruction of negatively stained single particles [ 17 ], and a similar approach, augmented by SAXS, was used to determine a low resolution structure of the cyanobacterial ChlH subunit [ 18 ]. In contrast with the more open BchH structure, ChlH forms a more enclosed cage-like assembly, connected to an N-terminal ‘head’ region adjacent to a 5 nm-diameter opening in the structure.…”

Section: Introductionmentioning

confidence: 99%

“…In contrast with the more open BchH structure, ChlH forms a more enclosed cage-like assembly, connected to an N-terminal ‘head’ region adjacent to a 5 nm-diameter opening in the structure. It was suggested that the more enclosed ChlH structure affords some protection for the labile MgProto product, given the potentially damaging combination of light and oxygen within cells of oxygenic phototrophs such as cyanobacteria and plants [ 18 ]. A more complex structure for the ChlH with respect to BchH could also be a consequence of interactions with the Gun4 protein [ 19 , 20 ], which stimulates Mg-chelatase at low magnesium concentrations [ 21 ].…”

Section: Introductionmentioning

confidence: 99%

“…The N-terminal ‘head’ domain of ChlH of T. elongatus was identified by binding NTA–Nanogold to the N-terminal His 6 tag [ 18 ]. This domain, estimated with the ‘neck’ to have a molecular mass of ~17.6 kDa, is of interest given its location adjacent to the entrance to the lumen within ChlH and its connection to the main body of ChlH through a narrow linker region between Gly 127 and Phe 156 .…”

Section: Introductionmentioning

confidence: 99%

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Structural and functional consequences of removing the N-terminal domain from the magnesium chelatase ChlH subunit of Thermosynechococcus elongatus

Adams

Marklew

Qian

et al. 2014

Biochemical Journal

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Magnesium chelatase (MgCH) initiates chlorophyll biosynthesis by catalysing the ATP-dependent insertion of Mg2+ into protoporphyrin. This large enzyme complex comprises ChlH, I and D subunits, with I and D involved in ATP hydrolysis, and H the protein that handles the substrate and product. The 148 kDa ChlH subunit has a globular N-terminal domain attached by a narrow linker to a hollow cage-like structure. Following deletion of this ~18 kDa domain from the Thermosynechoccus elongatus ChlH, we used single particle reconstruction to show that the apo- and porphyrin-bound forms of the mutant subunit consist of a hollow globular protein with three connected lobes; superposition of the mutant and native ChlH structures shows that, despite the clear absence of the N-terminal ‘head’ region, the rest of the protein appears to be correctly folded. Analyses of dissociation constants shows that the ΔN159ChlH mutant retains the ability to bind protoporphyrin and the Gun4 enhancer protein, although the addition of I and D subunits yields an extremely impaired active enzyme complex. Addition of the Gun4 enhancer protein, which stimulates MgCH activity significantly especially at low Mg2+ concentrations, partially reactivates the ΔN159ChlH–I–D mutant enzyme complex, suggesting that the binding site or sites for Gun4 on H do not wholly depend on the N-terminal domain.

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Chlorophylls

Fujita

2015

Encyclopedia of Life Sciences

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Chlorophylls (Chls) are a group of cyclic tetrapyrrole pigments that are involved in the light reactions of photosynthesis. There are many Chls differing in chemical structures; Chls a , b , c , d and f and bacteriochlorophylls (BChls) a , b , c , d , e , f and g . All Chls are classified into three groups by their parental structure; porphyrins, chlorins and bacteriochlorins. Upon absorption of light the Chl molecule transitions into the first excited singlet state, and the captured energy is transferred to the neighbouring Chl molecules reaching the reaction centre Chl molecules to ignite the photosynthetic electron transfer. All Chls are synthesised from 5‐aminolevulinic acid via multiple enzymatic reactions. The first half of this biosynthetic pathway is shared with haem biosynthesis and the second half is specific for Chls, which is the so‐called magnesium (Mg) branch. In the Mg branch, the reactions from protoporphyrin IX to chlorophyllide a constitute a common pathway for all Chls. Key Concepts Chlorophylls have a central role in light harvesting and ignition of photosynthetic electron transfer. Chlorophylls are functionally divided into antenna chlorophylls and reaction centre chlorophylls. A variety of chemically different chlorophylls absorb different wavelengths of light, and photosynthetic organisms have specific sets of chlorophylls for utilising light in their natural habitats. All chlorophylls are synthesised from 5‐aminolaevulinic acid, and the subsequent six reactions leading to protoporphyrin IX are common to haem biosynthesis. Five reactions from protoporphyrin IX to chlorophyllide a are shared with the biosynthetic pathways of all chlorophylls. The diversity of the biosynthetic pathways of different chlorophylls results from the evolution of photosynthetic organisms to adapt their light environments. Chlorophyll biosynthesis is tightly regulated by multiple layers of regulatory mechanisms to avoid photooxidative damage caused by biosynthetic intermediates. Elucidation of the reaction mechanisms of enzymes involved in the magnesium branch is one of the most important goals in plant physiology.

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Structure of the Cyanobacterial Magnesium Chelatase H Subunit Determined by Single Particle Reconstruction and Small-angle X-ray Scattering

Cited by 20 publications

References 63 publications

CHLH/GUN5 Function in Tetrapyrrole Metabolism Is Correlated with Plastid Signaling but not ABA Responses in Guard Cells

CHLH/GUN5 Function in Tetrapyrrole Metabolism Is Correlated with Plastid Signaling but not ABA Responses in Guard Cells

Structural and functional consequences of removing the N-terminal domain from the magnesium chelatase ChlH subunit of Thermosynechococcus elongatus

Chlorophylls

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