Regulation of the Tetrapyrrole Biosynthetic Pathway

Zeilstra-Ryalls, Jill H.

doi:10.1007/978-1-4020-8815-5_39

Cited by 4 publications

(4 citation statements)

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“…The connectivity between regulated ALA production and the ability to effectively and efficiently transition between different energy metabolisms in not just R. sphaeroides , but also other anoxygenic phototrophic bacteria, makes it important to develop a complete picture of this interplay of events. We have already noted that R. sphaeroides is not exceptional in having multiple ALA synthase genes (Zeilstra‐Ryalls, ) and, as we have found here for HemA and HemT, in Rhodopseudomonas palustris , differential feedback inhibition by hemin of its two ALA synthases enzymes, HemA and HemO, has also been reported (Zhang et al ., ). However, in the absence of an accompanying description of the ALA synthase gene transcription patterns, it is not known whether or not the situation is analogous to what we have presented herein for R. sphaeroides 2.4.9.…”

Section: Discussionsupporting

confidence: 86%

“…For over 20 years following the initial discovery (Tai et al ., ), R. sphaeroides remained the only bacterium known to have two ALA synthase genes coding for enzymes that catalyze the pyridoxal‐dependent condensation of glycine and succinyl‐CoA reaction producing ALA. Then genomic sequencing of other α‐proteobacteria, the only prokaryotes that use this so‐called Shemin pathway of ALA formation in tetrapyrrole production, revealed that some among them have as many as four ALA synthase genes (Zeilstra‐Ryalls, ). Such an astounding number of these enzymes in bacteria has remained unexplained, although it is well‐established in animals that one ALA synthase gene is expressed in all tissues, while the second is erythroid‐specific (Riddle et al ., ; Bishop et al ., ; Cox et al ., ).…”

Section: Introductionmentioning

confidence: 99%

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Resolving the roles of the Rhodobacter sphaeroides HemA and HemT 5‐aminolevulinic acid synthases

Stoian

Kaganjo

Zeilstra-Ryalls

2018

Molecular Microbiology

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Strains of the phototrophic alpha-proteobacterium Rhodobacter sphaeroides vary in the number of enzymes catalyzing the formation of 5-aminolevulinic acid (ALA synthases) that are encoded in their genomes. All have hemA, but not all have hemT. This study compared transcription of these genes, and also properties of their products among three wild-type strains; 2.4.3 has hemA alone, 2.4.1 and 2.4.9 have both hemA and hemT. Using lacZ reporter plasmids all hemA genes were found to be upregulated under anaerobic conditions, but induction amplitudes differ. hemT is transcriptionally silent in 2.4.1 but actively transcribed in 2.4.9, and strongly upregulated under anaerobic-dark growth conditions when cells are respiring dimethyl sulfoxide, vs. aerobic-dark or phototrophic (anaerobic-light) conditions. Two extracytoplasmic function (ECF)-type sigma factors present in 2.4.9, but absent from 2.4.1 are directly involved in hemT transcription. Kinetic properties of the ALA synthases of all three strains were similar, but HemT enzymes are far less sensitive to feedback inhibition by hemin than HemA enzymes, and HemT is less active under oxidizing conditions. A model is presented that compares and contrast events in strains 2.4.1 and 2.4.9.

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Section: Discussionsupporting

confidence: 86%

Section: Introductionmentioning

confidence: 99%

Resolving the roles of the Rhodobacter sphaeroides HemA and HemT 5‐aminolevulinic acid synthases

Stoian

Kaganjo

Zeilstra-Ryalls

2018

Molecular Microbiology

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“…Tetrapyrrole synthesis is thus strictly regulated (for a review, see reference 50). There are two major points at which the biosynthetic pathway is controlled as a function of oxygen tension (50). One is at the first reaction shown in Fig.…”

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confidence: 99%

Coproporphyrin Excretion and Low Thiol Levels Caused by Point Mutation in the Rhodobacter sphaeroides S -Adenosylmethionine Synthetase Gene

et al. 2010

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A spontaneous mutant of Rhodobacter sphaeroides f. sp. denitrificans IL-106 was found to excrete a large amount of a red compound identified as coproporphyrin III, an intermediate in bacteriochlorophyll and heme synthesis. The mutant, named PORF, is able to grow under phototrophic conditions but has low levels of intracellular cysteine and glutathione and overexpresses the cysteine synthase CysK. The expression of molybdoenzymes such as dimethyl sulfoxide (DMSO) and nitrate reductases is also affected under certain growth conditions. Excretion of coproporphyrin and overexpression of CysK are not directly related but were both found to be consequences of a diminished synthesis of the key metabolite S-adenosylmethionine (SAM). The wild-type phenotype is restored when the gene metK encoding SAM synthetase is supplied in trans. The metK gene in the mutant strain has a mutation leading to a single amino acid change (H145Y) in the encoded protein. This point mutation is responsible for a 70% decrease in intracellular SAM content which probably affects the activities of numerous SAM-dependent enzymes such as coproporphyrinogen oxidase (HemN); uroporphyrinogen III methyltransferase (CobA), which is involved in siroheme synthesis; and molybdenum cofactor biosynthesis protein A (MoaA). We propose a model showing that the attenuation of the activities of SAM-dependent enzymes in the mutant could be responsible for the coproporphyrin excretion, the low cysteine and glutathione contents, and the decrease in DMSO and nitrate reductase activities.

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“…It is possible that FnrL-dependant genes are essential for anaerobic respiration and anaerobic PS. One important function of FnrL is activation of transcription of the hemN (RSP0317) and hemZ (RSP0699) genes whose products catalyse the anoxic decarboxylation of coproporphyrinogen III to protoporphyrinogen IX, the common precursor of haem and bacteriochlorophyll synthesis (reviewed in Zeilstra-Ryalls, 2008). In the absence of DorS, its cognate response regulator DorR does not turn on expression of the DMSO reductase operon dorCBA (Mouncey & Kaplan, 1998a,b).…”

Section: The Fnrl Regulonmentioning

confidence: 99%