My favorite cell: Giardia

Upcroft, Jacqueline; Upcroft, Peter

doi:10.1002/(sici)1521-1878(199803)20:3<256::aid-bies9>3.0.co;2-p

Cited by 77 publications

(68 citation statements)

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“…So essential is pyruvate oxidation to the anaerobic metabolism of some microbes and amitochondriate eukaryotes that it is the target of metronidazole and tinidazole, which are common treatments against infections by Helicobacter pylori and the protozoan parasites, Giardia and Trichomonas vaginalis. 16 The low potential generated by the pyruvate/acetylCoA redox couple leads to the formation of nitro radicals by these pharmaceuticals. 17 …”

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confidence: 99%

Pulsed Electron Paramagnetic Resonance Experiments Identify the Paramagnetic Intermediates in the Pyruvate Ferredoxin Oxidoreductase Catalytic Cycle

et al. 2006

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Pyruvate ferredoxin oxidoreductase (PFOR) 1 is a thiamine pyrophosphate (TPP)-dependent enzyme that catalyzes the anaerobic oxidation of pyruvate (with CoA) to acetyl-CoA, CO 2 , and two electrons that are transferred to ferredoxin (eq 1). 2 In this paper, the PFOR electrontransfer mechanism is examined. Early steps in the catalytic cycle follow the Breslow 3 mechanism of TPP activation. After deprotonation, the carbanion at C-2 of TPP reacts with pyruvate to form 2-lactyl-TPP, which decarboxylates to generate CO 2 and the resonant enamine/carbanion intermediate, hydroxyethylidene-TPP (HE-TPP). The fate of this intermediate differs among the TPP-dependent enzymes. In PFOR, oxidation of the intermediate is linked to reduction of an external electron acceptor, for example, the clostridial ferredoxin, which contains two [4Fe-4S] clusters.(1)After formation of HE-TPP, the next step in the PFOR mechanism is one-electron transfer from HE-TPP to one of three [4Fe-4S] 2+ clusters, which generates a paramagnetic [4Fe-4S] 1+ cluster and an HE-TPP radical. 4 This paramagnetic intermediate forms at a rate constant of 140 s −1 at 10 °C (~3000 s −1 at the growth temperature of 55 °C). 4 On the basis of the PFOR structure, 5 cluster A, located only 9.5 Å from the thiazole sulfur of HE-TPP, is one of three [4Fe-4S] clusters that are separated by 10-12 Å (Figure 1). 6 Since biological electron transfer is facile whenever the donor and acceptor are within ~15 Å, clusters A (proximal), B (medial), and C (distal, ~4 Å from the surface) are ideally positioned to sequentially transfer electrons to the surface and the external ferredoxin. Cluster A is logically the first to be reduced, since clusters B and C are >20 Å from the radical center on HE-TPP. In the pulsed ELDOR experiment, the primary electron spin-echo (ESE) signal of the [4Fe-4S] 1+ cluster was observed, while the pumping microwave pulse was in resonance with the HE-TPP radical. The Fourier transform (FT) spectrum of the time-domain ELDOR trace exhibits a prominent peak at 1.5 MHz and a smaller feature at 2.7 MHz (trace 1 in Figure 2). Although this spectral shape is reasonably close to that expected in a situation of complete orientational disorder, some orientational selectivity caused by the g-anisotropy of the [4Fe-4S] 1+ center cannot be excluded. To remove the ambiguity, a RIDME experiment was performed. 11 In this experiment, we observed a refocused stimulated ESE signal of the HE-TPP radical, while the longitudinal relaxation of the [4Fe-4S] 1+ center (instead of pumping at a different microwave frequency) served the purpose of modifying the local magnetic field for the radical spin. Since the [4Fe-4S] 1+ center at any orientation is subject to longitudinal relaxation, 12 there is no orientational selectivity in the RIDME experiment.The RIDME experiment was performed at 13 and 4.2 K. At 13 K, the cluster relaxes much more rapidly than at 4.2 K. The difference between the two stimulated ESE spectra gave the RIDME spectrum shown by trace 2 in Figure 2. The only reli...

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Pulsed Electron Paramagnetic Resonance Experiments Identify the Paramagnetic Intermediates in the Pyruvate Ferredoxin Oxidoreductase Catalytic Cycle

et al. 2006

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“…lamblia, also known as G. intestinalis or G. duodenalis, is a unicellular parasite infecting human large intestine and causing severe diarrhea [1][2][3][4][5][6]. According to B. Ford, it was first observed by Antony van Leeuwenhoeck back in 1681 [7], as very small organisms, with a large body and a flattish belly with little paws and stir movements.…”

Section: Introductionmentioning

confidence: 99%

“…lamblia also belongs to early divergent lineages of eukaryotes as revealed by protein or nucleic acids sequence analysis [9][10][11], although reduced processes also may have occurred [12]. Studies on the cell biology of G. lamblia have described several organelles as nuclei, mitosomes, flagella, several elements of cytoskeleton, but definite proof for the presence of Golgi apparatus or endoplasmic reticulum have not been documented [1][2][3][4][5][6]. For a long time G. lamblia was known as the only eukaryote lacking nucleoli.…”

Section: Introductionmentioning

confidence: 99%

The Nucleolus of Giardia lamblia

Jiménez‐García¹

2017

MOJAP

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The nucleolus is the major site of ribosome biogenesis in eukaryotes. Until recently, G. lamblia was considered the only eukaryote lacking nucleoli. Recently, light and electron microscopy cytochemical techniques have been used to demonstrate the presence of nucleoli in the interphase nucleus of G. lamblia. Here we review the work made during the last few years on the nucleolus of G. lamblia in interphase and cell division. This mini review indicates that nucleoli are present in G. lamblia interphase cell nuclei. Also, the persistence of nucleoli during cell division was documented more recently. Therefore, microscopical anatomy of G. lamblia should include the presence of authentic morphological nucleoli.

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“…Lamblia, also known as G. Intestinalis or G. DSuodenalis, is a unicellular parasite infecting human large intestine and causing severe diarrhea. [1][2][3][4][5][6] According to B. Ford, it was first observed by Antony van Leeuwenhoeck back in 1681, 7 as very small organisms, with a large body and a flattish belly with little paws and stir movements. G. Lamblia was later described taxonomically.…”

Section: Introductionmentioning

confidence: 99%

“…12 Studies on the cell biology of G. Lamblia have described several organelles as nuclei, mitosomes, flagella, several elements of cytoskeleton, but definite proof for the presence of Golgi apparatus or endoplasmic reticulum have not been documented. [1][2][3][4][5][6] For a long time G. Lamblia was known as the only eukaryote lacking nucleoli. Since the detailed analysis searching for nucleoli failed to show the presence of nucleoli in Giardia even by using immunocytochemistry and in situ hybridization combined with the use of confocal microscopy, 13 it was asked whether classical cytochemical staining as silver staining for nucleolar organizer would produce better contrast than fluorescent techniques.…”

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confidence: 99%

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2017

MOJAP

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Abbreviations: AgNOR, silver staining for nucleolar organizer region; NOR, nucleolar organizer region; Rrna, ribosomal rna; TEM, transmission electron microscopy Introduction G. Lamblia, also known as G. Intestinalis or G. DSuodenalis, is a unicellular parasite infecting human large intestine and causing severe diarrhea.1-6 According to B. Ford, it was first observed by Antony van Leeuwenhoeck back in 1681, 7 as very small organisms, with a large body and a flattish belly with little paws and stir movements. G. Lamblia was later described taxonomically. 8G. Lamblia also belongs to early divergent lineages of eukaryotes as revealed by protein or nucleic acids sequence analysis, 9-11 although reduced processes also may have occurred.12 Studies on the cell biology of G. Lamblia have described several organelles as nuclei, mitosomes, flagella, several elements of cytoskeleton, but definite proof for the presence of Golgi apparatus or endoplasmic reticulum have not been documented.1-6 For a long time G. Lamblia was known as the only eukaryote lacking nucleoli. Since the detailed analysis searching for nucleoli failed to show the presence of nucleoli in Giardia even by using immunocytochemistry and in situ hybridization combined with the use of confocal microscopy, 13 it was asked whether classical cytochemical staining as silver staining for nucleolar organizer would produce better contrast than fluorescent techniques.The first evidence for the presence of nucleoli in G. Duodenalis, G. Intestinalis or G. Lamblia was obtained after using silver staining for nucleolar organizer regions (AgNOR) for light microscopy. Nucleolar material was observed as small fiber-granular areas of impregnation around 0.3µm large (Figure 1).14 Then, transmission electron microscopy (TEM) confirmed this result. In fact, standard technique for TEM produced results indicating an intranuclear electron dense material at the periphery of nuclei (Figure 2), that in addition was positive to silver staining for NOR, for RNA using the EDTA method for RNA, silver staining for NOR at the EM level followed by immunoelectron microscopy for fibrillarin and high resolution in situ hybridization for rRNA. Analysis of expression of transfected rRNA-pseudouridine synthase (CBF5) and confocal microscopy confirmed these results. Later on, additional light and electron microscopy techniques also revealed the presence of nucleoli (Figure 3). 15 Microscopical anatomy of G. Lamblia therefore, includes the presence of nucleoli. 4-6,16 Figure 1A) Bright field light microscopy after silver staining for nucleolar organizer region (AgNOR) staining in G. lamblia. B)Same image as A processed to enhance the silver stained material. Nucleolus is present as peripheral structures within both cell nuclei.More recently, it was reported further confirmation of the presence of nucleoli in G. Lamblia in interphase and also the persistence of this organelle through cell division, 17 therefore indicating that the process of nucleolar biogenesis does not include the formation of th...

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My favorite cell: Giardia

Cited by 77 publications

References 79 publications

Pulsed Electron Paramagnetic Resonance Experiments Identify the Paramagnetic Intermediates in the Pyruvate Ferredoxin Oxidoreductase Catalytic Cycle

Pulsed Electron Paramagnetic Resonance Experiments Identify the Paramagnetic Intermediates in the Pyruvate Ferredoxin Oxidoreductase Catalytic Cycle

The Nucleolus of Giardia lamblia

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