Plant mitochondrial carriers: an overview

Laloi, Maryse

doi:10.1007/s000180050484

Cited by 107 publications

(90 citation statements)

References 213 publications

(244 reference statements)

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“…Animal mitochondria under normal physiological conditions do not transport oxaloacetate significantly, and only a minor amount is transported through the dicarboxylate or oxoglutaratemalate translocator. On the other hand, plant mitochondria transport oxaloacetate at rapid rates across the inner mitochondrial membrane (44). A BLAST search highlighted several translocators with unknown functions in P. falciparum (38), which will require further characterization with regard to their cellular localization and specificity for different dicarboxylic acids.…”

Section: Discussionmentioning

confidence: 99%

Metabolic Fate of Fumarate, a Side Product of the Purine Salvage Pathway in the Intraerythrocytic Stages of Plasmodium falciparum

Bulusu¹,

Jayaraman²,

Balaram

2011

Journal of Biological Chemistry

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In aerobic respiration, the tricarboxylic acid cycle is pivotal to the complete oxidation of carbohydrates, proteins, and lipids to carbon dioxide and water. Plasmodium falciparum, the causative agent of human malaria, lacks a conventional tricarboxylic acid cycle and depends exclusively on glycolysis for ATP production. However, all of the constituent enzymes of the tricarboxylic acid cycle are annotated in the genome of P. Plasmodium falciparum is a parasitic protozoan, which causes the most severe form of malaria in humans. Because of the emergence in the parasite of widespread drug resistance to most of the first-line antimalarials, the development of new drugs that target the parasite metabolism is needed. Over several years, malarial parasites have been studied to understand various novel biochemical features, which not only gives opportunities for chemotherapeutic interventions but also stimulates broader scientific interests.During the intraerythrocytic stages of P. falciparum, the tricarboxylic acid cycle does not seem to function like a conventional tricarboxylic acid cycle for the following reasons. (a) The bulk of the glucose is metabolized to lactate by anaerobic glycolysis, which is then secreted by the parasite as a metabolic waste (1) (2). As a result, unlike aerobic cells, in P. falciparum there is minimal carbon flow from the cytoplasm to the mitochondrial tricarboxylic acid cycle. (b) The multi-enzyme complex pyruvate dehydrogenase, which channels pyruvate into the tricarboxylic acid cycle through acetyl-CoA, has been found to localize on the apicoplast membrane in P. falciparum (3), unlike mammalian cells, where the enzyme is present on the inner mitochondrial membrane (4). (c) The enzyme isocitrate dehydrogenase generates NADPH rather than NADH (5), thereby implying that its main role is probably to act as a redox sensor rather than donating reducing equivalents to the electron transport chain. In addition, P. falciparum synthesizes ATP mainly by substrate level phosphorylation through glycolysis and not through oxidative phosphorylation (6), suggesting that the primary function of the tricarboxylic acid cycle in generating reducing equivalents for the electron transport chain might be dispensable for the parasite. However, genes for all of the enzymes of the tricarboxylic acid cycle are present and are expressed in P. falciparum (7,8) during the intraerythrocytic stages, thereby implying that the pathway probably has important, yet unidentified biosynthetic functions.Unlike its human host, P. falciparum lacks the de novo purine biosynthetic pathway and is hence completely dependent on the purine salvage pathway to meet its purine nucleotide requirements (9). In the purine salvage pathway, hypoxanthine salvaged from the host is phosphoribosylated to IMP, which then branches out to form AMP and GMP (Fig. 1). IMP is converted to AMP in two steps, catalyzed by two distinct enzymes: (a) adenylosuccinate synthetase, which adds a molecule of aspartate to the 6-oxo position of IMP with a concomitan...

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Section: Discussionmentioning

confidence: 99%

Metabolic Fate of Fumarate, a Side Product of the Purine Salvage Pathway in the Intraerythrocytic Stages of Plasmodium falciparum

Bulusu¹,

Jayaraman²,

Balaram

2011

Journal of Biological Chemistry

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“…Furthermore, the plant and animal mitochondrial AAC proteins share similarities but also differences with respect to the mechanism of nucleotide transport (13,14). In animal mitochondria, the transport is limited to ATP and ADP and is driven by the membrane potential whereas plant mitochondrial carriers also can transport GDP and GTP and do not depend on a membrane potential (32).…”

Section: Discussionmentioning

confidence: 99%

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confidence: 99%

“…On the other hand, luminal preparations have been tested for presence of ATP and ATPase activity without any conclusive results (12), and none of the proteins identified through proteomics have shown to have any conventional nucleotide-binding motifs (10). Furthermore, transport of nucleotides across the thylakoid membrane has not been considered, in contrast to mitochondrial membranes, where an ATP͞ADP carrier (AAC) has been extensively studied (13,14).Chloroplast metabolism has mainly been associated with ATP, but more recent results also point to the physiological significance of GTP. Thus, requirement for stromal GTP has been reported for the integration of light-harvesting complex proteins into the thylakoid membrane (15) and the proteolytic removal of the PSII reaction center D1 protein during repair of photoinhibitory damage to this photosystem (16).…”

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Multiple evidence for nucleotide metabolism in the chloroplast thylakoid lumen

Spetea

Hundal

Lundin

et al. 2004

Proc. Natl. Acad. Sci. U.S.A.

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The apparatus of photosynthetic energy conversion in chloroplasts is quite well characterized with respect to structure and function. Light-driven electron transport in the thylakoid membrane is coupled to synthesis of ATP, used to drive energy-dependent metabolic processes in the stroma and the outer surface of the thylakoid membrane. The role of the inner (luminal) compartment of the thylakoids has, however, remained largely unknown although recent proteomic analyses have revealed the presence of up to 80 different proteins. Further, there are no reports concerning the presence of nucleotides in the thylakoid lumen. Here, we bring three lines of experimental evidence for nucleotide-dependent processes in this chloroplast compartment. T he thylakoid membrane of chloroplasts is the site for the photosynthetic electron transport coupled to ATP synthesis (1). This membrane is surrounded by the soluble stroma, which contains the enzymes involved in CO 2 fixation, and it encloses the luminal space. In contrast to the other chloroplast compartments, the thylakoid lumen has been considered to have a limited functional significance for the photosynthetic process and mainly viewed as a sink for protons from a chemio-osmotic perspective. Until recently the protein composition of the thylakoid lumen was thought to be very simple and dominated by three extrinsic photosystem (PS) II proteins and plastocyanin (2). In the last few years, however, many different categories of proteins have been found in the thylakoid lumen by applying biochemical and proteomic approaches, pointing to several unexpected functions for this chloroplast compartment. Thus, the thylakoid lumen has been found to contain chaperones (3), immunophilins (4), carbonic anhydrases (5), violaxanthin deepoxidases (6), peroxidases (7), and proteases (8). Furthermore, systematic mass spectrometric analyses after two-dimensional electrophoretic separation of luminal preparations combined with prediction of transit peptides estimated the existence of Ϸ80 different thylakoid luminal proteins of Arabidopsis thaliana (9, 10), out of which only half have been assigned a putative function.This considerably more complex view of the thylakoid lumen raises several questions of mechanistic and physiological nature related to chloroplast function and regulation. One of these questions concerns the presence of nucleotides in such a potentially multifunctional cellular compartment as particularly suggested by indications for luminal chaperones (3, 9) and ATP binding to luminal proteins (11). On the other hand, luminal preparations have been tested for presence of ATP and ATPase activity without any conclusive results (12), and none of the proteins identified through proteomics have shown to have any conventional nucleotide-binding motifs (10). Furthermore, transport of nucleotides across the thylakoid membrane has not been considered, in contrast to mitochondrial membranes, where an ATP͞ADP carrier (AAC) has been extensively studied (13,14).Chloroplast metabolism has mainly ...

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“…This large protein family is eukaryotic-specific, and supposedly arose after the appearance of mitochondria in the eukaryotic lineage, although its members are exclusively localized in the mitochondria (El Moualij et al, 1997). Plant mitochondrial carriers are attracting interest (Laloi, 1999) and our search found many members of this family (Table III). The uncoupling proteins found in plants and animals are a subfamily of mitochondrial carriers (Ricquier and Bouillaud, 2000) with a proposed role in cell defense.…”

Section: Discussionmentioning

confidence: 99%

Sugarcane genes related to mitochondrial function

et al. 2001

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Mitochondria function as metabolic powerhouses by generating energy through oxidative phosphorylation and have become the focus of renewed interest due to progress in understanding the subtleties of their biogenesis and the discovery of the important roles which these organelles play in senescence, cell death and the assembly of iron-sulfur (Fe/S) centers. Using proteins from the yeast Saccharomyces cerevisiae, Homo sapiens and Arabidopsis thaliana we searched the sugarcane expressed sequence tag (SUCEST) database for the presence of expressed sequence tags (ESTs) with similarity to nuclear genes related to mitochondrial functions. Starting with 869 protein sequences, we searched for sugarcane EST counterparts to these proteins using the basic local alignment search tool TBLASTN similarity searching program run against 260,781 sugarcane ESTs contained in 81,223 clusters. We were able to recover 367 clusters likely to represent sugarcane orthologues of the corresponding genes from S. cerevisiae, H. sapiens and A. thaliana with E-value ≤ 10 -10 . Gene products belonging to all functional categories related to mitochondrial functions were found and this allowed us to produce an overview of the nuclear genes required for sugarcane mitochondrial biogenesis and function as well as providing a starting point for detailed analysis of sugarcane gene structure and physiology.

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Plant mitochondrial carriers: an overview

Cited by 107 publications

References 213 publications

Metabolic Fate of Fumarate, a Side Product of the Purine Salvage Pathway in the Intraerythrocytic Stages of Plasmodium falciparum

Metabolic Fate of Fumarate, a Side Product of the Purine Salvage Pathway in the Intraerythrocytic Stages of Plasmodium falciparum

Multiple evidence for nucleotide metabolism in the chloroplast thylakoid lumen

Sugarcane genes related to mitochondrial function

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