4 results on '"Fui-Ching Tan"'
Search Results
2. Molecular characterisation of coproporphyrinogen oxidase from Glycine max and Arabidopsis thaliana
- Author
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Maria Angélica Santana, Alison G. Smith, and Fui-Ching Tan
- Subjects
Coproporphyrinogen III oxidase ,biology ,Physiology ,fungi ,Saccharomyces cerevisiae ,Plant Science ,biology.organism_classification ,Coproporphyrinogen III ,Molecular biology ,Green fluorescent protein ,chemistry.chemical_compound ,Coproporphyrinogen Oxidase ,chemistry ,Biochemistry ,Arabidopsis ,Complementary DNA ,Genetics ,Arabidopsis thaliana - Abstract
Coproporphyrinogen III oxidase (CPO; E.C. 1.3.3.3 ) is an enzyme of haem and chlorophyll synthesis. Biochemical studies have indicated that the majority of CPO activity is present in plastids, with no detectable levels in mitochondria. However, this approach cannot rule out low (less than 5%) activity in the mitochondria, nor the possible presence of CPO in the cytosol, where it is found in yeast (Saccharomyces cerevisiae). We have studied this question further using molecular techniques. A cDNA encoding the mature protein of soybean (Glycine max L.) CPO was used to overexpress the enzyme 200-fold in Escherichia coli. The recombinant enzyme, purified to homogeneity in three steps, is a dimer, with a Km for coproporphyrinogen III of 0.25 ± 0.03 μM and a Vmax of 1.48 pkat. Antibodies raised against the purified soybean CPO were used in western blots to show that the enzyme is present in etioplasts but not in mitochondria. In the completely sequenced genome of Arabidopsis thaliana, we identified two genes encoding CPO, but only one of them (AtCPO-I ) was able to complement a yeast mutant defective in the enzyme; the other is likely to be a pseudogene. A construct encoding the first 92 residues of AtCPO-I fused to green fluorescent protein (GFP) was introduced into Arabidopsis plants by Agrobacterium-mediated transformation. Confocal microscopy demonstrated that the CPO–GFP fusion protein was confined exclusively to plastids in leaves and roots, with no GFP seen in the mitochondria or cytosol.
- Published
- 2002
3. Two Types of Ferrochelatase in Photosynthetic and Nonphotosynthetic Tissues of Cucumber
- Author
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Hiroyuki Ohta, Davinder Pal Singh, Takuo Suzuki, Tohru Tsuchiya, Fui-Ching Tan, Tatsuru Masuda, Hiroshi Shimada, Alison G. Smith, and Ken-ichiro Takamiya
- Subjects
Gene isoform ,biology ,Protoporphyrin IX ,Cell Biology ,Ferrochelatase ,Reductase ,biology.organism_classification ,Biochemistry ,Tetrapyrrole ,Conserved sequence ,chemistry.chemical_compound ,chemistry ,Complementary DNA ,biology.protein ,Arabidopsis thaliana ,Molecular Biology - Abstract
Ferrochelatase catalyzes the insertion of Fe2+ into protoporphyrin IX to generate protoheme. In higher plants, there is evidence for two isoforms of this enzyme that fulfill different roles. Here, we describe the isolation of a second ferrochelatase cDNA from cucumber (CsFeC2) that was less similar to a previously isolated isoform (CsFeC1) than it was to some ferrochelatases from other higher plants. Inin vitro import experiments, the two cucumber isoforms showed characteristics similar to their respective ferrochelatase counterparts of Arabidopsis thaliana. The C-terminal region of CsFeC2 but not CsFeC1 contained a conserved motif found in light-harvesting chlorophyll proteins, and CsFeC2 belonged to a phylogenetic group of plant ferrochelatases containing this conserved motif. We demonstrate that CsFeC2 was localized predominantly in thylakoid membranes as an intrinsic protein, and forming complexes probably with the C-terminal conserved motif, but a minor portion was also detected in envelope membranes. CsFeC2 mRNA was detected in all tissues and was light-responsive in cotyledons, whereasCsFeC1 mRNA was detected in nonphotosynthetic tissues and was not light-responsive. Interestingly, tissue-, light-, and cycloheximide-dependent expressions of the two isoforms of ferrochelatase were similar to those of two glutamyl-tRNA reductase isoforms involved in the early step of tetrapyrrole biosynthesis, suggesting the existence of distinctly controlled tetrapyrrole biosynthetic pathways in photosynthetic and nonphotosynthetic tissues.
- Published
- 2002
4. Identification and characterization of the Arabidopsis gene encoding the tetrapyrrole biosynthesis enzyme uroporphyrinogen III synthase
- Author
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Alison G. Smith, Dieter Jahn, Kaushik Saha, Martina Jahn, Fui-Ching Tan, Qi Cheng, and Ilka U. Heinemann
- Subjects
Uroporphyrinogen III synthase ,Saccharomyces cerevisiae ,Mutant ,Molecular Sequence Data ,Arabidopsis ,Biochemistry ,chemistry.chemical_compound ,Cloning, Molecular ,Molecular Biology ,Gene ,DNA Primers ,Expression vector ,biology ,Base Sequence ,Arabidopsis Proteins ,Genetic Complementation Test ,Cell Biology ,biology.organism_classification ,Molecular biology ,Fusion protein ,Uroporphyrinogen III Synthetase ,Recombinant Proteins ,Open reading frame ,chemistry ,Tetrapyrroles ,Uroporphyrinogen III ,biology.protein - Abstract
UROS (uroporphyrinogen III synthase; EC 4.2.1.75) is the enzyme responsible for the formation of uroporphyrinogen III, the precursor of all cellular tetrapyrroles including haem, chlorophyll and bilins. Although UROS genes have been cloned from many organisms, the level of sequence conservation between them is low, making sequence similarity searches difficult. As an alternative approach to identify the UROS gene from plants, we used functional complementation, since this does not require conservation of primary sequence. A mutant of Saccharomyces cerevisiae was constructed in which the HEM4 gene encoding UROS was deleted. This mutant was transformed with an Arabidopsis thaliana cDNA library in a yeast expression vector and two colonies were obtained that could grow in the absence of haem. The rescuing plasmids encoded an ORF (open reading frame) of 321 amino acids which, when subcloned into an Escherichia coli expression vector, was able to complement an E. coli hemD mutant defective in UROS. Final proof that the ORF encoded UROS came from the fact that the recombinant protein expressed with an N-terminal histidine-tag was found to have UROS activity. Comparison of the sequence of AtUROS (A. thaliana UROS) with the human enzyme found that the seven invariant residues previously identified were conserved, including three shown to be important for enzyme activity. Furthermore, a structure-based homology search of the protein database with AtUROS identified the human crystal structure. AtUROS has an N-terminal extension compared with orthologues from other organisms, suggesting that this might act as a targeting sequence. The precursor protein of 34 kDa translated in vitro was imported into isolated chloroplasts and processed to the mature size of 29 kDa. Confocal microscopy of plant cells transiently expressing a fusion protein of AtUROS with GFP (green fluorescent protein) confirmed that AtUROS was targeted exclusively to chloroplasts in vivo.
- Published
- 2007
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