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Biochemistry. PhysiologyMy research focuses on sulfur metabolism in higher plants. Plants and microorganisms are able to assimilate inorganic sulfate into organic forms. primarily cysteine and methionine. Animals are unable to assimilate sulfate. and so are dependent on ingesting plants and microorganisms for this nutrient. Both cysteine and methionine participate in a multitude of universally essential cellular functions. To name a few; (1) the thiol group of cysteine is required for protein structure and function. (2) methionine is required for initiation of translation. (3) glutathione functions as the primary modulator of cellular redox potential. (4) thiol groups of the protein metallothionein or the peptides known as phytochelatins are the primary defense against the toxic affects of heavy metals. Despite their importance. the pathways for cysteine and methionine biosynthesis or their regulation in plants are not fully understood. My laboratory is using a molecular genetic approach to explore this topic. We have used microorganisms for which mutants are known. to clone by functional complementation. the genes encoding enzymes in the cysteine and methionine biosynthetic pathways from higher plants. The cloning of these genes demonstrates. first. that they exist in higher plants and provides the tools with which to explore such questions as: (1) what are the kinetic and physical properties of the enzymes. (2) how are the enzymes and the pathway regulated. (3) does modification of the pathway affect the ability of an organism to tolerate heavy metals or oxidative stress? Selected PublicationsHudson AO, Gilvarg C, Leustek T. (2008) Biochemical and phylogenetic characterization of a novel diaminopimelate biosynthesis pathway in prokaryotes identifies a diverged form of LL-diaminopimelate aminotransferase. J Bacteriol. 190(9):3256-63. Martin MN, Saladores PH, Lambert E, Hudson AO, Leustek T. (2007) Localization of members of the gamma-glutamyl transpeptidase family identifies sites of glutathione and glutathione S-conjugate hydrolysis. Plant Physiol. 144(4):1715-32. Muralla R, Sweeney C, Stepansky A, Leustek T, Meinke D. (2007) Genetic dissection of histidine biosynthesis in Arabidopsis. Plant Physiol. 144(2):890-903. Kim SK, Gomes V, Gao Y, Chandramouli K, Johnson MK, Knaff DB, Leustek T. (2007) The two-domain structure of 5'-adenylylsulfate (APS) reductase from Enteromorpha intestinalis is a requirement for efficient APS reductase activity. Biochemistry. 46(2):591-601. McCoy AJ, Adams NE, Hudson AO, Gilvarg C, Leustek T, Maurelli AT. (2006) L,L-diaminopimelate aminotransferase, a trans-kingdom enzyme shared by Chlamydia and plants for synthesis of diaminopimelate/lysine. Proc Natl Acad Sci U S A. 103(47):17909-14. Stepansky A, Leustek T. (2006) Histidine biosynthesis in plants. Amino Acids. 30(2):127-42. Review. Kim SK. Rahman A. Conover RC. Johnson MK. Mason JT. Gomes V. Hirasawa M. Moore ML. Leustek T. Knaff DB. (2006) Properties of the cysteine residues and the iron-sulfur cluster of the assimilatory 5'-adenylyl sulfate reductase from Enteromorpha intestinalis. Biochemistry. 45(15):5010-8. Hudson AO. Singh BK. Leustek T. Gilvarg C. (2006) An LL-diaminopimelate aminotransferase defines a novel variant of the lysine biosynthesis pathway in plants. Plant Physiol. 140(1):292-301. Martin MN. Tarczynski MC. Shen B. Leustek T. (2005) The role of 5'-adenylylsulfate reductase in controlling sulfate reduction in plants. Photosynth Res. 86(3):309-23. Hell R. Leustek T. (2005) Sulfur metabolism in plants and algae--a case study for an integrative scientific approach. Photosynth Res. 86(3):297-8. Kim SK. Rahman A. Mason JT. Hirasawa M. Conover RC. Johnson MK. Miginiac-Maslow M. Keryer E. Knaff DB. Leustek T. (2005) The interaction of 5'-adenylylsulfate reductase from Pseudomonas aeruginosa with its substrates. Biochim Biophys Acta. 1710(2-3):103-12. Sors TG. Ellis DR. Na GN. Lahner B. Lee S. Leustek T. Pickering IJ. Salt DE. (2005) Analysis of sulfur and selenium assimilation in Astragalus plants with varying capacities to accumulate selenium. Plant J. 42(6):785-97. Lee M. Martin MN. Hudson AO. Lee J. Muhitch MJ. Leustek T. (2005) Methionine and threonine synthesis are limited by homoserine availability and not the activity of homoserine kinase in Arabidopsis thaliana. Plant J. 41(5):685-96. Hudson AO. Bless C. Macedo P. Chatterjee SP. Singh BK. Gilvarg C. Leustek T. (2005) Biosynthesis of lysine in plants: evidence for a variant of the known bacterial pathways. Biochim Biophys Acta. 1721(1-3):27-36. Kim SK. Rahman A. Bick JA. Conover RC. Johnson MK. Mason JT. Hirasawa M. Leustek T. Knaff DB. (2004) Properties of the cysteine residues and iron-sulfur cluster of the assimilatory 5'-adenylyl sulfate reductase from Pseudomonas aeruginosa. Biochemistry. 43(42):13478-86. Tsakraklides G. Martin M. Chalam R. Tarczynski MC. Schmidt A. Leustek T. (2002) Sulfate reduction is increased in transgenic Arabidopsis thaliana expressing 5'-adenylylsulfate reductase from Pseudomonas aeruginosa. Plant J. 32(6):879-89. Ravina CG. Chang CI. Tsakraklides GP. McDermott JP. Vega JM. Leustek T. Gotor C. Davies JP. (2002) The sac mutants of Chlamydomonas reinhardtii reveal transcriptional and posttranscriptional control of cysteine biosynthesis. Plant Physiol. 130(4):2076-84. Kim J. Lee M. Chalam R. Martin MN. Leustek T. Boerjan W. (2002) Constitutive overexpression of cystathionine gamma-synthase in Arabidopsis leads to accumulation of soluble methionine and S-methylmethionine. Plant Physiol. 128(1):95-107. Bick JA. Setterdahl AT. Knaff DB. Chen Y. Pitcher LH. Zilinskas BA,Leustek (2001) Regulation of the plant-type 5'-adenylylsulfate reductase by oxidative stress. Biochemistry 40: 9040-9048. Sanda SL. Leustek T. Theisen MJ. Garavito M. Benning C (2001) Recombinant ArabidopsisSQD1 converts UDP-glucose and sulfite to the sulfolipid head group precursor UDP-sulfoquinovose in vitro. J Biol Chem 276: 3941-3946. Rotte C. Leustek T (2000) Differential subcellular localization and expression of ATP sulfurylase and APS reductase during ontogenesis of Arabidopsis thaliana leaves indicates that cytosolic and plastid forms of ATP sulfurylase may have specialized functions. Plant Physiol 124: 715-724. Gao Y. Schofield O. Leustek T (2000) Characterization of sulfate assimilation in marine algae focusing on the enzyme 5'-adenylylsulfate (APS) reductase. Plant Physiol 123: 1087-1096. Hatzfeld Y. Lee S. Lee M. Leustek T. Saito K (2000) Functional characterization of a gene encoding afourth ATP sulfurylase isoform from Arabidopsis thaliana. Gene 248: 51-58 Leustek T. Bick JA (2000) The evolution of sulfur assimilation in plants. In: Sulfur nutrition and sulfur assimilation in higher plants. C Brunold. J-C Davidian. L De Kok. H Rennenberg. I Stulen. eds. Paul Haupt Publishers. Bern. Switzerland. The Netherlands. pp 1-15 Crawford NM. Kahn ML. Leustek T. Long SR (2000) Chapter 16-Nitrogen and Sulfur. In:Biochemistry and Molecular Biology of Plants. BB Buchanan. W Gruissem. RL Jones. eds. American Society of Plant Physiologists. Rockville. MD. pp. 786-849. Leustek T. Martin MN. Bick JA. Davies JP (2000) Pathways and regulation of sulfur metabolism revealed through molecular and genetic studies. Annu Rev Plant Physiol Plant Mol Biol 51: 141-166. Bick JA. Dennis JJ. Zylstra GJ Nowack J. Leustek T (2000) Identification of a new class of 5'-adenylylsulfate (APS) reductase from sulfate-assimilating bacteria. J Bacteriol 182: 135-142. Kim J. Leustek T (2000) Repression of cystathionine g -synthase in Arabidopsis thaliana produces partial methionine auxotrophy and developmental abnormalities. Plant Sci 151: 9-18. Marty I. Douat C. Tichit L. Kim J. Leustek T. Abagnac G (2000) The cystathionine-g -synthase gene involved in methionine biosynthesis is highly expressed and auxin-repressed during wild strawberry (Fragaria vesca L.) fruit ripening. Theor Appl Genet 100: 1129-1136.
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