Regulation of lysine catabolism through lysine-ketoglutarate reductase and saccharopine dehydrogenase in Arabidopsis.

Lysine-ketoglutarate reductase/saccharopine dehydrogenase (LKR/SDH) is a bifunctional enzyme catalyzing the first two steps of lysine catabolism in animals and plants. To elucidate the biochemical signification of the linkage between the two enzymes of LKR/SDH, namely lysine ketoglutarate and saccharopine dehydrogenase, we employed various truncated and mutatedArabidopsisLKR/SDH polypeptides expressed in yeast. Activity analyses of the different recombinant polypeptides under conditions of varying NaCl levels implied that LKR, but not SDH activity, is regulated by functional interaction between the LKR and SDH domains, which is mediated by the structural conformation of the linker region connecting them. Because LKR activity of plant LKR/SDH enzymes is also regulated by casein kinase 2 phosphorylation, we searched for such potential regulatory phosphorylation sites using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and site-directed mutagenesis. This analysis identified Ser-458 as a candidate for this function. We also tested a hypothesis suggesting that an EF-hand-like sequence at the C-terminal part of the LKR domain functions in a calcium-dependent assembly of LKR/SDH into a homodimer. We found that this region is essential for LKR activity but that it does not control a calcium-dependent assembly of LKR/SDH. The relevance of our results to thein vivofunction of LKR/SDH in lysine catabolism in plants is discussed. In addition, because the linker region between LKR and SDH exists only in plants but not in animal LKR/SDH enzymes, our results suggest that the regulatory properties of LKR/SDH and, hence, the regulation of lysine catabolism are different between plants and animals.

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The Enzymology of Lysine Catabolism in Rice Seeds - Isolation, Characterization, and Regulatory Properties of a Lysine 2-Oxoglutarate Reductase/Saccharopine Dehydrogenase Bifunctional Polypeptide

European Journal of Biochemistry ◽

10.1111/j.1432-1033.1997.00364.x ◽

1997 ◽

Vol 247 (1) ◽

pp. 364-371 ◽

Cited By ~ 39

Author(s):

Salete A. Gaziola ◽

Cristiana M. O. Teixeira ◽

Juverlande Luoli ◽

Ladaslav Sodek ◽

Ricardo A. Azevedo

Keyword(s):

Saccharopine Dehydrogenase ◽

Rice Seeds ◽

Regulatory Properties ◽

Lysine Catabolism

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L-Lysine catabolism is osmo-regulated at the level of lysine-ketoglutarate reductase and saccharopine dehydrogenase in rapeseed leaf discs

Plant Physiology and Biochemistry ◽

10.1016/s0981-9428(00)00777-4 ◽

2000 ◽

Vol 38 (7-8) ◽

pp. 577-585 ◽

Cited By ~ 25

Author(s):

Michaël Moulin ◽

Carole Deleu ◽

François Larher

Keyword(s):

Leaf Discs ◽

Saccharopine Dehydrogenase ◽

Lysine Catabolism

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Characterization of the Two Saccharopine Dehydrogenase Isozymes of Lysine Catabolism Encoded by the Single Composite AtLKR/SDHLocus of Arabidopsis

PLANT PHYSIOLOGY ◽

10.1104/pp.124.3.1363 ◽

2000 ◽

Vol 124 (3) ◽

pp. 1363-1372 ◽

Cited By ~ 14

Author(s):

Xiaohong Zhu ◽

Guiliang Tang ◽

Gad Galili

Keyword(s):

Saccharopine Dehydrogenase ◽

Lysine Catabolism

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Lysine catabolism: flow, metabolic role and regulation

Brazilian Journal of Plant Physiology ◽

10.1590/s1677-04202003000100002 ◽

2003 ◽

Vol 15 (1) ◽

pp. 9-18 ◽

Cited By ~ 6

Author(s):

Ricardo Francisco Fornazier ◽

Ricardo Antunes Azevedo ◽

Renato Rodrigues Ferreira ◽

Vanderlei Aparecido Varisi

Keyword(s):

Environmental Changes ◽

Lysine Biosynthesis ◽

Direct Result ◽

Physiological Processes ◽

Saccharopine Dehydrogenase ◽

Metabolic Role ◽

Lysine Concentration ◽

Lysine Degradation ◽

Acid Pathway ◽

Lysine Catabolism

Lysine is an essential amino acid, synthesized in plants in the aspartic acid pathway. The lysine catabolism is performed by the action of two consecutive enzymes, lysine 2-oxoglutarate reductase (LOR) and saccharopine dehydrogenase (SDH). The steady state of lysine is controlled by both, synthesis and catabolism rates, with the final soluble lysine concentration in cereal seeds a direct result of these processes. In the last 40 years, the enzymes involved in lysine biosynthesis have been purified and characterized from some plant species such as carrot, maize, barley, rice, and coix. Recent reports have revealed that lysine degradation might be related to various physiological processes, for instance growth, development and response to environmental changes and stress. The understanding of the regulatory aspects of the lysine biosynthetic and catabolic pathways and manipulation of related enzymes is important for the production of high-lysine plants.

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