Escherichia coli threonine biosynthesis

Theze, J. Kleidman, L. Saint Girons, L Homoserine kinase from Escherichia coli K-12 properties, inhibition by L-threonine, and regulation of biosynthesis. J. Bacteriol., 118, 577-581 (1974)... 

Biosynthesis metabolism Asp is formed from oxaloacetic acid by aspartate aminotransferase (EC 2.6.1.1) and serves as starting material in the biosyntheses of threonine, methionine, and lysine. The first step is catalysed by aspartate kinase (EC 2.7.24) which only occurs in plants and microorganisms. This enzyme exists as 3 isozymes in Escherichia coli and exhibits a typical example of feedback regulation. Asp plays a central role in the biosyntheses of pyrimidines and purines. In the urea cycle Asp condenses with " citrulline to aigininosuccinate, a stimulating neuro-transmitter. ... 

Lee KH, Park JH, Kim TY, Kim HU, Lee SY (2007) Systems metabolic engineering of Escherichia coli for L-threonine production. Mol Syst Biol 3 1-8 Lim SJ, Jung YM, Shin HD, Lee YH (2002) Amplification of the NADPH-related genes zfvf and gnd for the oddball biosynthesis of PHB in an E. coli transformant harboring a cloned phbCAB Operon. J Biosci Bioeng 93 543-549... 

Two pathways for PLP biosynthesis de novo are known in plant and microorganisms. The first was extensively studied in Escherichia coli. This pathway is articulated in two branches which join in a ring closure reaction catalysed by PNP synthase. One branch started from pyruvate and glycer-aldehyde 3-phosphate and the other from 4-phosphohydroxy-L-threonine (derived from erythrose 4-phosphate). The second route is when PLP is formed from glutamine, either ribose 5-phosphate or ribulose 5-phosphate and either dihydroxyacetone phosphate or glyceraldehyde 3-phosphate by action of the PLP synthase complex (Roje 2007). This pathway was discovered in fungi and it has become clear that it is much more widely distributed than the first pathway. It exists in Archaea, most eubacteria and plants. 

Isoenzymes of enzymes involved in the first step of a branched biosynthetic pathway may differ in their sensitivity to inhibitors. Thus the enzyme aspartate kinase catalyses in Escherichia coli the first step in the synthesis of lysine, methionine and threonine. Three isoenzymes occur, the synthesis and activity of one is suppressed by L-lysine, the activity of the second is depressed by L-threonine and the activity of the third by homoserine (an intermediate in methionine biosynthesis). Thus accumulation of L-lysine or L-threonine suppresses their own further S3mthesis but does not prevent the activity of the aspartokinase isoenzyme involved in methionine synthesis. Again peroxidase isoenzymes differ in their activity in destroying indol-3yl-acetic acid (lAA) and the pattern of peroxidase isoenzymes can be altered by feeding lAA or gibberellic acid (GA) to plant tissues. 

---