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Category: Bacterial Pathogenesis; Microbial Genetics and Molecular Biology
Biosynthesis of the Aspartate Family of Amino Acids, Page 1 of 2
< Previous page | Next page > /docserver/preview/fulltext/10.1128/9781555818388/9781555810535_Chap18-1.gif /docserver/preview/fulltext/10.1128/9781555818388/9781555810535_Chap18-2.gifAbstract:
Diaminopimelate, lysine, methionine, and threonine derive most of their carbon atoms from L-aspartate, and these amino acids are therefore often referred to as the aspartate family. Their biosynthesis is effected by a complex pathway involving common intermediates from which multiple branches lead to the end products. The so-called aspartate pathway has several features that distinguish it from other pathways of amino acid biosynthesis and lend its study particular interest in the contexts of bacterial physiology and biochemical evolution. A number of different mechanisms for the control of the aspartate pathway that has evolved in the eubacteria and even within the genus Bacillus is discussed in this chapter. The primary focus of this chapter is on B. subtilis and closely related species. The aspartate pathway splits after the synthesis of aspartate semialdehyde, one branch leading to biosynthesis of diaminopimelate and lysine and the other leading to biosynthesis of threonine and methionine. The branch point enzyme homoserine dehydrogenase is the counterpart of dihydrodipicolinate synthase in controlling the utilization of aspartate semialdehyde for the biosynthesis of threonine and methionine by catalyzing the NADPH-dependent reduction of L-aspartate semialdehyde to L-homoserine. The major route for the biosynthesis of aspartate from glycolytic intermediates involves the carboxylation of pyruvate to oxaloacetate and subsequent transamination.
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Overview of the pathway for biosynthesis of the aspartate family of amino acids. ADOMET, S-adenosyl-methionine.
Overview of the pathway for biosynthesis of the aspartate family of amino acids. ADOMET, S-adenosyl-methionine.
The branch of the aspartate pathway leading to biosynthesis of diaminopimelate and lysine. The reaction catalyzed by diaminopimelate dehydrogenase, indicated by the dotted arrows, occurs in a few Bacillus species and in coryneform bacteria but not in B. subtilis. Ac-SCoA, acetyl-CoA; CoASH, coenzyme A; Ac, acetyl.
The branch of the aspartate pathway leading to biosynthesis of diaminopimelate and lysine. The reaction catalyzed by diaminopimelate dehydrogenase, indicated by the dotted arrows, occurs in a few Bacillus species and in coryneform bacteria but not in B. subtilis. Ac-SCoA, acetyl-CoA; CoASH, coenzyme A; Ac, acetyl.
The branch of the aspartate pathway leading to biosynthesis of threonine and methionine. The reaction catalyzed by O-acetylhomoserine sulfhydrylase, indicated by dotted arrows, occurs in coryneform bacteria. CoASH, coenzyme A; Ac-SCoA, acetyl-CoA; Ac, aceryl; THF, tetrahydrofolate.
The branch of the aspartate pathway leading to biosynthesis of threonine and methionine. The reaction catalyzed by O-acetylhomoserine sulfhydrylase, indicated by dotted arrows, occurs in coryneform bacteria. CoASH, coenzyme A; Ac-SCoA, acetyl-CoA; Ac, aceryl; THF, tetrahydrofolate.
Common reactions in the biosynthesis of diaminopimelate, lysine, threonine, and methionine.
Common reactions in the biosynthesis of diaminopimelate, lysine, threonine, and methionine.
Postulated folding domains of aspartokinases. (A) Proposed biglobular structure of the a subunit of B. subtilis aspartokinase II (left) and arrangements of the a and β subunits in the native enzyme (right). (B) Proposed triglobular structure of a subunit of E. coli aspartokinase-homoserine dehydrogenase I (left) and arrangements of subunits in the native tetrameric enzyme (right) (modified from reference 27 ). AK, aspartokinase domain; HSD, homoserine dehydrogenase domain; I, interdomain.
Postulated folding domains of aspartokinases. (A) Proposed biglobular structure of the a subunit of B. subtilis aspartokinase II (left) and arrangements of the a and β subunits in the native enzyme (right). (B) Proposed triglobular structure of a subunit of E. coli aspartokinase-homoserine dehydrogenase I (left) and arrangements of subunits in the native tetrameric enzyme (right) (modified from reference 27 ). AK, aspartokinase domain; HSD, homoserine dehydrogenase domain; I, interdomain.
Sequence homology of B. subtilis aspartokinase II and the E. coli aspartokinases. A and B are the sites at which trypsin cleaves B. subtilis aspartokinase II and E. coli aspartokinase-homoserine dehydrogenase I, respectively. AK, aspartokinase; HSD, homoserine dehydrogenase.
Sequence homology of B. subtilis aspartokinase II and the E. coli aspartokinases. A and B are the sites at which trypsin cleaves B. subtilis aspartokinase II and E. coli aspartokinase-homoserine dehydrogenase I, respectively. AK, aspartokinase; HSD, homoserine dehydrogenase.
Physical map of the B. subtilis chromosome near the dapG locus at 144°. The diagram shows positions of various restriction endonuclease cleavage sites and locations of deduced coding regions. Dotted arrows indicate polarities of transcription.
Physical map of the B. subtilis chromosome near the dapG locus at 144°. The diagram shows positions of various restriction endonuclease cleavage sites and locations of deduced coding regions. Dotted arrows indicate polarities of transcription.
Possible secondary structures of RNA transcribed from the asd-dapG intercistronic region of B. subtilis ( 24 ). Stabilization free energies were estimated by using the parameters of Freier et al. ( 36 ). RBS, ribosome-binding site; Fmet, formylmethionyl.
Possible secondary structures of RNA transcribed from the asd-dapG intercistronic region of B. subtilis ( 24 ). Stabilization free energies were estimated by using the parameters of Freier et al. ( 36 ). RBS, ribosome-binding site; Fmet, formylmethionyl.
Diagram of the B. subtilis lysC operon and adjacent regions (modified from reference 26 ). The diagram shows positions of various restriction endonuclease cleavage sites and locations of deduced coding regions. Arrows indicate the polarities of transcription. P, promoter; SD, ribosome-binding site; T, transcription terminator; ORF, open reading frame.
Diagram of the B. subtilis lysC operon and adjacent regions (modified from reference 26 ). The diagram shows positions of various restriction endonuclease cleavage sites and locations of deduced coding regions. Arrows indicate the polarities of transcription. P, promoter; SD, ribosome-binding site; T, transcription terminator; ORF, open reading frame.
Nucleotide sequence of the untranslated leader region of the B. subtilis lysC operon ( 23 , 80 , 81 ). The sequence from B. subtilis 168 is shown in its entirety. Sequences from aecA strains VB217, FB59, and KA120 ( 80 ) and from A34, ATR1, ATR4, AT9, AT10, TSH9, TSH25, TSH112, and TSHL2 ( 81 ) are shown only where they differ from that of strain 168. The sequence is annotated to show elements of potential regulatory significance, with inverted repeats indicated by arrows and ribosome-binding sites (R.B.S.) indicated by asterisks. Nucleotide residues are numbered from the transcription start site.
Nucleotide sequence of the untranslated leader region of the B. subtilis lysC operon ( 23 , 80 , 81 ). The sequence from B. subtilis 168 is shown in its entirety. Sequences from aecA strains VB217, FB59, and KA120 ( 80 ) and from A34, ATR1, ATR4, AT9, AT10, TSH9, TSH25, TSH112, and TSHL2 ( 81 ) are shown only where they differ from that of strain 168. The sequence is annotated to show elements of potential regulatory significance, with inverted repeats indicated by arrows and ribosome-binding sites (R.B.S.) indicated by asterisks. Nucleotide residues are numbered from the transcription start site.
Biosynthesis of l-aspartate. Ac-SCoA, acetyl-CoA.
Biosynthesis of l-aspartate. Ac-SCoA, acetyl-CoA.
Aspartokinase isozymes of B. subtilis a
Aspartokinase isozymes of B. subtilis a
Enzymes of the diaminopimelate-lysine pathway
Enzymes of the diaminopimelate-lysine pathway
Enzymes of the threonine-methionme pathway
Enzymes of the threonine-methionme pathway