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The X-ray crystal structure of Escherichia coli succinic semialdehyde dehydrogenase; structural insights into NADP+/enzyme interactions.

Langendorf CG, Key TL, Fenalti G, Kan WT, Buckle AM, Caradoc-Davies T, Tuck KL, Law RH, Whisstock JC - PLoS ONE (2010)

Bottom Line: In the E. coli SSADH structure, electron density for the complete NADP+ cofactor in the binding sites is clearly evident; these data in particular revealing how the nicotinamide ring of the cofactor is positioned in each active site.Our structural data suggest that a deletion of three amino acids in E. coli SSADH permits this enzyme to use NADP+, whereas in contrast the human enzyme utilises NAD+.Furthermore, the structure of E. coli SSADH gives additional insight into human mutations that result in disease.

View Article: PubMed Central - PubMed

Affiliation: Department of Biochemistry and Molecular Biology, Monash University, Clayton Campus, Melbourne, Victoria, Australia.

ABSTRACT

Background: In mammals succinic semialdehyde dehydrogenase (SSADH) plays an essential role in the metabolism of the inhibitory neurotransmitter gamma-aminobutyric acid (GABA) to succinic acid (SA). Deficiency of SSADH in humans results in elevated levels of GABA and gamma-Hydroxybutyric acid (GHB), which leads to psychomotor retardation, muscular hypotonia, non-progressive ataxia and seizures. In Escherichia coli, two genetically distinct forms of SSADHs had been described that are essential for preventing accumulation of toxic levels of succinic semialdehyde (SSA) in cells.

Methodology/principal findings: Here we structurally characterise SSADH encoded by the E coli gabD gene by X-ray crystallographic studies and compare these data with the structure of human SSADH. In the E. coli SSADH structure, electron density for the complete NADP+ cofactor in the binding sites is clearly evident; these data in particular revealing how the nicotinamide ring of the cofactor is positioned in each active site.

Conclusions/significance: Our structural data suggest that a deletion of three amino acids in E. coli SSADH permits this enzyme to use NADP+, whereas in contrast the human enzyme utilises NAD+. Furthermore, the structure of E. coli SSADH gives additional insight into human mutations that result in disease.

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Related in: MedlinePlus

Enzymes and metabolites involved in the GABA shunt.Enzymes catalysing reactions are numbered, (1) glutamate decarboxylase (GAD), (2) γ-aminobutyric transaminase (GABA-T), (3) succinic semialdehyde dehydrogenase (SSADH) and (4) succinic semialdehyde reductase (SSR). The blue highlighted boxes show enzymes that are found in the gab operon of E. coli. The thick black line indicates the pathway is blocked, SSA is then converted to γ-hydroxybutyrate (GHB) by succinic semialdehyde reductase (SSR), pathway coloured in red, which is described in SSDAH deficiency. Figure adapted from Blasi et al. [9]
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pone-0009280-g001: Enzymes and metabolites involved in the GABA shunt.Enzymes catalysing reactions are numbered, (1) glutamate decarboxylase (GAD), (2) γ-aminobutyric transaminase (GABA-T), (3) succinic semialdehyde dehydrogenase (SSADH) and (4) succinic semialdehyde reductase (SSR). The blue highlighted boxes show enzymes that are found in the gab operon of E. coli. The thick black line indicates the pathway is blocked, SSA is then converted to γ-hydroxybutyrate (GHB) by succinic semialdehyde reductase (SSR), pathway coloured in red, which is described in SSDAH deficiency. Figure adapted from Blasi et al. [9]

Mentions: Succinic semialdehyde dehydrogenase (SSADH) belongs to the aldehyde dehydrogenases (ALDH) superfamily [1] and has been identified and purified from mammals [2], [3], [4], [5] as well as from microorganisms [6], [7], [8]. SSADH plays a key role in mammalian neurobiology, where it functions in the metabolic pathway termed the “γ-aminobutyric acid (GABA) shunt” in the brain. In the GABA shunt, the inhibitory neurotransmitter GABA is synthesised from glutamic acid by glutamic acid decarboxylase (GAD) [9], [10]. GABA is then metabolised in a two-step reaction. First, GABA-transaminase (EC 2.6.1.19) catalyses the breakdown of GABA in the presence of α-ketoglutarate to produce succinic semialdehyde (SSA) and glutamic acid (Figure 1). SSA is then converted to succinic acid (SA) by the NAD+/NADP+-dependant enzyme succinic semialdehyde dehydrogenase (SSADH; EC 1.2.1.24) [11]. Hence, GABA is channelled into the tricarboxylic acid cycle in the form of SA. Alternatively, SSA can be converted to γ-hydroxybutyric acid (GHB) by succinic semialdehyde reductase [12] (see Figure 1).


The X-ray crystal structure of Escherichia coli succinic semialdehyde dehydrogenase; structural insights into NADP+/enzyme interactions.

Langendorf CG, Key TL, Fenalti G, Kan WT, Buckle AM, Caradoc-Davies T, Tuck KL, Law RH, Whisstock JC - PLoS ONE (2010)

Enzymes and metabolites involved in the GABA shunt.Enzymes catalysing reactions are numbered, (1) glutamate decarboxylase (GAD), (2) γ-aminobutyric transaminase (GABA-T), (3) succinic semialdehyde dehydrogenase (SSADH) and (4) succinic semialdehyde reductase (SSR). The blue highlighted boxes show enzymes that are found in the gab operon of E. coli. The thick black line indicates the pathway is blocked, SSA is then converted to γ-hydroxybutyrate (GHB) by succinic semialdehyde reductase (SSR), pathway coloured in red, which is described in SSDAH deficiency. Figure adapted from Blasi et al. [9]
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2823781&req=5

pone-0009280-g001: Enzymes and metabolites involved in the GABA shunt.Enzymes catalysing reactions are numbered, (1) glutamate decarboxylase (GAD), (2) γ-aminobutyric transaminase (GABA-T), (3) succinic semialdehyde dehydrogenase (SSADH) and (4) succinic semialdehyde reductase (SSR). The blue highlighted boxes show enzymes that are found in the gab operon of E. coli. The thick black line indicates the pathway is blocked, SSA is then converted to γ-hydroxybutyrate (GHB) by succinic semialdehyde reductase (SSR), pathway coloured in red, which is described in SSDAH deficiency. Figure adapted from Blasi et al. [9]
Mentions: Succinic semialdehyde dehydrogenase (SSADH) belongs to the aldehyde dehydrogenases (ALDH) superfamily [1] and has been identified and purified from mammals [2], [3], [4], [5] as well as from microorganisms [6], [7], [8]. SSADH plays a key role in mammalian neurobiology, where it functions in the metabolic pathway termed the “γ-aminobutyric acid (GABA) shunt” in the brain. In the GABA shunt, the inhibitory neurotransmitter GABA is synthesised from glutamic acid by glutamic acid decarboxylase (GAD) [9], [10]. GABA is then metabolised in a two-step reaction. First, GABA-transaminase (EC 2.6.1.19) catalyses the breakdown of GABA in the presence of α-ketoglutarate to produce succinic semialdehyde (SSA) and glutamic acid (Figure 1). SSA is then converted to succinic acid (SA) by the NAD+/NADP+-dependant enzyme succinic semialdehyde dehydrogenase (SSADH; EC 1.2.1.24) [11]. Hence, GABA is channelled into the tricarboxylic acid cycle in the form of SA. Alternatively, SSA can be converted to γ-hydroxybutyric acid (GHB) by succinic semialdehyde reductase [12] (see Figure 1).

Bottom Line: In the E. coli SSADH structure, electron density for the complete NADP+ cofactor in the binding sites is clearly evident; these data in particular revealing how the nicotinamide ring of the cofactor is positioned in each active site.Our structural data suggest that a deletion of three amino acids in E. coli SSADH permits this enzyme to use NADP+, whereas in contrast the human enzyme utilises NAD+.Furthermore, the structure of E. coli SSADH gives additional insight into human mutations that result in disease.

View Article: PubMed Central - PubMed

Affiliation: Department of Biochemistry and Molecular Biology, Monash University, Clayton Campus, Melbourne, Victoria, Australia.

ABSTRACT

Background: In mammals succinic semialdehyde dehydrogenase (SSADH) plays an essential role in the metabolism of the inhibitory neurotransmitter gamma-aminobutyric acid (GABA) to succinic acid (SA). Deficiency of SSADH in humans results in elevated levels of GABA and gamma-Hydroxybutyric acid (GHB), which leads to psychomotor retardation, muscular hypotonia, non-progressive ataxia and seizures. In Escherichia coli, two genetically distinct forms of SSADHs had been described that are essential for preventing accumulation of toxic levels of succinic semialdehyde (SSA) in cells.

Methodology/principal findings: Here we structurally characterise SSADH encoded by the E coli gabD gene by X-ray crystallographic studies and compare these data with the structure of human SSADH. In the E. coli SSADH structure, electron density for the complete NADP+ cofactor in the binding sites is clearly evident; these data in particular revealing how the nicotinamide ring of the cofactor is positioned in each active site.

Conclusions/significance: Our structural data suggest that a deletion of three amino acids in E. coli SSADH permits this enzyme to use NADP+, whereas in contrast the human enzyme utilises NAD+. Furthermore, the structure of E. coli SSADH gives additional insight into human mutations that result in disease.

Show MeSH
Related in: MedlinePlus