This view shows enzymes only for those organisms listed below, in the list of taxa known to possess the pathway. If an enzyme name is shown in bold, there is experimental evidence for this enzymatic activity.
|Superclasses:||Biosynthesis → Cofactors, Prosthetic Groups, Electron Carriers Biosynthesis|
Expected Taxonomic Range: Bacteria
Citrate lyase is an anaerobic enzyme that catalyzes the cleavage of citrate to acetate and oxaloacetate [Nilekani83] (see citrate degradation). Because the citrate molecule is very stable, it has to be activated by forming a thioester bond with the enzyme before cleavage can take place.
The enzyme is a complex of three subunits (in a 6:6:6 configuration), one of them a dedicated acyl carrier protein (acp). The acp protein is synthesized in an apo form, and is converted to its holo form by the covalent binding of the prosthetic group 2'-(5''-phosphoribosyl)-3'-dephospho-CoA to a serine residue. This prosthetic group is very unusual and the only other enzyme known to use it is malonate decarboxylase.
The synthesis and attachment of the prosthetic group are catalyzed by two different enzymes. The first step, catalyzed by EC 220.127.116.11, triphosphoribosyl-dephospho-CoA synthase is the formation of an unusual α-1,2-glycosidic linkage between ATP and dephospho-CoA, forming the prosthetic group and releaing adenine [Schneider00a]. In the second step, catalyzed by EC 18.104.22.168, citrate lyase holo-[acyl-carrier protein] synthase, the group is transferred to the apo-[acp] protein, generating the holo-[acp] form [Schneider02].
The holo form is still not active - in order to be fully active, the prosthetic group needs to be acetylated. The most common enzyme performing the acetylation is EC 22.214.171.124, [citrate (pro-3S)-lyase] ligase, which uses acetate as the donor [Schmellenkamp74]. A different enzyme, EC 126.96.36.199, deacetyl-[citrate-(pro-3S)-lyase] S-acetyltransferase, that uses S-acetyl phosphopantetheine as the acetyl donor, has been characterized from the bacterium Enterobacter aerogenes [Singh73].
Another enzyme that modulates the activity of citrate lyase has been reported in the bacterium Rubrivivax gelatinosus. That enzyme, EC 188.8.131.52, citrate-lyase deacetylase, converts the active acetyl form back into the inactive thiol form by removal of its acetyl groups [Giffhorn80].
Unification Links: EcoCyc:P2-PWY
Giffhorn80: Giffhorn F, Rode H, Kuhn A, Gottschalk G (1980). "Citrate lyase deacetylase of Rhodopseudomonas gelatinosa. Isolation of the enzyme and studies on the inhibition by L-glutamate." Eur J Biochem 111(2);461-71. PMID: 7460909
Schneider00: Schneider K, Dimroth P, Bott M (2000). "Identification of triphosphoribosyl-dephospho-CoA as precursor of the citrate lyase prosthetic group." FEBS Lett 2000;483(2-3);165-8. PMID: 11042274
Schneider02: Schneider K, Kastner CN, Meyer M, Wessel M, Dimroth P, Bott M (2002). "Identification of a gene cluster in Klebsiella pneumoniae which includes citX, a gene required for biosynthesis of the citrate lyase prosthetic group." J Bacteriol 2002;184(9);2439-46. PMID: 11948157
Singh73: Singh M, Bottger B, Stewart C, Brooks GC, Srere PA (1973). "S-acetyl phosphopantetheine: deacetyl citrate lyase S-acetyl transferase from Klebsiella aerogenes." Biochem Biophys Res Commun 53(1);1-9. PMID: 4741546
DiazMejia09: Diaz-Mejia JJ, Babu M, Emili A (2009). "Computational and experimental approaches to chart the Escherichia coli cell-envelope-associated proteome and interactome." FEMS Microbiol Rev 33(1);66-97. PMID: 19054114
Giffhorn75: Giffhorn F, Gottschalk G (1975). "Inactivation of citrate lyase from Rhodopseudomonas gelatinosa by a specific deacetylase and inhibition of this inactivation by L-(+1-glutamate." J Bacteriol 124(3);1052-61. PMID: 356
Giffhorn81: Giffhorn F, Zimmermann T, Kuhn A (1981). "Substrate specificity of citrate lyase deacetylase of Rhodopseudomonas gelatinosa and Rhodopseudomonas palustris." J Bacteriol 147(2);463-70. PMID: 6167565
Hoenke00: Hoenke S, Wild MR, Dimroth P (2000). "Biosynthesis of triphosphoribosyl-dephospho-coenzyme A, the precursor of the prosthetic group of malonate decarboxylase." Biochemistry 39(43);13223-32. PMID: 11052675
Hoenke00a: Hoenke S, Schmid M, Dimroth P (2000). "Identification of the active site of phosphoribosyl-dephospho-coenzyme A transferase and relationship of the enzyme to an ancient class of nucleotidyltransferases." Biochemistry 39(43);13233-40. PMID: 11052676
Hoenke97: Hoenke S, Schmid M, Dimroth P (1997). "Sequence of a gene cluster from Klebsiella pneumoniae encoding malonate decarboxylase and expression of the enzyme in Escherichia coli." Eur J Biochem 246(2);530-8. PMID: 9208947
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