Browsing Pathways

Phospholipids are membrane components in E. coli. The major phospholipids of E. coli are phosphatidylethanolamine, phosphatidylglycerol, and cardiolipin. All phospholipids contain sn-glycerol-3-phosphate esterified with fatty acids at the sn-1 and sn-2 positions. The reaction starts from a glycerone phosphate (dihydroxyacetone phosphate) produced in glycolysis. The glycerone phosphate is transformed into an sn-glycerol 3-phosphate (glycerol 3 phosphate) by NADPH-driven glycerol-3-phosphate dehydrogenase. sn-Glycerol 3-phosphate is transformed to a 1-acyl-sn-glycerol 3-phosphate (lysophosphatidic acid). This can be achieved by an sn-glycerol-3-phosphate acyltransferase that interacts either with a long-chain acyl-CoA or with an acyl-[acp]. The 1-acyl-sn-glycerol 3-phosphate is transformed into a 1,2-diacyl-sn-glycerol 3-phosphate (phosphatidic acid) through a 1-acylglycerol-3-phosphate O-acyltransferase. This compound is then converted into a CPD-diacylglycerol through a CTP phosphatidate cytididyltransferase. CPD-diacylglycerol can be transformed either into an L-1-phosphatidylserine or an L-1-phosphatidylglycerol-phosphate through a phosphatidylserine synthase or a phosphatidylglycerophosphate synthase, respectively. The L-1-phosphatidylserine transforms into L-1-phosphatidylethanolamine through a phosphatidylserine decarboxylase. On the other hand, L-1-phosphatidylglycerol-phosphate gets transformed into an L-1-phosphatidyl-glycerol through a phosphatidylglycerophosphatase. These 2 products combine to produce a cardiolipin and an ethanolamine. The L-1 phosphatidyl-glycerol can also interact with cardiolipin synthase resulting in a glycerol and a cardiolipin.

Cardiolipin (CL) is an important component of the inner mitochondrial membrane where it constitutes about 20% of the total lipid composition. It is essential for the optimal function of numerous enzymes that are involved in mitochondrial energy metabolism (Wikipedia). Cardiolipin biosynthesis occurs mainly in the mitochondria, but there also exists an alternative synthesis route for CDP-diacylglycerol that takes place in the endoplasmic reticulum. This second route may supplement this pathway. All membrane-localized enzymes are coloured dark green in the image. First, dihydroxyacetone phosphate (or glycerone phosphate) from glycolysis is used by the cytosolic enzyme glycerol-3-phosphate dehydrogenase [NAD(+)] to synthesize sn-glycerol 3-phosphate. Second, the mitochondrial outer membrane enzyme glycerol-3-phosphate acyltransferase esterifies an acyl-group to the sn-1 position of sn-glycerol 3-phosphate to form 1-acyl-sn-glycerol 3-phosphate (lysophosphatidic acid or LPA). Third, the enzyme 1-acyl-sn-glycerol-3-phosphate acyltransferase converts LPA into phosphatidic acid (PA or 1,2-diacyl-sn-glycerol 3-phosphate) by esterifying an acyl-group to the sn-2 position of the glycerol backbone. PA is then transferred to the inner mitochondrial membrane to continue cardiolipin synthesis. Fourth, magnesium-dependent phosphatidate cytidylyltransferase catalyzes the conversion of PA into CDP-diacylglycerol. Fifth, CDP-diacylglycerol--glycerol-3-phosphate 3-phosphatidyltransferase synthesizes phosphatidylglycerophosphate (PGP). Sixth, phosphatidylglycerophosphatase and protein-tyrosine phosphatase dephosphorylates PGP to form phosphatidylglycerol (PG). Last, cardiolipin synthase catalyzes the synthesis of cardiolipin by transferring a phosphatidyl group from a second CDP-diacylglycerol to PG. It requires a divalent metal cation cofactor.

Dihydrofolic acid, a product of the folate biosynthesis pathway, can be metabolized by multiple enzymes. Dihydrofolic acid can be reduced by a NADP-driven dihydrofolate reductase resulting in a NADPH, hydrogen ion and folic acid. Dihydrofolic acid can also be reduced by an NADPH-driven dihydrofolate reductase resulting in a NADP and a tetrahydrofolic acid. Folic acid can also produce a tetrahydrofolic acid through a NADPH-driven dihydrofolate reductase. Dihydrofolic acid also interacts with 5-thymidylic acid through a thymidylate synthase resulting in the release of dUMP and 5,10-methylene-THF Tetrahydrofolic acid can be converted into 5,10-methylene-THF through two different reversible reactions. Tetrahydrofolic acid interacts with a S-Aminomethyldihydrolipoylprotein through a aminomethyltransferase resulting in the release of ammonia, a dihydrolipoylprotein and 5,10-Methylene-THF Tetrahydrofolic acid interacts with L-serine through a glycine hydroxymethyltransferase resulting in a glycine, water and 5,10-Methylene-THF. The compound 5,10-methylene-THF reacts with an NADPH dependent methylenetetrahydrofolate reductase [NAD(P)H] resulting in NADP and 5-Methyltetrahydrofolic acid. This compound interacts with homocysteine through a methionine synthase resulting in L-methionine and tetrahydrofolic acid. Tetrahydrofolic acid can be metabolized into 10-formyltetrahydrofolate through 4 different enzymes: 1.- Tetrahydrofolic acid interacts with FAICAR through a phosphoribosylaminoimidazolecarboxamide formyltransferase resulting in a 1-(5'-Phosphoribosyl)-5-amino-4-imidazolecarboxamide and a 10-formyltetrahydrofolate 2.-Tetrahydrofolic acid interacts with 5'-Phosphoribosyl-N-formylglycinamide through a phosphoribosylglycinamide formyltransferase 2 resulting in a Glycineamideribotide and a 10-formyltetrahydrofolate 3.-Tetrahydrofolic acid interacts with Formic acid through a formyltetrahydrofolate hydrolase resulting in water and a 10-formyltetrahydrofolate 4.-Tetrahydrofolic acid interacts with N-formylmethionyl-tRNA(fMet) through a 10-formyltetrahydrofolate:L-methionyl-tRNA(fMet) N-formyltransferase resulting in a L-methionyl-tRNA(Met) and a 10-formyltetrahydrofolate 10-formyltetrahydrofolate can interact with a hydrogen ion through a bifunctional 5,10-methylene-tetrahydrofolate dehydrogenase resulting in water and 5,10-methenyltetrahydrofolic acid. Tetrahydrofolic acid can be metabolized into 5,10-methenyltetrahydrofolic acid by reacting with a 5'-phosphoribosyl-a-N-formylglycineamidine through a phosphoribosylglycinamide formyltransferase 2 resulting in water, glycineamideribotide and 5,10-methenyltetrahydrofolic acid. The latter compound can either interact with water through an aminomethyltransferase resulting in a N5-Formyl-THF, or it can interact with a NADPH driven bifunctional 5,10-methylene-tetrahydrofolate dehydrogenase resulting in a NADP and 5,10-Methylene THF.

Methylglyoxal, also known as pyruvaldehyde, is a cytotoxic compound derived from pyruvic acid. In E. coli, there are at least eight pathways that are responsible for the detoxification of methylglyoxal. The first reaction in this pathway is the reduction of pyruvaldehyde to (S)-lactaldehyde, along with the cofactor NADH, catalyzed by 2,5-diketo-D-gluconic acid reductase subunits A and B. Following this, (S)-lactaldehyde is dehydrogenated into L-lactic acid by the lactaldehyde dehydrogenase enzyme, also using NAD as a cofactor. Finally, L-lactic acid is converted to pyruvic acid by L-lactate dehydrogenase in a reaction involving the reduction of an electron acceptor. Pyruvic acid is then used in glycolysis and pyruvate dehydrogenase pathways.

Cardiolipin (CL) is an important component of the inner mitochondrial membrane where it constitutes about 20% of the total lipid composition. It is essential for the optimal function of numerous enzymes that are involved in mitochondrial energy metabolism (Wikipedia). Cardiolipin biosynthesis occurs mainly in the mitochondria, but there also exists an alternative synthesis route for CDP-diacylglycerol that takes place in the endoplasmic reticulum. This second route may supplement this pathway. All membrane-localized enzymes are coloured dark green in the image. First, dihydroxyacetone phosphate (or glycerone phosphate) from glycolysis is used by the cytosolic enzyme glycerol-3-phosphate dehydrogenase [NAD(+)] to synthesize sn-glycerol 3-phosphate. Second, the mitochondrial outer membrane enzyme glycerol-3-phosphate acyltransferase esterifies an acyl-group to the sn-1 position of sn-glycerol 3-phosphate to form 1-acyl-sn-glycerol 3-phosphate (lysophosphatidic acid or LPA). Third, the enzyme 1-acyl-sn-glycerol-3-phosphate acyltransferase converts LPA into phosphatidic acid (PA or 1,2-diacyl-sn-glycerol 3-phosphate) by esterifying an acyl-group to the sn-2 position of the glycerol backbone. PA is then transferred to the inner mitochondrial membrane to continue cardiolipin synthesis. Fourth, magnesium-dependent phosphatidate cytidylyltransferase catalyzes the conversion of PA into CDP-diacylglycerol. Fifth, CDP-diacylglycerol--glycerol-3-phosphate 3-phosphatidyltransferase synthesizes phosphatidylglycerophosphate (PGP). Sixth, phosphatidylglycerophosphatase and protein-tyrosine phosphatase dephosphorylates PGP to form phosphatidylglycerol (PG). Last, cardiolipin synthase catalyzes the synthesis of cardiolipin by transferring a phosphatidyl group from a second CDP-diacylglycerol to PG. It requires a divalent metal cation cofactor.

Cardiolipin (CL) is an important component of the inner mitochondrial membrane where it constitutes about 20% of the total lipid composition. It is essential for the optimal function of numerous enzymes that are involved in mitochondrial energy metabolism (Wikipedia). Cardiolipin biosynthesis occurs mainly in the mitochondria, but there also exists an alternative synthesis route for CDP-diacylglycerol that takes place in the endoplasmic reticulum. This second route may supplement this pathway. All membrane-localized enzymes are coloured dark green in the image. First, dihydroxyacetone phosphate (or glycerone phosphate) from glycolysis is used by the cytosolic enzyme glycerol-3-phosphate dehydrogenase [NAD(+)] to synthesize sn-glycerol 3-phosphate. Second, the mitochondrial outer membrane enzyme glycerol-3-phosphate acyltransferase esterifies an acyl-group to the sn-1 position of sn-glycerol 3-phosphate to form 1-acyl-sn-glycerol 3-phosphate (lysophosphatidic acid or LPA). Third, the enzyme 1-acyl-sn-glycerol-3-phosphate acyltransferase converts LPA into phosphatidic acid (PA or 1,2-diacyl-sn-glycerol 3-phosphate) by esterifying an acyl-group to the sn-2 position of the glycerol backbone. PA is then transferred to the inner mitochondrial membrane to continue cardiolipin synthesis. Fourth, magnesium-dependent phosphatidate cytidylyltransferase catalyzes the conversion of PA into CDP-diacylglycerol. Fifth, CDP-diacylglycerol--glycerol-3-phosphate 3-phosphatidyltransferase synthesizes phosphatidylglycerophosphate (PGP). Sixth, phosphatidylglycerophosphatase and protein-tyrosine phosphatase dephosphorylates PGP to form phosphatidylglycerol (PG). Last, cardiolipin synthase catalyzes the synthesis of cardiolipin by transferring a phosphatidyl group from a second CDP-diacylglycerol to PG. It requires a divalent metal cation cofactor.

L-lyxose is a sugar and a monosaccharide containing five carbon atoms and aldehyde group. Wild-type E.coli can't utilize L-lyxose as its source of carbon and energy. In mutated E.coli, it can metabolize l-lyxose through utilization of enzymes of the rhamnose, arabinose and 2,3-diketo-L-gulonate systems. β-L-lyxopyranose enter cell by L-rhamnose-proton symporter, then convert to l-xylulose by L-rhamnose isomerase. L-xylulose is further metabolized to L-xylulose-5-phosphate with energy ATP. Putative L-ribulose-5-phosphate 3-epimerase can convert L-xylulose -5-phosphate to L-ribulose 5-phosphate, and L-ribulose 5-phosphate 4-epimerase can catalyze L-ribulose 5-phosphate to xylulose 5-phosphate for further pentose phosphate.

The benzoate catabolism pathway is a key metabolic pathway that allows bacteria to utilize benzoate as a carbon source and involves the conversion of benzoate into intermediates that can enter the citric acid cycle. The benABCD operon responsible contains 4 genes benA, benB, benC, benD. The operon is activated by the benM gene which encodes for a transcriptional regulator and is outside of this operon. This operon is activated in the presence of benzoate, which binds to the transcriptional regulator, enhancing its ability to bind the promoter and facilitate RNA polymerase recruitment, thus initiating transcription. benA encodes benzoate 1,2-dioxygenase alpha subunit, which is part of the enzyme complex that catalyzes the initial dioxygenation of benzoate to form catechol which enters the catechil ortho-cleavage pathway and eventually feeds the TCA cycle. benB encodes benzoate 1,2-dioxygenase beta subunit, which works in conjunction with BenA to catalyze the same reaction. benC encodes a reductase that reduces NAD to NADH which is required in the BenAB complex for the dioxygenation reaction to form dihydrodiol. benD encodes cis-1,2-dihydroxycyclohexa-3,5-diene-1-carboxylate dehydrogenase, which converts the intermediate product (dihydrodiol) into catechol. Additionally, the operon is influenced by benK and benP which are also outside of the operon and encode for membrane transporters involved in the uptake of benzoate into the cell.

The areCBA operon in Acinetobacter sp. strain ADP1 is activated in response to the presence of aromatic compounds, particularly benzyl acetate, which diffuses into the bacterial cell when its extracellular concentration reaches a threshold level. Upon entry into the cell, benzyl acetate serves as an inducer that triggers the transcriptional activation of the operon through the action of the regulatory protein AreR. AreR, a member of the NtrC/XylR family, binds to specific regulatory sequences located upstream of the promoter region of the areCBA operon, enhancing the RNA polymerase recruitment and initiation of transcription. The operon comprises three genes: areA, areB, and areC. The AreA protein, an esterase, catalyzes the hydrolysis of benzyl acetate, converting it into benzyl alcohol and acetic acid, thereby initiating the degradation process. Subsequently, the alcohol is converted into benzaldehyde by the action of AreB, an alcohol dehydrogenase, which facilitates the oxidation of benzyl alcohol to its corresponding aldehyde. Finally, AreC, a dehydrogenase, further processes benzaldehyde into salicylate, which integrates into the β-ketoadipate pathway for subsequent degradation, allowing the bacteria to utilize these aromatic compounds as carbon sources. This structured sequence of reactions, coupled with AreR's regulatory function, ensures efficient catabolism of benzyl alkanoates, allowing Acinetobacter sp. strain ADP1 to thrive in environments rich in these compounds. The coordinate induction of the areCBA operon through AreR exemplifies a finely tuned mechanism that responds dynamically to environmental cues, ultimately facilitating the bacterium's adaptability and metabolic versatility.