Subsystem: Choline and Betaine Uptake and Betaine Biosynthesis
This subsystem's description is:
Glycine betaine (N,N,N-trimethylglycine) has been shown to be a very efficient osmolyte found in a wide range of bacterial and plant species, where it is accumulated at high cytoplasmic concentrations in response to osmotic stress.
Was shown that S. meliloti (in contrast to Escherichia coli, Bacillus subtilis, and other bacteria), can use glycine betaine not only as osmoprotectants but as carbon, nitrogen, and energy sources as well.
Glycine betaine either can be taken up directly from the environment by specific transport systems or synthesized from choline by a two-step pathway with betaine aldehyde as intermediate. This pathway appears to be conserved in bacteria and plants, but shows divergence in the enzymes involved. Gram-positive bacteria such as Arthrobacter pascens and A. globiformis and the fungus Cylindrocarpon didymun use a soluble choline oxidase to catalyze both steps .
Higher plants and Gram-negative bacteria both are using a conserved betaine aldehyde dehydrogenase to catalyze the betaine aldehyde to glycine betaine reaction. The choline-to-betaine aldehyde reaction, however, is catalyzed by a choline monooxygenase in plants and by a choline dehydrogenase in bacteria such as E. coli, Pseudomonas aeruginosa, and S. meliloti.
In most organisms, betaine is synthesized as a result of the two-step oxidation of choline via betaine aldehyde, a toxic intermediate.The glycine betaine biosynthesis pathway has been characterized at the molecular level in E. coli and Bacillus subtilis.
In several higher plants from taxonomically unrelated families, the relevant enzymes are choline monooxygenase (CMO), a ferredoxin-dependent soluble Rieske-type protein, and betaine aldehyde dehydrogenase (BADH; EC 184.108.40.206), a soluble NAD+-dependent enzyme. These enzymes are found mostly in the chloroplast stroma and their activities, as well as levels of betaine, increase in response to salt stress. BADH has also been found in several plants that barely accumulate any betaine. In mammalian cells and in microorganisms such as Escherichia coli, betaine is synthesized by choline dehydrogenase (EC 220.127.116.11), a membrane-bound oxygen-dependent enzyme, in combination with betaine aldehyde dehydrogenase (EC 18.104.22.168).
Some bacteria, such as Synrhizobium meliloti and Pseudomonas aeruginosa, can degrade choline-O-sulfate to choline, which is then converted to glycine betaine and catabolized further into ammonia and pyruvate. The key enzyme for this process is choline sulfatase, encoded by the betC gene.
In contrast to these two pathways that each involve two enzymes, the biosynthesis of betaine is catalysed by a single flavoenzyme, choline oxidase (EC 22.214.171.124), in certain microorganisms, such as the soil bacterium Arthrobacter globiformis. As far as is known, to date this enzyme has only been found in microorganisms.
1.0 - choline monooxygenase/betaine aldehyde dehydrogenase pathway (betaine is synthesized as a result of the two-step pathway with betaine aldehyde as intermediate);
1.1 – variant 1 + choline-O-sulfate degradation pathway;
2.0 - choline oxidase pathway;
3.0 – only Glycine betaine transport systems are present, no synthesis;
_3 - any of synthesis + transport system
( like in Escherichia coli – variant 1.13 -Choline-sulfatase + choline monooxygenase/betaine aldehyde dehydrogenase pathway + transport system);
-1 - indicates a genome without a functioning subsystem;
x - indicates that the genome possesses a functioning system, but a gene or genes that performs a role has not yet been identified.
For more information, please check out the description and the additional notes tabs, below
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