Name: sulfur uptake and cysteine synthesis
Uploaded: 2025-06-12T09:37:55.000Z
Duration: 1 min 20 s
Channel: JoVE

Le soufre est essentiel à la synthèse des acides aminés, tels que la cystéine et la méthionine, et des coenzymes, telles que la coenzyme A et la biotine. Les micro-organismes absorbent le soufre principalement sous forme de sulfates du sol et de l’eau. Étant donné que le sulfate est fortement oxydé, il doit subir le processus de réduction assimilatoire du soufre avant d’être incorporé dans les biomolécules. Ce processus commence par l’activation du sulfate, catalysé par l’ATP sulfurylase, formant l’adénosine-5-phosphosulfate. Celui-ci est phosphorylé en 3-phosphoadénosine-5-phosphosulfate ou PAPS. Le PAPS libère du sulfite, qui est ensuite réduit en sulfure d’hydrogène par la sulfite réductase. Chez les champignons, le sulfure d’hydrogène se combine avec la sérine pour former de la cystine, qui est ensuite réduite en cystéine. Chez les bactéries et certaines archées, le sulfure d’hydrogène se combine avec l’O-acétylsérine ou l’O-phosphosérine pour former de la cystéine. Une fois formée, la cystéine fournit du soufre pour la synthèse de la méthionine et d’autres composés soufrés, tels que la coenzyme A et la biotine.

assimilation du soufre

Sulfur Assimilation

Le soufre est un &#233;l&#233;ment essentiel dans les syst&#232;mes biologiques, intervenant dans la synth&#232;se de biomol&#233;cules cl&#233;s, notamment des acides amin&#233;s comme la cyst&#233;ine et la m&#233;thionine, ainsi que des cofacteurs tels que la coenzyme A et la biotine. Les micro-organismes assimilent principalement le soufre sous forme de sulfate (SO_4^2-) pr&#233;sent dans l&#8217;environnement, lequel doit subir une s&#233;rie de transformations biochimiques avant d&#8217;&#234;tre incorpor&#233; dans les composants cellulaires. &#201;tant donn&#233; que le sulfate est sous une forme tr&#232;s oxyd&#233;e, il doit &#234;tre r&#233;duit par le biais d&#8217;une r&#233;duction assimilatrice du sulfate pour devenir biologiquement utilisable. Certains micro-organismes peuvent &#233;galement utiliser des acides amin&#233;s soufr&#233;s (cyst&#233;ine, m&#233;thionine) ou des compos&#233;s soufr&#233;s r&#233;duits (thiosulfate, soufre &#233;l&#233;mentaire) comme sources alternatives de soufre, contournant ainsi les &#233;tapes d&#8217;activation et de r&#233;duction du sulfate, ce qui permet une assimilation plus &#233;conome en &#233;nergie.
Voie d&#8217;activation et de r&#233;duction du sulfate
Le processus d&#233;bute par l&#8217;activation du sulfate via l&#8217;ATP sulfurylase, une enzyme qui catalyse la formation de l&#8217;ad&#233;nosine-5&#8242;-phosphosulfate (APS). L&#8217;APS constitue un interm&#233;diaire cl&#233; du m&#233;tabolisme du sulfate, pouvant &#234;tre phosphoryl&#233; pour former du phosphoad&#233;nosine-5&#8242;-phosphosulfate (PAPS), ou &#234;tre directement r&#233;duit chez certaines bact&#233;ries. Le PAPS est essentiel non seulement &#224; l&#8217;assimilation du sulfate mais &#233;galement aux r&#233;actions de sulfation dans les processus cellulaires.
La r&#233;duction du PAPS en sulfite (SO_3^2-) est assur&#233;e par la PAPS r&#233;ductase, suivie de la conversion du sulfite en sulfure d&#8217;hydrog&#232;ne (H_2S) par la sulfite r&#233;ductase. Ces r&#233;ductions s&#233;quentielles permettent de convertir le soufre en une forme biologiquement assimilable pour les mol&#233;cules organiques. Des &#233;quivalents r&#233;ducteurs tels que le NADPH fournissent les &#233;lectrons n&#233;cessaires &#224; ces conversions.
Incorporation du sulfure d&#8217;hydrog&#232;ne dans la cyst&#233;ine
L&#8217;&#233;tape finale de l&#8217;assimilation du soufre consiste en l&#8217;incorporation du sulfure d&#8217;hydrog&#232;ne dans le m&#233;tabolisme des acides amin&#233;s. Chez les champignons, le H_2S r&#233;agit avec la s&#233;rine pour former de la cyst&#233;ine. Chez les bact&#233;ries et certaines arch&#233;es, le H_2S se combine soit avec l&#8217;O-ac&#233;tyls&#233;rine, soit avec l&#8217;O-phosphos&#233;rine, pour former de la cyst&#233;ine via des voies enzymatiques. L&#8217;O-ac&#233;tyls&#233;rine est plus fr&#233;quemment utilis&#233;e chez Escherichia coli et les bact&#233;ries apparent&#233;es, tandis que les voies d&#233;pendant de l&#8217;O-phosphos&#233;rine se retrouvent chez certaines arch&#233;es comme Methanocaldococcus jannaschii.
La cyst&#233;ine constitue un pr&#233;curseur essentiel &#224; la biosynth&#232;se de la m&#233;thionine et &#224; la production de cofacteurs soufr&#233;s tels que la coenzyme A et la biotine. Par ailleurs, le m&#233;tabolisme du soufre joue un r&#244;le important dans le maintien de l&#8217;hom&#233;ostasie redox, notamment par la synth&#232;se du glutathion, qui prot&#232;ge les cellules contre le stress oxydatif.

Assimilation du soufre

Le soufre est un &#233;l&#233;ment essentiel dans les syst&#232;mes biologiques, intervenant dans la synth&#232;se de biomol&#233;cules cl&#233;s, ...

Education

Enseignement

JoVE Core

Microbiology

Microbiologie

Unit

Unité

Microbial Metabolism

Métabolisme microbien

KEY TERMS AND CONCEPTS

TERMES ET CONCEPTS CLÉS

sulfur uptake and cysteine synthesis

Sulfur uptake and cysteine synthesis are key parts of microbial metabolism. Sulfur is needed to build important biomolecules, including the amino acids cysteine and methionine, as well as cofactors such as coenzyme A and biotin. Microorganisms usually take in sulfur from the environment as sulfate, but sulfate must be changed before cells can use it.

Because sulfate is highly oxidized, it must go through assimilatory sulfate reduction to become biologically useful. Some microorganisms can also use sulfur-containing amino acids like cysteine and methionine, or reduced sulfur compounds such as thiosulfate and elemental sulfur. These sources bypass sulfate activation and reduction, so they provide a more energy-efficient route for sulfur assimilation.

The pathway starts when ATP sulfurylase activates sulfate and forms adenosine-5′-phosphosulfate, or APS. APS is an important intermediate in sulfate metabolism. In some bacteria, it is reduced directly, while in others it is first phosphorylated to phosphoadenosine-5′-phosphosulfate, or PAPS. PAPS also has a role in sulfation reactions inside cells.

PAPS reductase converts PAPS to sulfite, and sulfite reductase then reduces sulfite to hydrogen sulfide, or H2S. These steps use reducing equivalents such as NADPH to provide electrons. The sequence of reductions turns sulfur into a form that cells can build into organic molecules.

The final step is the use of hydrogen sulfide in amino acid metabolism. In fungi, H2S reacts with serine to form cysteine. In bacteria and some archaea, H2S combines with O-acetylserine or O-phosphoserine to make cysteine. O-acetylserine is common in Escherichia coli and related bacteria, while O-phosphoserine pathways occur in some archaea, including Methanocaldococcus jannaschii.

Cysteine then helps make methionine and sulfur-containing cofactors such as coenzyme A and biotin. Sulfur metabolism also supports redox balance through glutathione synthesis. Glutathione helps protect cells from oxidative stress.

Sulfur Uptake and Cysteine Synthesis

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atp and energy production

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introduction to metabolism

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glycolysis

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Microbes Use Proteins for Energy

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lipid catabolism

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oxygenic photosynthesis

How Plants Make Oxygen and ATP

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Bacterial Light Capture Without Oxygen

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biosynthesis of polysaccharides

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inorganic nitrogen assimilation

Nitrogen Uptake by Microbes

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sulfur assimilation

Sulfur uptake and cysteine synthesis are key parts of microbial metabolism. Sulfur is needed to build important biomolecules, including the amino acids cysteine and methionine, as well as cofactors such as coenzyme A and biotin. Microorganisms usually take in sulfur from the environment as sulfate, but sulfate must be changed before cells can use it. Because sulfate is highly oxidized, it must go through assimilatory sulfate reduction to become biologically useful. Some microorganisms can also...

amino acid biosynthetic pathways

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key terms and concepts

Learn how microbes activate sulfate, reduce it to hydrogen sulfide, and use it to make cysteine, methionine, and sulfur-containing cofactors.

Sulfur Uptake and Cysteine Synthesis | JoVE K12

JoVE Core Microbiology provides an engaging introduction to the microbial world and its influence on health, industry, and the environment. This comprehensive collection covers key concepts such as microbial structure, metabolism, genetics, and ecology. It introduces essential laboratory techniques and microscopy methods through visually engaging animations. Corresponding scientist-in-action videos bridge classroom concepts with real-world research and applications.

microbiology

Sulfur Uptake and Cysteine Synthesis

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