FeS cluster assembly in bacteria Flashcards
Why is iron important?
- Fe is the 4th most abundant element on earth
- high redox potential
important in the following process
1. Cellular respiration
2. Oxygen transport
3. Electron transport
4. DNA synthesis
Name the diffrent most common Ironsulfur Clusters and draw their structures
FeS Cliusters are inorganic compounds which are present in all kingdoms of life
Name the Redox potentials of electrons transport sites in FeS cluster
- FeS clusters are involved in 1e- electron transfer reactions
- Redoxpotential: (-0,43, -0,4, -0,06V)
1. Rubredoxin (einfach) -60mV
2. Ferredoxin (zweifach) -430mV
3. Ferredoxin (vierfach) -400mV
What is the origin of life theory?
1. Origin in an “Iron-Sulfur World”
* Life is believed to have originated in an environment abundant in iron and sulfur, where iron-sulfur clusters were integral to early metabolic reactions and the emergence of life.
2. Favorable Conditions for FeS Cluster Assembly:
* The primordial atmosphere provided suitable conditions for the spontaneous assembly of FeS clusters, which are crucial for electron transfer and catalytic reactions.
3 . Utilization of FeS Clusters in Early Metabolic Reactions:
* Early life forms likely utilized FeS clusters to capture and release electrons in primitive metabolic reactions, enabling essential chemical processes.
4. Evolution of the TCA Cycle from a Reductive Citric Acid Cycle:
* The tricarboxylic acid (TCA) cycle, a central metabolic pathway, might have evolved from an ancient reductive citric acid cycle that utilized two FeS enzymes: aconitase and succinate dehydrogenase.
5. Challenges in an Oxidative Environment:
* As the environment transitioned to an oxidative state, ferrous iron (Fe2+) bioavailability became limited, presenting challenges for early life forms that relied on iron for various metabolic processes.
Why are FeS clusters important?
Fe-S Clusters are essential Cofactors (prosthetic group) and important for e-transfer in
1. cellular respiration
(In Citric Acid Cycle –> Aconitase, Succinat-Dehydrogenase & Electron transport chain –> Protein complex 1,2,3)
2. photosynthesis
3. nitrogen fixation
–> central role of life
name 4 proteins that contain FeS clusters
- Aconitas
- Succinyl-Dehydrogenase
- NADH:Q-Oxidoreduktase (PS 1) and 2,3
- Biotin Synthase
How are FeS Clusters assembled in vitro?
- Synthetic Fe-S clusters self- assemble
Apo forms of the [2Fe-2S] and [4Fe-4S] proteins can be activated by simple addition of HS- and Fe2+/3+ - Why do we need metallochaperone systems for Fe-S cluster assembly?
= To control metabolic resources or to minimize the toxicity of free iron and sulfide
How are metals bound in proteins?
There are 2 main classes of Co-factors
1. Coenzymes (organic molecules derived from vitamins)
2. Metals
Tightly bound coenzymes are called prosthetic group
Enzyme + Cofactore = Holoenzmyme
Enzyme - Cofactor = Apoenzyme
Which Protein is the iron donor in the FeS Cluster biosythesis?
in vivo
- iron (Fe3+) is transported in the cell via siderophores
- it can be released from the siderophore (Fe2+/Fe3+)
- it can be stored in bacterioferritin
- IscA is the Irondonor Protein –> involved in mobilization and transfer of iron for the assembly of FeS Clusters. Transfers Iron to IscU (Scaffolf protein)
Where the actual assembly of FeS occurs
Where does the sulfur comes from?
From the IscS Operon.
- Desulfurase of L-Cys to L-Ala.
- PLP (Pyridoxal-5´-Phosphat) is a cofactor for desulfurases
- PLP is an inactive Form of vitamin B6
- Catalyze the generation of sulfur from L-cystein
Explain briefly th function of PLP (Pyridoxal-5´-Phosphat)
- PLP is kovalently bound to a Lysin residue in the enzyme (Schiff’sche Base, internal aldimin)
- During the reaction this bond is broken and a new bond with the substrate amino acid is formed (external aldimine)
Side Chain cleavage (aldol-cleveage or retro-aldol reaction)
1. Cystein-Desulfurase with coenzyme PLP break down amino acids
2. Amino acids are degraded to compounds that can be metablosed to CO2 and H2O or used in gluconeogenesis and can be the source of the buildign blocks for complicated protein co-factors e.g: cystein desulferase
3. Cystein desulferase - catalyses the conversion of L-Cystein to L-Alanine
4. The Sulfur of Cystein is transferred to many substrates
What Role does PLP has in other Enzymes?
- Decarboxylation of aminoacids
- Transaminations
- Racemizations
- Aldolecleavagereactions
- Transulfurations
Name the FeS cluster biosynthesis operon structure
Scheme: Proposed mechanism for the reaction catalyzed by cystein desulferase
How are the clusters assembled?
- Isc-Operon
* iscR = Regulator
* iscS= Sulfur donor (L-Cystein desulferas)
* icU= Scaffold Protein
* iscA = FeS Cluster insertion
* hscB and hscA= chaperon
* fdx = e-transfer
* iscX = unknwon (maybe Fe-donor CyaY) - There are two steps
- assembly Step
- Transfer step