High potential iron–sulfur protein

Key takeaways

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Reference excerpt

High potential iron-sulfur proteins (HIPIP) are a class of iron-sulfur proteins. They are ferredoxins that participate in electron transfer in photosynthetic bacteria as well as in Paracoccus denitrificans.

Structure The HiPIPs are small proteins, typically containing 63 to 85 amino acid residues. The sequences show significant variation. As shown in the following schematic representation the iron-sulfur cluster is bound by four conserved cysteine residues.

[ 4Fe-4S cluster] | | | | xxxxxxxxxxxxxxxxxxxCxCxxxxxxxCxxxxxCxxxx

C: conserved cysteine residue involved in the binding of the 4Fe-4S core.

[Fe4S4] clusters The [Fe4S4] clusters are abundant cofactors of metalloproteins. They participate in electron-transfer sequences. The core structure for the [Fe4S4] cluster is a cube with alternating Fe and S vertices. These clusters exist in two oxidation states with a small structural change. Two families of [Fe4S4] clusters are known: the ferredoxin (Fd) family and the high-potential iron–suflur protein (HiPIP) family. Both HiPIP and Fd share the same resting state: [Fe4S4]2+, which have the same geometric and spectroscopic features. Differences arise when it comes to their active state: HiPIP forms by oxidation to [Fe4S4]3+, and Fd is formed by reduction to [Fe4S4]+.

[ Fe 4 S 4 ] 3 + ( for HiPIP ) ⇌ oxidation [ Fe 4 S 4 ] 2 + ( resting state ) ⇌ reduction [ Fe 4 S 4 ] + ( for Fd ) {\displaystyle {\ce {{\underset {(for\ HiPIP)}{[Fe4S4]^{3}+}}<=>[{\ce {oxidation}}]{\underset {(resting\ state)}{[Fe4S4]^{2}+}}<=>[{\ce {reduction}}]{\underset {(for\ Fd)}{[Fe4S4]+}}}}}

The different oxidation states are explained by the proteins that combined with the [Fe4S4] cluster. Analysis from crystallographic data suggests that HiPIP is capable of preserving its higher oxidation state by forming fewer hydrogen bonds with water. The characteristic fold of the proteins wraps the [Fe4S4] cluster in a hydrophobic core, only being able to form about five conserved H-bond to the cluster ligands from the backbone. In contrast, the protein associated with the Fd's allows these clusters to contact solvent resulting in 8 protein H-bonding interactions. The protein binds Fd via conserved CysXXCysXXCys structure (X stands for any amino acid). Also, the unique protein structure and dipolar interactions from peptide and intermolecular water contribute to shielding the [Fe4S4]3+ cluster from the attack of random outside electron donors, which protects itself from hydrolysis.

Synthetic analogues HiPIP analogues can be synthesized by ligand exchange reactions of [Fe4S4{N(SiMe3)2}4]− with 4 equiv of thiols (HSR) as follows:

[Fe4S4{N(SiMe3)2}4]− + 4RSH → [Fe4S4(SR)4]− + 4 HN(SiMe3)2 The precursor cluster [Fe4S4{N(SiMe3)2}4]− can be synthesized by one-pot reaction of FeCl3, NaN(SiMe3)2, and NaSH. The synthesis of HiPIP analogues can help people understand the factors that cause variety redox of HiPIP.

Biochemical reactions HiPIPs take part in many oxidizing reactions in creatures, and are especially known with photosynthetic anaerobic bacteria, such as Chromatium, and Ectothiorhodospira. HiPIPs are periplasmic proteins in photosynthetic bacteria. They play a role of electron shuttles in the cyclic electron flow between the photosynthetic reaction center and the cytochrome bc1 complex. Other oxidation reactions HiPIP involved include catalyzing Fe(II) oxidation, being electron donor to reductase and electron accepter for some thiosulfate-oxidizing enzyme.

References

External links PDOC00515 - High potential iron-sulfur proteins in PROSITE

Further reading Nogi T, Fathir I, Kobayashi M, Nozawa T, Miki K (2000). "Crystal structures of photosynthetic reaction center and high-potential iron-sulfur protein from Thermochromatium tepidum: Thermostability and electron transfer". Proceedings of the National Academy of Sciences. 97 (25): 13561–13566. Bibcode:2000PNAS...9713561N. doi:10.1073/pnas.240224997. PMC 17615. PMID 11095707.

Illustrations

Worked examples

Example 1 — a first encounter with High potential iron–sulfur protein

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Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to High potential iron–sulfur protein before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about High potential iron–sulfur protein ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of High potential iron–sulfur protein

In research: High potential iron–sulfur protein appears in biology research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses High potential iron–sulfur protein in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: High potential iron–sulfur protein is common in secondary-school and first-year university syllabi. It links to neighbouring topics Peripheral membrane proteins, Protein families, so understanding it makes those chapters shorter.
In everyday life: Look for High potential iron–sulfur protein outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study High potential iron–sulfur protein in 20 minutes

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Frequently asked questions

What is High potential iron–sulfur protein in simple terms?

High potential iron-sulfur proteins (HIPIP) are a class of iron-sulfur proteins. They are ferredoxins that participate in electron transfer in photosynthetic bacteria as well as in Paracoccus denitrificans.

Why does High potential iron–sulfur protein matter?

Because it connects several biology ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study High potential iron–sulfur protein?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

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