1 / 18

Electrontransfer proteins

Electrontransfer proteins. Electrontransfer proteins. In biological systems the elecetrontransfer proteins make possible to carry out oxidation and reduction separated from each other in space. Complex I. Complex III. Complex IV.

leone
Download Presentation

Electrontransfer proteins

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Electrontransfer proteins

  2. Electrontransfer proteins In biological systems the elecetrontransfer proteins make possible to carry out oxidation and reduction separated from each other in space. Complex I Complex III Complex IV A schematic drawing of the mitochondrium respiratory chain (FMN: flavin mononucleotide, FeS: iron-sulphur protein, Q: ubiquinone, Cyt: cytochrome, CuA: type 1 blue copper protein).

  3. Electrontransfer proteins I. Function: Transport electrons to oxidise the substrate and reduce molecular oxygen. → „One-electron” change of a metal ion with saturated coordination sphere in the interactions with electron- donor or acceptor molecules. Condition: Molecules with easy oxidability or reducibility. The electrontransfer molecules should cover wide redox potential range. Structure: small organic molecules: e.g. NAD/NADH, FAD/FADH2,.... metalloproteins

  4. Electrontransfer proteins II. A schematic representation of the biological fuel cell The gross process: 2H2 + O2 → 2H2O Oxidation of H2 inside the membrane, reduct- ion of the O2 outside the membrane → electrons are trans- ferred by cytochromes while the energy is stored in the form of proton/ATP gradient.

  5. Electrontransferproteins III. • Conditions of electron transfer: • The various proteins should cover a wide redox potential range • (e.g. Fe-S → blue copper proteins ~ − 0.4 - + 0.7 V) • The coordination sphere of the metal ion should be saturated and • should not change practically during electron transfer. • Change in the oxidation state should not be accompanied by changes • in the coordination geometry, bond length/bond angles. → • the specific coordination geometry should be suitable for both • oxidation states of the metal ion. • Electron uptake and removal should not result in significant change • in the structure of the metal complex, e.g. it should be a low energy • process.

  6. Electrontransferproteins IV. • Types and structures of electrontransfer proteins: • Cytochromes: hem proteinsmay be: cytochrome a, b, c, (f): they differ in the type of the hem, the form of the hem-protein binding and the value of the redox potential (−200 - + 500 mV). • Iron-sulphur proteins:[FeII/IIIa(S2−)b(RS−)c]redox potential: (−700) − 400 - 0.0 (+400) mV • Blue copper proteins:distorted terahedral CuII complexes [CuIIN(His),N(His),S(Cys),S(Met)]redox potential: + 300 - +700 mV Oxidation chain: Fe-S → cytochrome b → cytochrome c → ciyochrome a → blue copper

  7. Cytochromes I. Electrontransfer proteins containing hem prosthetic groups, i.e. they are in relation with hemo- and myoglobins. Nomenclature: colouring material of the cells, characteristic absorption band in the range 400-450 (600) nm Types: based on the hem group:

  8. Cytochromes II. • Structural features of cytochromes: • The coordination sphere of FeIII/II ions should be saturated axial amino acids: His, Met, (Lys, Cys, Tyr) • In the case of cytochrome a and b the hem is bound strongly but not • covalently to the protein. In the case of cytochrome c the hem • and the protein bind covalently. • Most of the cytochromes are 1:1 units (1 hem + 1 protein), but there are cytochromes with multiple hem units. • The cytochromes always participate in one electron processes: FeII → FeIII reversible electron transfers. • Redox potential values: (fairly wide range) characteristic values: cytochrome a: ~ + 400 mV cytochrome b: ~ + 0.0 mV cytochrome c: ~ + 260 mV

  9. Iron-sulphur proteins I. • They can be characterised by the following general composition: • [FeII/IIIaS2−b](RS−)c • where: S2−: sulphide ion (inorganic sulphur) • RS−: protein Cys side chain (organic sulphur) • General feature: • widely spread in mammals and in plants • participate in one electron steps • the reduction potential is usually negative (0 - − 400 with the exception of HIPIP: High Potential Iron Protein = +350 mV) • - usually electrontransfer coenzymes of enzyme systems, but e.g. the aconitase itself is an enzyme.

  10. Iron-sulphurproteins II. Main types of iron-sulphur proteins: [FeIII(RS−)4]: rubredoxin [FeIII2(S2−)2]2+ RS−)4 : plant ferredoxin [FeII2FeIII2(S2−)4]2+(RS−)4 : bacterial ferredoxin and HIPIP [FeIIFeIII2(S2−)4](RS−)3: „irregular” clusters (One edge of the cube is empty, which can be occupied by other metal ions, e.g. Ni, V, Mo,... Further clusters are also possible, e.g. Fe7S8, etc.)

  11. Iron-sulphurproteins III. Structures of the iron-sulphur proteins: • rubredoxin, [FeIII(RS−)4]: • Iron(III) ion is in a little distorted tetrahedral • environment. Reduction is not accompanied by a • significant change in geometry. • Electrontransfer component of the sulphur-bacteria. 2. Plant-type ferredoxin: [FeIII2(S2−)2]2+(RS−)4 In resting state 2 FeIII, but only one of them is reduced to FeII FeII−FeIII (1 unpaired electron, significant Fe-Fe interaction, but not complete electron delocalisation

  12. Iron-sulphurproteins IV. 3. Fe4-S4 clusters: [FeIII3FeIIS4]3+ [FeIII2FeII2S4]2+ [FeIIIFeII3S4]+ HIPIPresting state bacterial ferredoxin + 350 mV −400 mV In resting state both Fe4-S4 clusters are in FeIII2FeII2 state and can take up or release only a single electron. The large difference in the redox potential is explained by the differences in the amino acid sequence of the two proteins.

  13. Fe4-S4 Iron-sulphur protein (HIPIP)

  14. Blue copper proteins Occur mostly in plants (preparation from algae) Participate primarily in photosynthesis, as electrontransfer proteins (plastocyanin, azurin, cytochrome c oxidase CuA centre). Characteristics: - low molecular mass (M ~ 10 000 ~ 100 amino acid + 1 db CuII) - Intense blue colour λ ~ 600 nm, ε ~ 3000 - 5000 - EPR active, low coupling constant (A||) - high redox potential (ε ~ + 0.3-0.7 V) (easy to reduce) Action: Cu(II) - SR  Cu(I) +.SR fast process Structure: Cu(II) in unusual chemical environment distorted tetrahedron (usually: 2 His + 1 Cys + 1Met)

  15. Plastocyanin I. Relatively low molecular mass. M ~ 10.500 (99 amino acids) Globular protein, cylindrical shape. 420 x 320 x 280 nm → CuII ion in 60 nm depth.

  16. Plastocyanin II. Coordination geometry of CuII-ion: distorted tetrahedron Bond lengths (nm) Bonds CuII CuI CuI pH=7.0 pH=3.8 Cu-S(Cys) 2.13 2.17 2.13 Cu-S(Met) 2.90 2.87 2.51 Cu-N(His37) 2.04 2.13 2.12 Cu-N(His87) 2.10 2.39 < 4

  17. Ellenőrző kérdések • Mi az elektronszállító fehérjék funkciója a biológiai rendszerekben? Milyen elektronszállító fehérjéket ismer? • Jellemezze a citokromokat szerkezeti szempontból! • Hasonlítsa össze a vas-kén proteineket és a citokrómokat szerkezeti sajátságaikat tekintve! • A vas-kén proteinek milyen kéntartalommal rendelkeznek? • Mi a jellemzője a réztartalmú elektrontranszfer fehérjéknek? • A kémiai evolúcióban való keletkezésük szempontjából elemezze a vas-kén fehérjék, a citokrómok és a kékréz fehérjék családját!

More Related