Cytochrome c

Cytochrome c, somatic

Three-dimensional structure of cytochrome c (green) with a heme molecule coordinating a central Iron atom (orange).
Available structures
PDB Ortholog search: PDBe, RCSB
Identifiers
Symbols CYCS ; CYC; HCS; THC4
External IDs OMIM: 123970 MGI: 88578 HomoloGene: 133055 GeneCards: CYCS Gene
RNA expression pattern
More reference expression data
Orthologs
Species Human Mouse
Entrez 54205 13063
Ensembl ENSG00000172115 ENSMUSG00000063694
UniProt P99999 P62897
RefSeq (mRNA) NM_018947 NM_007808
RefSeq (protein) NP_061820 NP_031834
Location (UCSC) Chr 7:
25.12 – 25.13 Mb		 Chr 6:
50.56 – 50.57 Mb
PubMed search

The cytochrome complex, or cyt c is a small hemeprotein found loosely associated with the inner membrane of the mitochondrion. It belongs to the cytochrome c family of proteins. Cytochrome c is highly water-soluble, unlike other cytochromes, and is an essential component of the electron transport chain, where it carries one electron. It is capable of undergoing oxidation and reduction, but does not bind oxygen. It transfers electrons between Complexes III (Coenzyme Q – Cyt C reductase) and IV (Cyt C oxidase). In humans, cytochrome c is encoded by the CYCS gene.[1][2]

Species distribution

Cytochrome c is a highly conserved protein across the spectrum of species, found in plants, animals, and many unicellular organisms. This, along with its small size (molecular weight about 12,000 daltons),[3] makes it useful in studies of cladistics.[4] The cytochrome c molecule has been studied for the glimpse it gives into evolutionary biology.

Its primary structure consists of a chain of about 100 amino acids. Many higher-order organisms possess a chain of 104 amino acids.[5] The sequences of cytochrome c in humans is identical to that of chimpanzees (our closest relatives), but differs more from that of horses.[6]

Its amino acid sequence is highly conserved in eukaryotes, differing by only a few residues. In more than thirty species, 34 of the 104 amino acids are conserved; identical at that position.[7] For example, human cytochrome oxidase reacts with wheat cytochrome c, in vitro; this is true for all pairs of species tested.[7] In addition the redox potential of +0.25 volts is the same in all cytochrome c molecules studied.[7]

Structure

Tunafish cytochrome c crystals (~5 mm long) grown by liquid–liquid diffusion under microgravity conditions in outer space.[8]

All cytochrome c proteins contain a characteristic CXXCH (cysteine-any-any-cysteine-histidine) amino acid motif that binds heme. However, there are four classes of cytochrome c, each possessing a different fold.[9]

Classes

In 1991 R. P. Ambler recognized four classes of cytochrome c:[10]

Heme c

Structure of heme c

While most heme proteins are attached to the prosthetic group through iron ion ligation and tertiary interactions, the heme group of cytochrome c makes thioether bonds with two cysteine side chains of the protein.[11] One of the main properties of heme c, which allows cytochrome c to have variety of functions, is its ability to have different reduction potentials in nature. This property determines the kinetics and thermodynamics of an electron transfer reaction.[12]

Dipole moment

The dipole moment has an important role in orienting proteins to the proper directions and enhancing their abilities to bind to other molecules.[13][14] The dipole moment of cytochrome c is a result from a cluster of negatively charged amino acid side chains at the "back" of the enzyme.[14] Despite variations in the number of bound heme groups and variations in sequence, the dipole moment of vertebrate cytochromes c is remarkably conserved. For examples, vertebrate cytochromes c all have dipole moment of approximately 320 debye while cytochromes c of plants and insects have dipole moment of approximately 340 debye.[14]

Function

Cytochrome c is a component of the electron transport chain in mitochondria. The heme group of cytochrome c accepts electrons from the bc1 complex and transfers electrons to the complex IV. Cytochrome c is also involved in initiation of apoptosis. Upon release of cytochrome c to the cytoplasm, the protein binds apoptotic protease activating factor-1 (Apaf-1).[1]

Cytochrome c can also catalyze several redox reactions such as hydroxylation and aromatic oxidation, and shows peroxidase activity by oxidation of various electron donors such as 2,2-azino-bis(3-ethylbenzthiazoline-6-sulphonic acid) (ABTS), 2-keto-4-thiomethyl butyric acid and 4-aminoantipyrine.

A bacterial cytochrome c functions as a nitrite reductase.[15]

Role in apoptosis

Cytochrome c is also an intermediate in apoptosis, a controlled form of cell death used to kill cells in the process of development or in response to infection or DNA damage.[16]

Cytochrome c binds to cardiolipin in the inner mitochondrial membrane, thus anchoring its presence and keeping it from releasing out of the mitochondria and initiating apoptosis. While the initial attraction between cardiolipin and cytochrome c is electrostatic due to the extreme positive charge on cytochrome c, the final interaction is hydrophobic, where a hydrophobic tail from cardiolipin inserts itself into the hydrophobic portion of cytochrome c.

During the early phase of apoptosis, mitochondrial ROS production is stimulated, and cardiolipin is oxidized by a peroxidase function of the cardiolipin–cytochrome c complex. The hemoprotein is then detached from the mitochondrial inner membrane and can be extruded into the soluble cytoplasm through pores in the outer membrane.[17]

The sustained elevation in calcium levels precedes cyt c release from the mitochondria. The release of small amounts of cyt c leads to an interaction with the IP3 receptor (IP3R) on the endoplasmic reticulum (ER), causing ER calcium release. The overall increase in calcium triggers a massive release of cyt c, which then acts in the positive feedback loop to maintain ER calcium release through the IP3Rs.[18] This explains how the ER calcium release can reach cytotoxic levels. This release of cytochrome c in turn activates caspase 9, a cysteine protease. Caspase 9 can then go on to activate caspase 3 and caspase 7, which are responsible for destroying the cell from within.

Inhibition of apoptosis

One of the ways cell apoptosis is activated is by release of cytochrome c from the mitochondria into cytosol. A recent study has shown that cells are able to protect themselves from apoptosis by block the release of cytochrome c using Bcl-xL.[19] Another way that cells can control apoptosis is by phosphorylation of Tyr48 which would turn cytochrome c into an anti-apoptotic switch.[20]

As an antioxidative enzyme

Removal of O2- and H2O2 by cytochrome c

Cytochrome c is known to play a role in the electron transport chain and cell apoptosis. However, a recent study has shown that it can also act as an antioxidative enzyme in the mitochondria; and it does so by removing superoxide (O2–) and hydrogen peroxide (H2O2) from mitochondria.[21] Therefore, not only is cytochrome c required in the mitochondria for cell respiration, but it is also needed in the mitochondria to limit the production of O2- and H2O2.[21]

Extramitochondrial localization

Cytochrome c is widely believed to be localized solely in the mitochondrial intermembrane space under normal physiological conditions.[22] The release of cytochrome-c from mitochondria to the cytosol, where it activates the caspase family of proteases is believed to be primary trigger leading to the onset of apoptosis.[23] Measuring the amount of cytochrome c leaking from mitochondria to cytosol, and out of the cell to culture medium, is a sensitive method to monitor the degree of apoptosis.[24][25] However, detailed immunoelectron microscopic studies with rat tissues sections employing cytochrome c-specific antibodies provide compelling evidence that cytochrome-c under normal cellular conditions is also present at extramitochondrial locations.[26] In pancreatic acinar cells and the anterior pituitary, strong and specific presence of cytochrome-c was detected in zymogen granules and in growth hormone granules respectively. In the pancreas, cytochrome-c was also found in condensing vacuoles and in the acinar lumen. The extramitochondrial localization of cytochrome c was shown to be specific as it was completely abolished upon adsorption of the primary antibody with the purified cytochrome c.[26] The presence of cytochrome-c outside of mitochondria at specific location under normal physiological conditions raises important questions concerning its cellular function and translocation mechanism.[26] Besides cytochrome c, extramitochondrial localization has also been observed for large numbers of other proteins including those encoded by mitochondrial DNA.[27][28][29] This raises the possibility about existence of yet-unidentified specific mechanisms for protein translocation from mitochondria to other cellular destinations.[29][30]

Applications

Superoxide detection

Peroxynitrous acid

Cytochrome c has been used to detect peroxide production in biological systems. Throughout this process the number of cytochrome c3+ being reduced to cytochrome c2+ quantitatively shows the amount of superoxide being produced.[31] However, superoxide is often produced with nitric oxide. In the presence of nitric oxide, the reduction of cytochrome c3+ is inhibited.[32] This leads to the oxidization of cytochrome c2+ to cytochrome c3+ by peroxynitrous acid, an intermediate made through the reaction of nitric oxide and superoxide.[32] Presence of peroxynitrite, H2O2, or nitrogen dioxide NO2 in the mitochondria can be lethal since they nitrate tyrosine residues of cytochrome c which leads to disruption of cytochrome c’s function as an electron carrier in the electron transfer chain.[33]

Low-level laser therapy

Cytochrome c is suspected to be the functional complex in so called LLLT: Low-level laser therapy. In LLLT, red light and some near infra-red wavelengths penetrate tissue in order to increase cellular regeneration. Light of this wavelength appears capable of increasing activity of cytochrome c, thus increasing metabolic activity and freeing up more energy for the cells to repair the tissue.[34]

See also

References

  1. 1 2 "Entrez Gene: cytochrome c".
  2. ↑ Tafani M, Karpinich NO, Hurster KA, Pastorino JG, Schneider T, Russo MA, Farber JL (Mar 2002). "Cytochrome c release upon Fas receptor activation depends on translocation of full-length bid and the induction of the mitochondrial permeability transition". The Journal of Biological Chemistry 277 (12): 10073–82. doi:10.1074/jbc.M111350200. PMID 11790791.
  3. ↑ "Cytochrome c – Homo sapiens (Human)". P99999. UniProt Consortium. mass is 11,749 Daltons
  4. ↑ Margoliash E (Oct 1963). "Primary structure and evolution of cytochrome c". Proceedings of the National Academy of Sciences of the United States of America 50 (4): 672–9. doi:10.1073/pnas.50.4.672. PMC 221244. PMID 14077496.
  5. ↑ Amino acid sequences in cytochrome c proteins from different species, adapted from Strahler, Arthur; Science and Earth History, 1997. page 348.
  6. ↑ Lurquin PF, Stone L, Cavalli-Sforza LL (2007). Genes, culture, and human evolution: a synthesis. Oxford: Blackwell. p. 79. ISBN 978-1-4051-5089-7.
  7. 1 2 3 Stryer L (1975). Biochemistry (1st ed.). San Francisco: W.H. Freeman and Company. p. 362. ISBN 978-0-7167-0174-3.
  8. ↑ McPherson A, Delucas LJ (2015). "Microgravity protein crystallization". Npj Microgravity 1: 15010. doi:10.1038/npjmgrav.2015.10.
  9. ↑ Mavridou DA, Ferguson SJ, Stevens JM (2013). "Cytochrome c assembly". IUBMB Life 65 (3): 209–16. doi:10.1002/iub.1123. PMID 23341334.
  10. ↑ Ambler RP (May 1991). "Sequence variability in bacterial cytochromes c". Biochimica et Biophysica Acta 1058 (1): 42–7. doi:10.1016/S0005-2728(05)80266-X. PMID 1646017.
  11. ↑ Kang X, Carey J (Nov 1999). "Role of heme in structural organization of cytochrome c probed by semisynthesis". Biochemistry 38 (48): 15944–51. PMID 10625461.
  12. ↑ Zhao Y, Wang ZB, Xu JX (Jan 2003). "Effect of cytochrome c on the generation and elimination of O2– and H2O2 in mitochondria". The Journal of Biological Chemistry 278 (4): 2356–60. doi:10.1074/jbc.M209681200. PMID 12435729.
  13. ↑ Koppenol WH, Margoliash E (Apr 1982). "The asymmetric distribution of charges on the surface of horse cytochrome c. Functional implications". The Journal of Biological Chemistry 257 (8): 4426–37. PMID 6279635.
  14. 1 2 3 Koppenol WH, Rush JD, Mills JD, Margoliash E (Jul 1991). "The dipole moment of cytochrome c". Molecular Biology and Evolution 8 (4): 545–58. PMID 1656165.
  15. ↑ Schneider J, Kroneck PM (2014). "Chapter 9: The Production of Ammonia by Multiheme Cytochromes c". In Kroneck PM, Torres ME. The Metal-Driven Biogeochemistry of Gaseous Compounds in the Environment. Metal Ions in Life Sciences 14. Springer. pp. 211–236. doi:10.1007/978-94-017-9269-1_9.
  16. ↑ Liu X, Kim CN, Yang J, Jemmerson R, Wang X (Jul 1996). "Induction of apoptotic program in cell-free extracts: requirement for dATP and cytochrome c". Cell 86 (1): 147–57. doi:10.1016/S0092-8674(00)80085-9. PMID 8689682.
  17. ↑ Orrenius S, Zhivotovsky B (Sep 2005). "Cardiolipin oxidation sets cytochrome c free". Nature Chemical Biology 1 (4): 188–9. doi:10.1038/nchembio0905-188. PMID 16408030.
  18. ↑ Boehning D, Patterson RL, Sedaghat L, Glebova NO, Kurosaki T, Snyder SH (Dec 2003). "Cytochrome c binds to inositol (1,4,5) trisphosphate receptors, amplifying calcium-dependent apoptosis". Nature Cell Biology 5 (12): 1051–61. doi:10.1038/ncb1063. PMID 14608362.
  19. ↑ Kharbanda S, Pandey P, Schofield L, Israels S, Roncinske R, Yoshida K, Bharti A, Yuan ZM, Saxena S, Weichselbaum R, Nalin C, Kufe D (Jun 1997). "Role for Bcl-xL as an inhibitor of cytosolic cytochrome C accumulation in DNA damage-induced apoptosis". Proceedings of the National Academy of Sciences of the United States of America 94 (13): 6939–42. PMID 9192670.
  20. ↑ García-Heredia JM, Díaz-Quintana A, Salzano M, Orzáez M, Pérez-Payá E, Teixeira M, De la Rosa MA, Díaz-Moreno I (Dec 2011). "Tyrosine phosphorylation turns alkaline transition into a biologically relevant process and makes human cytochrome c behave as an anti-apoptotic switch". Journal of Biological Inorganic Chemistry 16 (8): 1155–68. doi:10.1007/s00775-011-0804-9. PMID 21706253.
  21. 1 2 Bowman SE, Bren KL (Dec 2008). "The chemistry and biochemistry of heme c: functional bases for covalent attachment". Natural Product Reports 25 (6): 1118–30. doi:10.1039/b717196j. PMID 19030605.
  22. ↑ Neupert W (1997). "Protein import into mitochondria". Annual Review of Biochemistry 66: 863–917. doi:10.1146/annurev.biochem.66.1.863. PMID 9242927.
  23. ↑ Kroemer G, Dallaporta B, Resche-Rigon M (1998). "The mitochondrial death/life regulator in apoptosis and necrosis". Annual Review of Physiology 60: 619–42. doi:10.1146/annurev.physiol.60.1.619. PMID 9558479.
  24. ↑ Loo JF, Lau PM, Ho HP, Kong SK (Oct 2013). "An aptamer-based bio-barcode assay with isothermal recombinase polymerase amplification for cytochrome-c detection and anti-cancer drug screening". Talanta 115: 159–65. doi:10.1016/j.talanta.2013.04.051. PMID 24054573.
  25. ↑ Waterhouse NJ, Trapani JA (Jul 2003). "A new quantitative assay for cytochrome c release in apoptotic cells". Cell Death and Differentiation 10 (7): 853–5. doi:10.1038/sj.cdd.4401263. PMID 12815469.
  26. 1 2 3 Soltys BJ, Andrews DW, Jemmerson R, Gupta RS (2001). "Cytochrome-C localizes in secretory granules in pancreas and anterior pituitary". Cell Biology International 25 (4): 331–8. doi:10.1006/cbir.2000.0651. PMID 11319839.
  27. ↑ Gupta RS, Ramachandra NB, Bowes T, Singh B (2008). "Unusual cellular disposition of the mitochondrial molecular chaperones Hsp60, Hsp70 and Hsp10". Novartis Foundation Symposium. Novartis Foundation Symposia 291: 59–68; discussion 69–73, 137–40. doi:10.1002/9780470754030.ch5. ISBN 978-0-470-75403-0. PMID 18575266.
  28. ↑ Sadacharan SK, Singh B, Bowes T, Gupta RS (Nov 2005). "Localization of mitochondrial DNA encoded cytochrome c oxidase subunits I and II in rat pancreatic zymogen granules and pituitary growth hormone granules". Histochemistry and Cell Biology 124 (5): 409–21. doi:10.1007/s00418-005-0056-2. PMID 16133117.
  29. 1 2 Soltys BJ, Gupta RS (2000). "Mitochondrial proteins at unexpected cellular locations: export of proteins from mitochondria from an evolutionary perspective". International Review of Cytology. International Review of Cytology 194: 133–96. doi:10.1016/s0074-7696(08)62396-7. ISBN 978-0-12-364598-2. PMID 10494626.
  30. ↑ Soltys BJ, Gupta RS (May 1999). "Mitochondrial-matrix proteins at unexpected locations: are they exported?". Trends in Biochemical Sciences 24 (5): 174–7. doi:10.1016/s0968-0004(99)01390-0. PMID 10322429.
  31. ↑ McCord JM, Fridovich I (Nov 1969). "Superoxide dismutase. An enzymic function for erythrocuprein (hemocuprein)". The Journal of Biological Chemistry 244 (22): 6049–55. PMID 5389100.
  32. 1 2 Thomson L, Trujillo M, Telleri R, Radi R (Jun 1995). "Kinetics of cytochrome c2+ oxidation by peroxynitrite: implications for superoxide measurements in nitric oxide-producing biological systems". Archives of Biochemistry and Biophysics 319 (2): 491–7. doi:10.1006/abbi.1995.1321. PMID 7786032.
  33. ↑ Domazou AS, Gebicka L, Didik J, Gebicki JL, van der Meijden B, Koppenol WH (Apr 2014). "The kinetics of the reaction of nitrogen dioxide with iron(II)- and iron(III) cytochrome c". Free Radical Biology & Medicine 69: 172–80. doi:10.1016/j.freeradbiomed.2014.01.014. PMID 24447894.
  34. ↑ Karu TI, Pyatibrat LV, Afanasyeva NI (Apr 2005). "Cellular effects of low power laser therapy can be mediated by nitric oxide". Lasers in Surgery and Medicine 36 (4): 307–14. doi:10.1002/lsm.20148. PMID 15739174.

Further reading

  • Kumarswamy R, Chandna S (Feb 2009). "Putative partners in Bax mediated cytochrome-c release: ANT, CypD, VDAC or none of them?". Mitochondrion 9 (1): 1–8. doi:10.1016/j.mito.2008.10.003. PMID 18992370. 
  • Skulachev VP (Feb 1998). "Cytochrome c in the apoptotic and antioxidant cascades". FEBS Letters 423 (3): 275–80. doi:10.1016/S0014-5793(98)00061-1. PMID 9515723. 
  • Mannella CA (1998). "Conformational changes in the mitochondrial channel protein, VDAC, and their functional implications". Journal of Structural Biology 121 (2): 207–18. doi:10.1006/jsbi.1997.3954. PMID 9615439. 
  • Ferri KF, Jacotot E, Blanco J, Esté JA, Kroemer G (2000). "Mitochondrial control of cell death induced by HIV-1-encoded proteins". Annals of the New York Academy of Sciences 926: 149–64. doi:10.1111/j.1749-6632.2000.tb05609.x. PMID 11193032. 
  • Britton RS, Leicester KL, Bacon BR (Oct 2002). "Iron toxicity and chelation therapy". International Journal of Hematology 76 (3): 219–28. doi:10.1007/BF02982791. PMID 12416732. 
  • Haider N, Narula N, Narula J (Dec 2002). "Apoptosis in heart failure represents programmed cell survival, not death, of cardiomyocytes and likelihood of reverse remodeling". Journal of Cardiac Failure 8 (6 Suppl): S512–7. doi:10.1054/jcaf.2002.130034. PMID 12555167. 
  • Castedo M, Perfettini JL, Andreau K, Roumier T, Piacentini M, Kroemer G (Dec 2003). "Mitochondrial apoptosis induced by the HIV-1 envelope". Annals of the New York Academy of Sciences 1010: 19–28. doi:10.1196/annals.1299.004. PMID 15033690. 
  • Ng S, Smith MB, Smith HT, Millett F (Nov 1977). "Effect of modification of individual cytochrome c lysines on the reaction with cytochrome b5". Biochemistry 16 (23): 4975–8. doi:10.1021/bi00642a006. PMID 199233. 
  • Lynch SR, Sherman D, Copeland RA (Jan 1992). "Cytochrome c binding affects the conformation of cytochrome a in cytochrome c oxidase". The Journal of Biological Chemistry 267 (1): 298–302. PMID 1309738. 
  • Garber EA, Margoliash E (Feb 1990). "Interaction of cytochrome c with cytochrome c oxidase: an understanding of the high- to low-affinity transition". Biochimica et Biophysica Acta 1015 (2): 279–87. doi:10.1016/0005-2728(90)90032-Y. PMID 2153405. 
  • Bedetti CD (May 1985). "Immunocytochemical demonstration of cytochrome c oxidase with an immunoperoxidase method: a specific stain for mitochondria in formalin-fixed and paraffin-embedded human tissues". The Journal of Histochemistry and Cytochemistry 33 (5): 446–52. doi:10.1177/33.5.2580882. PMID 2580882. 
  • Tanaka Y, Ashikari T, Shibano Y, Amachi T, Yoshizumi H, Matsubara H (Jun 1988). "Construction of a human cytochrome c gene and its functional expression in Saccharomyces cerevisiae". Journal of Biochemistry 103 (6): 954–61. PMID 2844747. 
  • Evans MJ, Scarpulla RC (Dec 1988). "The human somatic cytochrome c gene: two classes of processed pseudogenes demarcate a period of rapid molecular evolution". Proceedings of the National Academy of Sciences of the United States of America 85 (24): 9625–9. doi:10.1073/pnas.85.24.9625. PMC 282819. PMID 2849112. 
  • Passon PG, Hultquist DE (Jul 1972). "Soluble cytochrome b 5 reductase from human erythrocytes". Biochimica et Biophysica Acta 275 (1): 62–73. doi:10.1016/0005-2728(72)90024-2. PMID 4403130. 
  • Dowe RJ, Vitello LB, Erman JE (Aug 1984). "Sedimentation equilibrium studies on the interaction between cytochrome c and cytochrome c peroxidase". Archives of Biochemistry and Biophysics 232 (2): 566–73. doi:10.1016/0003-9861(84)90574-5. PMID 6087732. 
  • Michel B, Bosshard HR (Aug 1984). "Spectroscopic analysis of the interaction between cytochrome c and cytochrome c oxidase". The Journal of Biological Chemistry 259 (16): 10085–91. PMID 6088481. 
  • Broger C, Nałecz MJ, Azzi A (Oct 1980). "Interaction of cytochrome c with cytochrome bc1 complex of the mitochondrial respiratory chain". Biochimica et Biophysica Acta 592 (3): 519–27. doi:10.1016/0005-2728(80)90096-1. PMID 6251869. 
  • Smith HT, Ahmed AJ, Millett F (May 1981). "Electrostatic interaction of cytochrome c with cytochrome c1 and cytochrome oxidase". The Journal of Biological Chemistry 256 (10): 4984–90. PMID 6262312. 
  • Geren LM, Millett F (Oct 1981). "Fluorescence energy transfer studies of the interaction between adrenodoxin and cytochrome c". The Journal of Biological Chemistry 256 (20): 10485–9. PMID 6270113. 
  • Favre B, Zolnierowicz S, Turowski P, Hemmings BA (Jun 1994). "The catalytic subunit of protein phosphatase 2A is carboxyl-methylated in vivo". The Journal of Biological Chemistry 269 (23): 16311–7. PMID 8206937. 
  • Gao B, Eisenberg E, Greene L (Jul 1996). "Effect of constitutive 70-kDa heat shock protein polymerization on its interaction with protein substrate". The Journal of Biological Chemistry 271 (28): 16792–7. doi:10.1074/jbc.271.28.16792. PMID 8663341. 

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