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== Introduction == | == Introduction == | ||
| - | [http://en.wikipedia.org/wiki/Cytochrome Cytochromes] are a class of heme-containing proteins found in bacteria and the mitochondria of eukaryotes.<ref name=main /> These proteins are generally membrane-bound and are known as respiratory pigments because they are involved in various electron transport systems in oxidative phosphorylation.<ref name="heme">PMID:14871137</ref> Cytochromes can be categorized into several different types, three of which are based on the type of prosthetic heme group the cytochrome contains: cytochromes ''a'' contains heme ''a'', cyt ''b'' contains heme ''b'', and cyt ''d'' containing a tetrapyrrolic chelate of iron.<ref name="cytd"> | + | [http://en.wikipedia.org/wiki/Cytochrome Cytochromes] are a class of heme-containing proteins found in bacteria and the mitochondria of eukaryotes.<ref name=main /> These proteins are generally membrane-bound and are known as respiratory pigments because they are involved in various electron transport systems in oxidative phosphorylation.<ref name="heme">PMID:14871137</ref> Cytochromes can be categorized into several different types, three of which are based on the type of prosthetic heme group the cytochrome contains: cytochromes ''a'' contains heme ''a'', cyt ''b'' contains heme ''b'', and cyt ''d'' containing a tetrapyrrolic chelate of iron.<ref name="cytd">MeSH|cytochrome ''d'' http://www.nlm.nih.gov/cgi/mesh/2011/MB_cgi?mode=&term=Cytochrome+d</ref> Cytochrome ''c'' is named such because it contains the heme ''c'', which is distinguished from hemes ''a'', ''b'', and ''d'' by its coordination to the protein scaffold by cysteinyl residues to either one or both of the heme's vinyl side chains<ref name=heme /> |
Cyt ''c'' has been split into four classes.<ref name=”amb”>PMID:1646017</ref> Class I contains single domain C-type cytochromes, of which there has been at least six subclasses found in prokaryotes including [http://en.wikipedia.org/wiki/Desulfovibrio ''Desulfovibrio desulfuricans''], [http://en.wikipedia.org/wiki/Rhodospirillum_rubrum ''Rhodospirillum rubrum''], and ''Rhodothermus marinus''. Class II cyt ''c'' contains | Cyt ''c'' has been split into four classes.<ref name=”amb”>PMID:1646017</ref> Class I contains single domain C-type cytochromes, of which there has been at least six subclasses found in prokaryotes including [http://en.wikipedia.org/wiki/Desulfovibrio ''Desulfovibrio desulfuricans''], [http://en.wikipedia.org/wiki/Rhodospirillum_rubrum ''Rhodospirillum rubrum''], and ''Rhodothermus marinus''. Class II cyt ''c'' contains | ||
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| This Sandbox is Reserved from January 10, 2010, through April 10, 2011 for use in BCMB 307-Proteins course taught by Andrea Gorrell at the University of Northern British Columbia, Prince George, BC, Canada. |
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| 3cp5, resolution 1.24Å () | |||||||||
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| Gene: | cytC (Rhodothermus marinus) | ||||||||
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| Resources: | FirstGlance, OCA, PDBsum, RCSB | ||||||||
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The cytochrome c (cyt c) proteins are a superfamily belonging to the class of all-α proteins, which are denoted as such by having an α-helical core. Each protein in this superfamily also contains one or more covalently-bound heme prosthetic groups.[1][2] The cyt c superfamily contains many different families, some of which are better characterized than others. These families include monodomain and multi-domain C-type cytochromes, such as cyt c4, a diheme C-type cytochrome, and NrfB, a pentaheme C-type cytochrome. In particular, the monoheme cyt c from Rhodothermus marinus has been previously studied and provides an excellent example of how some protein characteristics and structures can be extremely diverse, yet conserved, through evolution.
Contents |
Introduction
Cytochromes are a class of heme-containing proteins found in bacteria and the mitochondria of eukaryotes.[2] These proteins are generally membrane-bound and are known as respiratory pigments because they are involved in various electron transport systems in oxidative phosphorylation.[3] Cytochromes can be categorized into several different types, three of which are based on the type of prosthetic heme group the cytochrome contains: cytochromes a contains heme a, cyt b contains heme b, and cyt d containing a tetrapyrrolic chelate of iron.[4] Cytochrome c is named such because it contains the heme c, which is distinguished from hemes a, b, and d by its coordination to the protein scaffold by cysteinyl residues to either one or both of the heme's vinyl side chains[3]
Cyt c has been split into four classes.[5] Class I contains single domain C-type cytochromes, of which there has been at least six subclasses found in prokaryotes including Desulfovibrio desulfuricans, Rhodospirillum rubrum, and Rhodothermus marinus. Class II cyt c contains
Rhodothermus marinus
Rhodothermus marinus is a Gram-negative bacterium in the class Sphingobacteria, in phylum Bacteroidetes. These bacteria are thermophilic, obligate aerobes that have been previously isolated from shallow-water submarine hot springs located in Iceland.[6] A monoheme cytochrome c that has been thought to be the first member of a new class of cyt c was recently purified from R. marinus.[2]
Structure
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All members in the C-type cytochrome superfamily contain a heme prosthetic group that is covalently attached to the protein via two thioether bonds to cysteine residues; most cytochromes c occur in a , where a histidine residue is one of the two axial ligands of the heme iron.[2][3] In Rmcytc, XX represents a threonine and an alanine residue. The other axial position, in monoheme cytochromes c, may be left vacant or be occupied by histidine or methionine residues, but can sometimes be occupied by cysteine or leucine residues.[2]. The typical monoheme cyt c fold is formed by helices . In Rmcytc there are seven α-helices that are folded around the porphyrin ring, all connected by random coils.[2] The heme group is axially coordinated by
The heme prosthetic group is almost completely shielded from solvent, being in a mostly hydrophobic pocket. This pocket is formed in part by the seven helices surrounding the ring, but also by two structures that are uncommon in cyt c.
As determined by X-ray crystallography, the Rmcytc structure was found to also contain a coordinated sulfate ion; this ion has been seen to mediate crystal contact between neighbouring protein molecules. The carboxylate oxygen of Glu122 was also found to be involved in hydrogen bonding with this sulfate ion.[2]
Function
Monoheme cytochromes c are involved in electron transport chains in both prokaryotes and eukaryotic mitochondria.[2] They mediate the transfer of electrons mainly from the bc1 complexes, or their analogs, in the electron transport chain to heme-copper oxygen reductases (HCOs) during oxidative phosphorylation. Heme c containing domains are often found fused to other protein domains such as these HCOs, including the caa3 oxygen reductases[2][7]; these enzymes are membrane-bound and catalyze the reduction of O2 to water.[8] In addition to being involved in the electron transport systems in oxidative phosphorylation, monoheme cyt c has also been seen to participate in the electron transport chain of photosynthesis.[2]
In addition to being involved in the electron transfer in many systems, cyt c is involved in cell apoptosis, the programmed death of a cell due to cellular signals. Cyt c is
Mechanism
In the electron transport chain, cyt c shuttles electrons between the respiratory complexes III and IV.
Importance
References
- ↑ Gough J, Karplus K, Hughey R, Chothia C. Assignment of homology to genome sequences using a library of hidden Markov models that represent all proteins of known structure. J Mol Biol. 2001 Nov 2;313(4):903-19. PMID:11697912 doi:10.1006/jmbi.2001.5080
- ↑ 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 Stelter M, Melo AM, Pereira MM, Gomes CM, Hreggvidsson GO, Hjorleifsdottir S, Saraiva LM, Teixeira M, Archer M. A Novel Type of Monoheme Cytochrome c: Biochemical and Structural Characterization at 1.23 A Resolution of Rhodothermus marinus Cytochrome c. Biochemistry. 2008 Oct 15. PMID:18855424 doi:10.1021/bi800999g
- ↑ 3.0 3.1 3.2 Reedy CJ, Gibney BR. Heme protein assemblies. Chem Rev. 2004 Feb;104(2):617-49. PMID:14871137 doi:10.1021/cr0206115
- ↑ MeSH|cytochrome d http://www.nlm.nih.gov/cgi/mesh/2011/MB_cgi?mode=&term=Cytochrome+d
- ↑ Ambler RP. Sequence variability in bacterial cytochromes c. Biochim Biophys Acta. 1991 May 23;1058(1):42-7. PMID:1646017
- ↑ Alfredsson GA, Kristjansson JK, Hjörleifsdottir S, Stetter, KO. Rhodothermus marinus, gen. nov., sp. nov., a thermophilic, halophilic bacterium from submarine hot springs in Iceland. J Gen Microbiol. 1988 Feb;134(2):299-306.
- ↑ Soares CM, Baptista AM, Pereira MM, Teixeira M. Investigation of protonatable residues in Rhodothermus marinus caa3 haem-copper oxygen reductase: comparison with Paracoccus denitrificans aa3 haem-copper oxygen reductase. J Biol Inorg Chem. 2004 Mar;9(2):124-34. Epub 2003 Dec 23. PMID:14691678 doi:10.1007/s00775-003-0509-9
- ↑ Pereira MM, Santana M, Teixeira M. A novel scenario for the evolution of haem-copper oxygen reductases. Biochim Biophys Acta. 2001 Jun 1;1505(2-3):185-208. PMID:11334784
