Editing Cytochrome c (section)

== Structure ==

[[File:Tunafish cytochrome c crystals grown in microgravity.jpg|left|thumb|Tunafish cytochrome c crystals (~5 mm long) grown by liquid–liquid diffusion under microgravity conditions in outer space.<ref>{{Cite journal |vauthors=McPherson A, DeLucas LJ |year=2015 |title=Microgravity protein crystallization |journal=npj Microgravity |volume=1 |pages=15010 |doi=10.1038/npjmgrav.2015.10 |pmc=5515504 |pmid=28725714}}</ref>]]

Cytochrome c belongs to class I of the [[Cytochrome c family|c-type cytochrome family]]<ref name="pmid1646017">{{Cite journal |vauthors=Ambler RP |date=May 1991 |title=Sequence variability in bacterial cytochromes c |journal=Biochimica et Biophysica Acta (BBA) - Bioenergetics |volume=1058 |issue=1 |pages=42–7 |doi=10.1016/S0005-2728(05)80266-X |pmid=1646017}}</ref> and contains a characteristic CXXCH (cysteine-any-any-cysteine-histidine) amino acid motif that binds heme.<ref name="pmid23341334">{{Cite journal |vauthors=Mavridou DA, Ferguson SJ, Stevens JM |date=March 2013 |title=Cytochrome c assembly |journal=IUBMB Life |volume=65 |issue=3 |pages=209–16 |doi=10.1002/iub.1123 |pmid=23341334 |s2cid=32216217}}</ref> This motif is located towards the [[N-terminus]] of the [[peptide]] chain and contains a histidine as the 5th ligand of the heme iron. The 6th ligand is provided by a [[methionine]] residue found towards the [[C-terminus]]. The protein backbone is folded into five [[Alpha helix|α-helices]] that are numbered α1-α5 from N-terminus to C-terminus. Helices α3, α4 and α5 are referred to as 50s, 60s and 70s helices, respectively, when referring to mitochondrial cytochrome c.<ref>{{Cite journal |vauthors=Liu J, Chakraborty S, Hosseinzadeh P, Yu Y, Tian S, Petrik I, Bhagi A, Lu Y |date=2014-04-23 |title=Metalloproteins Containing Cytochrome, Iron–Sulfur, or Copper Redox Centers |journal=Chemical Reviews |language=EN |volume=114 |issue=8 |pages=4366–4469 |doi=10.1021/cr400479b |issn=0009-2665 |pmc=4002152 |pmid=24758379}}</ref>

=== Heme c ===

[[File:Heme c.svg|thumb|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.<ref>{{Cite journal |vauthors=Kang X, Carey J |date=November 1999 |title=Role of heme in structural organization of cytochrome c probed by semisynthesis |journal=[[Biochemistry (journal)|Biochemistry]] |volume=38 |issue=48 |pages=15944–51 |doi=10.1021/bi9919089 |pmid=10625461}}</ref> 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.<ref>{{Cite journal |vauthors=Zhao Y, Wang ZB, Xu JX |date=January 2003 |title=Effect of cytochrome c on the generation and elimination of O{{sub|2}}{{sup|–}} and H{{sub|2}}O{{sub|2}} in mitochondria |journal=[[The Journal of Biological Chemistry]] |volume=278 |issue=4 |pages=2356–60 |doi=10.1074/jbc.M209681200 |pmid=12435729 |doi-access=free}}</ref>

=== 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.<ref>{{Cite journal |vauthors=Koppenol WH, Margoliash E |date=April 1982 |title=The asymmetric distribution of charges on the surface of horse cytochrome c. Functional implications |journal=The Journal of Biological Chemistry |volume=257 |issue=8 |pages=4426–37 |doi=10.1016/S0021-9258(18)34740-9 |pmid=6279635 |doi-access=free}}</ref><ref name="Koppenol_1982">{{Cite journal |vauthors=Koppenol WH, Rush JD, Mills JD, Margoliash E |date=July 1991 |title=The dipole moment of cytochrome c |journal=[[Molecular Biology and Evolution]] |volume=8 |issue=4 |pages=545–58 |doi=10.1093/oxfordjournals.molbev.a040659 |pmid=1656165 |doi-access=free}}</ref> The dipole moment of cytochrome c results from a cluster of negatively charged amino acid side chains at the "back" of the enzyme.<ref name="Koppenol_1982" /> Despite variations in the number of bound heme groups and variations in sequence, the dipole moment of vertebrate cytochromes c is remarkably conserved. For example, vertebrate cytochromes c all have a dipole moment of approximately 320 [[debye]] while cytochromes c of plants and insects have a dipole moment of approximately 340 debye.<ref name="Koppenol_1982" />