Sandbox Reserved 335: Difference between revisions

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Cyt ''c'' has been split into four classes.<ref name=amb>PMID:1646017</ref> Class I contains soluble, low spin<ref name=main /> 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''. Cyt ''c'' in this class have a single heme attached close to the N-terminus of the polypeptide, with a methionine residue being the sixth iron coordination site. Class II contains higher spin-state cytochromes ''c'', such as cyt ''c''', with the heme being attached closer to the C-terminus. Class III contains cytochromes with multiple heme groups; these proteins have lower redox potentials compared to the other three classes<ref name=amb />. Finally, Class IV is comprised of more complex proteins with higher molecular weights containing heme ''c'' as well as other prosthetic groups.<ref name=class>Cookson DJ, Moore GR, Pitt RC, Williams RJP, Campbell ID, Ambler RP, Bruschi M, Le Gall J. Structural homology of cytochromes c. Eur J Biochem. 1978 Feb;83(1):261-75.</ref>
Cyt ''c'' has been split into four classes.<ref name=amb>PMID:1646017</ref> Class I contains soluble, low spin<ref name=main /> 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''. Cyt ''c'' in this class have a single heme attached close to the N-terminus of the polypeptide, with a methionine residue being the sixth iron coordination site. Class II contains higher spin-state cytochromes ''c'', such as cyt ''c''', with the heme being attached closer to the C-terminus. Class III contains cytochromes with multiple heme groups; these proteins have lower redox potentials compared to the other three classes<ref name=amb />. Finally, Class IV is comprised of more complex proteins with higher molecular weights containing heme ''c'' as well as other prosthetic groups.<ref name=class>Cookson DJ, Moore GR, Pitt RC, Williams RJP, Campbell ID, Ambler RP, Bruschi M, Le Gall J. Structural homology of cytochromes c. Eur J Biochem. 1978 Feb;83(1):261-75.</ref>
=== ''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.<ref name="bacteria">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.</ref> 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''.<ref name=main />


== Structure ==
== Structure ==
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<Structure load='3cp5' size='300' frame='true' align='right' caption='Figure 2' scene='Sandbox_Reserved_335/Heme/1' />
<Structure load='3cp5' size='300' frame='true' align='right' caption='Figure 2' scene='Sandbox_Reserved_335/Heme/1' />


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 <scene name='Sandbox_Reserved_335/Motif/1'>CXXCH motif</scene>, where a histidine residue is one of the two axial ligands of the heme iron.<ref name=main>PMID:18855424</ref><ref name=heme /> In ''Rm''cyt''c'', 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.<ref name=main />. The typical monoheme cyt ''c'' fold is formed by helices <scene name='Sandbox_Reserved_335/Helices/2'>A, C, and E</scene>. In ''Rm''cyt''c'' there are seven α-helices that are folded around the porphyrin ring, all connected by random coils.<ref name=main /> The heme group is axially coordinated by <scene name='Sandbox_Reserved_335/Axial/3'>His49 and Met100</scene>
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 <scene name='Sandbox_Reserved_335/Motif/1'>CXXCH motif</scene> where a histidine residue is one of the two axial ligands of the heme iron.<ref name=main>PMID:18855424</ref><ref name=heme /> In monoheme cytochromes ''c'', the other axial position may be left vacant or be occupied by histidine or methionine residues; however, it can sometimes be occupied by cysteine or leucine residues.<ref name=main />. In ''Rm''cyt''c'', '''XX represents a threonine (Thr46) and an alanine residue (Ala47); these two residues are not involved in coordinating the iron ligand.''' The typical monoheme cyt ''c'' fold is formed by helices <scene name='Sandbox_Reserved_335/Helices/2'>A, C, and E</scene>. ''Rm''cyt''c'' contains seven α-helices that are folded around the heme, all connected by random coils.<ref name=main /> The heme group is axially coordinated by <scene name='Sandbox_Reserved_335/Axial/3'>His49 and Met100</scene>, and the disulfide linkages exist at '''CysBLABLA and BLALBA'''.




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