Journal:JBIC:7
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| - | < | + | <StructureSection load="Cytc6.pdb" size="450" color="" frame="true" spin="on" Scene ="Journal:JBIC:7/Cv/2" side="right" caption="Cytochrome c6"> |
=== Structural and kinetic studies of imidazole binding to two members of the cytochrome c6 family reveal an important role for a conserved heme pocket residue === | === Structural and kinetic studies of imidazole binding to two members of the cytochrome c6 family reveal an important role for a conserved heme pocket residue === | ||
| - | <big>Badri S. Rajagopal, Michael T. Wilson, Derek S. Bendall, Christopher J. Howe and Jonathan A.R. Worrall</big><ref>DOI</ref> | + | <big>Badri S. Rajagopal, Michael T. Wilson, Derek S. Bendall, Christopher J. Howe and Jonathan A.R. Worrall</big><ref>DOI 10.1007/s00775-011-0758-y</ref> |
<hr/> | <hr/> | ||
<b>Molecular Tour</b><br> | <b>Molecular Tour</b><br> | ||
<scene name='Journal:JBIC:7/Cv/4'>Cytochrome c6</scene> is a member of the class I family of c-type cytochromes with a distinctive <scene name='Journal:JBIC:7/Cv/5'>α-helical fold</scene> and a <scene name='Journal:JBIC:7/Cv/6'>methionine and histidine residue serving as axial heme iron ligands</scene>. They function in the photosynthetic electron transport chain of cyanobacteria where they shuttle an electron from the cytochrome b6f complex to photosystem I. Structures of numerous cytochrome ''c''<sub>6</sub> proteins have been determined and all have the <scene name='Journal:JBIC:7/Cv/7'>methionine ligand coordinating to the iron</scene>. In the present work we have solved the structure of the '''Q51V''' site-directed variant of ''Phormidium laminosum'' cytochrome ''c''<sub>6</sub>. This project is part of a study that is aimed at gaining insight into protein factors which modulate the heme mid-point redox potential in the cytochrome ''c''<sub>6</sub> family. The '''Q51V''' variant has been shown to tune over 100 mV of heme redox potential, which for a single heme pocket mutation is very significant and has consequences for function. | <scene name='Journal:JBIC:7/Cv/4'>Cytochrome c6</scene> is a member of the class I family of c-type cytochromes with a distinctive <scene name='Journal:JBIC:7/Cv/5'>α-helical fold</scene> and a <scene name='Journal:JBIC:7/Cv/6'>methionine and histidine residue serving as axial heme iron ligands</scene>. They function in the photosynthetic electron transport chain of cyanobacteria where they shuttle an electron from the cytochrome b6f complex to photosystem I. Structures of numerous cytochrome ''c''<sub>6</sub> proteins have been determined and all have the <scene name='Journal:JBIC:7/Cv/7'>methionine ligand coordinating to the iron</scene>. In the present work we have solved the structure of the '''Q51V''' site-directed variant of ''Phormidium laminosum'' cytochrome ''c''<sub>6</sub>. This project is part of a study that is aimed at gaining insight into protein factors which modulate the heme mid-point redox potential in the cytochrome ''c''<sub>6</sub> family. The '''Q51V''' variant has been shown to tune over 100 mV of heme redox potential, which for a single heme pocket mutation is very significant and has consequences for function. | ||
| - | The '''Q51V''' structure confirms that the <scene name='Journal:JBIC:7/Cv/8'>Val replacing the Gln</scene> has the same side-chain orientation in the heme pocket as found in other cytochrome ''c''<sub>6</sub> proteins, that naturally have a Val at this position. The significance of this structure is that the <scene name='Journal:JBIC:7/Cv/14'>axial heme iron methionine is dissociated</scene> and an <scene name='Journal:JBIC:7/Cv/15'>exogenous ligand present in the crystallisation solution, imidazole, is now bound to the heme iron</scene>. Two other structures of imidazole cyt c-adducts have been reported, but neither appear to undergo the <scene name='Journal:JBIC:7/Cv/17'>large structural changes seen in the Q51V structure</scene>. Both protein and heme structural changes are observed, with the later centered on a <scene name='Journal:JBIC:7/Cv/ | + | The '''Q51V''' structure confirms that the <scene name='Journal:JBIC:7/Cv/8'>Val replacing the Gln</scene> has the same side-chain orientation in the heme pocket as found in other cytochrome ''c''<sub>6</sub> proteins, that naturally have a Val at this position. The significance of this structure is that the <scene name='Journal:JBIC:7/Cv/14'>axial heme iron methionine is dissociated</scene> and an <scene name='Journal:JBIC:7/Cv/15'>exogenous ligand present in the crystallisation solution, imidazole, is now bound to the heme iron</scene>. Two other structures of imidazole cyt c-adducts have been reported, but neither appear to undergo the <scene name='Journal:JBIC:7/Cv/17'>large structural changes seen in the Q51V structure</scene>. Both protein and heme structural changes are observed, with the later centered on a <scene name='Journal:JBIC:7/Cv/22'>180 degree rotation around the CA atom of the two heme propionate groups</scene> accompanied by the <scene name='Journal:JBIC:7/Cv/20'>upward movement of an alpha helix</scene> and the <scene name='Journal:JBIC:7/Cv/21'>displacement of two loop regions</scene>. |
Protein (un)folding studies on cytochrome c have revealed that (un)folding involves structural units called 'foldons'. The regions in the Q51V imidazole-adduct where structural changes occur map well to the two foldons predicted to unfold first in cytochrome c. Thus <scene name='Journal:JBIC:7/Cv/14'>imidazole triggers the release of the methionine ligand in the Q51V variant</scene>, leading to the formation of an early unfolding intermediate that is stabilised by <scene name='Journal:JBIC:7/Cv/15'>imidazole binding to the vacant heme iron coordination position</scene>, enabling it to be captured in the crystalline form. | Protein (un)folding studies on cytochrome c have revealed that (un)folding involves structural units called 'foldons'. The regions in the Q51V imidazole-adduct where structural changes occur map well to the two foldons predicted to unfold first in cytochrome c. Thus <scene name='Journal:JBIC:7/Cv/14'>imidazole triggers the release of the methionine ligand in the Q51V variant</scene>, leading to the formation of an early unfolding intermediate that is stabilised by <scene name='Journal:JBIC:7/Cv/15'>imidazole binding to the vacant heme iron coordination position</scene>, enabling it to be captured in the crystalline form. | ||
| + | '''PDB reference:''' Structure of the imidazole-adduct of the ''Phormidium laminosum'' cytochrome c6 Q51V variant, [[3ph2]]. | ||
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| + | </StructureSection> | ||
<references/> | <references/> | ||
__NOEDITSECTION__ | __NOEDITSECTION__ | ||
Current revision
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- ↑ Rajagopal BS, Wilson MT, Bendall DS, Howe CJ, Worrall JA. Structural and kinetic studies of imidazole binding to two members of the cytochrome c (6) family reveal an important role for a conserved heme pocket residue. J Biol Inorg Chem. 2011 Jan 26. PMID:21267610 doi:10.1007/s00775-011-0758-y
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