Sandbox 177: Difference between revisions
From Proteopedia
Jump to navigationJump to search
Taya O'Neill (talk | contribs) No edit summary |
Taya O'Neill (talk | contribs) No edit summary |
||
| Line 5: | Line 5: | ||
==='''General Information'''=== | ==='''General Information'''=== | ||
---- | ---- | ||
NADPH-cytochrome | Horecker first identified this protein in 1950 as NADPH-specific cytochrome c reductase, based on his assumption that it was the redox partner for cytochrome c, found in the mitochondria.<ref name="1TSON">Horecker BL. Triphosphopyridine nucleotide-cytochrome ''c'' reductase in liver. J Biol Chem 1950 Apr 1;183(2):593-605</ref> However, studies in the 1960s and later showed that its main function is actually as the redox partner for cytochrome P450 in microsomal electron transport chains, resulting in a name change.<ref name="5TSON"/><ref name="4TSON">Phillips AH, Langdon RG. Hepatic triphosphopyridine nucleotide-cytochrome c reductase: Isolation, characterization, and kinetic studies. J Biol Chem 1962 Aug 1;237:2652-60</ref> Today this protein is known as NADPH-cytochrome P450 oxidoreductase (CYPOR). | ||
CYPOR is a ~78kDa, multidomain flavoprotein.<ref name="5TSON">PMID:19171935</ref> Containing three co-factors, <scene name='Sandbox_177/Cyporfmn/2'>FMN</scene>, <scene name='Sandbox_177/Cyporfad/2'>FAD</scene> and <scene name='Sandbox_177/Cypornadph/2'>NADPH</scene>, CYPOR is the archetype for the mammalian diflavin-containing enzyme family.<ref name="5TSON"/> Research indicates that the protein, and other FAD/FMN binding proteins, are likely the product of the fusion of two ancestral genes.<ref name="6TSON">PMID:8078947</ref> This would account for the two distinct binding domain areas, FMN and FAD/NADPH, which each provide different functional capabilities to the overall protein.<ref name="6TSON"/> | |||
Regulation of this protein, which is found all tissues to some extent, is largely at the transcriptional level.<ref name="3cTSON">PMID:11306680</ref> The thyroid hormone T3 in most cases, while adrenocorticotrophic hormone acts as a regulator in a few specific cases.<ref name="3aTSON">PMID:2495435</ref><ref name="3bTSON">PMID:1737785</ref> | Regulation of this protein, which is found all tissues to some extent, is largely at the transcriptional level.<ref name="3cTSON">PMID:11306680</ref> The thyroid hormone T3 in most cases, while adrenocorticotrophic hormone acts as a regulator in a few specific cases.<ref name="3aTSON">PMID:2495435</ref><ref name="3bTSON">PMID:1737785</ref> | ||
| Line 13: | Line 13: | ||
==='''Structure'''=== | ==='''Structure'''=== | ||
---- | ---- | ||
<applet load='3es9' size='200' color='black' frame='true' align='left' scene='Sandbox_177/Cyporplain/2' caption='Highlighting the chains and associated ligands of CYPOR'/> | <applet load='3es9' size='200' color='black' frame='true' align='left' scene='Sandbox_177/Cyporplain/2' caption='Figure 1: Highlighting the chains and associated ligands of CYPOR'/> | ||
CYPOR is a complex, multidomain protein composed of three chains (<scene name='Sandbox_177/Cyporchaina/2'>A</scene>, <scene name='Sandbox_177/Cyporchainb/1'>B</scene>, <scene name='Sandbox_177/Cyporchainc/1'>C</scene>). It also has three different types of associated ligands; one <scene name='Sandbox_177/Cyporfmn/2'>FMN</scene>, three <scene name='Sandbox_177/Cyporfad/2'>FAD</scene> and two <scene name='Sandbox_177/Cypornadph/2'>NADPH</scene>.<ref name="5TSON"/> The three associated binding domains for these | CYPOR is a complex, multidomain protein composed of three chains (<scene name='Sandbox_177/Cyporchaina/2'>A</scene>, <scene name='Sandbox_177/Cyporchainb/1'>B</scene>, <scene name='Sandbox_177/Cyporchainc/1'>C</scene>). It also has three different types of associated ligands; one <scene name='Sandbox_177/Cyporfmn/2'>FMN</scene>, three <scene name='Sandbox_177/Cyporfad/2'>FAD</scene> and two <scene name='Sandbox_177/Cypornadph/2'>NADPH</scene> (Fig 1).<ref name="5TSON"/> The three associated binding domains for these ligand types, a connecting domain and a transmembrane anchor make up the important structural elements of CYPOR (Fig 2). | ||
The N-terminus consists of a single alpha-helix that functions as a transmembrane anchor (~6kDa), holding the protein in the endoplasmic reticulum. The portion of the protein responsible for reducing cytochrome P450 is soluble and ~66kDa.<ref name="5TSON"/> The first 170 residues of the soluble region are very similar to those of flavodoxin, which correlates to the fact that this is the area that binds FMN. The FAD and NADPH binding domains are located closer to the C-terminus, and are very similar to the FAD domain in ferredoxin-NADP<sup>+</sup> oxidoreductase, both in terms of sequence and structure.<ref name="5TSON"/> | The N-terminus of CYPOR consists of a single alpha-helix that functions as a transmembrane anchor (~6kDa), holding the protein in the endoplasmic reticulum. The portion of the protein responsible for reducing cytochrome P450 is soluble and ~66kDa.<ref name="5TSON"/> The first 170 residues of the soluble region are very similar to those of flavodoxin, which correlates to the fact that this is the area that binds FMN. The FAD and NADPH binding domains are located closer to the C-terminus, and are very similar to the FAD domain in ferredoxin-NADP<sup>+</sup> oxidoreductase, both in terms of sequence and structure.<ref name="5TSON"/> | ||
Between the FMN and FAD/NADPH bind domains is a connecting domain, which is a highly flexible random coil.<ref name="5TSON"/> The hinge region is composed of 12 residues from Gly232 to Arg243, and is highly conserved among most known CYPOR | Between the FMN and FAD/NADPH bind domains is a connecting domain, which is a highly flexible random coil.<ref name="5TSON"/> The hinge region is composed of 12 residues from Gly232 to Arg243, and is highly conserved among most known CYPOR proteins, including those found in humans, rats and even yeast.<ref name="5TSON"/> This section is presumed to be responsible for the relatively increased mobility of the FMN domain, changes to conformation and the relative orientation of the binding domains.<ref name="5TSON"/> Studies that examined the rate of electron transfer within CYPOR seem to confirm this, as electron transfer rate appears to decrease proportionally to increases in the viscosity of the fluid medium it is in.<ref name="5TSON"/> When residues within the the hinge are mutated so it is no longer flexible, studies have found that CYPOR cannot effectively transfer electrons to cytochrome P450, unless there is a high electron pool available.<ref name="5TSON"/> This indicates that without the hinge movement electrons are not able to be efficiently moved from FAD to FMN, decreasing the reductase capabilities of CYPOR.<ref name="5TSON"/> | ||
==='''Function'''=== | ==='''Function'''=== | ||
---- | ---- | ||
[[Image:CPR chargepair.gif|thumb|right|250px|Electrostatic charge pairing between Cyt P450 and the FMN binding domain induces the interaction between CYPOR and Cyt P450.]] | [[Image:CPR chargepair.gif|thumb|right|250px|Figure 2: Electrostatic charge pairing between Cyt P450 and the FMN binding domain induces the interaction between CYPOR and Cyt P450.]] | ||
''In vivo'' CYPOR is believe to alternate between a one and a three electron reduced form. While the 1 electron form is fairly stable, forming a neutral blue semiquinone, it is the hydroquinone, or 3 electron form, that is able to donate electrons to the desired redox partners. | ''In vivo'' CYPOR is believe to alternate between a one and a three electron reduced form. While the 1 electron form is fairly stable, forming a neutral blue semiquinone, it is the hydroquinone, or 3 electron form, that is able to donate electrons to the desired redox partners. | ||
| Line 34: | Line 34: | ||
A function that is of particular interest currently is CYPOR’s ability to activate anticancer prodrugs reductively.<ref name="5TSON"/> This makes it a potential target for anticancer research and therapy.<ref name="5TSON"/> | A function that is of particular interest currently is CYPOR’s ability to activate anticancer prodrugs reductively.<ref name="5TSON"/> This makes it a potential target for anticancer research and therapy.<ref name="5TSON"/> | ||
==='''Medical Significance'''=== | |||
---- | |||
