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Cao C, Zhang Q, Wang ZQ, Wang YF, Wang YH, Wu H, Huang ZX. 1H NMR studies of the effect of mutation at Valine45 on heme microenvironment of cytochrome b5. Biochimie 2003; 85:1007-16. [PMID: 14644556 DOI: 10.1016/j.biochi.2003.08.005] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
1D and 2D (1)H NMR were employed to probe the effects on the heme microenvironment of cytochrome b(5) caused by the mutation from Val45 to Tyr45, His45 and Glu45. Compared with wild type (WT) cytochrome b(5), in all mutants the heme ring are CCW rotated relative to the imidazole planes of axial ligands and the angles beta between two axial ligand imidazole planes are not changed, being in agreement with the temperature dependence of the shifts of the heme protons. The ratios of heme isomers (major to minor) are smaller than that in WT. The 4-vinyl group of the heme in V45Y assumes cis-orientation, being similar to that of WT, while in V45E and V45H, both cis and trans orientation are found. The relationships between the structure and biological function of the mutants are discussed in terms of the geometry of heme and axial ligands, the hydrophobicity of heme pocket and the electrostatic potential of the heme-exposed area.
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Whitney HM, Michaelson LV, Sayanova O, Pickett JA, Napier JA. Functional characterisation of two cytochrome b5-fusion desaturases from Anemone leveillei: the unexpected identification of a fatty acid Delta6-desaturase. PLANTA 2003; 217:983-992. [PMID: 12898253 DOI: 10.1007/s00425-003-1069-5] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/03/2003] [Accepted: 05/13/2003] [Indexed: 05/24/2023]
Abstract
The Ranunculaceae are known to accumulate a wide range of unusual fatty acids in their seed lipids, and this variability has been advocated as a taxonomic marker. The Anemone species, Anemone leveillei L. and Anemone rivularis Buch.-Ham., have previously been reported to accumulate Delta5-desaturated fatty acids in their seed tissue [K. Aitzetmüller (1995) Plant Syst Evol 9:229-240]. Two cDNAs, AL1 and AL2, with similarity to plant cytochrome b5-fusion "front-end" desaturases were isolated from developing seeds of A. leveillei and their function identified by expression in Saccharomyces cerevisiae. AL2 was characterised as a sphingolipid long-chain-base Delta8-desaturase, while AL1 acted as a fatty acid desaturase. However, AL1 did not produce Delta5-desaturated fatty acids as expected; instead, when expressed in transgenic S. cerevisiae or Arabidopsis thaliana this enzyme was functionally characterised as a Delta6-desaturase. Northern analysis confirmed the expression of this gene in seed tissue and leaf tissue of A. leveillei, though Delta6-desaturated fatty acids were found to accumulate only in the leaf tissue. The unexpected characterisation of a Delta6-desaturase in A. leveillei has implications for the use of fatty acids in chemotaxonomic studies. This is also the first report of a higher-plant Delta6-desaturase from a family other than the Boraginaceae.
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Nikou D, Ranson H, Hemingway J. An adult-specific CYP6 P450 gene is overexpressed in a pyrethroid-resistant strain of the malaria vector, Anopheles gambiae. Gene 2003; 318:91-102. [PMID: 14585502 DOI: 10.1016/s0378-1119(03)00763-7] [Citation(s) in RCA: 154] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Many malaria control programmes are based on insecticide application as adulticides, often in the form of pyrethroid-impregnated bed nets. However, the efficacy of this control measure can be reduced by genetic changes in vector insecticide susceptibility. Pyrethroid resistance has been detected in the major African malaria vector, Anopheles gambiae, and has been attributed to a combination of target site insensitivity and increased oxidative metabolism of the insecticide, catalysed by cytochrome P450s. An adult-specific cytochrome P450 monooxygenase 6 (CYP6) P450 gene, CYP6Z1, located within a large cluster of cytochrome P450 genes in chromosome arm 3R of An. gambiae, is expressed approximately 11-fold higher in males and 4.5-fold in females from a pyrethroid-resistant strain than in a susceptible strain from the same geographical area. In both strains, CYP6Z1 expression is higher in males than females. Southern blot analysis discounted gene amplification as a cause of this overexpression. The isolation of An. gambiae cDNAs encoding cytochrome b(5) and nicotinamide adenine dinucleotide phosphate (reduced form) (NADPH)-cytochrome P450 reductase cDNAs is also reported.
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MESH Headings
- Amino Acid Sequence
- Animals
- Anopheles/enzymology
- Anopheles/genetics
- Anopheles/growth & development
- Chromosomes/genetics
- Cytochrome P-450 Enzyme System/genetics
- Cytochrome P450 Family 6
- Cytochromes b5/genetics
- DNA/chemistry
- DNA/genetics
- DNA/isolation & purification
- DNA, Complementary/chemistry
- DNA, Complementary/genetics
- DNA, Complementary/isolation & purification
- Female
- Gene Expression Regulation, Developmental/drug effects
- Gene Expression Regulation, Enzymologic/drug effects
- Gene Order
- Genes, Insect/genetics
- Insect Proteins
- Insect Vectors/enzymology
- Insect Vectors/genetics
- Insect Vectors/growth & development
- Insecticide Resistance/genetics
- Insecticides/pharmacology
- Malaria/transmission
- Male
- Molecular Sequence Data
- Multigene Family/genetics
- NADPH-Ferrihemoprotein Reductase/genetics
- Pyrethrins/pharmacology
- RNA, Messenger/drug effects
- RNA, Messenger/genetics
- RNA, Messenger/metabolism
- Sequence Alignment
- Sequence Analysis, DNA
- Sequence Homology, Amino Acid
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104
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Rehman KS, Carr BR, Rainey WE. Profiling the steroidogenic pathway in human fetal and adult adrenals. JOURNAL OF THE SOCIETY FOR GYNECOLOGIC INVESTIGATION 2003; 10:372-80. [PMID: 12969781 DOI: 10.1016/s1071-5576(03)00118-7] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
OBJECTIVE Gene expression clearly underlies the marked structural and functional differences between the human fetal adrenal (HFA) and adult adrenal. We thus measured expression of steroidogenic enzymes and associated cofactors in these tissues. METHODS Real-time reverse transcriptase polymerase chain reaction was used to quantify transcripts encoding steroidogenic enzymes and the cofactors steroidogenic acute regulatory protein (StAR), cytochrome b5 (CYb5), and P450 oxidoreductase (POR). RESULTS Cholesterol side-chain cleavage mRNA levels were 1.9-fold higher in the HFA than in the adult adrenal. Compared with a nonsignificant difference in 17alpha-hydroxylase/17,20 lyase mRNA abundance, CYb5 and POR were expressed 2.3-fold and 2.0-fold higher, respectively, in the HFA. Dehydroepiandrosterone (DHEA) sulfotransferase transcript (SULT2A1) was present at 13-fold higher levels in the HFA than the adult. 3beta-Hydroxysteroid dehydrogenase type II (HSD3B2) mRNA was 127-fold higher in the adult adrenal. StAR, 21-hydroxylase, 11beta hydroxylase, and aldosterone synthase mRNA abundance did not differ significantly. CONCLUSION In the HFA, increased mRNA for cholesterol side-chain cleavage reflects high cholesterol utilization for steroidogenesis. Both CYb5 and POR cofactors may up-regulate 17alpha-hydroxylase/17,20 lyase activity and thus DHEA sulfate production in the HFA. High levels of SULT2A1 mRNA reflect high DHEA sulfonation in the HFA and restricted expression in the adult. Lack of HSD3B2 in the HFA facilitates DHEA synthesis. The novel finding of high levels of 21-hydroxylase and 11beta hydroxylase transcripts in the midgestational HFA merits further investigation. Thus different patterns of steroidogenic enzyme and cofactor gene expression might account for some of the phenotypic differences between the fetal and adult adrenal.
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105
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Cao C, Zhang Q, Xue LL, Ma J, Wang YH, Wu H, Huang ZX. The solution structure of the oxidized bovine microsomal cytochrome b(5) mutant V61H. Biochem Biophys Res Commun 2003; 307:600-9. [PMID: 12893266 DOI: 10.1016/s0006-291x(03)01225-7] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Using 1488 NOE constraints, 19 stereo-specific assignments, 13 pairs of H-bond constraints, and 140 pseudo-contact shift constraints, a family of 35 structures of bovine microsomal cytochrome b(5) mutant V61H has been obtained through the program PSEUDYANA. The family has been further refined by restrained energy minimization to give a family of final structures. The RMSD values of final structures with respect to the average structure are 0.45+/-0.11 and 0.96+/-0.10A for backbone and heavy atoms, respectively. The final Deltachi(ax) and Deltachi(rh) values are 2.34 x 10(-32) and -0.67 x 10(-32)m(3), respectively. The comparisons between the solution structures of mutant V61H and WT cytochrome b(5), and X-ray structure of the mutant V61H show that the global folding of the molecule in solution is unchanged and the side-chain of His61 deviates from the heme pocket and extends into the solvent like in its crystal structure. However, the helices around the heme pocket undergo outward global displacement while their local conformations are well maintained. Meanwhile, the heme ring shows a little off the heme pocket, which accounts for the lower stability of the mutant. Additionally, the axial ligand rings counterclockwise rotate around His39 N-Fe axis due to the mutation, which is confirmed by variation of the hyperfine shifts of the heme protons of V61H compared to those of WT cytochrome b(5).
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Sayanova OV, Beaudoin F, Michaelson LV, Shewry PR, Napier JA. Identification of primula fatty acid delta 6-desaturases with n-3 substrate preferences. FEBS Lett 2003; 542:100-4. [PMID: 12729906 DOI: 10.1016/s0014-5793(03)00358-2] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Fatty acid Delta(6)-desaturation, the first committed step in C(20) polyunsaturated fatty acid biosynthesis, is generally considered not to discriminate between n-3 and n-6 substrates. We previously identified higher plant species that showed preferential Delta(6)-desaturation of n-3 C(18) fatty acid substrates. A polymerase chain reaction-based approach was used to isolate 'front-end' cytochrome b(5) fusion desaturases from Primula vialii Franchet and Primula farinosa L. Functional analysis in Saccharomyces cerevisiae identified fatty acid Delta(6)-desaturases with a strong specificity for the n-3 substrate alpha-linolenic acid (18:3 Delta(9,12,15)). These results indicate that the accumulation of octadecatetraenoic acid (18:4 Delta(6,9,12,15)) in planta is due to the activity of a novel n-3-specific fatty acid Delta(6)-desaturase.
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107
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Kaderbhai MA, Morgan R, Kaderbhai NN. The membrane-interactive tail of cytochrome b(5) can function as a stop-transfer sequence in concert with a signal sequence to give inversion of protein topology in the endoplasmic reticulum. Arch Biochem Biophys 2003; 412:259-66. [PMID: 12667490 DOI: 10.1016/s0003-9861(03)00051-1] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Sequence analyses of the C-terminal membrane intercalative region of the rat cytochrome b(5) indicated that this domain has, in addition to a signal sequence, a combined element of the classic stop-transfer sequence typically found in a variety of transmembrane proteins. Such bitopic protein arrangements arise by tandem but topogenically displaced activities of cleavable/noncleavable signal and stop-transfer sequences. A fusion precursor comprising an N-terminally linked prokaryotic signal sequence and the full-length of mammalian cytochrome b(5), including its C-terminal membrane insertion sequence, was engineered to investigate the outcome of this combination of signals on the targeting and topology of the cytochrome b(5) in the endoplasmic reticulum membrane. Precytochrome b(5) was cotranslationally translocated across the endoplasmic reticulum membrane. The signal-processed cytochrome b(5) was integrally anchored in the membrane with the globular domain facing the lumen. Thus, the topology of the signal sequence-directed cytochrome b(5) in the microsomal vesicle was reversed with respect to that of the native form. Posttranslational incubation of the precytochrome b(5) with microsomes resulted in a "loose" incorporation of the unprocessed form onto the surface of the vesicle. Our findings suggest that the membrane-insertion sequence of cytochrome b(5) has a functional stop-transfer sequence. We discuss the implications of these findings with respect to selective targeting of cytochrome b(5) to the endoplasmic reticulum membrane in the view that signal and stop-transfer sequences are often interchangeable or combined for topogenic functions.
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108
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Avila L, Huang HW, Damaso CO, Lu S, Moënne-Loccoz P, Rivera M. Coupled oxidation vs heme oxygenation: insights from axial ligand mutants of mitochondrial cytochrome b5. J Am Chem Soc 2003; 125:4103-10. [PMID: 12670231 DOI: 10.1021/ja029311v] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Mutation of His-39, one of the axial ligands in rat outer mitochondrial membrane cytochrome b(5) (OM cyt b(5)), to Val produces a mutant (H39V) capable of carrying out the oxidation of heme to biliverdin when incubated with hydrazine and O(2). The reaction proceeds via the formation of an oxyferrous complex (Fe(II)(-)O(2)) that is reduced by hydrazine to a ferric hydroperoxide (Fe(III)(-)OOH) species. The latter adds a hydroxyl group to the porphyrin to form meso-hydroxyheme. The observation that catalase does not inhibit the oxidation of the heme in the H39V mutant is consistent with the formation of a coordinated hydroperoxide (Fe(III)(-)OOH), which in heme oxygenase is the precursor of meso-hydroxyheme. By comparison, mutation of His-63, the other axial ligand in OM cyt b(5), to Val results in a mutant (H63V) capable of oxidizing heme to verdoheme in the absence of catalase. However, the oxidation of heme by H63V is completely inhibited by catalase. Furthermore, whereas the incubation of Fe(III)(-)H63V with H(2)O(2) leads to the nonspecific degradation of heme, the incubation of Fe(II)(-)H63V with H(2)O(2) results in the formation of meso-hydroxyheme, which upon exposure to O(2) is rapidly converted to verdoheme. These findings revealed that although meso-hydroxyheme is formed during the degradation of heme by the enzyme heme oxygenase or by the process of coupled oxidation of model hemes and hemoproteins not involved in heme catabolism, the corresponding mechanisms by which meso-hydroxyheme is generated are different. In the coupled oxidation process O(2) is reduced to noncoordinated H(2)O(2), which reacts with Fe(II)-heme to form meso-hydroxyheme. In the heme oxygenation reaction a coordinated O(2) molecule (Fe(II)(-)O(2)) is reduced to a coordinated peroxide molecule (Fe(III)(-)OOH), which oxidizes heme to meso-hydroxyheme.
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109
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Soucy P, Lacoste L, Luu-The V. Assessment of porcine and human 16-ene-synthase, a third activity of P450c17, in the formation of an androstenol precursor. Role of recombinant cytochrome b5 and P450 reductase. EUROPEAN JOURNAL OF BIOCHEMISTRY 2003; 270:1349-55. [PMID: 12631293 DOI: 10.1046/j.1432-1033.2003.03508.x] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Recently, we have shown that the biosynthesis of androstenol, a potential endogenous ligand for the orphan receptors constitutive androstane receptor and pregnane-X-receptor, requires the presence of enzymes of the steroidogenic pathway, such as 3 beta-hydroxysteroid dehydrogenase, 5 alpha-reductase and 3 alpha-hydroxysteroid dehydrogenase. In this report, we examine at the molecular level whether the enzyme 17 alpha-hydroxylase/17,20-lyase (P450c17), which possesses dual 17 alpha-hydroxylase and 17,20-lyase activities and catalyzes the production of precursors for glucocorticoids and sex steroids, is also able to catalyze the formation of a third class of active steroids, 16-ene steroids (including androstenol). The role of components of the P450 complex is also assessed. We transfected human embryonic kidney (HEK-293) cells with various amounts of vectors expressing P450c17, NADPH-cytochrome P450 reductase, and cytochrome b5. Our results showed that P450c17 possesses a 16-ene-synthase activity able to transform pregnenolone into 5,16-androstadien-3 beta-ol, without the formation of the precursor 17-hydroxypregnenolone. Cytochrome b5 has a much stronger effect on the 16-ene-synthase activity than on the 17 alpha-hydroxylase/17,20-lyase activities. On the other hand, P450reductase has a drastic effect on the latter, but a negligible one on 5,16-androstadien-3 beta-ol synthesis. Our results therefore demonstrate that human P450c17, as other enzymes of the classical steroidogenic pathway, is involved in the biosynthetic pathway leading to the formation of androstenol.
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110
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Tanaka S, Kinoshita JY, Kuroda R, Ito A. Integration of cytochrome b5 into endoplasmic reticulum membrane: participation of carboxy-terminal portion of the transmembrane domain. J Biochem 2003; 133:247-51. [PMID: 12761189 DOI: 10.1093/jb/mvg034] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Integration of cytochrome b(5) (b5), a tail-anchored protein located in the endoplasmic reticulum (ER) membrane, into the membrane was studied. Mutation of three amino acids, -Leu-Met-Tyr, at the carboxy-terminal end of the transmembrane segment of b5 to alanines resulted in localization of the mutated protein, b5LMY/AAA, in the cytosol as well as in the ER membrane. When an N-glycosylation site was introduced at the carboxy-terminal end of b5LMY/AAA, a substantial amount of the glycosylated form of the mutant protein was recovered in the cytosol fraction. A portion of the mutant protein recovered in the ER was released from the membrane by incubation with the cytosol fraction, but no further release was observed in the second incubation, suggesting that b5 is present in two different states, loosely-bound and firmly-integrated forms, in the ER membrane. These results suggest that b5 is integrated into the ER membrane via the loosely bound state, in which the carboxy-terminal end of the molecule is inserted into the luminal side of the vesicle but is easily translocated back to the cytosol, and that the three amino acids are important for conversion of the loosely-bound state to the firmly-integrated state.
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111
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Yabal M, Brambillasca S, Soffientini P, Pedrazzini E, Borgese N, Makarow M. Translocation of the C terminus of a tail-anchored protein across the endoplasmic reticulum membrane in yeast mutants defective in signal peptide-driven translocation. J Biol Chem 2003; 278:3489-96. [PMID: 12446686 DOI: 10.1074/jbc.m210253200] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
C-tail-anchored proteins are defined by an N-terminal cytosolic domain followed by a transmembrane anchor close to the C terminus. Their extreme C-terminal polar residues are translocated across membranes by poorly understood post-translational mechanism(s). Here we have used the yeast system to study translocation of the C terminus of a tagged form of mammalian cytochrome b(5), carrying an N-glycosylation site in its C-terminal domain (b(5)-Nglyc). Utilization of this site was adopted as a rigorous criterion for translocation across the ER membrane of yeast wild-type and mutant cells. The C terminus of b(5)-Nglyc was rapidly glycosylated in mutants where Sec61p was defective and incapable of translocating carboxypeptidase Y, a well known substrate for post-translational translocation. Likewise, inactivation of several other components of the translocon machinery had no effect on b(5)-Nglyc translocation. The kinetics of translocation were faster for b(5)-Nglyc than for a signal peptide-containing reporter. Depletion of the cellular ATP pool to a level that retarded Sec61p-dependent post-translational translocation still allowed translocation of b(5)-Nglyc. Similarly, only low ATP concentrations (below 1 microm), in addition to cytosolic protein(s), were required for in vitro translocation of b(5)-Nglyc into mammalian microsomes. Thus, translocation of tail-anchored b(5)-Nglyc proceeds by a mechanism different from that of signal peptide-driven post-translational translocation.
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112
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Cowley AB, Altuve A, Kuchment O, Terzyan S, Zhang X, Rivera M, Benson DR. Toward Engineering the Stability and Hemin-Binding Properties of Microsomal Cytochromesb5into Rat Outer Mitochondrial Membrane Cytochromeb5: Examining the Influence of Residues 25 and 71†. Biochemistry 2002; 41:11566-81. [PMID: 12269800 DOI: 10.1021/bi026005l] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
As part of a larger effort to engineer the stability and hemin-binding properties of microsomal (Mc) cytochromes b(5) into rat liver outer mitochondrial membrane (OM) cytochrome (cyt) b(5), several mutants of rat OM cyt b(5) were prepared to study the effect of gradual and complete elimination of two extended hydrophobic networks, which are present in the structure of the mitochondrial protein and are absent in the structure of mammalian Mc cytochromes b(5). One of the hydrophobic networks, identified in a previous study [Altuve, A., Silchenko, S., Lee, K.-H., Kuczera, K., Terzyan, S., Zhang, X., Benson, D. R., and Rivera, M. (2001) Biochemistry 40, 9469-9483], encompasses the side chains of Ala-18, Ile-32, Leu-36, and Leu-47, whereas a second hydrophobic network, identified as part of this work, encompasses the side chains of Ile-25, Phe-58, Leu-71, and the heme. The X-ray structure of the A18S/I25L/I32L/L47R/L71S quintuple mutant of rat OM cyt b(5) demonstrates that both hydrophobic networks have been eliminated and that the corresponding structural elements of the Mc isoform have been introduced. The stability of the rat OM mutant proteins studied was found to decrease in the order wild type > I25L > A18S/I32L/L47R > L71S > A18S/I32L/L47R/L71S > 18S/I25L/I32L/L47R/L71S, indicating that the two hydrophobic networks do indeed contribute to the high stability of rat OM cyt b(5) relative to the bovine Mc isoform. Surprisingly, the quintuple mutant of rat OM cyt b(5) is less stable than bovine Mc cyt b(5), even though the former exhibits significantly slower rates of hemin release and hemin reorientation at pH 7.0. However, at pH 5.0 the bovine Mc and rat OM quintuple mutant proteins release hemin at comparable rates, suggesting that one or both of the His axial ligands in the rat OM protein are more resistant to protonation under physiological conditions. Results obtained from chemical denaturation experiments conducted with the apoproteins demonstrated that mutants containing L71S are significantly less stable than bovine Mc apocyt b(5), strongly suggesting that Leu-71 plays a pivotal role in the stabilization of rat OM apocyt b(5), presumably via hydrophobic interactions with Ile-25 and Phe-58. Because comparable interactions are absent in bovine Mc apocyt b(5), which contains Ser at position 71, it must resort to different interactions to stabilize its fold, thus highlighting yet another difference between rat OM and bovine Mc cyt b(5). During the course of these investigations we also discovered that rat OM cyt b(5) can be made to strongly favor hemin orientational isomer A (I32L) or isomer B (L71S) with a single point mutation and that release of hemin orientational isomers A and B can be kinetically resolved in certain rat OM mutants.
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Yao P, Wu J, Wang YH, Sun BY, Xia ZX, Huang ZX. X-ray crystallography, CD and kinetic studies revealed the essence of the abnormal behaviors of the cytochrome b5 Phe35-->Tyr mutant. EUROPEAN JOURNAL OF BIOCHEMISTRY 2002; 269:4287-96. [PMID: 12199707 DOI: 10.1046/j.1432-1033.2002.03120.x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Conserved phenylalanine 35 is one of the hydrophobic patch residues on the surface of cytochrome b5 (cyt b5). This patch is partially exposed on the surface of cyt b5 while its buried face is in direct van der Waals' contact with heme b. Residues Phe35 and Phe/Tyr74 also form an aromatic channel with His39, which is one of the axial ligands of heme b. By site-directed mutagenesis we have produced three mutants of cyt b5: Phe35-->Tyr, Phe35-->Leu, and Phe35-->His. We found that of these three mutants, the Phe35-->Tyr mutant displays abnormal properties. The redox potential of the Phe35-->Tyr mutant is 66 mV more negative than that of the wild-type cyt b5 and the oxidized Phe35-->Tyr mutant is more stable towards thermal and chemical denaturation than wild-type cyt b5. In this study we studied the most interesting mutant, Phe35-->Tyr, by X-ray crystallography, thermal denaturation, CD and kinetic studies of heme dissociation to explore the origin of its unusual behaviors. Analysis of crystal structure of the Phe35-->Tyr mutant shows that the overall structure of the mutant is basically the same as that of the wild-type protein. However, the introduction of a hydroxyl group in the heme pocket, and the increased van der Waals' and electrostatic interactions between the side chain of Tyr35 and the heme probably result in enhancement of stability of the Phe35-->Tyr mutant. The kinetic difference of the heme trapped by the heme pocket also supports this conclusion. The detailed conformational changes of the proteins in response to heat have been studied by CD for the first time, revealing the existence of the folding intermediate.
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Gan JH, Wu J, Wang ZQ, Wang YH, Huang ZX, Xia ZX. Structures of V45E and V45Y mutants and structure comparison of a variety of cytochrome b5 mutants. ACTA CRYSTALLOGRAPHICA SECTION D: BIOLOGICAL CRYSTALLOGRAPHY 2002; 58:1298-306. [PMID: 12136141 DOI: 10.1107/s0907444902010016] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/11/2002] [Accepted: 06/05/2002] [Indexed: 11/10/2022]
Abstract
Val45 is a highly conserved residue and a component of the heme-pocket wall of cytochrome b(5). The crystal structures of cytochrome b(5) mutants V45E and V45Y have been determined at high resolution. Their overall structures were very similar to that of the wild-type protein. However, Val45 of the wild-type protein points towards the heme, but the large side chains of both Glu45 and Tyr45 of the mutants point towards the solvent. A channel is thus opened and the hydrophobicity of the heme pocket is decreased. The rotation of the porphyrin ring and the conformational change of the axial ligand His39 in the V45Y mutant indicate that the microenvironment of the heme is disturbed because of the mutation. The binding constants and the electron-transfer rates between cytochrome b(5) and cytochrome c decrease owing to the mutation, which can be accounted for by molecular modeling: the inter-iron distances increase in order to eliminate the unreasonably close contacts resulting from the large volumes of the mutated side chains. The influence of the mutations on the redox potentials and protein stability is also discussed. The structures of seven mutants of cytochrome b(5) are compared with each other and the effects of these mutations on the protein properties and functions are summarized.
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115
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Mapes S, Tarantal AF, Parker CR, Moran FM, Bahr JM, Pyter L, Conley AJ. Adrenocortical cytochrome b5 expression during fetal development of the rhesus macaque. Endocrinology 2002; 143:1451-8. [PMID: 11897703 DOI: 10.1210/endo.143.4.8718] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The developmental expressions of cytochrome b5 (b5), 17 alpha-hydroxylase/17,20-lyase cytochrome P450 (P450c17), and 3 beta-hydroxysteroid dehydrogenase were examined in primate fetal adrenals by immunocytochemistry from 50-160 d gestation. The expression of b5 was evident at 50 d in the developing fetal zone (FZ), but decreased markedly through midgestation, then increased again from 150 d to term. Similar changes in the temporal expression was observed for P450c17. Whereas P450c17 was induced largely in the transitional zone (TZ; outer-most FZ), b5 expression was strongest in FZ cells further from the capsule, although overlap between these regions involved a narrow band of cells beneath the TZ that may represent the developing zona reticularis. Thus, the induction of b5 in the FZ and of P450c17 in the TZ of the fetal adrenal late in gestation coincided temporally with the prepartum rise in dehydroepiandrosterone previously reported. These data are consistent with the proposed role of b5 in supporting 17,20-lyase activity of P450c17. However, the lack of cytochrome b5 and P450c17 expression in the FZ of the developing macaque adrenal cortex for much of the second and third trimesters distinguishes it from the mature zona reticularis seen in adult animals.
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Andrade FH, Merriam AP, Porter JD. Extraocular muscle gene expression and function after dark rearing. Ann N Y Acad Sci 2002; 956:391-3. [PMID: 11960821 DOI: 10.1111/j.1749-6632.2002.tb02836.x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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117
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Yao P, Wang YH, Sun BY, Xie Y, Hirota S, Yamauchi O, Huang ZX. Kinetic studies on the oxidation of cytochrome b(5) Phe35 mutants with cytochrome c, plastocyanin and inorganic complexes. J Biol Inorg Chem 2002; 7:375-83. [PMID: 11941495 DOI: 10.1007/s00775-001-0309-z] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2001] [Accepted: 10/09/2001] [Indexed: 11/26/2022]
Abstract
To illustrate the functions of the aromatic residue Phe35 of cytochrome b(5) and to give further insight into the roles of the Phe35-containing hydrophobic patch and/or aromatic channel of cytochrome b(5), we studied electron transfer reactions of cytochrome b(5) and its Phe35Tyr and Phe35Leu variants with cytochrome c, with the wild-type and Tyr83Phe and Tyr83Leu variants of plastocyanin, and with the inorganic complexes [Fe(EDTA)](-), [Fe(CDTA)](-) and [Ru(NH(3))(6)](3+). The changes at Phe35 of cytochrome b(5) and Tyr83 of plastocyanin do not affect the second-order rate constants for the electron transfer reactions. These results show that the invariant aromatic residues and aromatic patch/channel are not essential for electron transfer in these systems.
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118
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Nakajima M, Tane K, Nakamura S, Shimada N, Yamazaki H, Yokoi T. Evaluation of approach to predict the contribution of multiple cytochrome P450s in drug metabolism using relative activity factor: effects of the differences in expression levels of NADPH-cytochrome P450 reductase and cytochrome b(5) in the expression system and the differences in the marker activities. J Pharm Sci 2002; 91:952-63. [PMID: 11948533 DOI: 10.1002/jps.10091] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
The concept of relative activity factor (RAF) to extrapolate data obtained with recombinant cytochrome P450(CYP)s to human liver microsomes has been proposed. To evaluate the approach to predict the contribution of multiple CYPs using RAF, we investigated the effects of the differences in the expression levels of NADPH-cytochrome P450 reductase (OR) and cytochrome b(5) (b(5)) in recombinant CYPs from baculovirus-infected insect cells and the differences in the marker activities. Because we previously clarified that azelastine, an antiallergy and antiasthmatic drug, is N-demethylated by CYP1A2, CYP2D6, and CYP3A4 in humans, the reaction was used as a model. For calculation of RAF, three lots of recombinant CYP1A2, CYP2D6, and CYP3A4 from baculovirus-infected insect cells with different expression levels of OR and b(5) were used. The OR/CYP ratios for recombinant CYP1A2, CYP2D6, and CYP3A4 were 3.9-4.8, 5.1-8.7, and 8.0-11.3, respectively. The b(5)/CYP ratio for recombinant CYP3A4 was 2.1-18.7. As marker activities, ethoxyresorufin O-deethylation and phenacetin O-deethylation for CYP1A2, bufuralol 1'-hydroxylation and debrisoquin 4-hydroxylation for CYP2D6, testosterone 6beta-hydroxylation and midazolam 1'-hydroxylation for CYP3A4 were compared. Our results indicated that the differences in the expression levels of OR and b(5) coexpressed in baculovirus-infected insect cells would not be a critical factor for the quantitative prediction using RAF. In addition, we confirmed that differences in the marker activities did not significantly affect the calculation of RAF values, when the marker activities are specific for a certain CYP isoform. It was suggested that the RAF approach using recombinant CYPs from baculovirus-infected insect cells coexpressing OR (and b(5) if required) could be valuable for the prediction of the contribution of each CYP in drug metabolism.
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Soucy P, Luu-The V. Assessment of the ability of type 2 cytochrome b5 to modulate 17,20-lyase activity of human P450c17. J Steroid Biochem Mol Biol 2002; 80:71-5. [PMID: 11867265 DOI: 10.1016/s0960-0760(01)00171-6] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
The 17 alpha-hydroxylase and 17,20-lyase activities of P450c17 lead to the production of 17 alpha-hydroxypregnenolone (17 alpha-OH-Preg) and dehydroepiandrosterone (DHEA), respectively, in different tissues. The mechanisms of differential regulation of these two activities are not yet fully elucidated. It has been previously shown that cytochrome b5 (cyt-b5) could facilitate the 17,20-lyase activity of human P450c17. Recently, a cDNA (type 2 cyt-b5) sharing 45.8% homology with type 1 cyt-b5 has been isolated from human testis. Since high 17,20-lyase activity is required for the production of androgens in the testis, we wanted to determine the importance of this second cDNA in the modulation of P450c17 17,20-lyase activity and hence, its role in the formation of active androgens. We therefore isolated type 2 cyt-b5 from human testis by RT-PCR and analyzed, by transient transfection in transformed human embryonic kidney cells (HEK-293) of various amounts of vectors expressing cyt-b5, P450-reductase and P450c17, its ability to modulate the 17,20-lyase activity of human P450c17. Results show that, in the presence of NADPH cytochrome P450 reductase (P450-red), type 2 cyt-b5 increases 17,20-lyase activity to a level comparable to that of type 1. These results support the idea that types 1 and 2 cyt-b5 could be involved in the differential modulation of 17 alpha-hydroxylase and 17,20-lyase activities of P450c17. Furthermore, the analysis of mRNA expression of types 1 and 2 cyt-b5 by RT-PCR using primers specific to each type showed that both types are present in the liver but also in the adrenal and testis.
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120
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Mauk MR, Mauk AG, Chen YL, Douglas DJ. Tandem mass spectrometry of protein-protein complexes: cytochrome c-cytochrome b5. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2002; 13:59-71. [PMID: 11777200 DOI: 10.1016/s1044-0305(01)00331-2] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
An improved method to interpret triple quadrupole MS/MS experiments of complexes of large ions is presented and applied to a study of the complex formed by the proteins cytochrome c and cytochrome b5. Modeling of the activation and dissociation process shows that most of the reaction occurs near the collision cell exit where ions have the highest internal energies. Experiments at different collision cell pressures or with different collision gases (Ne, Ar, Kr) are interpreted with a previously proposed collision model (Chen et al., Rapid Commun. Mass Spectrom. 1998, 12, 1003-1010) to calculate the internal energy added to ions to cause dissociation. Small but systematic differences under different experimental conditions are attributed to different times available for reaction. A method to correct for this is presented. Ne, Ar, and Kr are found to have similar energy transfer efficiencies. Complexes of cytochrome c and cytochrome b5 are detected in ESI mass spectra but with abundances less than expected from the solution equilibrium. Dissociation of the cytochrome c-cytochrome b5 complexes with charge k gives as the most abundant fragments, cytochrome b5(+3) and cytochrome c+(k-3). Adding charges to the complex destabilizes it. A series of cytochrome c variants with Lys residues thought to be involved in solution binding replaced by Ala showed no differences in the energy required to induce dissociation of the gas phase complex. The implications for the binding of the gas phase ions are inconclusive.
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Mifsud W, Bateman A. Membrane-bound progesterone receptors contain a cytochrome b5-like ligand-binding domain. Genome Biol 2002; 3:RESEARCH0068. [PMID: 12537557 PMCID: PMC151170 DOI: 10.1186/gb-2002-3-12-research0068] [Citation(s) in RCA: 105] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2002] [Revised: 09/18/2002] [Accepted: 09/26/2002] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Membrane-associated progesterone receptors (MAPRs) are thought to mediate a number of rapid cellular effects not involving changes in gene expression. They do not show sequence similarity to any of the classical steroid receptors. We were interested in identifying distant homologs of MAPR better to understand their biological roles. RESULTS We have identified MAPRs as distant homologs of cytochrome b5. We have also found regions homologous to cytochrome b5 in the mammalian HERC2 ubiquitin transferase proteins and a number of fungal chitin synthases. CONCLUSIONS In view of these findings, we propose that the heme-binding cytochrome b5 domain served as a template for the evolution of membrane-associated binding pockets for non-heme ligands.
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Cooper MT, Porter TD. Cytochrome b(5) coexpression increases the CYP2E1-dependent mutagenicity of dialkylnitrosamines in methyltransferase-deficient strains of Salmonella typhimurium. Mutat Res 2001; 484:61-8. [PMID: 11733072 DOI: 10.1016/s0027-5107(01)00236-6] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Addition of cytochrome b(5) to recombinant cytochrome P450 2E1 systems has been shown to enhance the metabolism of dialkylnitrosamines in vitro. To determine if this effect could be observed with recombinant expression systems in vivo, we have constructed mutagenicity tester strains that coexpress full-length human cytochrome P450 2E1 (CYP2E1), rat cytochrome P450 reductase, and human cytochrome b(5) in Salmonella typhimurium lacking ogt and ada methyltransferases (YG7104, ogt(-); and YG7108, ogt(-), ada(-)). These new recombinant strains exhibit a four- to five-fold greater mutagenic response to dimethylnitrosamine, diethylnitrosamine, and dipropylnitrosamine than strains that contain only CYP2E1 and reductase, and are over 100-fold more sensitive to nitrosamines than the parental strains in the presence of an exogenous activating system (S9 fraction). The four-fold increase in mutagenicity in the presence of cytochrome b(5) was consistent with increasing alkyl chain length up to dibutylnitrosamine, which was poorly activated by CYP2E1. The greatest enhancement was obtained with a tricistronic construct in which the b(5) cDNA preceded the P450 and reductase cDNAs; placing the b(5) cDNA after the reductase cDNA was substantially less effective. These new, highly sensitive strains may prove useful in the detection of nitrosamine contamination of food and environmental samples.
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Qian C, Yao Y, Ye K, Wang J, Tang W, Wang Y, Wang W, Lu J, Xie Y, Huang Z. Effects of charged amino-acid mutation on the solution structure of cytochrome b(5) and binding between cytochrome b(5) and cytochrome c. Protein Sci 2001; 10:2451-9. [PMID: 11714912 PMCID: PMC2374031 DOI: 10.1110/ps.12401] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
Abstract
The solution structure of oxidized bovine microsomal cytochrome b(5) mutant (E48, E56/A, D60/A) has been determined through 1524 meaningful nuclear Overhauser effect constraints together with 190 pseudocontact shift constraints. The final family of 35 conformers has rmsd values with respect to the mean structure of 0.045+/-0.009 nm and 0.088+/-0.011 nm for backbone and heavy atoms, respectively. A characteristic of this mutant is that of having no significant changes in the whole folding and secondary structure compared with the X-ray and solution structures of wild-type cytochrome b(5). The binding of different surface mutants of cytochrome b(5) with cytochrome c shows that electrostatic interactions play an important role in maintaining the stability and specificity of the protein complex formed. The differences in association constants demonstrate the electrostatic contributions of cytochrome b(5) surface negatively charged residues, which were suggested to be involved in complex formation in the Northrup and Salemme models, have cumulative effect on the stability of cyt c-cyt b(5) complex, and the contribution of Glu48 is a little higher than that of Glu44. Moreover, our result suggests that the docking geometry proposed by Northrup, which is involved in the participation of Glu48, Glu56, Asp60, and heme propionate of cytochrome b(5), do occur in the association between cytochrome b(5) and cytochrome c.
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Gallagher J, Kaderbhai NN, Kaderbhai MA. Kinetic constants of signal peptidase I using cytochrome b5 as a precursor substrate. BIOCHIMICA ET BIOPHYSICA ACTA 2001; 1550:1-5. [PMID: 11738082 DOI: 10.1016/s0167-4838(01)00265-5] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
A procedure is described for measuring Escherichia coli signal peptidase I activity which exploits an intact precursor protein composed of the alkaline phosphatase signal peptide fused to the full length mammalian cytochrome b5. This cytochrome b5 precursor protein has been extensively characterised and shown to be processed accurately by purified signal peptidase I [Protein Expr. Purif. 7 (1996) 237]. The amphipathic, chimaeric cytochrome b5 precursor was isolated in mg quantities in a highly homogeneous state under non-denaturing conditions. The processing of the cytochrome b5 precursor by signal peptidase displayed Michaelis-Menten kinetics with K(m)=50 microM and k(cat)=11 s(-1). The K(m) was 20-fold lower than that obtained with signal peptide substrates and 3-fold higher than that reported for pro-OmpA-nuclease A precursor fusion. The corresponding turnover number, k(cat), was four orders of magnitude greater than the peptide substrates but was 2-fold lower than pro-OmpA-nuclease A precursor fusion. These results confirm that both the affinities and the catalytic power of the signal peptidase are significantly higher for macromolecular precursor substrates than for the shorter signal peptide substrates.
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Lamb DC, Kaderbhai NN, Venkateswarlu K, Kelly DE, Kelly SL, Kaderbhai MA. Human sterol 14alpha-demethylase activity is enhanced by the membrane-bound state of cytochrome b(5). Arch Biochem Biophys 2001; 395:78-84. [PMID: 11673868 DOI: 10.1006/abbi.2001.2566] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Human sterol 14alpha-demethylase (P45051; CYP51) catalyzes the oxidative removal of the C32 methyl group of dihydrolanosterol, an essential step in the cholesterol biosynthetic pathway. The reaction is dependent upon NADPH cytochrome P450 reductase (CPR) that donates the electrons for the catalytic cycle. Here we used a recombinant yeast CPR to investigate the abilities of four different forms of cytochrome b(5) to support sterol demethylation activity of CYP51. The cytochrome b(5) derivatives were genetically engineered forms of the native rat cytochrome b(5) core-tail: the soluble globular b(5) core (core), the core linked at its N-terminus with the secretory signal sequence of alkaline phosphatase (signal-core), and the signal sequence linked to the native b(5) (signal-core-tail). The rat core-tail enzyme greatly stimulated sterol demethylation, whereas the signal-core-tail was only marginally active. In contrast, the core and signal-core constructs were completely inactive in stimulating the demethylation reaction. Additionally, cytochrome b(5) enhanced sterol demethylation by more than threefold by accepting electrons from soluble yeast CPR and in its ability to reduce P450. We show that the nature of transient linkage between the hemoproteins and the redox partners is most likely brought about electrostatically, although productive interaction between cytochrome b(5) and CYP51 is governed by the membrane-insertable hydrophobic region in the cytochrome b(5) which in turn determines the correct spatial orientation of the core. This is the first report showing the stimulation of CYP51 by cytochrome b(5).
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