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Mirzaei MS, Ivanov MV, Taherpour AA, Mirzaei S. Mechanism-Based Inactivation of Cytochrome P450 Enzymes: Computational Insights. Chem Res Toxicol 2021; 34:959-987. [PMID: 33769041 DOI: 10.1021/acs.chemrestox.0c00483] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Mechanism-based inactivation (MBI) refers to the metabolic bioactivation of a xenobiotic by cytochrome P450s to a highly reactive intermediate which subsequently binds to the enzyme and leads to the quasi-irreversible or irreversible inhibition. Xenobiotics, mainly drugs with specific functional units, are the major sources of MBI. Two possible consequences of MBI by medicinal compounds are drug-drug interaction and severe toxicity that are observed and highlighted by clinical experiments. Today almost all of these latent functional groups (e.g., thiophene, furan, alkylamines, etc.) are known, and their features and mechanisms of action, owing to the vast experimental and theoretical studies, are determined. In the past decade, molecular modeling techniques, mostly density functional theory, have revealed the most feasible mechanism that a drug undergoes by P450 enzymes to generate a highly reactive intermediate. In this review, we provide a comprehensive and detailed picture of computational advances toward the elucidation of the activation mechanisms of various known groups with MBI activity. To this aim, we briefly describe the computational concepts to carry out and analyze the mechanistic investigations, and then, we summarize the studies on compounds with known inhibition activity including thiophene, furan, alkylamines, terminal acetylene, etc. This study can be reference literature for both theoretical and experimental (bio)chemists in several different fields including rational drug design, the process of toxicity prevention, and the discovery of novel inhibitors and catalysts.
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Affiliation(s)
- M Saeed Mirzaei
- Department of Organic Chemistry, Faculty of Chemistry, Razi University, Kermanshah, Iran 67149-67346
| | - Maxim V Ivanov
- Department of Chemistry, University of Southern California, Los Angeles, California 90089, United States
| | - Avat Arman Taherpour
- Department of Organic Chemistry, Faculty of Chemistry, Razi University, Kermanshah, Iran 67149-67346.,Medical Biology Research Centre, University of Medical Sciences, Kermanshah, Iran 67149-67346
| | - Saber Mirzaei
- Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, United States
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2
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Aschenbrenner JC, Ebrecht AC, Tolmie C, Smit MS, Opperman DJ. Structure of the fungal hydroxylase, CYP505A30, and rational transfer of mutation data from CYP102A1 to alter regioselectivity. Catal Sci Technol 2021. [DOI: 10.1039/d1cy01348c] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Regioselective oxyfunctionalisation of n-alkanes and production of non-vicinal diols by evolved CYP505A30 through rational transfer of knowledge between protein scaffolds.
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Affiliation(s)
- Jasmin C. Aschenbrenner
- Department of Microbiology and Biochemistry, University of the Free State, 205 Nelson Mandela Drive, Bloemfontein, 9300, South Africa
- South African DST-NRF Centre of Excellence in Catalysis, c*change, University of Cape Town, South Africa
| | - Ana C. Ebrecht
- Department of Microbiology and Biochemistry, University of the Free State, 205 Nelson Mandela Drive, Bloemfontein, 9300, South Africa
| | - Carmien Tolmie
- Department of Microbiology and Biochemistry, University of the Free State, 205 Nelson Mandela Drive, Bloemfontein, 9300, South Africa
| | - Martha S. Smit
- Department of Microbiology and Biochemistry, University of the Free State, 205 Nelson Mandela Drive, Bloemfontein, 9300, South Africa
- South African DST-NRF Centre of Excellence in Catalysis, c*change, University of Cape Town, South Africa
| | - Diederik J. Opperman
- Department of Microbiology and Biochemistry, University of the Free State, 205 Nelson Mandela Drive, Bloemfontein, 9300, South Africa
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3
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Colthart AM, Tietz DR, Ni Y, Friedman JL, Dang M, Pochapsky TC. Detection of substrate-dependent conformational changes in the P450 fold by nuclear magnetic resonance. Sci Rep 2016; 6:22035. [PMID: 26911901 PMCID: PMC4766564 DOI: 10.1038/srep22035] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2015] [Accepted: 02/03/2016] [Indexed: 01/23/2023] Open
Abstract
Cytochrome P450 monooxygenases typically catalyze the insertion of one atom of oxygen from O2 into unactivated carbon-hydrogen and carbon-carbon bonds, with concomitant reduction of the other oxygen atom to H2O by NAD(P)H. Comparison of the average structures of the camphor hydroxylase cytochrome P450(cam) (CYP101) obtained from residual dipolar coupling (RDC)-restrained molecular dynamics (MD) in the presence and absence of substrate camphor shows structural displacements resulting from the essential collapse of the active site upon substrate removal. This collapse has conformational consequences that extend across the protein structure, none of which were observed in analogous crystallographic structures. Mutations were made to test the involvement of the observed conformational changes in substrate binding and recognition. All of the mutations performed based upon the NMR-detected perturbations, even those remote from the active site, resulted in modified substrate selectivity, enzyme efficiency and/or haem iron spin state. The results demonstrate that solution NMR can provide insights into enzyme structure-function relationships that are difficult to obtain by other methods.
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Affiliation(s)
- Allison M. Colthart
- Departments of Chemistry and Biochemistry Brandeis University, 415 South St., Waltham MA 02454-9110, USA
| | - Drew R. Tietz
- Departments of Chemistry and Biochemistry Brandeis University, 415 South St., Waltham MA 02454-9110, USA
| | - Yuhua Ni
- Departments of Chemistry and Biochemistry Brandeis University, 415 South St., Waltham MA 02454-9110, USA
| | - Jessica L. Friedman
- Departments of Chemistry and Biochemistry Brandeis University, 415 South St., Waltham MA 02454-9110, USA
| | - Marina Dang
- Departments of Chemistry and Biochemistry Brandeis University, 415 South St., Waltham MA 02454-9110, USA
| | - Thomas C. Pochapsky
- Departments of Chemistry and Biochemistry Brandeis University, 415 South St., Waltham MA 02454-9110, USA
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4
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Examining how enzymes self-organize in a membrane. Proc Natl Acad Sci U S A 2014; 111:3659-60. [PMID: 24567406 DOI: 10.1073/pnas.1401325111] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
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Asciutto EK, Young MJ, Madura J, Pochapsky SS, Pochapsky TC. Solution structural ensembles of substrate-free cytochrome P450(cam). Biochemistry 2012; 51:3383-93. [PMID: 22468842 DOI: 10.1021/bi300007r] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Removal of substrate (+)-camphor from the active site of cytochrome P450(cam) (CYP101A1) results in nuclear magnetic resonance-detected perturbations in multiple regions of the enzyme. The (1)H-(15)N correlation map of substrate-free diamagnetic Fe(II) CO-bound CYP101A permits these perturbations to be mapped onto the solution structure of the enzyme. Residual dipolar couplings (RDCs) were measured for (15)N-(1)H amide pairs in two independent alignment media for the substrate-free enzyme and used as restraints in solvated molecular dynamics (MD) simulations to generate an ensemble of best-fit structures of the substrate-free enzyme in solution. Nuclear magnetic resonance-detected chemical shift perturbations reflect changes in the electronic environment of the NH pairs, such as hydrogen bonding and ring current shifts, and are observed for residues in the active site as well as in hinge regions between secondary structural features. RDCs provide information about relative orientations of secondary structures, and RDC-restrained MD simulations indicate that portions of a β-rich region adjacent to the active site shift so as to partially occupy the vacancy left by removal of the substrate. The accessible volume of the active site is reduced in the substrate-free enzyme relative to the substrate-bound structure calculated using the same methods. Both symmetric and asymmetric broadening of multiple resonances observed upon substrate removal as well as localized increased errors in RDC fits suggest that an ensemble of enzyme conformations are present in the substrate-free form.
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Affiliation(s)
- Eliana K Asciutto
- Department of Chemistry and Biochemistry, Duquesne University, Pittsburgh, PA 15282-1530, USA
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6
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Brunel A, Wilson A, Henry L, Dorlet P, Santolini J. The proximal hydrogen bond network modulates Bacillus subtilis nitric-oxide synthase electronic and structural properties. J Biol Chem 2011; 286:11997-2005. [PMID: 21310962 DOI: 10.1074/jbc.m110.195446] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Bacterial nitric-oxide synthase (NOS)-like proteins are believed to be genuine NOSs. As for cytochromes P450 (CYPs), NOS-proximal ligand is a thiolate that exerts a push effect crucial for the process of dioxygen activation. Unlike CYPs, this catalytic electron donation seems controlled by a hydrogen bond (H-bond) interaction between the thiolate ligand and a vicinal tryptophan. Variations of the strength of this H-bond could provide a direct way to tune the stability along with the electronic and structural properties of NOS. We generated five different mutations of bsNOS Trp66, which can modulate this proximal H-bond. We investigated the effects of these mutations on different NOS complexes (FeIII, FeIICO, and FeIINO), using a combination of UV-visible absorption, EPR, FTIR, and resonance Raman spectroscopies. Our results indicate that (i) the proximal H-bond modulation can selectively decrease or increase the electron donating properties of the proximal thiolate, (ii) this modulation controls the σ-competition between distal and proximal ligands, (iii) this H-bond controls the stability of various NOS intermediates, and (iv) a fine tuning of the electron donation by the proximal ligand is required to allow at the same time oxygen activation and to prevent uncoupling reactions.
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Affiliation(s)
- Albane Brunel
- Commissariat à l'Energie Atomique, iBiTec-S, SBSM, F-91191 Gif-sur-Yvette, France
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Luthra A, Denisov IG, Sligar SG. Spectroscopic features of cytochrome P450 reaction intermediates. Arch Biochem Biophys 2010; 507:26-35. [PMID: 21167809 DOI: 10.1016/j.abb.2010.12.008] [Citation(s) in RCA: 111] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2010] [Revised: 12/06/2010] [Accepted: 12/07/2010] [Indexed: 11/24/2022]
Abstract
Cytochromes P450 constitute a broad class of heme monooxygenase enzymes with more than 11,500 isozymes which have been identified in organisms from all biological kingdoms [1]. These enzymes are responsible for catalyzing dozens chemical oxidative transformations such as hydroxylation, epoxidation, N-demethylation, etc., with very broad range of substrates [2,3]. Historically these enzymes received their name from 'pigment 450' due to the unusual position of the Soret band in UV-vis absorption spectra of the reduced CO-saturated state [4,5]. Despite detailed biochemical characterization of many isozymes, as well as later discoveries of other 'P450-like heme enzymes' such as nitric oxide synthase and chloroperoxidase, the phenomenological term 'cytochrome P450' is still commonly used as indicating an essential spectroscopic feature of the functionally active protein which is now known to be due to the presence of a thiolate ligand to the heme iron [6]. Heme proteins with an imidazole ligand such as myoglobin and hemoglobin as well as an inactive form of P450 are characterized by Soret maxima at 420nm [7]. This historical perspective highlights the importance of spectroscopic methods for biochemical studies in general, and especially for heme enzymes, where the presence of the heme iron and porphyrin macrocycle provides rich variety of specific spectroscopic markers available for monitoring chemical transformations and transitions between active intermediates of catalytic cycle.
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Affiliation(s)
- Abhinav Luthra
- Department of Biochemistry, School of Molecular and Cellular Biology, University of Illinois, Urbana, IL 61801, USA
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8
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Pochapsky TC, Kazanis S, Dang M. Conformational plasticity and structure/function relationships in cytochromes P450. Antioxid Redox Signal 2010; 13:1273-96. [PMID: 20446763 PMCID: PMC2959183 DOI: 10.1089/ars.2010.3109] [Citation(s) in RCA: 96] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
The cytochrome P450s are a superfamily of enzymes that are found in all kingdoms of living organisms, and typically catalyze the oxidative addition of atomic oxygen to an unactivated C-C or C-H bond. Over 8000 nonredundant sequences of putative and confirmed P450 enzymes have been identified, but three-dimensional structures have been determined for only a small fraction of these. While all P450 enzymes for which structures have been determined share a common global fold, the flexibility and modularity of structure around the active site account for the ability of P450 enzymes to accommodate a vast number of structurally dissimilar substrates and support a wide range of selective oxidations. In this review, known P450 structures are compared, and some structural criteria for prediction of substrate selectivity and reaction type are suggested. The importance of dynamic processes such as redox-dependent and effector-induced conformational changes in determining catalytic competence and regio- and stereoselectivity is discussed, and noncrystallographic methods for characterizing P450 structures and dynamics, in particular, mass spectrometry and nuclear magnetic resonance spectroscopy are reviewed.
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Affiliation(s)
- Thomas C Pochapsky
- Department of Chemistry, Brandeis University, Waltham, Massachusetts 02454-9110, USA.
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Xu LH, Fushinobu S, Takamatsu S, Wakagi T, Ikeda H, Shoun H. Regio- and stereospecificity of filipin hydroxylation sites revealed by crystal structures of cytochrome P450 105P1 and 105D6 from Streptomyces avermitilis. J Biol Chem 2010; 285:16844-53. [PMID: 20375018 DOI: 10.1074/jbc.m109.092460] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The polyene macrolide antibiotic filipin is widely used as a probe for cholesterol and a diagnostic tool for type C Niemann-Pick disease. Two position-specific P450 enzymes are involved in the post-polyketide modification of filipin during its biosynthesis, thereby providing molecular diversity to the "filipin complex." CYP105P1 and CYP105D6 from Streptomyces avermitilis, despite their high sequence similarities, catalyze filipin hydroxylation at different positions, C26 and C1', respectively. Here, we determined the crystal structure of the CYP105P1-filipin I complex. The distal pocket of CYP105P1 has the second largest size among P450 hydroxylases that act on macrolide substrates. Compared with previously determined substrate-free structures, the FG helices showed significant closing motion on substrate binding. The long BC loop region adopts a unique extended conformation without a B' helix. The binding site is essentially hydrophobic, but numerous water molecules are involved in recognizing the polyol side of the substrate. Therefore, the distal pocket of CYP105P1 provides a specific environment for the large filipin substrate to bind with its pro-S side of position C26 directed toward the heme iron. The ligand-free CYP105D6 structure was also determined. A small sub-pocket accommodating the long alkyl side chain of filipin I was observed in the CYP105P1 structure but was absent in the CYP105D6 structure, indicating that filipin cannot bind to CYP105D6 with a similar orientation due to steric hindrance. This observation can explain the strict regiospecificity of these enzymes.
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Affiliation(s)
- Lian-Hua Xu
- Department of Biotechnology, Graduate School of Agriculture and Life Sciences, the University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan
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10
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Lepesheva GI, Park HW, Hargrove TY, Vanhollebeke B, Wawrzak Z, Harp JM, Sundaramoorthy M, Nes WD, Pays E, Chaudhuri M, Villalta F, Waterman MR. Crystal structures of Trypanosoma brucei sterol 14alpha-demethylase and implications for selective treatment of human infections. J Biol Chem 2010; 285:1773-80. [PMID: 19923211 PMCID: PMC2804335 DOI: 10.1074/jbc.m109.067470] [Citation(s) in RCA: 98] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2009] [Revised: 10/29/2009] [Indexed: 11/06/2022] Open
Abstract
Sterol 14alpha-demethylase (14DM, the CYP51 family of cytochrome P450) is an essential enzyme in sterol biosynthesis in eukaryotes. It serves as a major drug target for fungal diseases and can potentially become a target for treatment of human infections with protozoa. Here we present 1.9 A resolution crystal structures of 14DM from the protozoan pathogen Trypanosoma brucei, ligand-free and complexed with a strong chemically selected inhibitor N-1-(2,4-dichlorophenyl)-2-(1H-imidazol-1-yl)ethyl)-4-(5-phenyl-1,3,4-oxadi-azol-2-yl)benzamide that we previously found to produce potent antiparasitic effects in Trypanosomatidae. This is the first structure of a eukaryotic microsomal 14DM that acts on sterol biosynthesis, and it differs profoundly from that of the water-soluble CYP51 family member from Mycobacterium tuberculosis, both in organization of the active site cavity and in the substrate access channel location. Inhibitor binding does not cause large scale conformational rearrangements, yet induces unanticipated local alterations in the active site, including formation of a hydrogen bond network that connects, via the inhibitor amide group fragment, two remote functionally essential protein segments and alters the heme environment. The inhibitor binding mode provides a possible explanation for both its functionally irreversible effect on the enzyme activity and its selectivity toward the 14DM from human pathogens versus the human 14DM ortholog. The structures shed new light on 14DM functional conservation and open an excellent opportunity for directed design of novel antiparasitic drugs.
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Affiliation(s)
- Galina I Lepesheva
- Department of Biochemistry, Vanderbilt University, Nashville, Tennessee 37232, USA.
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11
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Shakunthala N. New cytochrome P450 mechanisms: implications for understanding molecular basis for drug toxicity at the level of the cytochrome. Expert Opin Drug Metab Toxicol 2010; 6:1-15. [PMID: 19947890 PMCID: PMC2826162 DOI: 10.1517/17425250903329095] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
IMPORTANCE OF THE FIELD Cytochrome (CYP) P450 is a collective name for a very large group of heme enzymes, which catalyze largely oxidative reactions, including those of pharmacological and toxicological importance. Their efficient operation requires coupling of specific electron donor and O(2) consumption and substrate hydroxylation. Many drug oxidation reactions are partially uncoupled, leading to the formation of highly toxic reactive oxygen species, which can cause unpredictable toxic effects on the cell. Rational approaches to avoid uncoupling require knowledge of the underlying mechanisms. AREAS COVERED IN THIS REVIEW In this communication, attempts have been made to bring together past as well as present information indicating that i) the P450 active site has two differently accessible allosterically interacting subsites geared for entirely different types of functionally relevant interactions; and ii) substrate binding to the specific protein residues (Site I) forming the reducible high-spin complex and product binding at L(6) (Site II) of the heme iron forming inhibited low-spin complex can regulate the functional state of the enzyme during catalysis. WHAT THE READER WILL GAIN Since P450 enzymes catalyze a wide variety of reactions, understanding the molecular basis for their efficient operation is of interest to many fields, including rational approaches to design safer drugs, tailoring P450 for a given task (e.g., bioremediation). TAKE HOME MESSAGE It is important to take into account that the two sub-sites function as interacting sites rather than parts of a site functioning as single site for rational approaches to P450 mechanisms. This is important especially in regard to interpretation of the observed effects of drugs, products and inhibitors on these enzymes.
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Asciutto EK, Madura JD, Pochapsky SS, OuYang B, Pochapsky TC. Structural and dynamic implications of an effector-induced backbone amide cis-trans isomerization in cytochrome P450cam. J Mol Biol 2009; 388:801-14. [PMID: 19327368 DOI: 10.1016/j.jmb.2009.03.046] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2008] [Revised: 02/06/2009] [Accepted: 03/13/2009] [Indexed: 11/18/2022]
Abstract
Experimental evidence has been provided for a functionally relevant cis-trans isomerization of the Ile88-Pro89 peptide bond in cytochrome P450(cam) (CYP101). The isomerization is proposed to be a key element of the structural reorganization leading to the catalytically competent form of CYP101 upon binding of the effector protein putidaredoxin (Pdx). A detailed comparison of the results of molecular dynamics simulations on the cis and trans conformations of substrate- and carbonmonoxy-bound ferrous CYP101 with sequence-specific Pdx-induced structural perturbations identified by nuclear magnetic resonance is presented, providing insight into the structural and dynamic consequences of the isomerization. The mechanical coupling between the Pdx binding site on the proximal face of CYP101 and the site of isomerization is described.
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Affiliation(s)
- Eliana K Asciutto
- Department of Chemistry and Biochemistry, Duquesne University, Pittsburgh, PA 15282-1530, USA
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Crystal structures of cytochrome P450 105P1 from Streptomyces avermitilis: conformational flexibility and histidine ligation state. J Bacteriol 2008; 191:1211-9. [PMID: 19074393 DOI: 10.1128/jb.01276-08] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The polyene macrolide antibiotic filipin is widely used as a probe for cholesterol in biological membranes. The filipin biosynthetic pathway of Streptomyces avermitilis contains two position-specific hydroxylases, C26-specific CYP105P1 and C1'-specific CYP105D6. In this study, we describe the three X-ray crystal structures of CYP105P1: the ligand-free wild-type (WT-free), 4-phenylimidazole-bound wild-type (WT-4PI), and ligand-free H72A mutant (H72A-free) forms. The BC loop region in the WT-free structure has a unique feature; the side chain of His72 within this region is ligated to the heme iron. On the other hand, this region is highly disordered and widely open in WT-4PI and H72A-free structures, respectively. Histidine ligation of wild-type CYP105P1 was not detectable in solution, and a type II spectral change was clearly observed when 4-phenylimidazole was titrated. The H72A mutant showed spectroscopic characteristics that were almost identical to those of the wild-type protein. In the H72A-free structure, there is a large pocket that is of the same size as the filipin molecule. The highly flexible feature of the BC loop region of CYP105P1 may be required to accept a large hydrophobic substrate.
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A functional proline switch in cytochrome P450cam. Structure 2008; 16:916-23. [PMID: 18513977 DOI: 10.1016/j.str.2008.03.011] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/01/2008] [Revised: 03/18/2008] [Accepted: 03/22/2008] [Indexed: 11/21/2022]
Abstract
The two-protein complex between putidaredoxin (Pdx) and cytochrome P450(cam) (CYP101) is the catalytically competent species for camphor hydroxylation by CYP101. We detected a conformational change in CYP101 upon binding of Pdx that reorients bound camphor appropriately for hydroxylation. Experimental evidence shows that binding of Pdx converts a single X-proline amide bond in CYP101 from trans or distorted trans to cis. Mutation of proline 89 to isoleucine yields a mixture of both bound camphor orientations, that seen in Pdx-free and that seen in Pdx-bound CYP101. A mutation in CYP101 that destabilizes the cis conformer of the Ile 88-Pro 89 amide bond results in weaker binding of Pdx. This work provides direct experimental evidence for involvement of X-proline isomerization in enzyme function.
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