Andy Zöllner

Deletions in the loop surrounding the iron–sulfur cluster of adrenodoxin severely affect the interactions with its native redox partners adrenodoxin reductase and cytochrome P450scc (CYP11A1)

The redox active iron-sulfur center of bovine adrenodoxin is coordinated by four cysteine residues in positions 46, 52, 55 and 92 and is covered by a loop containing the residues Glu-47, Gly-48, Thr-49, Leu-50 and Ala-51. In plant-type [2Fe-2S] ferredoxins, the corresponding loop consists of only four amino acids. The loop is positioned at the surface of the proteins and forms a boundary separating the [2Fe-2S] cluster from solvent. In order to analyze the biological function of the five amino acids of the loop in adrenodoxin (Adx) for this electron transfer protein each residue was deleted by site-directed mutagenesis. The resulting five recombinant Adx variants show dramatic differences among each other regarding their spectroscopic characteristics and functional properties. The redox potential is affected differently depending on the position of the conducted deletion. In contrast, all mutations in the protein loop influence the binding to the redox partners adrenodoxin reductase (AdR) and cytochrome P450(scc) (CYP11A1) indicating the importance of this loop for the physiological function of this iron--sulfur protein.

Purification and functional characterization of human 11β hydroxylase expressed in Escherichia coli

The human 11β‐hydroxylase (hCYP11B1) is responsible for the conversion of 11‐deoxycortisol into the major mammalian glucocorticoid, cortisol. The reduction equivalents needed for this reaction are provided via a short electron transfer chain consisting of a [2Fe‐2S] ferredoxin and a FAD‐containing reductase. On the biochemical and biophysical level, little is known about hCYP11B1 because it is very unstable for analyses performed in vitro. This instability is also the reason why it has not been possible to stably express it so far in Escherichia coli and subsequently purify it. In the present study, we report on the successful and reproducible purification of recombinant hCYP11B1 coexpressed with molecular chaperones GroES/GroEL in E. coli. The protein was highly purified to apparent homogeneity, as observed by SDS/PAGE. Upon mass spectrometry, the mass‐to‐charge ratio (m/z) of the protein was estimated to be 55 761, which is consistent with the value 55 760.76 calculated for the form lacking the translational initiator Met. The functionality of hCYP11B1 was analyzed using different methods (substrate conversion assays, stopped‐flow, Biacore). The results clearly demonstrate that the enzyme is capable of hydroxylating its substrates at position 11‐beta. Moreover, the determined NADPH coupling percentage for the hCYP11B1 catalyzed reactions using either 11‐deoxycortisol or 11‐deoxycorticosterone as substrates was approximately 75% in both cases. Biacore and stopped‐flow measurements indicate that hCYP11B1 possesses more than one binding site for its redox partner adrenodoxin, possibly resulting in the formation of more than one productive complexes. In addition, we performed CD measurements to obtain information about the structure of hCYP11B1.

CYP21-catalyzed production of the long-term urinary metandienone metabolite 17β-hydroxymethyl-17α-methyl-18-norandrosta-1,4,13-trien-3-one: a contribution to the fight against doping

Abstract Anabolic-androgenic steroids are some of the most frequently misused drugs in human sports. Recently, a previously unknown urinary metabolite of metandienone, 17β-hydroxymethyl-17α-methyl-18-norandrosta-1,4,13-trien-3-one (20OH-NorMD), was discovered via LC-MS/MS and GC-MS. This metabolite was reported to be detected in urine samples up to 19 days after administration of metandienone. However, so far it was not possible to obtain purified reference material of this metabolite and to confirm its structure via NMR. Eleven recombinant strains of the fission yeast Schizosaccharomyces pombe that express different human hepatic or steroidogenic cytochrome P450 enzymes were screened for production of this metabolite in a whole-cell biotransformation reaction. 17,17-Dimethyl-18-norandrosta-1,4,13-trien-3-one, chemically derived from metandienone, was used as substrate for the bioconversion, because it could be converted to the final product in a single hydroxylation step. The obtained results demonstrate that CYP21 and to a lesser extent also CYP3A4 expressing strains can catalyze this steroid hydroxylation. Subsequent 5 l-scale fermentation resulted in the production and purification of 10 mg of metabolite and its unequivocal structure determination via NMR. The synthesis of this urinary metandienone metabolite via S. pombe-based whole-cell biotransformation now allows its use as a reference substance in doping control assays.

Cyanobacterial electron carrier proteins as electron donors to CYP106A2 from Bacillus megaterium ATCC 13368

The CYP450 from Bacillus megaterium (BmCYP106A2) catalyzes the 15beta-hydroxylation of several steroids and also synthesizes mono-hydroxylated 9alpha- and 11alpha-OH-progesterone. This study reports on the ability of BmCYP106A2 to be efficiently reduced by the photosynthetic flavodoxin and, particularly, ferredoxin electron carriers from the cyanobacterium Anabaena. These results open the possibility for the design of a hybrid system to provide reducing equivalents for the hydroxylation process. Additionally, they suggest that despite the interaction of BmCYP106A2 with these proteins, particularly with flavodoxin, they do not rely on a precise complementarity of the reacting molecules, rearrangements might be required and alternative binding modes might contribute to the observed electron transfer reactions.

Purification and functional characterization of human 11beta hydroxylase expressed in Escherichia coli.

The human 11β‐hydroxylase (hCYP11B1) is responsible for the conversion of 11‐deoxycortisol into the major mammalian glucocorticoid, cortisol. The reduction equivalents needed for this reaction are provided via a short electron transfer chain consisting of a [2Fe‐2S] ferredoxin and a FAD‐containing reductase. On the biochemical and biophysical level, little is known about hCYP11B1 because it is very unstable for analyses performed in vitro. This instability is also the reason why it has not been possible to stably express it so far in Escherichia coli and subsequently purify it. In the present study, we report on the successful and reproducible purification of recombinant hCYP11B1 coexpressed with molecular chaperones GroES/GroEL in E. coli. The protein was highly purified to apparent homogeneity, as observed by SDS/PAGE. Upon mass spectrometry, the mass‐to‐charge ratio (m/z) of the protein was estimated to be 55 761, which is consistent with the value 55 760.76 calculated for the form lacking the translational initiator Met. The functionality of hCYP11B1 was analyzed using different methods (substrate conversion assays, stopped‐flow, Biacore). The results clearly demonstrate that the enzyme is capable of hydroxylating its substrates at position 11‐beta. Moreover, the determined NADPH coupling percentage for the hCYP11B1 catalyzed reactions using either 11‐deoxycortisol or 11‐deoxycorticosterone as substrates was approximately 75% in both cases. Biacore and stopped‐flow measurements indicate that hCYP11B1 possesses more than one binding site for its redox partner adrenodoxin, possibly resulting in the formation of more than one productive complexes. In addition, we performed CD measurements to obtain information about the structure of hCYP11B1.

The dipole moment of the electron carrier adrenodoxin is not critical for redox partner interaction and electron transfer.

Dipole moments of proteins arise from helical dipoles, hydrogen bond networks and charged groups at the protein surface. High protein dipole moments were suggested to contribute to the electrostatic steering between redox partners in electron transport chains of respiration, photosynthesis and steroid biosynthesis, although so far experimental evidence for this hypothesis was missing. In order to probe this assumption, we changed the dipole moment of the electron transfer protein adrenodoxin and investigated the influence of this on protein-protein interactions and electron transfer. In bovine adrenodoxin, the [2Fe-2S] ferredoxin of the adrenal glands, a dipole moment of 803 Debye was calculated for a full-length adrenodoxin model based on the Adx(4-108) and the wild type adrenodoxin crystal structures. Large distances and asymmetric distribution of the charged residues in the molecule mainly determine the observed high value. In order to analyse the influence of the resulting inhomogeneous electric field on the biological function of this electron carrier the molecular dipole moment was systematically changed. Five recombinant adrenodoxin mutants with successively reduced dipole moment (from 600 to 200 Debye) were analysed for their redox properties, their binding affinities to the redox partner proteins and for their function during electron transfer-dependent steroid hydroxylation. None of the mutants, not even the quadruple mutant K6E/K22Q/K24Q/K98E with a dipole moment reduced by about 70% showed significant changes in the protein function as compared with the unmodified adrenodoxin demonstrating that neither the formation of the transient complex nor the biological activity of the electron transfer chain of the endocrine glands was affected. This is the first experimental evidence that the high dipole moment observed in electron transfer proteins is not involved in electrostatic steering among the proteins in the redox chain.

Substitution of lysine with glutamic acid at position 193 in bovine CYP11A1 significantly affects protein oligomerization and solubility but not enzymatic activity

CYP11A1, a mitochondrial cytochrome P450, catalyzes the conversion from cholesterol to pregnenolone, the crucial step in the steroid hormone biosynthesis of mammals. It was shown in prior investigations, that the putative F-G loop of this enzyme is involved in membrane attachment. We produced different bovine CYP11A1 variants by rational protein design and could show that a deletion of 20 amino acids comprising parts of the F-G loop results in an enzyme with a three-fold increased solubility, the highest solubility of a CYP11A1 variant obtained so far. Furthermore, a single amino acid mutation, K193E, could be identified which leads not only to a higher solubility of CYP11A1 as well as a 4-fold improved expression rate, but also lowers the oligomerization of the protein while its activity is only slightly decreased. Therefore, this mutant has many advantages for the biotechnological application of CYP11A1 and is an important step towards crystallization of this mitochondrial P450.

Kinetic and optical biosensor study of adrenodoxin mutant AdxS112W displaying an enhanced interaction towards the cholesterol side chain cleavage enzyme (CYP11A1)

In mammals, steroid hormones are synthesized from cholesterol that is metabolized by the mitochondrial CYP11A1 system leading to pregnenolone. The reduction equivalents for this reaction are provided by NADPH, via a small electron transfer chain, consisting of adrenodoxin reductase (AdR) and adrenodoxin (Adx). The reaction partners are involved in a series of transient interactions to realize the electron transfer from NADPH to CYP11A1. Here, we compared the ionic strength effect on the AdR/Adx and Adx/CYP11A1 interactions for wild-type Adx and mutant AdxS112W. Using surface plasmon resonance measurements, stopped flow kinetic investigations and analyses of the product formation, we were able to obtain new insights into the mechanism of these interactions. The replacement of serine 112 by tryptophan was demonstrated to lead to a dramatically decreased koff rate of the Adx/CYP11A1 complex, resulting in a four-fold decreased Kd value and indicating a much higher stability of the complex involving the mutant. Stopped flow analysis at various ionic strengths and in different mixing modes revealed that the binding of reduced Adx to CYP11A1 seems to display the limiting step for electron transfer to CYP11A1 with pre-reduced AdxS112W being much more efficient than wild-type Adx. Finally, the dramatic increase in pregnenolone formation at higher ionic strength using the mutant demonstrates that the interaction of CYP11A1 with Adx is the rate-limiting step in substrate conversion and that hydrophobic interactions may considerably improve this interaction and the efficiency of product formation. The data are discussed using published structural data of the complexes.

Purification and functional characterization of human 11β hydroxylase expressed in Escherichia coli: Functional characterization of hCYP11B1

The human 11β‐hydroxylase (hCYP11B1) is responsible for the conversion of 11‐deoxycortisol into the major mammalian glucocorticoid, cortisol. The reduction equivalents needed for this reaction are provided via a short electron transfer chain consisting of a [2Fe‐2S] ferredoxin and a FAD‐containing reductase. On the biochemical and biophysical level, little is known about hCYP11B1 because it is very unstable for analyses performed in vitro. This instability is also the reason why it has not been possible to stably express it so far in Escherichia coli and subsequently purify it. In the present study, we report on the successful and reproducible purification of recombinant hCYP11B1 coexpressed with molecular chaperones GroES/GroEL in E. coli. The protein was highly purified to apparent homogeneity, as observed by SDS/PAGE. Upon mass spectrometry, the mass‐to‐charge ratio (m/z) of the protein was estimated to be 55 761, which is consistent with the value 55 760.76 calculated for the form lacking the translational initiator Met. The functionality of hCYP11B1 was analyzed using different methods (substrate conversion assays, stopped‐flow, Biacore). The results clearly demonstrate that the enzyme is capable of hydroxylating its substrates at position 11‐beta. Moreover, the determined NADPH coupling percentage for the hCYP11B1 catalyzed reactions using either 11‐deoxycortisol or 11‐deoxycorticosterone as substrates was approximately 75% in both cases. Biacore and stopped‐flow measurements indicate that hCYP11B1 possesses more than one binding site for its redox partner adrenodoxin, possibly resulting in the formation of more than one productive complexes. In addition, we performed CD measurements to obtain information about the structure of hCYP11B1.