N-methyl Leucine Research Articles

Structure-guided manipulation of the regioselectivity of the cyclosporine A hydroxylase CYP-sb21 from Sebekia benihana

The cytochrome P450 enzyme CYP-sb21 from the rare actinomycete Sebekia benihana is capable of hydroxylating the immunosuppressive drug molecule cyclosporine A (CsA) primarily at the 4th N-methyl leucine (MeLeu4), giving rise to γ-hydroxy-N-methyl-l-Leu4-CsA (CsA-4-OH). This oxidative modification of CsA leads to dramatically reduced immunosuppressive activity while retaining the hair growth-promoting side-effect, thus demonstrating great application potential in both pharmaceutical and cosmetic industries. However, this P450 enzyme also hydroxylates CsA at the unwanted position of the 9th N-methyl leucine (MeLeu9), indicating that the regioselectivity needs to be improved for the development of CsA-4-OH into a commercial hair growth stimulator. Herein, we report the crystal structure of CYP-sb21 in its substrate-free form at 1.85 Å. Together with sequence and 3D structure comparisons, Autodock-based substrate docking, molecular dynamics (MD) simulation, and site-directed mutagenesis, we identified a number of key residues including R294, E264, and M179 that can improve catalytic efficiency or change the regioselectivity of CYP-sb21 towards CsA, setting the stage for better enzymatic preparation of CsA-4-OH. This study also provides new insights into the substrate recognition and binding mechanism of P450 enzymes that accommodate bulky substrates.

Synthesis of Norfijimycin A with Activity against Mycobacterium tuberculosis

The total synthesis of norfijimycin A, a simplified analogue of the marine natural product fijimycin A, is described. Fijimycin A is a cyclic depsipeptide that has been shown to possess activity against methicillin-resistant Staphylococcus aureus. The natural product contains a rare N,β-dimethyl leucine unit with unknown stereochemistry at the β-carbon. To evaluate the importance of the β-methyl group for antimicrobial activity, we introduced N-methyl leucine into the natural product scaffold. The resulting norfijimycin A was shown to possess significant activity against Mycobacterium tuberculosis, the etiological agent of tuberculosis.

Domain Characterization of Cyclosporin Regio-Specific Hydroxylases in Rare Actinomycetes.

Cytochrome P450 hydroxylase (CYP) in actinomycetes plays an important role in the biosynthesis and bioconversion of various secondary metabolites. Two unique CYPs named CYP-sb21 and CYP-pa1, which were identified from Sebekia benihana and Pseudonocardia autotrophica, respectively, were proven to transfer a hydroxyl group at the 4(th) or 9(th) N-methyl leucine position of immunosuppressive agent cyclosporin A (CsA). Interestingly, these two homologous CYPs showed different CsA regio-selectivities. CYP-sb21 exhibited preferential hydroxylation activity at the 4(th) position over the 9(th) position, whereas CYP-pa1 showed the opposite preference. To narrow down the CYP domain critical for CsA regio-selectivity, each CYP was divided into four domains, and each domain was swapped with its counterpart from the other CYP. A total of 18 hybrid CYPs were then individually tested for CsA regioselectivity. Although most of the hybrid CYPs failed to exhibit a significant change in regioselectivity in the context of CsA hydroxylation, hybrid CYP-pa1 swapped with the second domain of CYP-sb21 showed a higher preference for the 9th position. Moreover, hybrid CYPsb21 containing seven amino acids from the 2nd domain of CYP-pa1 showed higher preference for the 4(th) position. These results imply that the 2nd domain of CsA-specific CYP plays a critical role in CsA regio-selectivity, thereby setting the stage for biotechnological application of CsA regio-selective hydroxylation.

A novel regio-specific cyclosporin hydroxylase gene revealed through the genome mining of Pseudonocardia autotrophica

The regio-specific hydroxylation at the 4th N-methyl leucine of the immunosuppressive agent cyclosporin A (CsA) was previously proposed to be mediated by a unique cytochrome P450 hydroxylase (CYP), CYP-sb21 from the rare actinomycetes Sebekia benihana. Interestingly, a different rare actinomycetes species, Pseudonocardia autotrophica, was found to possess a different regio-selectivity, the preferential hydroxylation at the 9th N-methyl leucine of CsA. Through an in silico analysis of the whole genome of P. autotrophica, we describe here the classification of 31 total CYPs in P. autotrophica. Three putative CsA CYP genes, showing the highest sequence homologies with CYPsb21, were successfully inactivated using PCR-targeted gene disruption. Only one knock-out mutant, ΔCYP-pa1, failed to convert CsA to its hydroxylated forms. The hydroxylation activity of CsA by CYP-pa1 was confirmed by CYP-pa1 gene complementation as well as heterologous expression in the CsA non-hydroxylating Streptomyces coelicolor. Moreover, the cyclosporine regio-selectivity of CYP-pa1 expressed in the ΔCYP-sb21 S. benihana mutant strain was also confirmed unchanged through cross complementation. These results show that preferential regio-specific hydroxylation at the 9th N-methyl leucine of CsA is carried out by a specific P450 hydroxylase gene in P. autotrophica, CYP-pa1, setting the stage for the biotechnological application of CsA regioselective hydroxylation.

Targeted Gene Disruption and Functional Complementation of Cytochrome

A cyclic undecapeptide-family natural product, cyclosporin A (CyA), which is one of the most valuable immunosuppressive drugs, is produced nonribosomally by a multifunctional cyclosporin synthetase enzyme complex in a filamentous fungal strain named Tolypocladium niveum. Previously, structural modifications of cyclosporins such as a regionspecific hydroxylation at the 4th N-methyl leucine in a rare actinomycetes called Sebekia benihana were reported to lead to dramatic changes in their bioactive spectra. However, the reason behind this change could not be determined since a system to genetically manipulate S. benihana has not yet been developed. To address this limitation, in this study, we utilized the most commonly practiced gene manipulation techniques including conjugation-based foreign gene transfer-and-expression as well as targeted gene disruption to genetically manipulate S. benihana. Using these optimized genetic manipulation systems, a putative cytochrome P450 hydroxylase (CYP) gene named CYP506, which is involved in CyA hydroxylation in S. benihana, was specifically disrupted and genetically complemented. The S. benihana deltaCYP506 exhibited a significantly reduced CyA hydroxylation yield as well as considerable yield restoration by functional complementation of the S. benihana CYP506 gene, suggesting that the genetically manipulated S. benihana CYP mutant strains may serve as a more efficient bioconversion host for various valuable metabolites including CyA.

Fourier transform infrared spectroscopic characterization of complexes of carbamoylated quinidine chiral selector and N-derivatized leucine enantiomers in solution : Evidence for stereoselective intermolecular interactions

Fourier transform infrared (FT-IR) spectra of 1 : 1 complexes of O-allylcarbamoyl-10,11-dihydroquinidine with (S) and (R) enantiomers of N-3,5-dinitrobenzoyl (DNB) and N-2,4-dinitrophenyl (DNP) protected leucine (Leu) and N-methyl leucine ( N-Me-Leu), respectively, as well as of the pure binding partners are reported. For the study of the various intermolecular interaction effects, IR spectra were monitored in acetonitrile and acetonitrile/water solutions using attenuated total reflectance with a cylindrical internal reflection cell. The results of the FT-IR measurements are correlated with findings of liquid chromatographic studies in which O-allylcarbamoyl-10,11-dihydroquinidine is used as a chiral selector immobilized onto silica for the direct chromatographic enantioseparation of N-derivatized amino acids.

Quinine- versus carbamoylated quinine-based chiral anion exchangers: A comparison regarding enantioselectivity for N-protected amino acids and other chiral acids

First, a chiral stationary phase was prepared by immobilization of the naturally occurring alkaloid quinine onto a 3-mercaptopropyl-modified silica gel via a radical addition reaction and it was evaluated for direct HPLC enantioseparation of acidic chiral compounds under buffered hydro-organic mobile phase conditions. Second, its enantioselectivity and retention characteristics for a representative set of N-derivatized α-amino acids and other chiral acids were compared with those of a similar weak chiral anion exchanger based on tert.-butyl carbamoylated quinine derivative as chiral selector. The results clearly indicate that the introduction of the carbamoyl functionality at the secondary hydroxyl group at C 9 of quinine provides new and additional sites for intermolecular interactions with chiral analytes and this can profoundly change and improve chiral recognition ability, especially for amide, carbamate and sulfonamide derivatives of amino acids including DNB, Bz, Ac, For, Z, Fmoc, Boc and DNS-protected amino acids. The impact of this new and rigid hydrogen donor–acceptor group – directing stereoselective selector–selectand complexation by intermolecular hydrogen bonding – in comparison to the plain quinine selector is further evaluated by alkylation of the nitrogen atom of either the selector carbamate and/or of the amino function of leucine ( N-methyl leucine) derivatized either by DNB or DNP groups.

Isolation, identification and immunosuppressive activity of SDZ-IMM-125 metabolites from human liver microsomes.

SDZ-IMM-125 N-methyl leucine 9 hydroxylated in the gamma position is a metabolite which was extracted from incubated human liver microsomes and subsequently separated by normal and reverse-phase HPLC. This metabolite was identified by fast atom bombardment mass spectrometry, electrospray-ms/ms mass spectrometry and nuclear magnetic resonance spectroscopy. The in vitro 50% inhibitory concentration, tested against bidirectional mixed lymphocyte reaction was 80 microg/l indicating that this metabolite does not retain in vitro immunosuppressive activity most probably due to the structural modification of SDZ-IMM-125 in the recognized binding region to cyclophilin A reducing its binding affinity relative to the parent drug.

PF1022A--a novel anthelmintic cyclooctadepsipeptide. Modification and exchange of the N-methyl leucine residues.

The first structure-activity relationships of the anthelmintic cyclooctadepsipeptide PF1022A have been established via a systematic exchange of the leucine residues by a series of related N-alkylated amino acids. The data presented strongly suggest that (L)-N-methyl-leucine is crucial for high in vivo activity.

Comparison of the structures of the endothelin A receptor antagonists BQ123 and N-methyl leucine BQ123 with the crystal structure of the C-terminal tail of endothelin-1

The functionally important regions of the cyclic pentapeptide endothelin A receptor antagonist BQ123 are shown to correlate with the structure of the C-terminal tail of endothelin-1, as found in the recently-determined X-ray crystal structure. Residues 18 and 21 of endothelin-1 are spatially juxtaposed such that they superpose extremely well withd-Asp andd-Trp of the antagonist, consistent with the residues on this surface of the endothelin helix being important for binding. This study provides new information on the three-dimensional nature of the endothelin A receptor binding site which may prove useful for rational drug design.

Mass spectrometric analysis of cyclosporine metabolites.

Cyclosporine (CsA, mol. wt 1202) is a cyclic undecapeptide with potent immunosuppressive properties which have made it extremely useful for preventing the rejection of transplanted organs. The drug has severe side-effects, however, which may be related to its metabolism. Sensitive methods to determine the structure of metabolites of CsA have, therefore, been developed using mass spectrometric techniques. First, the molecular weight of the metabolite is determined using fast atom bombardment mass spectrometry or thermospray liquid chromatography/mass spectrometry. The metabolite is then hydrolysed to its component amino acids, which are esterified and acylated and identified by gas chromatography/mass spectrometry. To distinguish metabolism at the four identical N-methyl leucines, the metabolite is partially hydrolysed, the resulting peptides are derivatized to the trimethylsilyl-polyamino alcohols, and these in turn are analysed by gas chromatography/mass spectrometry. These procedures have been used to determine the structure of metabolites of CsA isolated from rabbit bile. The determination of the structure of one metabolite carboxylated on the eta-carbon of amino acid 1, and of one metabolite hydroxylated on the eta-carbon of amino acid 1 and on the gamma-carbon of N-methyl leucine 9 is presented. These procedures should be generally useful for the structural analysis of microgram amounts of CsA metabolites and analogs.