A Review of the Antimicrobial Properties of Cyanobacterial Natural Products

The development of multiple-drug-resistant pathogens has prompted medical research toward the development of new and effective antimicrobial therapies. Much research into novel antibiotics has focused on bacterial and fungal compounds, and on chemical modification of existing compounds to increase their efficacy or reactivate their antimicrobial properties. In contrast, cyanobacteria have been relatively overlooked for antibiotic discovery, and much more work is required. This may be because some cyanobacterial species produce environmental toxins, leading to concerns about the safety of cyanobacterial compounds in therapy. Despite this, several cyanobacterial-derived compounds have been identified with noteworthy inhibitory activity against bacterial, fungal and protozoal growth, as well as viral replication. Additionally, many of these compounds have relatively low toxicity and are therefore relevant targets for drug development. Of particular note, several linear and heterocyclic peptides and depsipeptides with potent activity and good safety indexes have been identified and are undergoing development as antimicrobial chemotherapies. However, substantial further studies are required to identify and screen the myriad other cyanobacterial-derived compounds to evaluate their therapeutic potential. This study reviews the known phytochemistry of cyanobacteria, and where relevant, the effects of those compounds against bacterial, fungal, protozoal and viral pathogens, with the aim of highlighting gaps in the literature and focusing future studies in this field.

The Art of War with Pseudomonas aeruginosa: Targeting Mex Efflux Pumps Directly to Strategically Enhance Antipseudomonal Drug Efficacy

Pseudomonas aeruginosa (P. aeruginosa) poses a grave clinical challenge due to its multidrug resistance (MDR) phenotype, leading to severe and life-threatening infections. This bacterium exhibits both intrinsic resistance to various antipseudomonal agents and acquired resistance against nearly all available antibiotics, contributing to its MDR phenotype. Multiple mechanisms, including enzyme production, loss of outer membrane proteins, target mutations, and multidrug efflux systems, contribute to its antimicrobial resistance. The clinical importance of addressing MDR in P. aeruginosa is paramount, and one pivotal determinant is the resistance-nodulation-division (RND) family of drug/proton antiporters, notably the Mex efflux pumps. These pumps function as crucial defenders, reinforcing the emergence of extensively drug-resistant (XDR) and pandrug-resistant (PDR) strains, which underscores the urgency of the situation. Overcoming this challenge necessitates the exploration and development of potent efflux pump inhibitors (EPIs) to restore the efficacy of existing antipseudomonal drugs. By effectively countering or bypassing efflux activities, EPIs hold tremendous potential for restoring the antibacterial activity against P. aeruginosa and other Gram-negative pathogens. This review focuses on concurrent MDR, highlighting the clinical significance of efflux pumps, particularly the Mex efflux pumps, in driving MDR. It explores promising EPIs and delves into the structural characteristics of the MexB subunit and its substrate binding sites.

Hamamelis virginiana L. Leaf Extracts Inhibit the Growth of Antibiotic-Resistant Gram-Positive and Gram-Negative Bacteria

Virginian witch hazel (WH; Hamamelis virginiana L.; family: Hamamelidaceae) is a North American plant that is used traditionally to treat a variety of ailments, including bacterial infections. Solvents of varying polarity (water, methanol, ethyl acetate, hexane and chloroform) were used to prepare extracts from this plant. Resuspensions of each extract in an aqueous solution were tested for growth-inhibitory activity against a panel of bacteria (including three antibiotic-resistant strains) using agar disc diffusion and broth microdilution assays. The ethyl acetate, hexane and chloroform extracts were completely ineffective. However, the water and methanolic extracts were good inhibitors of E. coli, ESBL E. coli, S. aureus, MRSA, K. pneumoniae and ESBL K. pneumoniae growth, with the methanolic extract generally displaying substantially greater potency than the other extracts. Combining the active extracts with selected conventional antibiotics potentiated the bacterial growth inhibition of some combinations, whilst other combinations remained non-interactive. No synergistic or antagonistic interactions were observed for any WH extracts/antibiotic combinations. Gas chromatography-mass spectrometry analysis of the extracts identified three molecules of interest that may contribute to the activities observed, including phthalane and two 1,3-dioxolane compounds. Putative modes of action of the active WH extracts and these molecules of interest are discussed herein.

Technology-assisted viva voce exams: A novel approach aimed at addressing student anxiety and assessor burden in oral assessment

BACKGROUND AND PURPOSE

Viva voce (VIVA) exams are resource intensive, can be prone to inter-rater reliability issues, and induce anxiety in many students. Costs, reliability, validity, and student welfare have been targeted for VIVA re-design. The objective of this study is to design and assess if a less labour-intensive approach to VIVA exams is acceptable to students, reducing student anxiety, whilst maintaining authenticity of the assessment.

EDUCATIONAL ACTIVITY AND SETTING

The School of Pharmacy and Medical Sciences (Griffith University) delivers undergraduate and postgraduate pharmacy degrees, which contain multiple VIVAs. We have designed and implemented a modified VIVA called the technology-assisted VIVA exam (TaVIVA) utilising remote recording, retrospective marking, and pre-recorded multimedia delivered questions to test student acceptability, impact on student anxiety, and inform potential delivery as a summative assessment.

FINDINGS

Student responses were overwhelmingly positive, reporting satisfaction with the TaVIVA. There was strong agreement that the school should continue to develop the TaVIVA. Students perceived that it was fairer than traditional VIVAs and less anxiety inducing. However, students indicated that the traditional VIVA was more authentic and that they eventually need to conduct a VIVA in the presence of an assessor.

SUMMARY

The TaVIVA is an innovative assessment approach with potential benefits over the traditional VIVA, including facilitation of assessment consistency and reductions in student anxiety. We postulate that the TaVIVA is a useful and valid means of scaffolding student performance in VIVA assessment.

Can a virtual microbiology simulation be as effective as the traditional Wetlab for pharmacy student education?

BACKGROUND

Pharmacy practice education requires the development of proficiencies and an understanding of clinical microbiology. Learning in this area could be delivered using practical laboratory exercises, or potentially, simulation-based education. Simulation has previously successfully enhanced learning in health professional education. The current global climate due to COVID-19 has further highlighted the important role of technology-enhanced learning in delivering outcomes that meet the requisite learning objectives of a course. The aim of the present study was to compare the impact of a commercially available virtual microbiology simulation (VUMIE™) with a traditional wet laboratory (wetlab) on learner knowledge, skills and confidence in a second-year integrated pharmacotherapeutics course for Bachelor of Pharmacy students.

METHODS

A randomised, crossover study was employed to determine whether the simulation intervention (VUMIE™) improves learning outcomes (knowledge, skills and confidence) of pharmacy students, when compared to a traditional wetlab intervention. Each student completed three 1-2 h length sessions, for both the wetlab and VUMIE™ interventions (6 sessions total). Data was collected using surveys deployed at baseline (pre-interventions), post-intervention 1 or 2 (VUMIE™ or wetlab) and endpoint (post-interventions 1 and 2). Statistical analysis was conducted using SPSS Statistics 25 and Instat™ software.

RESULTS

Response rates were approximately 50% at initial survey and approximately 25% at endpoint survey. VUMIE™ produced higher post-intervention knowledge scores for the multiple-choice questions compared to the wetlab, however, the highest score was achieved at endpoint. Both interventions produced statistically significant differences for mean scores compared to baseline (pre-VUMIE™ and wetlab) across the domains of knowledge, skills and confidence. VUMIE™ produced higher post-intervention mean scores for knowledge, skills and confidence compared to post-intervention mean scores for the wetlab, however there was no statistical significance between the mean score for the two interventions, thus the VUMIE™ activity produced learning outcomes comparable to the wetlab activity.

CONCLUSION

These findings suggest VUMIE™ provides similar effects on students' knowledge, skills, and confidence as a wetlab. The simulation's implementation was not cost-prohibitive, provided students with a physically and psychologically safe learning environment, and the benefit of being able to repeat activities, supporting deliberate practice.

An assessment of the growth inhibition profiles of Hamamelis virginiana L. extracts against Streptococcus and Staphylococcus spp

Staphylococcal and streptococcal species trigger a wide variety of infections involving epithelial tissues. Virginian witch hazel (WH; Hamamelis virginiana L.; family: Hamamelidaceae) is a plant that has been used traditionally by Native Americans to treat a variety of skin conditions. Extracts from the leaves were examined for their inhibitory effects on these bacterial species. Solvents of different polarity (water, methanol, ethyl acetate, hexane and chloroform) were used to prepare extracts from WH leaves, and the aqueous resuspensions were screened for antibacterial activities using disc diffusion and liquid dilution assays. Extract phytochemical profiles and toxicities were also examined, and combinations of extracts with conventional antibiotics were tested against each bacterial strain. The methanolic and aqueous extracts inhibited the growth of S. oralis, S. pyogenes, S. epidermidis and S. aureus, but not S. mutans. The extracts were especially active against staphylococcal species, with MIC values between 200 and 500 μg/ml. Combinations of active extracts with conventional antibiotics failed to yield beneficial interactions, except for two cases where additive interactions were observed (aqueous WH extract combined with chloramphenicol against S. oralis, and methanolic WH extract combined with ciprofloxacin against S. aureus). Phytochemical assays indicated an abundance of tannins, triterpenoids and phenolics in the water and methanol extracts, with trace amounts of these components in the ethyl acetate extract. Phytochemicals were not detected in hexane and chloroform extracts. Thus, phytochemical abundance in extracts was concordant with antibacterial activities. All extracts were found to be non-toxic in Artemia nauplii assays. These findings indicate the potential for WH leaf extracts for clinical use in treating staphylococcal and streptococcal infections, while substantiating their traditional Native American uses.

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H. virginiana extracts inhibited the growth of common bacterial skin pathogens.

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MIC values were determined and indicated strong inhibitory activity.

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The aqueous extract potentiated the antibacterial activity of chloramphenicol.

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The methanolic extracts potentiated activity of ciprofloxacin.

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All extracts were determined to be non-toxic by Artemia nauplii assays.

Use of specific combinations of the triphala plant component extracts to potentiate the inhibition of gastrointestinal bacterial growth

ETHNOPHARMACOLOGICAL RELEVANCE

Triphala is used in Ayurveda to treat a wide variety of diseases, including numerous bacterial infections. Interestingly, the plant components of triphala (Terminalia bellirica, Terminalia chebula and Emblica officinalis) are also good inhibitors of bacterial growth when used individually, yet plant preparations are generally used in combination in traditional medicine. Surprisingly, no previous studies have addressed the reason why the combination is preferred over the individual components to treat bacterial infections.

AIM OF THE STUDY

To test and compare the antibacterial efficacy of triphala and its component parts to quantify their relative efficacies. The individual plant components will also be tested as combinations, thereby determining whether combining the individual components potentiates the antibacterial activity of the components used alone.

MATERIALS AND METHODS

Triphala and the three individual plant components were extracted using solvents of varying polarity (methanol, water, ethyl acetate) and the antibacterial activity of the aqueous resuspensions was quantified by disc diffusion and broth microdilution MIC assays. Combinations of extracts produced from the individual components were also tested against each bacterial species and the ΣFICs was calculated to determine the class of interaction. Where synergy was detected, isobologram analysis was used to determine the optimal component ratios. The Artemia nauplii bioassay was used to test for toxicity and GC-MS headspace profiling analysis was used to highlight terpenoid components that may contribute to the antibacterial activity of triphala.

RESULTS

The aqueous and methanolic triphala, T. bellirica, T. chebula and E. officinalis extracts displayed good inhibitory activity against all bacterial strains, with MICs often in the 250-750 μg/mL range. The methanolic extracts were generally more potent than the aqueous extracts and T. chebula was the most potent of the individual plant components. Combining the extracts of the different plant species resulted in potentiation of the growth inhibitory activity of most combinations compared to that of the individual components. Indeed, with the exception of S. flexneri, all bacterial species were potentiated by at least one combination of methanolic plant extracts, with a substantial proportion of these displaying synergistic interactions. All extracts were found to be either non-toxic, or of low to moderate toxicity in Artemia nauplii assays.

CONCLUSION

Whilst the individual plant components of triphala all inhibit the growth of multiple pathogenic bacteria, the activity is potentiated for multiple combinations. Therefore, the traditional usage of the combination of the three plant materials in triphala not only extends the activity profile of the mixture over that of the individual components, but it also substantially potentiates the inhibitory activity towards multiple bacteria, partially explaining the preference of triphala compared to the individual components.

Terminalia ferdinandiana Fruit and Leaf Extracts Inhibit Methicillin-Resistant Staphylococcus aureus Growth

The development of multiple antibiotic-resistant bacteria has vastly depleted our repertoire of effective antibiotic chemotherapies. The development of multi-β-lactam-resistant strains are particularly concerning due to our previous reliance on this class of antibiotics because of their initial efficacy and broad-spectrum activity. With increases in extended-spectrum β-lactam-resistance and an expanded resistance to other classes of antibiotics, there is an urgent need for the development of effective new antibiotic therapies. Terminalia ferdinandiana is an endemic Australian plant known for its high antioxidant and tannin contents. T. ferdinandiana fruit and leaf extracts have strong antibacterial activity against a wide variety of bacterial pathogens. However, T. ferdinandiana extracts have not been tested against ESBL and MRSA antibiotic-resistant pathogens. An objective of this study was to screen T. ferdinandiana fruit and leaf extracts for bacterial growth inhibitory activity by disc diffusion assay against β-lactam-sensitive and -resistant E. coli strains and against methicillin-sensitive and -resistant S. aureus. The minimum inhibitory concentration (MIC) was quantified by liquid dilution techniques. The fruit methanolic extract, as well as the methanolic, aqueous, and ethyl acetate leaf extracts strongly inhibited the growth of the MRSA, with MICs as low as 223 µg/mL. In contrast, the extracts were ineffective inhibitors of ESBL growth. Metabolomic fingerprint analysis identified a diversity and relative abundance of tannins, flavonoids, and terpenoids, several of which have been reported to inhibit MRSA growth in isolation. All extracts were nontoxic in the Artemia nauplii and HDF toxicity assays, further indicating their potential for medicinal use.

Developing New Antimicrobial Therapies: Are Synergistic Combinations of Plant Extracts/Compounds with Conventional Antibiotics the Solution?

The discovery of penicillin nearly 90 years ago revolutionized the treatment of bacterial disease. Since that time, numerous other antibiotics have been discovered from bacteria and fungi, or developed by chemical synthesis and have become effective chemotherapeutic options. However, the misuse of antibiotics has lessened the efficacy of many commonly used antibiotics. The emergence of resistant strains of bacteria has seriously limited our ability to treat bacterial illness, and new antibiotics are desperately needed. Since the discovery of penicillin, most antibiotic development has focused on the discovery of new antibiotics derived from microbial sources, or on the synthesis of new compounds using existing antibiotic scaffolds to the detriment of other lines of discovery. Both of these methods have been fruitful. However, for a number of reasons discussed in this review, these strategies are unlikely to provide the same wealth of new antibiotics in the future. Indeed, the number of newly developed antibiotics has decreased dramatically in recent years. Instead, a reexamination of traditional medicines has become more common and has already provided several new antibiotics. Traditional medicine plants are likely to provide further new antibiotics in the future. However, the use of plant extracts or pure natural compounds in combination with conventional antibiotics may hold greater promise for rapidly providing affordable treatment options. Indeed, some combinational antibiotic therapies are already clinically available. This study reviews the recent literature on combinational antibiotic therapies to highlight their potential and to guide future research in this field.

Soluble and membrane-bound Drosophila melanogaster CYP6G1 expressed in Escherichia coli: purification, activity, and binding properties toward multiple pesticides

Cytochrome P450 CYP6G1 has been implicated in the resistance of Drosophila melanogaster to numerous pesticides. While in vivo and in vitro studies have provided insight to the diverse functions of this enzyme, direct studies on the isolated CYP6G1 enzyme have not been possible due to the need for a source of recombinant enzyme. In the current study, the Cyp6g1 gene was isolated from D. melanogaster and re-engineered for heterologous expression in Escherichia coli. Approximately 460 nmol L⁻¹ of P450 holoenzyme were obtained in 500 mL cultures. The recombinant enzyme was located predominantly within the bacterial cytosol. A two-step purification protocol using Ni-chelate affinity chromatography followed by removal of detergent on a hydroxyapatite column produced essentially homogenous enzyme from both soluble and membrane fractions. Recombinant CYP6G1 exhibited p-nitroanisole O-dealkylation activity but was not active against eleven other typical P450 marker substrates. Substrate-induced binding spectra and IC₅₀ values for inhibition of p-nitroanisole O-dealkylation were obtained for a wide selection of pesticides, namely DDT, imidacloprid, chlorfenvinphos, malathion, endosulfan, dieldrin, dicyclanil, lufenuron and carbaryl, supporting previous in vivo and in vitro studies on Drosophila that have suggested that the enzyme is involved in multi-pesticide resistance in insects.

Intramolecular heme ligation of the cytochrome P450 2C9 R108H mutant demonstrates pronounced conformational flexibility of the B-C loop region: implications for substrate binding

A previous study [Dickmann, L., et al. (2004) Mol. Pharmacol. 65, 842-850] revealed some unusual properties of the R108H mutant of cytochrome P450 2C9 (CYP2C9), including elevated thermostability relative to that of CYP2C9, as well as a UV-visible absorbance spectrum that was indicative of nitrogenous ligation to the heme iron. In our study, size-exclusion chromatography and UV-visible absorbance spectroscopy of CYP2C9 R108H monomers demonstrated that nitrogen ligation is indeed intramolecular. Pulsed electron paramagnetic resonance of CYP2C9 R108H monomers showed that a histidine is most likely bound to the heme as previously hypothesized. An energy-minimized model of the R108H mutant maintained a CYP fold, despite substantial movement of several loop regions of the mutant, and, therefore, represents an extreme example of a closed conformation of the enzyme. Molecular dynamics (MD) simulations of CYP2C9 were performed to study the range of energetically accessible CYP2C9 conformations. These in silico studies showed that the B-C loop region of CYP2C9 moves away from the heme to a position resembling the putative open conformation described for rabbit CYP2B4. A model involving the movement of the B-C loop region and R108 between the open and closed conformations of CYP2C9 is presented, which helps to explain the enzyme's ability to regio- and stereospecifically metabolize some ligands while allosterically activating others.

The enzymatic basis for pesticide bioremediation

Enzymes are central to the biology of many pesticides, influencing their modes of action, environmental fates and mechanisms of target species resistance. Since the introduction of synthetic xenobiotic pesticides, enzymes responsible for pesticide turnover have evolved rapidly, in both the target organisms and incidentally exposed biota. Such enzymes are a source of significant biotechnological potential and form the basis of several bioremediation strategies intended to reduce the environmental impacts of pesticide residues. This review describes examples of enzymes possessing the major activities employed in the bioremediation of pesticide residues, and some of the strategies by which they are employed. In addition, several examples of specific achievements in enzyme engineering are considered, highlighting the growing trend in tailoring enzymatic activity to a specific biotechnologically relevant function.

Selective induction of intestinal CYP3A23 by 1alpha,25-dihydroxyvitamin D3 in rats

Enhancement of CYP3A transcription in both the small intestine and liver of the mouse by activation of a VDR signaling pathway was shown recently by Makishima et al. (Science, 2002). However, in humans and rats, hepatic VDR content is much lower than that found in small intestine, suggesting the possibility of tissue-selective responses to 1,25(OH)(2)D(3). The purpose of this study was to determine the effect of 1,25(OH)(2)D(3) on intestinal and hepatic CYP3A expression in the rat. We found that an acute intraperitoneal treatment (every 48 h) in adult male rats with 1,25(OH)(2)D(3) induced CYP3A transcription selectively in small intestine, but not in liver. At a dose of 100 ng, there was a 6.6-fold increase in intestinal CYP3A23 mRNA after the third treatment (p < 0.05). There were concordant effects of 1,25(OH)(2)D(3) treatment on intestinal CYP3A23 protein levels; 2.2-fold (p < 0.05), 3.5-fold (p < 0.05) and 4.8-fold (p < 0.01) increase following 1-3 doses of 100 ng 1,25(OH)(2)D(3), respectively. In contrast, there was no significant change of CYP3A23 protein content in liver at the 1,25(OH)(2)D(3) doses tested. In support of these findings, there was a 366-fold and 77-fold higher level of VDR mRNA expression in the respective rat and human jejunal mucosa, compared to the liver. These data suggest that the human liver will be less sensitive than the intestine to the transcriptional effects of 1,25(OH)(2)D(3) and that this regulatory pathway may contribute to inter-individual variability in constitutive intestinal CYP3A4 expression.

Sites of covalent attachment of CYP4 enzymes to heme: evidence for microheterogeneity of P450 heme orientation

Typical cytochrome P450s secure the heme prosthetic group with a cysteine thiolate ligand bound to the iron, electrostatic interactions with the heme propionate carboxylates, and hydrophobic interactions with the heme periphery. In addition to these interactions, CYP4B1 covalently binds heme through a monoester link furnished, in part, by a conserved I-helix acid, Glu310. Chromatography, mass spectrometry, and NMR have now been utilized to identify the site of attachment on the heme. Native CYP4B1 covalently binds heme solely at the C-5 methyl position. Unexpectedly, recombinant CYP4B1 from insect cells and Escherichia coli also bound their heme covalently at the C-8 methyl position. Structural heterogeneity may be common among recombinant CYP4 proteins because CYP4A3 exhibited this duality. Attempts to evaluate functional heterogeneity were complicated by the complexity of the system. The phenomenon of covalent heme binding to P450 provides a novel method for assessing microheterogeneity in heme orientation and raises questions about the fidelity of heme incorporation in recombinant systems.

Critical role of histidine residues in cyclohexanone monooxygenase expression, cofactor binding and catalysis

Cyclohexanone monooxygenase (CMO) is a member of the flavin monooxygenase superfamily of enzymes that catalyze both nucleophilic and electrophilic reactions involving a common C4a hydroperoxide intermediate. To begin to probe structure-function relationships for these enzymes, we investigated the roles of histidine residues in CMO derived from Acinetobacter NCIB 9871, with particular emphasis on the wholly conserved residue, His163 (H163). CMO activity was readily inactivated by diethyl pyrocarbonate (DEPC), a selective chemical modifier of histidine residues. Each of the seven histidines in CMO was then individually mutated to glutamine and the mutants expressed and purified from Escherichia coli. Only the H59Q mutant failed to express at significant levels. The H96Q enzyme was found to have a greatly reduced flavin adenine dinucleotide (FAD) content, indicative of compromised cofactor retention. The only significant effect on kcat occurred with the H163Q mutant, which exhibited an approximately 10-fold lower turnover of the prototypical substrate, cyclohexanone. This was accompanied by a doubling in the Km [NADPH] compared to the wild-type enzyme, suggesting that the functional decrement in H163Q is probably not solely a reflection of impaired NADPH binding. These data establish a critical role for H163 in CMO catalysis and prompt the hypothesis that this conserved residue plays a similarly important functional role across the flavin monooxygenase family of enzymes.

Rabbit CYP4B1 engineered for high-level expression in Escherichia coli: ligand stabilization and processing of the N-terminus and heme prosthetic group

Modifications at the N-terminus of the rabbit CYP4B1 gene resulted in expression levels in Escherichia coli of up to 660 nmol/L. Solubilization of the enzyme from bacterial membranes led to substantial conversion to cytochrome P420 unless alpha-naphthoflavone was added as a stabilizing ligand. Mass spectrometry analysis and Edman sequencing of purified enzyme preparations revealed differential N-terminal post-translational processing of the various constructs expressed. Notably, bacterial expression of CYP4B1 produced a holoenzyme with >98.5% of its heme prosthetic group covalently linked to the protein backbone. The near fully covalently linked hemoproteins exhibited similar rates and regioselectivities of lauric acid hydroxylation to that observed previously for the partially heme processed enzyme expressed in insect cells. These studies shed new light on the consequences of covalent heme processing in CYP4B1 and provide a facile system for future mechanistic and structural studies with the enzyme.

ESI- and MALDI-MS Analysis of Cyclohexanone Monooxygenase from Acinetobacter NCIB 9871

Recombinant and native forms of cyclohexanone monooxygenase (CMO) from Acinetobacter NCIB 9871 were analyzed by mass spectrometry to probe ambiguities arising from the presence of multiple DNA sequences for the enzyme in GenBank. A CMO gene corresponding exactly to the nucleotide sequence described by Iwaki et al. (10) was amplified from genomic DNA, cloned into pET15b, and the recombinant protein purified from a bacterial expression system. Electrospray mass spectrometry of both the recombinant material and the native form of CMO isolated from Acinetobacter yielded molecular weights within 0.01% of those predicted from the translated gene sequence of Iwaki et al. (10). Trypsin and chymotrypsin digests of native CMO, analyzed by electrospray and MALDI mass spectrometry, provided greater than 97% coverage of the protein and confirmed the presence of specific peptide sequences predicted by the Iwaki sequence alone. Therefore, the primary sequence of native Acinetobacter CMO is identical to the gene sequence for chnB deposited under accession number AB006902.

Purification and characterization of hexahistidine-tagged cyclohexanone monooxygenase expressed in Saccharomyces cerevisiae and Escherichia coli

Cyclohexanone monooxygenase (CMO) is a soluble flavoenzyme originally isolated from Acinetobacter spp. which carries out Baeyer-Villiger reactions with cyclic ketone substrates. In the present study we cloned the Acinetobacter CMO gene and modified it for facile purification from heterologous expression systems by incorporation of a His(6)-tag at its C-terminus. A single purification step employing metal (Ni(2+))-affinity column chromatography provided essentially homogeneous enzyme in yields of 69-72%. The properties of the purified, recombinant enzymes (rCMO) were compared with that of native CMO (nCMO) isolated from Acinetobacter cultures grown in the presence of cyclohexanone. The specific activities of His(6)-tagged rCMO and nCMO toward their index substrate, cyclohexanone, were similar and ranged from 14 to 20 micromol/min/mg. nCMO and rCMO from the Escherichia coli expression system exhibited molecular masses, determined by electrospray mass spectrometry, of 60,800 and 61,615 Da, respectively, an increase for the recombinant enzyme equivalent to the mass of the His(6)-tag. However, rCMO expressed in Saccharomyces cerevisiae consistently exhibited a mass some 50 Da larger than rCMO expressed in bacteria. Edman degradation confirmed that rCMO purified from the E. coli system and nCMO shared the same N-terminal sequence, whereas no sequence information could be obtained for rCMO expressed in yeast. Therefore, the yeast-expressed enzyme possesses an additional posttranslational modification(s), possibly acylation, at the N-terminus. Expression in E. coli is the preferred system for future site-directed mutagenesis studies and crystallization efforts.

Differential inducibility of specific mRNA corresponding to five CYP3A isoforms in female rat liver by RU486 and food deprivation: comparison with protein abundance and enzymic activities

The induction of cytochrome P450 3A (CYP3A) protein and mRNA by RU486 [17beta-hydroxy-11beta-(4-dimethylaminophenyl)-17alpha-1-pro pyl-estra-4,9-dien-3-one] treatment and food deprivation in female rat liver was studied using Western blotting and competitive reverse transcription-polymerase chain reaction (RT-PCR). CYP3A apoprotein levels increased in response to food deprivation and to RU486 treatment, and the combination of RU486 treatment plus food deprivation had an apparent additive effect. Food deprivation and RU486 treatment also caused increases in CYP3A1, CYP3A18, and CYP3A23 mRNA, and the combined effects of these treatments on each of these mRNA forms were synergistic. CYP3A2 mRNA was not detected in any of the treatment groups, and there was a lack of concordance between CYP3A9 mRNA levels and the specific messages corresponding to the other CYP3A isoforms. CYP3A9 mRNA levels were highest in food-deprived animals, whereas RU486 inhibited CYP3A9 mRNA expression and suppressed the induction effect of food deprivation. Food deprivation and RU486 treatment each separately caused increased microsomal diazepam C3-hydroxylase activity, and the combined effects of these treatments on this monooxygenase were additive. In contrast, the [N-methyl-14C]erythromycin demethylase activity of the fasted, RU486-treated group of rats did not differ from that of the untreated group, and kinetic analyses revealed that both groups of animals exhibited similar Km and Vmax values. These results suggest that CYP3A9 may be primarily responsible for erythromycin N-demethylation and that the isoforms induced by the combination of fasting and RU486 administration are CYP3A1, CYP3A23, and, to a lesser extent, CYP3A18.

Effects of food deprivation and adrenalectomy on CYP3A induction by RU486 in female rats

We have studied the effects of food deprivation and adrenalectomy on the induction by RU486 of female rat liver microsomal CYP3A apoprotein, erythromycin N-demethylase and diazepam C3-hydroxylase activities. RU486 was a potent inducer of CYP3A apoprotein in intact animals and food deprivation enhanced this response. Food deprivation alone caused only weak CYP3A apoprotein induction suggesting a synergistic interaction in the regulation of protein expression. These results were reflected in the measurements of diazepam C3-hydroxylase activity. This confirms diazepam C3-hydroxylase as a useful and easily measured index of CYP3A monooxygenase content in female rat liver microsomes. Erythromycin N-demethylase did not show concordance with this pattern; this monooxygenase was much more strongly induced by food deprivation alone than by RU486 administration and, in addition, adrenalectomy abolished the induction response to food deprivation. The lack of correspondence between the apoprotein and erythromycin N-demethylase results suggests that non-CYP3A or novel, hitherto uncharacterized CYP3A isoforms may contribute to erythromycin N-demethylation in female rats. The close agreement between the results for CYP3A apoprotein and diazepam C3-hydroxylase indicates that although RU486 possesses a terminal acetylenic moeity it does not, at the dosages used here, cause mechanism-based inactivation of the CYP3A monooxygenase protein it induces. Current studies are directed to characterizing the particular CYP3A isoform(s) whose production is stimulated by RU486.