Structural analysis of cytochrome P450 105N1 involved in the biosynthesis of the zincophore, coelibactin

Structural determination and characterisation of the CYP105Q4 cytochrome P450 enzyme from Mycobacterium marinum

The cytochrome P450 family of heme metalloenzymes (CYPs) catalyse important biological monooxygenation reactions. Mycobacterium marinum contains a gene encoding a CYP105Q4 enzyme of unknown function. Other members of the CYP105 CYP family have key roles in bacterial metabolism including the synthesis of secondary metabolites. We produced and purified the cytochrome P450 enzyme CYP105Q4 to enable its characterization. Several nitrogen-donor atom-containing ligands were found to bind to CYP105Q4 generating type II changes in the UV-vis absorbance spectrum. Based on the UV-vis absorbance spectra none of the potential substrate ligands we tested with CYP105Q4 were able to displace the sixth distal aqua ligand from the heme, though there was evidence for binding of oleic acid and amphotericin B. The crystal structure of CYP105Q4 in the substrate-free form was determined in an open conformation. A computational structural similarity search (Dali) was used to find the most closely related characterized relatives within the CYP105 family. The structure of CYP105Q4 enzyme was compared to the GfsF CYP enzyme from Streptomyces graminofaciens which is involved in the biosynthesis of a macrolide polyketide. This structural comparison to GfsF revealed conformational changes in the helices and loops near the entrance to the substrate access channel. A disordered B/C loop region, usually involved in substrate recognition, was also observed.

Biocatalytic role of cytochrome P450s to produce antibiotics: A review

Cytochrome P450s belong to a family of heme-binding monooxygenases, which catalyze regio- and stereospecific functionalisation of C-H, C-C, and C-N bonds, including heteroatom oxidation, oxidative C-C bond cleavages, and nitrene transfer. P450s are considered useful biocatalysts for the production of pharmaceutical products, fine chemicals, and bioremediating agents. Despite having tremendous biotechnological potential, being heme-monooxygenases, P450s require either autologous or heterologous redox partner(s) to perform chemical transformations. Randomly distributed P450s throughout a bacterial genome and devoid of particular redox partners in natural products biosynthetic gene clusters (BGCs) showed an extra challenge to reveal their pharmaceutical potential. However, continuous efforts have been made to understand their involvement in antibiotic biosynthesis and their modification, and this review focused on such BGCs. Here, particularly, we have discussed the role of P450s involved in the production of macrolides and aminocoumarin antibiotics, nonribosomal peptide (NRPSs) antibiotics, ribosomally synthesized and post-translationally modified peptide (RiPPs) antibiotics, and others. Several reactions catalyzed by P450s, as well as the role of their redox partners involved in the BGCs of various antibiotics and their derivatives, have been primarily addressed in this review, which would be useful in further exploration of P450s for the biosynthesis of new therapeutics.

Discovery and Biosynthesis of Anthrochelin, a Growth-Promoting Metallophore of the Human Pathogen Luteibacter anthropi

Various human pathogens have emerged from environmental strains by adapting to higher growth temperatures and the ability to produce virulence factors. A remarkable example of a pathoadapted bacterium is found in the genus Luteibacter, which typically comprises harmless soil microbes, yet Luteibacter anthropi was isolated from the blood of a diseased child. Up until now, nothing has been known about the specialized metabolism of this pathogen. By comparative genome analyses we found that L. anthropi has a markedly higher biosynthetic potential than other bacteria of this genus and uniquely bears an NRPS gene locus tentatively coding for the biosynthesis of a metallophore. By metabolic profiling, stable isotope labeling, and NMR investigation of a gallium complex, we identified a new family of salicylate-derived nonribosomal peptides named anthrochelins A-D. Surprisingly, anthrochelins feature a C-terminal homocysteine tag, which might be introduced during peptide termination. Mutational analyses provided insight into the anthrochelin assembly and revealed the unexpected involvement of a cytochrome P450 monooxygenase in oxazole formation. Notably, this heterocycle plays a key role in the binding of metals, especially copper(II). Bioassays showed that anthrochelin significantly promotes the growth of L. anthropi in the presence of low and high copper concentrations, which occur during infections.

Genome features and secondary metabolite potential of the marine symbiont Streptomyces sp. RS2

Streptomyces sp. RS2 was isolated from an unidentified sponge collected around Randayan Island, Indonesia. The genome of Streptomyces sp. RS2 consists of a linear chromosome of 9,391,717 base pairs with 71.9% of G + C content, 8270 protein-coding genes, as well as 18 rRNA and 85 tRNA loci. Twenty-eight putative secondary metabolites biosynthetic gene clusters (BGCs) were identified in the genome sequence. Nine of them have 100% similarity to BGCs for albaflavenone, α-lipomycin, coelibactin, coelichelin, ectoine, geosmin, germicidin, hopene, and lanthionine (SapB). The remaining 19 BGCs have low (< 50%) or moderate (50-80%) similarity to other known secondary metabolite BGCs. Biological activity assays of extracts from 21 different cultures of the RS2 strain showed that SCB ASW was the best medium for the production of antimicrobial and cytotoxic compounds. Streptomyces sp. RS2 has great potential to be a producer of novel secondary metabolites, particularly those with antimicrobial and antitumor activities.

Genome-Based Analysis of the Potential Bioactivity of the Terrestrial Streptomyces vinaceusdrappus Strain AC-40

Streptomyces are factories of antimicrobial secondary metabolites. We isolated a Streptomyces species associated with the Pelargonium graveolens rhizosphere. Its total metabolic extract exhibited potent antibacterial and antifungal properties against all the tested pathogenic microbes. Whole genome sequencing and genome analyses were performed to take a look at its main characteristics and to reconstruct the metabolic pathways that can be associated with biotechnologically useful traits. AntiSMASH was used to identify the secondary metabolite gene clusters. In addition, we searched for known genes associated with plant growth-promoting characteristics. Finally, a comparative and pan-genome analysis with three closely related genomes was conducted. It was identified as Streptomyces vinaceusdrappus strain AC-40. Genome mining indicated the presence of several secondary metabolite gene clusters. Some of them are identical or homologs to gene clusters of known metabolites with antimicrobial, antioxidant, and other bioactivities. It also showed the presence of several genes related to plant growth promotion traits. The comparative genome analysis indicated that at least five of these gene clusters are highly conserved through rochei group genomes. The genotypic and phenotypic characteristics of S. vinaceusdrappus strain AC-40 indicate that it is a promising source of beneficial secondary metabolites with pharmaceutical and biotechnological applications.

Bioactivity of bacteria associated with Red Sea nudibranchs and whole genome sequence of Nocardiopsis dassonvillei RACA-4

Microorganisms associated with marine invertebrates consider an important source of bioactive products. This study aimed to screen for antimicrobial and anticancer activity of crude extracts of bacteria associated with Red sea nudibranchs and molecular identification of the bioactive isolates using 16Sr RNA sequencing, in addition to whole-genome sequencing of one of the most bioactive bacteria. This study showed that bacteria associated with Red sea nudibranchs are highly bioactive and 16Sr RNA sequencing results showed that two isolates belonged to Firmicutes, and two isolates belonged to Proteobacteria, and Actinobacteria. The whole genome sequence data of the isolated Nocardiopsis RACA4 isolate has an estimated genome length of 6,721,839 bp and the taxonomy showed it belongs to the bacteria Nocardiopsis dassonvillei. The De novo assembly of RACA-4 paired reads using Unicycler v0.4.8 initially yielded 97 contigs with an N50 value of 214,568 bp and L50 value of 10, The resulting assembly was further mapped to the reference genome Nocardiopsis dassonvillei strain NCTC10488 using RagTag software v.2.1.0 and a final genome assembly resulted in 39 contigs and N50 value of 6,726,007 and L50 of 1. Genome mining using anti-smash showed around 9.1% of the genome occupied with genes related to secondary metabolites biosynthesis. A wide variety of secondary metabolites belonging to Polyketides, Terpenes, and nonribosomal peptides were predicted with high degree of similarity to known compounds. Non-characterized clusters were also found which suggest new natural compounds discovered by further studies.

Metabolomics and Genomics Enable the Discovery of a New Class of Nonribosomal Peptidic Metallophores from a Marine Micromonospora

Although microbial genomes harbor an abundance of biosynthetic gene clusters, there remain substantial technological gaps that impair the direct correlation of newly discovered gene clusters and their corresponding secondary metabolite products. As an example of one approach designed to minimize or bridge such gaps, we employed hierarchical clustering analysis and principal component analysis (hcapca, whose sole input is MS data) to prioritize 109 marine Micromonospora strains and ultimately identify novel strain WMMB482 as a candidate for in-depth "metabologenomics" analysis following its prioritization. Highlighting the power of current MS-based technologies, not only did hcapca enable the discovery of one new, nonribosomal peptide bearing an incredible diversity of unique functional groups, but metabolomics for WMMB482 unveiled 16 additional congeners via the application of Global Natural Product Social molecular networking (GNPS), herein named ecteinamines A-Q (1-17). The ecteinamines possess an unprecedented skeleton housing a host of uncommon functionalities including a menaquinone pathway-derived 2-naphthoate moiety, 4-methyloxazoline, the first example of a naturally occurring Ψ[CH2NH] "reduced amide", a methylsulfinyl moiety, and a d-cysteinyl residue that appears to derive from a unique noncanonical epimerase domain. Extensive in silico analysis of the ecteinamine (ect) biosynthetic gene cluster and stable isotope-feeding experiments helped illuminate the novel enzymology driving ecteinamine assembly as well the role of cluster collaborations or "duets" in producing such structurally complex agents. Finally, ecteinamines were found to bind nickel, cobalt, zinc, and copper, suggesting a possible biological role as broad-spectrum metallophores.

Nutritional immunity: the battle for nutrient metals at the host-pathogen interface

Trace metals are essential micronutrients required for survival across all kingdoms of life. From bacteria to animals, metals have critical roles as both structural and catalytic cofactors for an estimated third of the proteome, representing a major contributor to the maintenance of cellular homeostasis. The reactivity of metal ions engenders them with the ability to promote enzyme catalysis and stabilize reaction intermediates. However, these properties render metals toxic at high concentrations and, therefore, metal levels must be tightly regulated. Having evolved in close association with bacteria, vertebrate hosts have developed numerous strategies of metal limitation and intoxication that prevent bacterial proliferation, a process termed nutritional immunity. In turn, bacterial pathogens have evolved adaptive mechanisms to survive in conditions of metal depletion or excess. In this Review, we discuss mechanisms by which nutrient metals shape the interactions between bacterial pathogens and animal hosts. We explore the cell-specific and tissue-specific roles of distinct trace metals in shaping bacterial infections, as well as implications for future research and new therapeutic development.

Complete Genome Analysis of Undecylprodigiosin Pigment Biosynthesizing Marine Streptomyces Species Displaying Potential Bioactive Applications

Marine Streptomyces species are underexplored for their pigment molecules and genes. In this study, we report the genome of the undecylprodigiosin biosynthesizing gene cluster carrying Streptomyces sp. strain BSE6.1, displaying antioxidant, antimicrobial, and staining properties. This Gram-positive obligate aerobic bacterium was isolated from the coastal sediment of the Andaman and Nicobar Islands, India. Pink to reddish pigmented colonies with whitish powdery spores on both agar and broth media are the important morphological characteristics of this bacterium. Growth tolerance to NaCl concentrations was 2 to 7%. The assembled genome of Streptomyces sp. BSE6.1 contains one linear chromosome 8.02 Mb in length with 7157 protein-coding genes, 82 tRNAs, 3 rRNAs and at least 11 gene clusters related to the synthesis of various secondary metabolites, including undecylprodigiosin. This strain carries type I, type II, and type III polyketide synthases (PKS) genes. Type I PKS gene cluster is involved in the biosynthesis of red pigment undecylprodigiosin of BSE6.1, similar to the one found in the S. coelicolor A3(2). This red pigment was reported to have various applications in the food and pharmaceutical industries. The genome of Streptomyces sp. BSE6.1 was submitted to NCBI with a BioProject ID of PRJNA514840 (Sequence Read Archive ID: SRR10849367 and Genome accession ID: CP085300).

Draft Genome Sequence of Marine Actinobacterium Streptomyces spinoverrucosus SNB-032

Actinobacteria represent a large source of diverse bioactive compounds of medical and economic importance. Here, we report the 8.8-Mb draft genome of the marine bacterium Streptomyces spinoverrucosus SNB-032. Bioinformatic sequence analysis proved similarities to known Streptomyces strains and revealed the capacity for the production of various secondary metabolites.

Actinobacteria represent a large source of diverse bioactive compounds of medical and economic importance. Here, we report the 8.8-Mb draft genome of the marine bacterium Streptomyces spinoverrucosus SNB-032. Bioinformatic sequence analysis proved similarities to known Streptomyces strains and revealed the capacity for the production of various secondary metabolites.

Extensive Reannotation of the Genome of the Model Streptomycete Streptomyces lividans TK24 Based on Transcriptome and Proteome Information

Streptomyces lividans TK24 is a relevant Gram-positive soil inhabiting bacterium and one of the model organisms of the genus Streptomyces. It is known for its potential to produce secondary metabolites, antibiotics, and other industrially relevant products. S. lividans TK24 is the plasmid-free derivative of S. lividans 66 and a close genetic relative of the strain Streptomyces coelicolor A3(2). In this study, we used transcriptome and proteome data to improve the annotation of the S. lividans TK24 genome. The RNA-seq data of primary 5'-ends of transcripts were used to determine transcription start sites (TSS) in the genome. We identified 5,424 TSS, of which 4,664 were assigned to annotated CDS and ncRNAs, 687 to antisense transcripts distributed between 606 CDS and their UTRs, 67 to tRNAs, and 108 to novel transcripts and CDS. Using the TSS data, the promoter regions and their motifs were analyzed in detail, revealing a conserved -10 (TAnnnT) and a weakly conserved -35 region (nTGACn). The analysis of the 5' untranslated region (UTRs) of S. lividans TK24 revealed 17% leaderless transcripts. Several cis-regulatory elements, like riboswitches or attenuator structures could be detected in the 5'-UTRs. The S. lividans TK24 transcriptome contains at least 929 operons. The genome harbors 27 secondary metabolite gene clusters of which 26 could be shown to be transcribed under at least one of the applied conditions. Comparison of the reannotated genome with that of the strain Streptomyces coelicolor A3(2) revealed a high degree of similarity. This study presents an extensive reannotation of the S. lividans TK24 genome based on transcriptome and proteome analyses. The analysis of TSS data revealed insights into the promoter structure, 5'-UTRs, cis-regulatory elements, attenuator structures and novel transcripts, like small RNAs. Finally, the repertoire of secondary metabolite gene clusters was examined. These data provide a basis for future studies regarding gene characterization, transcriptional regulatory networks, and usage as a secondary metabolite producing strain.

Zur: Zinc-Sensing Transcriptional Regulator in a Diverse Set of Bacterial Species

Zinc (Zn) is the quintessential d block metal, needed for survival in all living organisms. While Zn is an essential element, its excess is deleterious, therefore, maintenance of its intracellular concentrations is needed for survival. The living organisms, during the course of evolution, developed proteins that can track the limitation or excess of necessary metal ions, thus providing survival benefits under variable environmental conditions. Zinc uptake regulator (Zur) is a regulatory transcriptional factor of the FUR superfamily of proteins, abundant among the bacterial species and known for its intracellular Zn sensing ability. In this study, we highlight the roles played by Zur in maintaining the Zn levels in various bacterial species as well as the fact that in recent years Zur has emerged not only as a Zn homeostatic regulator but also as a protein involved directly or indirectly in virulence of some pathogens. This functional aspect of Zur could be exploited in the ventures for the identification of newer antimicrobial targets. Despite extensive research on Zur, the insights into its overall regulon and its moonlighting functions in various pathogens yet remain to be explored. Here in this review, we aim to summarise the disparate functional aspects of Zur proteins present in various bacterial species.

More P450s Are Involved in Secondary Metabolite Biosynthesis in Streptomyces Compared to Bacillus, Cyanobacteria, and Mycobacterium

Unraveling the role of cytochrome P450 monooxygenases (CYPs/P450s), heme-thiolate proteins present in living and non-living entities, in secondary metabolite synthesis is gaining momentum. In this direction, in this study, we analyzed the genomes of 203 Streptomyces species for P450s and unraveled their association with secondary metabolism. Our analyses revealed the presence of 5460 P450s, grouped into 253 families and 698 subfamilies. The CYP107 family was found to be conserved and highly populated in Streptomyces and Bacillus species, indicating its key role in the synthesis of secondary metabolites. Streptomyces species had a higher number of P450s than Bacillus and cyanobacterial species. The average number of secondary metabolite biosynthetic gene clusters (BGCs) and the number of P450s located in BGCs were higher in Streptomyces species than in Bacillus, mycobacterial, and cyanobacterial species, corroborating the superior capacity of Streptomyces species for generating diverse secondary metabolites. Functional analysis via data mining confirmed that many Streptomyces P450s are involved in the biosynthesis of secondary metabolites. This study was the first of its kind to conduct a comparative analysis of P450s in such a large number (203) of Streptomyces species, revealing the P450s’ association with secondary metabolite synthesis in Streptomyces species. Future studies should include the selection of Streptomyces species with a higher number of P450s and BGCs and explore the biotechnological value of secondary metabolites they produce.

Genome Mining Revealed a High Biosynthetic Potential for Antifungal Streptomyces sp. S-2 Isolated from Black Soot

The increasing resistance of fungal pathogens has heightened the necessity of searching for new organisms and compounds to combat their spread. Streptomyces are bacteria that are well-known for the production of many antibiotics. To find novel antibiotic agents, researchers have turned to previously neglected and extreme environments. Here, we isolated a new strain, Streptomyces sp. S-2, for the first time, from black soot after hard coal combustion (collected from an in-use household chimney). We examined its antifungal properties against plant pathogens and against fungi that potentially pose threat to human health (Fusarium avenaceum, Aspergillus niger and the environmental isolates Trichoderma citrinoviridae Cin-9, Nigrospora oryzae sp. roseF7, and Curvularia coatesieae sp. junF9). Furthermore, we obtained the genome sequence of S-2 and examined its potential for secondary metabolites production using anti-SMASH software. The S-2 strain shows activity against all of the tested fungi. Genome mining elucidated a vast number of biosynthetic gene clusters (55), which distinguish this strain from closely related strains. The majority of the predicted clusters were assigned to non-ribosomal peptide synthetases or type 1 polyketide synthetases, groups known to produce compounds with antimicrobial activity. A high number of the gene clusters showed no, or low similarity to those in the database, raising the possibility that S-2 could be a producer of novel antibiotics. Future studies on Streptomyces sp. S-2 will elucidate its full biotechnological potential.

Metabolomic tools used in marine natural product drug discovery

Introduction: The marine environment is a very promising resource for natural product research, with many of these reaching the market as new drugs, especially in the field of cancer therapy as well as the drug discovery pipeline for new antimicrobials. Exploitation for bioactive marine compounds with unique structures and novel bioactivity such as the isoquinoline alkaloid; trabectedin, the polyether macrolide; halichondrin B, and the peptide; dolastatin 10, requires the use of analytical techniques, which can generate unbiased, quantitative, and qualitative data to benefit the biodiscovery process. Metabolomics has shown to bridge this understanding and facilitate the development of new potential drugs from marine sources and particularly their microbial symbionts.Areas covered: In this review, articles on applied secondary metabolomics ranging from 1990-2018 as well as to the last quarter of 2019 were probed to investigate the impact of metabolomics on drug discovery for new antibiotics and cancer treatment.Expert opinion: The current literature review highlighted the effectiveness of metabolomics in the study of targeting biologically active secondary metabolites from marine sources for optimized discovery of potential new natural products to be made accessible to a R&D pipeline.

Isolation, Genomic and Metabolomic Characterization of Streptomyces tendae VITAKN with Quorum Sensing Inhibitory Activity from Southern India

Streptomyces are among the most promising genera in terms of production ability to biosynthesize a variety of bioactive secondary metabolites with pharmaceutical interest. Coinciding with the increase in genomic sequencing of these bacteria, mining of their genomes for biosynthetic gene clusters (BGCs) has become a routine component of natural product discovery. Herein, we describe the isolation and characterization of a Streptomyces tendae VITAKN with quorum sensing inhibitory (QSI) activity that was isolated from southern coastal part of India. The nearly complete genome consists of 8,621,231bp with a GC content of 72.2%. Sequence similarity networks of the BGCs detected from this strain against the Minimum Information about a Biosynthetic Gene Cluster (MIBiG) database and 3365 BGCs predicted by antiSMASH analysis of publicly available complete Streptomyces genomes were generated through the BiG-SCAPE-CORASON platform to evaluate its biosynthetic novelty. Crude extract analysis using high-performance liquid chromatography connected to high resolution tandem mass spectrometry (HPLC-HRMS/MS) and dereplication through the Global Natural Product Social Molecular Networking (GNPS) online workflow resulted in the identification of cyclic dipeptides (2, 5-diketopiperazines, DKPs) in the extract, which are known to possess QSI activity. Our results highlight the potential of genome mining coupled with LC-HRMS/MS and in silico tools (GNPS) as a valid approach for the discovery of novel QSI lead compounds. This study also provides the biosynthetic diversity of BGCs and an assessment of the predicted chemical space yet to be discovered.

Metal binding ability of microbial natural metal chelators and potential applications

Metallophores can chelate many different metal and metalloid ions next to iron, make them valuable for many applications.

Nutrient Zinc at the Host-Pathogen Interface

Zinc is an essential cofactor required for life and, as such, mechanisms exist for its homeostatic maintenance in biological systems. Despite the evolutionary distance between vertebrates and microbial life, there are parallel mechanisms to balance the essentiality of zinc with its inherent toxicity. Vertebrates regulate zinc homeostasis through a complex network of metal transporters and buffering systems that respond to changes in nutritional zinc availability or inflammation. Fine-tuning of this network becomes crucial during infections, where host nutritional immunity attempts to limit zinc availability to pathogens. However, accumulating evidence demonstrates that pathogens have evolved mechanisms to subvert host-mediated zinc withholding, and these metal homeostasis systems are important for survival within the host. We discuss here the mechanisms of vertebrate and bacterial zinc homeostasis and mobilization, as well as recent developments in our understanding of microbial zinc acquisition.

Streptomyces Cytochrome P450 Enzymes and Their Roles in the Biosynthesis of Macrolide Therapeutic Agents

The study of the genus Streptomyces is of particular interest because it produces a wide array of clinically important bioactive molecules. The genomic sequencing of many Streptomyces species has revealed unusually large numbers of cytochrome P450 genes, which are involved in the biosynthesis of secondary metabolites. Many macrolide biosynthetic pathways are catalyzed by a series of enzymes in gene clusters including polyketide and non-ribosomal peptide synthesis. In general, Streptomyces P450 enzymes accelerate the final, post-polyketide synthesis steps to enhance the structural architecture of macrolide chemistry. In this review, we discuss the major Streptomyces P450 enzymes research focused on the biosynthetic processing of macrolide therapeutic agents, with an emphasis on their biochemical mechanisms and structural insights.

Zinc transporters YbtX and ZnuABC are required for the virulence of Yersinia pestis in bubonic and pneumonic plague in mice

A number of bacterial pathogens require the ZnuABC Zinc (Zn²⁺) transporter and/or a second Zn²⁺ transport system to overcome Zn²⁺ sequestration by mammalian hosts. Previously we have shown that in addition to ZnuABC, Yersinia pestis possesses a second Zn²⁺ transporter that involves components of the yersiniabactin (Ybt), siderophore-dependent iron transport system. Synthesis of the Ybt siderophore and YbtX, a member of the major facilitator superfamily, are both critical components of the second Zn²⁺ transport system. Here we demonstrate that a ybtX znu double mutant is essentially avirulent in mouse models of bubonic and pneumonic plague while a ybtX mutant retains high virulence in both plague models. While sequestration of host Zn is a key nutritional immunity factor, excess Zn appears to have a significant antimicrobial role in controlling intracellular bacterial survival. Here, we demonstrate that ZntA, a Zn²⁺ exporter, plays a role in resistance to Zn toxicity in vitro, but that a zntA zur double mutant retains high virulence in both pneumonic and bubonic plague models and survival in macrophages. We also confirm that Ybt does not directly bind Zn²⁺in vitro under the conditions tested. However, we detect a significant increase in Zn²⁺-binding ability of filtered supernatants from a Ybt⁺ strain compared to those from a strain unable to produce the siderophore, supporting our previously published data that Ybt biosynthetic genes are involved in the production of a secreted Zn-binding molecule (zincophore). Our data suggest that Ybt or a modified Ybt participate in or promote Zn-binding activity in culture supernatants and is involved in Zn acquisition in Y. pestis.

Cytochromes P450 for natural product biosynthesis in Streptomyces: sequence, structure, and function

Covering: up to January 2017Cytochrome P450 enzymes (P450s) are some of the most exquisite and versatile biocatalysts found in nature. In addition to their well-known roles in steroid biosynthesis and drug metabolism in humans, P450s are key players in natural product biosynthetic pathways. Natural products, the most chemically and structurally diverse small molecules known, require an extensive collection of P450s to accept and functionalize their unique scaffolds. In this review, we survey the current catalytic landscape of P450s within the Streptomyces genus, one of the most prolific producers of natural products, and comprehensively summarize the functionally characterized P450s from Streptomyces. A sequence similarity network of >8500 P450s revealed insights into the sequence-function relationships of these oxygen-dependent metalloenzymes. Although only ∼2.4% and <0.4% of streptomycete P450s have been functionally and structurally characterized, respectively, the study of streptomycete P450s involved in the biosynthesis of natural products has revealed their diverse roles in nature, expanded their catalytic repertoire, created structural and mechanistic paradigms, and exposed their potential for biomedical and biotechnological applications. Continued study of these remarkable enzymes will undoubtedly expose their true complement of chemical and biological capabilities.

Crystal Structure of Cytochrome P450 (CYP105P2) from Streptomyces peucetius and Its Conformational Changes in Response to Substrate Binding

Cytochrome P450 monooxygenases (CYP, EC 1.14.14.1) belong to a large family of enzymes that catalyze the hydroxylation of various substrates. Here, we present the crystal structure of CYP105P2 isolated from Streptomyces peucetius ATCC27952 at a 2.1 Å resolution. The structure shows the presence of a pseudo-ligand molecule in the active site, which was co-purified fortuitously and is presumed to be a biphenyl derivative. Comparison with previously determined substrate-bound CYP structures showed that binding of the ligand produces large and distinctive conformational changes in α2-α3, α7-α9, and the C-terminal loop regions. This structural flexibility confirms our previous observation that CYP105P2 can accommodate a broad range of ligands. The structure complexed with a pseudo-ligand provides the first molecular view of CYP105P2-ligand interactions, and it indicates the involvement of hydrophobic residues (Pro82, Ala181, Met187, Leu189, Leu193, and Ile236) in the interactions between hydrophobic ligands and CYP105P2. These results provide useful insights into the structural changes involved in the recognition of different ligands by CYP105P2.

The role of transition metal transporters for iron, zinc, manganese, and copper in the pathogenesis of Yersinia pestis

Yersinia pestis, the causative agent of bubonic, septicemic and pneumonic plague, encodes a multitude of Fe transport systems. Some of these are defective due to frameshift or IS element insertions, while others are functional in vitro but have no established role in causing infections. Indeed only 3 Fe transporters (Ybt, Yfe and Feo) have been shown to be important in at least one form of plague. The yersiniabactin (Ybt) system is essential in the early dermal/lymphatic stages of bubonic plague, irrelevant in the septicemic stage, and critical in pneumonic plague. Two Mn transporters have been characterized (Yfe and MntH). These two systems play a role in bubonic plague but the double yfe mntH mutant is fully virulent in a mouse model of pneumonic plague. The same in vivo phenotype occurs with a mutant lacking two (Yfe and Feo) of four ferrous transporters. A role for the Ybt siderophore in Zn acquisition has been revealed. Ybt-dependent Zn acquisition uses a transport system completely independent of the Fe-Ybt uptake system. Together Ybt components and ZnuABC play a critical role in Zn acquisition in vivo. Single mutants in either system retain high virulence in a mouse model of septicemic plague while the double mutant is completely avirulent.

Beyond iron: non-classical biological functions of bacterial siderophores

Bacteria secrete small molecules known as siderophores to acquire iron from their surroundings. For over 60 years, investigations into the bioinorganic chemistry of these molecules, including fundamental coordination chemistry studies, have provided insight into the crucial role that siderophores play in bacterial iron homeostasis. The importance of understanding the fundamental chemistry underlying bacterial life has been highlighted evermore in recent years because of the emergence of antibiotic-resistant bacteria and the need to prevent the global rise of these superbugs. Increasing reports of siderophores functioning in capacities other than iron transport have appeared recently, but reports of "non-classical" siderophore functions have long paralleled those of iron transport. One particular non-classical function of these iron chelators, namely antibiotic activity, was documented before the role of siderophores in iron transport was established. In this Perspective, we present an exposition of past and current work into non-classical functions of siderophores and highlight the directions in which we anticipate that this research is headed. Examples include the ability of siderophores to function as zincophores, chalkophores, and metallophores for a variety of other metals, sequester heavy metal toxins, transport boron, act as signalling molecules, regulate oxidative stress, and provide antibacterial activity.

Functional characterization of CYP107W1 from Streptomyces avermitilis and biosynthesis of macrolide oligomycin A

Streptomyces avermitilis contains 33 cytochrome P450 genes in its genome, many of which play important roles in the biosynthesis process of antimicrobial agents. Here, we characterized the biochemical function and structure of CYP107W1 from S. avermitilis, which is responsible for the 12-hydroxylation reaction of oligomycin C. CYP107W1 was expressed and purified from Escherichia coli. Purified proteins exhibited the typical CO-binding spectrum of P450. Interaction of oligomycin C and oligomycin A (12-hydroxylated oligomycin C) with purified CYP107W1 resulted in a type I binding with Kd values of 14.4 ± 0.7 μM and 2.0 ± 0.1 μM, respectively. LC-mass spectrometry analysis showed that CYP107W1 produced oligomycin A by regioselectively hydroxylating C12 of oligomycin C. Steady-state kinetic analysis yielded a kcat value of 0.2 min(-1) and a Km value of 18 μM. The crystal structure of CYP107W1 was determined at 2.1 Å resolution. The overall P450 folding conformations are well conserved, and the open access binding pocket for the large macrolide oligomycin C was observed above the distal side of heme. This study of CYP107W1 can help a better understanding of clinically important P450 enzymes as well as their optimization and engineering for synthesizing novel antibacterial agents and other pharmaceutically important compounds.

CYP105-diverse structures, functions and roles in an intriguing family of enzymes in Streptomyces

The cytochromes P450 (CYP or P450) are a large superfamily of haem-containing enzymes found in all domains of life. They catalyse a variety of complex reactions, predominantly mixed-function oxidations, often displaying highly regio- and/or stereospecific chemistry. In streptomycetes, they are predominantly associated with secondary metabolite biosynthetic pathways or with xenobiotic catabolism. Homologues of one family, CYP105, have been found in all Streptomyces species thus far sequenced. This review looks at the diverse biological functions of CYP105s and the biosynthetic/catabolic pathways they are associated with. Examples are presented showing a range of biotransformative abilities and different contexts. As biocatalysts capable of some remarkable chemistry, CYP105s have great biotechnological potential and merit detailed study. Recent developments in biotechnological applications which utilize CYP105s are described, alongside a brief overview of the benefits and drawbacks of using P450s in commercial applications. The role of CYP105s in vivo is in many cases undefined and provides a rich source for further investigation into the functions these enzymes fulfil and the metabolic pathways they participate in, in the natural environment.

Metal limitation and toxicity at the interface between host and pathogen

Metals are required cofactors for numerous fundamental processes that are essential to both pathogen and host. They are coordinated in enzymes responsible for DNA replication and transcription, relief from oxidative stress, and cellular respiration. However, excess transition metals can be toxic due to their ability to cause spontaneous, redox cycling and disrupt normal metabolic processes. Vertebrates have evolved intricate mechanisms to limit the availability of some crucial metals while concurrently flooding sites of infection with antimicrobial concentrations of other metals. To compete for limited metal within the host while simultaneously preventing metal toxicity, pathogens have developed a series of metal regulatory, acquisition, and efflux systems. This review will cover the mechanisms by which pathogenic bacteria recognize and respond to host-induced metal scarcity and toxicity.

The Yersinia pestis siderophore, yersiniabactin, and the ZnuABC system both contribute to zinc acquisition and the development of lethal septicaemic plague in mice

Bacterial pathogens must overcome host sequestration of zinc (Zn(2+) ), an essential micronutrient, during the infectious disease process. While the mechanisms to acquire chelated Zn(2+) by bacteria are largely undefined, many pathogens rely upon the ZnuABC family of ABC transporters. Here we show that in Yersinia pestis, irp2, a gene encoding the synthetase (HMWP2) for the siderophore yersiniabactin (Ybt) is required for growth under Zn(2+) -deficient conditions in a strain lacking ZnuABC. Moreover, growth stimulation with exogenous, purified apo-Ybt provides evidence that Ybt may serve as a zincophore for Zn(2+) acquisition. Studies with the Zn(2+) -dependent transcriptional reporter znuA::lacZ indicate that the ability to synthesize Ybt affects the levels of intracellular Zn(2+) . However, the outer membrane receptor Psn and TonB as well as the inner membrane (IM) ABC transporter YbtPQ, which are required for Fe(3+) acquisition by Ybt, are not needed for Ybt-dependent Zn(2+) uptake. In contrast, the predicted IM protein YbtX, a member of the Major Facilitator Superfamily, was essential for Ybt-dependent Zn(2+) uptake. Finally, we show that the ZnuABC system and the Ybt synthetase HMWP2, presumably by Ybt synthesis, both contribute to the development of a lethal infection in a septicaemic plague mouse model.

Zinc'ing sensibly: controlling zinc homeostasis at the transcriptional level

Zinc-responsive transcription factors are found in all kingdoms of life and include the transcriptional activators ZntR, SczA, Zap1, bZip19, bZip23, and MTF-1, and transcriptional repressors Zur, AdcR, Loz1, and SmtB. These factors have two defining features; their activity is regulated by zinc and they all play a central role in zinc homeostasis by controlling the expression of genes that directly affect zinc levels or its availability. This review summarizes what is known about the mechanisms by which each of these factors sense changes in intracellular zinc levels and how they control zinc homeostasis through target gene regulation. Other factors that influence zinc ion sensing are also discussed.