Phylometagenomics of cycad coralloid roots reveals shared symbiotic signals

Cycads are known to host symbiotic cyanobacteria, including Nostocales species, as well as other sympatric bacterial taxa within their specialized coralloid roots. Yet, it is unknown if these bacteria share a phylogenetic origin and/or common genomic functions that allow them to engage in facultative symbiosis with cycad roots. To address this, we obtained metagenomic sequences from 39 coralloid roots sampled from diverse cycad species and origins in Australia and Mexico. Culture-independent shotgun metagenomic sequencing was used to validate sub-community co-cultures as an efficient approach for functional and taxonomic analysis. Our metanalysis shows a host-independent microbiome core consisting of seven bacterial orders with high species diversity within the identified taxa. Moreover, we recovered 43 cyanobacterial metagenome-assembled genomes, and in addition to Nostoc spp., symbiotic cyanobacteria of the genus Aulosira were identified for the first time. Using this robust dataset, we used phylometagenomic analysis to reveal three monophyletic cyanobiont clades, two host-generalist and one cycad-specific that includes Aulosira spp. Although the symbiotic clades have independently arisen, they are enriched in certain functional genes, such as those related to secondary metabolism. Furthermore, the taxonomic composition of associated sympatric bacterial taxa remained constant. Our research quadruples the number of cycad cyanobiont genomes and provides a robust framework to decipher cyanobacterial symbioses, with the potential of improving our understanding of symbiotic communities. This study lays a solid foundation to harness cyanobionts for agriculture and bioprospection, and assist in conservation of critically endangered cycads.

Highlights of biosynthetic enzymes and natural products from symbiotic cyanobacteria

Covering: up to 2023Cyanobacteria have long been known for their intriguing repertoire of natural product scaffolds, which are often distinct from other phyla. Cyanobacteria are ecologically significant organisms that form a myriad of different symbioses including with sponges and ascidians in the marine environment or with plants and fungi, in the form of lichens, in terrestrial environments. Whilst there have been several high-profile discoveries of symbiotic cyanobacterial natural products, genomic data is scarce and discovery efforts have remained limited. However, the rise of (meta-)genomic sequencing has improved these efforts, emphasized by a steep increase in publications in recent years. This highlight focuses on selected examples of symbiotic cyanobacterial-derived natural products and their biosyntheses to link chemistry with corresponding biosynthetic logic. Further highlighted are remaining gaps in knowledge for the formation of characteristic structural motifs. It is anticipated that the continued rise of (meta-)genomic next-generation sequencing of symbiontic cyanobacterial systems will lead to many exciting discoveries in the future.

Direct pathway cloning and expression of the radiosumin biosynthetic gene cluster

Radiosumins are a structurally diverse family of low molecular weight natural products that are produced by cyanobacteria and exhibit potent serine protease inhibition. Members of this family are dipeptides characterized by the presence of two similar non-proteinogenic amino acids. Here we used a comparative bioinformatic analysis to identify radiosumin biosynthetic gene clusters from the genomes of 13 filamentous cyanobacteria. We used direct pathway cloning to capture and express the entire 16.8 kb radiosumin biosynthetic gene cluster from Dolichospermum planctonicum UHCC 0167 in Escherichia coli. Bioinformatic analysis demonstrates that radiosumins represent a new group of chorismate-derived non-aromatic secondary metabolites. High-resolution liquid chromatography-mass spectrometry, nuclear magnetic resonance spectroscopy and chemical degradation analysis revealed that cyanobacteria produce a cocktail of novel radiosumins. We report the chemical structure of radiosumin D, an N-methyl dipeptide, containing a special Aayp (2-amino-3-(4-amino-2-cyclohexen-1-ylidene) propionic acid) with R configuration that differs from radiosumin A-C, an N-Me derivative of Aayp (Amyp) and two acetyl groups. Radiosumin C inhibits all three human trypsin isoforms at micromolar concentrations with preference for trypsin-1 and -3 (IC₅₀ values from 1.7 μM to >7.2 μM). These results provide a biosynthetic logic to explore the genetic and chemical diversity of the radiosumin family and suggest that these natural products may be a source of drug leads for selective human serine proteases inhibitors.

Streptomyces sp. BV410: Interspecies cross-talk for staurosporine production

AIMS

Sequencing and genome analysis of two co-isolated streptomycetes, named BV410-1 and BV410-10, and the effect of their co-cultivation on the staurosporine production.

METHODS AND RESULTS

Identification of two strains through genome sequencing and their separation using different growth media was conducted. Sequence analysis revealed that the genome of BV410-1 was 9.5 Mb, whilst that of BV410-10 was 7.1 Mb. AntiSMASH analysis identified 28 biosynthetic gene clusters (BGCs) from BV410-1, including that responsible for staurosporine biosynthesis, whilst 20 BGCs were identified from BV410-10. The addition of cell-free supernatant from BV410-10 monoculture to BV410-1 fermentations improved the staurosporine yield from 8.35 mg L^-1 up to 15.85 mg L^-1 , whilst BV410-10 monoculture ethyl acetate extract did not have the same effect. Also, there was no improvement in staurosporine production when artificial mixed cultures were created using three different BV410-1 and BV410-10 spore ratios.

CONCLUSIONS

The growth of BV410-10 was inhibited when the two strains were grown together on agar plates. Culture supernatants of BV410-10 showed potential to stimulate staurosporine production in BV410-1, but overall co-cultivation attempts did not restore the previously reported yield of staurosporine produced by the original mixed isolate.

SIGNIFICANCE AND IMPACT OF STUDY

This work confirmed complex relations between streptomycetes in soil that are difficult to recreate under the laboratory conditions. Also, mining of streptomycetes genomes that mainly produce known bioactive compounds could still be the fruitful approach in search for novel bioactive molecules.

Recent developments in quantitative PCR for monitoring harmful marine microalgae

Marine microalgae produce a variety of specialised metabolites that have toxic effects on humans, farmed fish, and marine wildlife. Alarmingly, many of these compounds bioaccumulate in the tissues of shellfish and higher trophic organisms, including species consumed by humans. Molecular methods are emerging as a potential alternative and complement to the conventional microscopic diagnosis of toxic or otherwise harmful microalgal species. Quantitative PCR (qPCR) in particular, has gained popularity over the past decade as a sensitive, rapid, and cost-effective method for monitoring harmful microalgae. Assays targeting taxonomic marker genes provide the opportunity to identify and quantify (or semi-quantify) microalgal species and importantly to pre-empt bloom events. Moreover, the discovery of paralytic shellfish toxin biosynthesis genes in dinoflagellates has enabled researchers to directly monitor toxigenic species in coastal waters and fisheries. This review summarises the recent developments in qPCR detection methods for harmful microalgae, with emphasis on emerging toxin gene monitoring technologies.

A collection of bacterial isolates from the pig intestine reveals functional and taxonomic diversity

Our knowledge about the gut microbiota of pigs is still scarce, despite the importance of these animals for biomedical research and agriculture. Here, we present a collection of cultured bacteria from the pig gut, including 110 species across 40 families and nine phyla. We provide taxonomic descriptions for 22 novel species and 16 genera. Meta-analysis of 16S rRNA amplicon sequence data and metagenome-assembled genomes reveal prevalent and pig-specific species within Lactobacillus, Streptococcus, Clostridium, Desulfovibrio, Enterococcus, Fusobacterium, and several new genera described in this study. Potentially interesting functions discovered in these organisms include a fucosyltransferase encoded in the genome of the novel species Clostridium porci, and prevalent gene clusters for biosynthesis of sactipeptide-like peptides. Many strains deconjugate primary bile acids in in vitro assays, and a Clostridium scindens strain produces secondary bile acids via dehydroxylation. In addition, cells of the novel species Bullifex porci are coccoidal or spherical under the culture conditions tested, in contrast with the usual helical shape of other members of the family Spirochaetaceae. The strain collection, called ‘Pig intestinal bacterial collection’ (PiBAC), is publicly available at www.dsmz.de/pibac and opens new avenues for functional studies of the pig gut microbiota.

The authors present a public collection of 117 bacterial isolates from the pig gut, including the description of 38 novel taxa. Interesting functions discovered in these organisms include a new fucosyltransferease and sactipeptide-like molecules encoded by biosynthetic gene clusters.

Comparative proteomics of the toxigenic diazotroph Raphidiopsis raciborskii (cyanobacteria) in response to iron

Raphidiopsis raciborskii is an invasive bloom-forming cyanobacteria with the flexibility to utilize atmospheric and fixed nitrogen. Since nitrogen-fixation has a high requirement for iron as an ezyme cofactor, we hypothesize that iron availability would determine the success of the species under nitrogen-fixing conditions. This study compares the proteomic response of cylindrospermopsin-producing and non-toxic strains of R. racibroskii to reduced iron concentrations, under nitrogen-fixing conditions, to examine any strain-specific adaptations that might increase fitness under these conditions. We also compared their proteomic responses at exponential and stationary growth phases to capture the changes throughout the growth cycle. Overall, the toxic strain was more competitive under Fe-starved conditions during exponential phase, with upregulated growth and transport-related proteins. The non-toxic strain showed reduced protein expression across multiple primary metabolism pathways. We propose that the increased expression of porin proteins during the exponential growth phase enables toxic strains to persist under Fe-starved conditions with this ability providing a potential explanation for the increased fitness of cylindrospermoipsin-producing strains during unfavourable environmental conditions.

Antarctic desert soil bacteria exhibit high novel natural product potential, evaluated through long-read genome sequencing and comparative genomics

Actinobacteria and Proteobacteria are important producers of bioactive natural products (NP), and these phyla dominate in the arid soils of Antarctica, where metabolic adaptations influence survival under harsh conditions. Biosynthetic gene clusters (BGCs) which encode NPs, are typically long and repetitious high G + C regions difficult to sequence with short-read technologies. We sequenced 17 Antarctic soil bacteria from multi-genome libraries, employing the long-read PacBio platform, to optimize capture of BGCs and to facilitate a comprehensive analysis of their NP capacity. We report 13 complete bacterial genomes of high quality and contiguity, representing 10 different cold-adapted genera including novel species. Antarctic BGCs exhibited low similarity to known compound BGCs (av. 31%), with an abundance of terpene, non-ribosomal peptide and polyketide-encoding clusters. Comparative genome analysis was used to map BGC variation between closely related strains from geographically distant environments. Results showed the greatest biosynthetic differences to be in a psychrotolerant Streptomyces strain, as well as a rare Actinobacteria genus, Kribbella, while two other Streptomyces spp. were surprisingly similar to known genomes. Streptomyces and Kribbella BGCs were predicted to encode antitumour, antifungal, antibacterial and biosurfactant-like compounds, and the synthesis of NPs with antibacterial, antifungal and surfactant properties was confirmed through bioactivity assays.

Identification of promoter elements in the Dolichospermum circinale AWQC131C saxitoxin gene cluster and the experimental analysis of their use for heterologous expression

Background

Dolichospermum circinale is a filamentous bloom-forming cyanobacterium responsible for biosynthesis of the paralytic shellfish toxins (PST), including saxitoxin. PSTs are neurotoxins and in their purified form are important analytical standards for monitoring the quality of water and seafood and biomedical research tools for studying neuronal sodium channels. More recently, PSTs have been recognised for their utility as local anaesthetics. Characterisation of the transcriptional elements within the saxitoxin (sxt) biosynthetic gene cluster (BGC) is a first step towards accessing these molecules for biotechnology.

Results

In D. circinale AWQC131C the sxt BGC is transcribed from two bidirectional promoter regions encoding five individual promoters. These promoters were identified experimentally using 5′ RACE and their activity assessed via coupling to a lux reporter system in E. coli and Synechocystis sp. PCC 6803. Transcription of the predicted drug/metabolite transporter (DMT) encoded by sxtPER was found to initiate from two promoters, PsxtPER1 and PsxtPER2. In E. coli, strong expression of lux from PsxtP, PsxtD and PsxtPER1 was observed while expression from Porf24 and PsxtPER2 was remarkably weaker. In contrast, heterologous expression in Synechocystis sp. PCC 6803 showed that expression of lux from PsxtP, PsxtPER1, and Porf24 promoters was statistically higher compared to the non-promoter control, while PsxtD showed poor activity under the described conditions.

Conclusions

Both of the heterologous hosts investigated in this study exhibited high expression levels from three of the five sxt promoters. These results indicate that the majority of the native sxt promoters appear active in different heterologous hosts, simplifying initial cloning efforts. Therefore, heterologous expression of the sxt BGC in either E. coli or Synechocystis could be a viable first option for producing PSTs for industrial or biomedical purposes.

Streptomyces sp. BV410 isolate from chamomile rhizosphere soil efficiently produces staurosporine with antifungal and antiangiogenic properties

Applying a bioactivity‐guided isolation approach, staurosporine was separated and identified as the active principle in the culture extract of the new isolate Streptomyces sp. BV410 collected from the chamomile rhizosphere. The biotechnological production of staurosporine by strain BV410 was optimized to yield 56 mg/L after 14 days of incubation in soy flour–glucose–starch–mannitol‐based fermentation medium (JS). The addition of FeSO₄ significantly improved the staurosporine yield by 30%, while the addition of ZnSO₄ significantly reduced staurosporine yield by 62% in comparison with the starting conditions. Although staurosporine was first isolated in 1977 from Lentzea albida (now Streptomyces staurosporeus) and its potent kinase inhibitory effect has been established, here, the biological activity of this natural product was assessed in depth in vivo using a selection of transgenic zebrafish (Danio rerio) models, including Tg(fli1:EGFP) with green fluorescent protein‐labeled endothelial cells allowing visualization and monitoring of blood vessels. This confirmed a remarkable antiangiogenic activity of the compound at doses of 1 ng/ml (2.14 nmol/L) which is below doses inducing toxic effects (45 ng/ml; 75 nmol/L). A new, efficient producing strain of commercially significant staurosporine has been described along with optimized fermentation conditions, which may lead to optimization of the staurosporine scaffold and its wider applicability.

Antifungal potential of bacterial rhizosphere isolates associated with three ethno-medicinal plants (poppy, chamomile, and nettle)

The objective of the present study was to isolate Actinobacteria, preferably Streptomyces spp. from the rhizosphere soils of three ethno-medicinal plants collected in Serbia (Papaver rhoeas, Matricaria chamomilla, and Urtica dioica) and to screen their antifungal activity against Candida spp. Overall, 103 sporulating isolates were collected from rhizosphere soil samples and determined as Streptomyces spp. Two different media and two extraction procedures were used to facilitate identification of antifungals. Overall, 412 crude cell extracts were tested against Candida albicans using disk diffusion assays, with 42% (43/103) of the strains showing the ability to produce antifungal agents. Also, extracts inhibited growth of important human pathogens: Candida krusei, Candida parapsilosis, and Candida glabrata. Based on the established degree and range of antifungal activity, nine isolates, confirmed as streptomycetes by 16S rRNA sequencing, were selected for further testing. Their ability to inhibit Candida growth in liquid culture, to inhibit biofilm formation, and to disperse pre-formed biofilms was assessed with active concentrations from 8 to 250 μg/mL. High-performance liquid chromatographic profiles of extracts derived from selected strains were recorded, revealing moderate metabolic diversity. Our results proved that rhizosphere soil of ethno-medicinal plants is a prolific source of streptomycetes, producers of potentially new antifungal compounds.

The genetics, biosynthesis and regulation of toxic specialized metabolites of cyanobacteria

The production of toxic metabolites by cyanobacterial blooms represents a significant threat to the health of humans and ecosystems worldwide. Here we summarize the current state of the knowledge regarding the genetics, biosynthesis and regulation of well-characterized cyanotoxins, including the microcystins, nodularin, cylindrospermopsin, saxitoxins and anatoxins, as well as the lesser-known marine toxins (e.g. lyngbyatoxin, aplysiatoxin, jamaicamides, barbamide, curacin, hectochlorin and apratoxins).

Advances in genomics, transcriptomics and proteomics of toxin-producing cyanobacteria

A common misconception persists that the genomes of toxic and non-toxic cyanobacterial strains are largely conserved with the exception of the presence or absence of the genes responsible for toxin production. Implementation of -omics era technologies has challenged this paradigm, with comparative analyses providing increased insight into the differences between strains of the same species. The implementation of genomic, transcriptomic and proteomic approaches has revealed distinct profiles between toxin-producing and non-toxic strains. Further, metagenomics and metaproteomics highlight the genomic potential and functional state of toxic bloom events over time. In this review, we highlight how these technologies have shaped our understanding of the complex relationship between these molecules, their producers and the environment at large within which they persist.

Genome mining for natural product biosynthetic gene clusters in the Subsection V cyanobacteria

BACKGROUND

Cyanobacteria are well known for the production of a range of secondary metabolites. Whilst recent genome sequencing projects has led to an increase in the number of publically available cyanobacterial genomes, the secondary metabolite potential of many of these organisms remains elusive. Our study focused on the 11 publically available Subsection V cyanobacterial genomes, together with the draft genomes of Westiella intricata UH strain HT-29-1 and Hapalosiphon welwitschii UH strain IC-52-3, for their genetic potential to produce secondary metabolites. The Subsection V cyanobacterial genomes analysed in this study are reported to produce a diverse range of natural products, including the hapalindole-family of compounds, microcystin, hapalosin, mycosporine-like amino acids and hydrocarbons.

RESULTS

A putative gene cluster for the cyclic depsipeptide hapalosin, known to reverse P-glycoprotein multiple drug resistance, was identified within three Subsection V cyanobacterial genomes, including the producing cyanobacterium H. welwitschii UH strain IC-52-3. A number of orphan NRPS/PKS gene clusters and ribosomally-synthesised and post translationally-modified peptide gene clusters (including cyanobactin, microviridin and bacteriocin gene clusters) were identified. Furthermore, gene clusters encoding the biosynthesis of mycosporine-like amino acids, scytonemin, hydrocarbons and terpenes were also identified and compared.

CONCLUSIONS

Genome mining has revealed the diversity, abundance and complex nature of the secondary metabolite potential of the Subsection V cyanobacteria. This bioinformatic study has identified novel biosynthetic enzymes which have not been associated with gene clusters of known classes of natural products, suggesting that these cyanobacteria potentially produce structurally novel secondary metabolites.

Exploring cyanobacterial genomes for natural product biosynthesis pathways

Cyanobacteria produce a vast array of natural products, some of which are toxic to human health, while others possess potential pharmaceutical activities. Genome mining enables the identification and characterisation of natural product gene clusters; however, the current number of cyanobacterial genomes remains low compared to other phyla. There has been a recent effort to rectify this issue by increasing the number of sequenced cyanobacterial genomes. This has enabled the identification of biosynthetic gene clusters for structurally diverse metabolites, including non-ribosomal peptides, polyketides, ribosomal peptides, UV-absorbing compounds, alkaloids, terpenes and fatty acids. While some of the identified biosynthetic gene clusters correlate with known metabolites, genome mining also highlights the number and diversity of clusters for which the product is unknown (referred to as orphan gene clusters). A number of bioinformatic tools have recently been developed in order to predict the products of orphan gene clusters; however, in some cases the complexity of the cyanobacterial pathways makes the prediction problematic. This can be overcome by the use of mass spectrometry-guided natural product genome mining, or heterologous expression. Application of these techniques to cyanobacterial natural product gene clusters will be explored.

Comparative proteomics reveals that a saxitoxin-producing and a nontoxic strain of Anabaena circinalis are two different ecotypes

In Australia, saxitoxin production is restricted to the cyanobacterial species Anabaena circinalis and is strain-dependent. We aimed to characterize a saxitoxin-producing and nontoxic strain of A. circinalis at the proteomic level using iTRAQ. Seven proteins putatively involved in saxitoxin biosynthesis were identified within our iTRAQ experiment for the first time. The proteomic profile of the toxic A. circinalis was significantly different from the nontoxic strain, indicating that each is likely to inhabit a unique ecological niche. Under control growth conditions, the saxitoxin-producing A. circinalis displayed a higher abundance of photosynthetic, carbon fixation and nitrogen metabolic proteins. Differential abundance of these proteins suggests a higher intracellular C:N ratio and a higher concentration of intracellular 2-oxoglutarate in our toxic strain compared with the nontoxic strain. This may be a novel site for posttranslational regulation because saxitoxin biosynthesis putatively requires a 2-oxoglutarate-dependent dioxygenase. The nontoxic A. circinalis was more abundant in proteins, indicating cellular stress. Overall, our study has provided the first insight into fundamental differences between a toxic and nontoxic strain of A. circinalis, indicating that they are distinct ecotypes.

Using GenBank® for genomic authentication: a tutorial

The GenBank(®) database is perhaps one of the most important repositories of genetic information. A researcher working in the field of genomic authentication must therefore be equipped with the skills needed to competently access the required information from this database whilst ultimately contributing their own data to it. This chapter presents a practical guide to using GenBank(®) to search for sequences, search and align unknown sequences using BLAST, and uploading and maintaining your own sequences. This chapter also details some other software helpful in sequence manipulation.

A confocal and electron microscopic comparison of interferon beta-induced changes in vesicular stomatitis virus infection of neuroblastoma and nonneuronal cells

Vesicular stomatitis virus (VSV) replication is highly sensitive to interferon (IFN)-induced antiviral responses. Pretreatment of sensitive cultured cells with IFNbeta results in a 10(4)-fold reduction in the release of infectious VSV particles. However, differences exist between the mechanisms of reduced infectious particle titers in cell lines of neuroblastoma and nonneuronal lineage. In L929-fibroblast-derived cells, using immunofluorescence confocal microscopy, infection under control conditions reveals the accumulation of VSV matrix, phosphoprotein (P), and nucleocapsid (N) proteins over time, with induced cellular morphological changes indicative of cytopathic effects (CPEs). Upon observing L929 cells that had been pretreated with IFNbeta, neither detectable VSV proteins nor CPEs were seen, consistent with type I IFN antiviral protection. When using the same techniques to observe VSV infections of NB41A3 cells, a neuroblastoma cell line, aside from similar viral progression in the untreated control cells, IFNbeta-treated cells illustrated a severely attenuated VSV infection. Attenuated VSV progression was observed through detection of VSV matrix, P, and N proteins in isolated cells during the first 8 h of infection. However, by 18-24 h postinfection all neuroblastomas had succumbed to the viral infection. Finally, upon closer inspection of IFNbeta-treated NB41A3 cells, no detectable changes in VSV protein localization were identified compared with untreated, virally infected neuroblastomas. Next, to extend our study to test our hypothesis that virion assembly is compromised within type I IFN-treated neuroblastoma cells, we employed electron microscopy to examine our experimental conditions at the ultrastructural level. Using VSV-specific antibodies in conjunction with immuno-gold reagents, we observed several similarities between the two cell lines, such as identification of viroplasmic regions containing VSV N and P proteins and signs of stress-induced CPEs of VSV-infected cells, which had either been mock-treated or pretreated with interferon-beta (IFNbeta). One difference we observed between nonneuronal and neuroblastoma cells was more numerous actively budding VSV virions across untreated L929 plasma membranes compared with untreated NB41A3 cells. Additionally, IFNbeta-treated, VSV-infected L929 cells exhibited neither cytoplasmic viroplasm nor viral protein expression. In contrast, IFNbeta-treated, VSV-infected NB41A3 cells showed evidence of VSV infection at a very low frequency as well as small-scale viroplasmic regions that colocalized with viral N and P proteins. Finally, we observed that VSV viral particles harvested from untreated VSV-infected L929 and NB41A3 cells were statistically similar in size and shape. A portion of VSV virions from IFNbeta-treated, virally infected NB41A3 cells were similar in size and shape to virus from both untreated cell types. However, among the sampling of virions, pleomorphic viral particles that were identified from IFNbeta-treated, VSV-infected NB41A3 cells were different enough to suggest a misassembly mechanism as part of the IFNbeta antiviral state in neuroblastoma cells.

DISTINCT MECHANISMS OF INHIBITION OF VSV REPLICATION IN NEURONS MEDIATED BY TYPE I AND TYPE II IFN

Acute viral infection of neurons presents a difficult problem to the host, since neurons are essential and not replaced, therefore cell-autonomous pathway(s) of suppressing viral replication are critical. We have examined the mechanisms by which neurons respond to exogenous interferons (IFNs) and observed that novel pathways inhibit acute vesicular stomatitis virus (VSV) replication. For both type I (IFN-beta) and Type II (IFN-gamma) interferons, post-translational modification of viral proteins contributed to the replication blockade, diminishing the efficiency of viral assembly and budding from the host neuron. IFN-gamma treatment induces the accumulation of NOS-1 in the absence of an increase of mRNA encoding this enzyme; a NOS-1-inhibiting protein, PIN, is rapidly ubiquitinated and eliminated in the presence of IFN-gamma. NOS-1 produces NO which combines with superoxide to form peroxynitrite (ONOO-), this binds tyrosines, cysteines, and serines; antagonism of NOS-1 with either non-specific or selective inhibitors block the antiviral effect of IFN-gamma. VSV proteins are decorated with -NO(2) in IFN-gamma-treated neurons, probably resulting in their diminished ability to interact properly and mature into budding virus. For IFN-beta, protein phosphorylation of the Matrix protein (M) and Phosphoprotein (P) were altered in infected neurons, with hyperphosphorylation of M (but not hypophosphorylated P) found in released virions. Hyperphosphorylated M protein does not immunoprecipitate with the viral ribonucleoprotein complex in IFN-beta-treated neurons. Thus both types of IFN interfere with viral assembly and release of infectious particles, but by distinct pathways.

The effects of reverse micelles on the reaction mechanism of alpha-chymotrypsin

Reverse micelles were employed to test the accuracy of the widely accepted mechanism for alpha-chymotrypsin in a highly structured aqueous system similar to intracellular conditions. Results yielded from spectrophotometrical assays of the alpha-chymotrypsin catalyzed hydrolysis of both p-nitrophenyl acetate (p-NPA) and p-nitrophenyl trimethylacetate (p-NPTA) were kinetically analyzed to determine constants typical of the proposed mechanistic model. This was accomplished through the establishment of a control, i.e. the well studied buffer system, for comparison between the reverse micellular environment and a bulk aqueous solution. Control group results yielded kinetic constants in favor of the proposed mechanism (Km = 1.55 x 10(-5) +/- 1.40 x 10(-6) M for p-NPA and a Km = 4.97 x 10(-6) +/- 2.29 x 10(-7) M, Km(app) = 4.92 x 10(-6) +/- 2.33 x 10(-8) M, k2 = 4.34 x 10(-3) +/- 1.31 x 10(-3), k(cat) = 1.96 x 10(-3) +/- 2.47 x 10(-4), and Ks = 1.60 x 10(-5) +/- 4.61 x 10(-6) M for p-NPTA). In contrast, similar reactions of the enzyme in a reverse micellular system produced kinetic constants atypical to that representative of the textbook mechanism. (Km = 1.59 x 10(-4) +/- 2.70 x 10(-5) M, Ks = -8.67 x 10(-5) +/- 4.46 x 10(-5) M and Km(app) = -4.80 x 10(-5) +/- 7.05 x 10(-5) M for p-NPA and Km = 1.95 x 10(-4) +/- 9.28 x 10(-5) M, Km(app) = -1.79 x 10(-4) +/- 2.36 x 10(-5) M, and Ks = -3.95 x 10(-4) +/- 1.18 x 10(-4) M for p-NPTA). In addition to negative kinetic constants, alpha-chymotrypsin seemed to display characteristics indicative of super-activity and a hysteretic response. Overall, the widely accepted mechanism for alpha-chymotrypsin appeared to fail within the confines of reverse micelles, due to the direct influence of the system's highly structured form.