Engineered biosynthesis of novel polyenes: a pimaricin derivative produced by targeted gene disruption in Streptomyces natalensis

AbstractBackground: The post-polyketide synthase biosynthetic tailoring of polyene macrolides usually involves oxidations catalysed by cytochrome P450 monooxygenases (P450s). Although members from this class of enzymes are common in macrolide biosynthetic gene clusters, their specificities vary considerably toward the substrates utilised and the positions of the hydroxyl functions introduced. In addition, some of them may yield epoxide groups. Therefore, the identification of novel macrolide monooxygenases with activities toward alternative substrates, particularly epoxidases, is a fundamental aspect of the growing field of combinatorial biosynthesis. The specific alteration of these activities should constitute a further source of novel analogues. We investigated this possibility by directed inactivation of one of the P450s belonging to the biosynthetic gene cluster of an archetype polyene, pimaricin.Results: A recombinant mutant of the pimaricin-producing actinomycete Streptomyces natalensis produced a novel pimaricin derivative, 4,5-deepoxypimaricin, as a major product. This biologically active product resulted from the phage-mediated targeted disruption of the gene pimD, which encodes the cytochrome P450 epoxidase that converts deepoxypimaricin into pimaricin. The 4,5-deepoxypimaricin has been identified by mass spectrometry and nuclear magnetic resonance following high-performance liquid chromatography purification.Conclusions: We have demonstrated that PimD is the epoxidase responsible for the conversion of 4,5-deepoxypimaricin to pimaricin in S. natalensis. The metabolite accumulated by the recombinant mutant, in which the epoxidase has been knocked out, constitutes the first designer polyene obtained by targeted manipulation of a polyene biosynthetic gene cluster. This novel epoxidase could prove to be valuable for the introduction of epoxy substituents into designer macrolides

Structural and Kinetic Characterization of Thymidine Kinase from Leishmania major

Leishmania spp. is a protozoan parasite and the causative agent of leishmaniasis. Thymidine kinase (TK) catalyses the transfer of the γ-phosphate of ATP to 2’-deoxythymidine (dThd) forming thymidine monophosphate (dTMP). L. major Type II TK (LmTK) has been previously shown to be important for infectivity of the parasite and therefore has potential as a drug target for anti-leishmanial therapy. In this study, we determined the enzymatic properties and the 3D structures of holo forms of the enzyme. LmTK efficiently phosphorylates dThd and dUrd and has high structural homology to TKs from other species. However, it significantly differs in its kinetic properties from Trypanosoma brucei TK since purines are not substrates of the enzyme and dNTPs such as dUTP inhibit LmTK. The enzyme had Km and kcat values for dThd of 1.1 μM and 2.62 s-1 and exhibits cooperative binding for ATP. Additionally, we show that the anti-retroviral prodrug zidovudine (3-azido-3-deoxythymidine, AZT) and 5’-modified dUrd can be readily phosphorylated by LmTK. The production of recombinant enzyme at a level suitable for structural studies was achieved by the construction of C-terminal truncated versions of the enzyme and the use of a baculoviral expression system. The structures of the catalytic core of LmTK in complex with dThd, the negative feedback regulator dTTP and the bi-substrate analogue AP5dT, were determined to 2.74, 3.00 and 2.40 Å, respectively, and provide the structural basis for exclusion of purines and dNTP inhibition. The results will aid the process of rational drug design with LmTK as a potential target for anti-leishmanial drugs.Peer reviewe

Effectiveness of Modified Vaccinia Ankara-Bavaria Nordic Vaccination in a Population at High Risk of Mpox: A Spanish Cohort Study

Background: With over 7,500 cases notified since April 2022, Spain has experienced the highest incidence of mpox in Europe. From July 12th onwards, the Modified Vaccinia Ankara-Bavaria Nordic (MVA-BN) smallpox vaccine was offered as pre-exposure prophylaxis for individuals at high-risk of mpox, including those receiving pre-exposure prophylaxis for HIV (HIV-PrEP). Our aim was to assess the effectiveness of one dose of MVA-BN vaccine as pre-exposure against mpox virus (MPXV) infection in persons on HIV-PrEP. Methods: We conducted a national retrospective cohort study between July 12 and December 12, 2022. Individuals ≥18 years, receiving HIV-PrEP as of July 12 and with no previous MPXV infection or vaccination were eligible. Each day, we matched individuals receiving a first dose of MVA-BN vaccine and unvaccinated controls of the same age group and region. We used a Kaplan-Meier estimator and calculate risk ratios (RR) and vaccine effectiveness (VE = 1-RR). Results: We included 5,660 matched pairs, with a median follow-up of 62 days (interquartile range 24-97). Mpox cumulative incidence was 5.6 per 1,000 (25 cases) in unvaccinated and 3.5 per 1,000 (18 cases) in vaccinated. No effect was found during days 0-6 post-vaccination (VE -38.3; 95% confidence interval (95%CI): -332.7; 46.4), but VE was 65% in ≥7 days (95%CI 22.9; 88.0) and 79% in ≥14 days (95%CI 33.3; 100.0) post-vaccination. Conclusions: One dose of MVA-BN vaccine offered protection against mpox in a most-at-risk population shortly after the vaccination. Further studies need to assess the VE of a second dose and the duration of protection over time.S

Spread of a SARS-CoV-2 variant through Europe in the summer of 2020

[EN] Following its emergence in late 2019, the spread of SARS-CoV-21,2 has been tracked by phylogenetic analysis of viral genome sequences in unprecedented detail3,4,5. Although the virus spread globally in early 2020 before borders closed, intercontinental travel has since been greatly reduced. However, travel within Europe resumed in the summer of 2020. Here we report on a SARS-CoV-2 variant, 20E (EU1), that was identified in Spain in early summer 2020 and subsequently spread across Europe. We find no evidence that this variant has increased transmissibility, but instead demonstrate how rising incidence in Spain, resumption of travel, and lack of effective screening and containment may explain the variant’s success. Despite travel restrictions, we estimate that 20E (EU1) was introduced hundreds of times to European countries by summertime travellers, which is likely to have undermined local efforts to minimize infection with SARS-CoV-2. Our results illustrate how a variant can rapidly become dominant even in the absence of a substantial transmission advantage in favourable epidemiological settings. Genomic surveillance is critical for understanding how travel can affect transmission of SARS-CoV-2, and thus for informing future containment strategies as travel resumes.S

Investigation of acyclic uridine amide and 5'-amido nucleoside analogues as potential inhibitors of the Plasmodium falciparum dUTPase

Previously we have shown that trityl and diphenyl deoxyuridine derivatives and their acyclic analogues can inhibit Plasmodium falciparum dUTPase (PfdUTPase). We report the synthesis of conformationally restrained amide derivatives as inhibitors PfdUTPase, including both acyclic and cyclic examples. Activity was dependent on the orientation and location of the amide constraining group. In the case of the acyclic series, we were able to obtain amide-constrained analogues which showed similar or greater potency than the unconstrained analogues. Unfortunately these compounds showed lower selectivity in cellular assays

Analytical ultracentrifugation of C-terminally His-tagged <i>Lm</i>TK.

<p>Superposition of the c(s) distributions of the unliganded <i>Lm</i>TK and <i>Lm</i>TK-dThd-AppNHp samples are shown at concentrations in the range of 1–8 S.</p

Kinetic constants and substrate specificity of recombinant <i>Lm</i>TK and <i>h</i>TK1.

<p>Kinetic parameters for <i>Lm</i>TK are means of two or more independent experiments.</p><p>N.D. Not determined.</p><p>^a Activity measurements at 10 mM substrate concentration.</p><p>^b Kinetic constants obtained at 37°C by Munch-Peterson et al. [<a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0003781#pntd.0003781.ref043" target="_blank">43</a>].</p><p>Kinetic constants and substrate specificity of recombinant <i>Lm</i>TK and <i>h</i>TK1.</p