Enhanced production of camptothecin and biological preparation of N 1-acetylkynuramine in Camptotheca acuminata cell suspension cultures

Multiomics-guided mining and characterization of epoxide hydrolase involved in camptothecin biosynthesis from Camptotheca acuminata

The 2,7-epoxy hydrolysis step is critical and inevitable for the biosynthesis of camptothecin (CPT). CPT-type drugs have excellent cytotoxic and antitumor activities. However, the genes responsible for this hydrolysis step remain unclear in Camptotheca acuminata Decne. In this study, multiomics resources of C. acuminata Decne have been utilized to mine and screen the genes involved in the epoxide hydrolase step. Three genes (CaEH1-CaEH3) have been identified, and their recombinant CaEH proteins have been prepared in a soluble form. All CaEHs display (S)-styrene oxide, (R)-styrene oxide, and trans-stilbene oxide oxirane ring-opening activities. Notably, CaEH1 displays excellent catalytic performance for (S)- and (R)-styrene oxides but poor enantioselectivity. On the other hand, CaEH2 and CaEH3 display a higher S isomer preference for styrene oxide. Furthermore, CaEH1-CaEH3 display strictosamide epoxide 2,7-epoxy ring opening activity. They exhibit inferior catalytic performance toward strictosamide epoxide compared to "slim" substrates but better catalytic performance for the larger substrates than characterized plant EHs. Functional verification in planta suggests that the newly identified CaEH1-CaEH3 are jointly responsible for CPT biosynthesis. These CaEH genes are expressed in all plantlet tissues and are enriched in the leaves. Evolutionary analysis indicates that CaEH1-CaEH3 originate from different ancestral EH genes. The convergent evolution of these CaEH genes likely results in the homofunctionalization of CaEH1-CaEH3. Overall, this study reveals one of the previously unexplored biosynthetic steps of camptothecin in C. acuminata.

Discovery of a novel flavonol O-methyltransferase possessing sequential 4'- and 7-O-methyltransferase activity from Camptotheca acuminata Decne

The biosynthetic route for flavonol in Camptotheca acuminata has been recently elucidated from a chemical point of view. However, the genes involved in flavonol methylation remain unclear. It is a critical step for fully uncovering the flavonol metabolism in this ancient plant. In this study, the multi-omics resource of this plant was utilized to perform flavonol O-methyltransferase-oriented mining and screening. Two genes, CaFOMT1 and CaFOMT2 are identified, and their recombinant CaFOMT proteins are purified to homogeneity. CaFOMT1 exhibits strict substrate and catalytic position specificity for quercetin, and selectively methylates only the 4'-OH group. CaFOMT2 possesses sequential O-methyltransferase activity for the 4'-OH and 7-OH of quercetin. These CaFOMT genes are enriched in the leaf and root tissues. The catalytic dyad and critical substrate-binding sites of the CaFOMTs are determined by molecular docking and further verified through site-mutation experiments. PHE181 and MET185 are designated as the critical sites for flavonol substrate selectivity. Genomic environment analysis indicates that CaFOMTs evolved independently and that their ancestral genes are different from that of the known Ca10OMT. This study provides molecular insights into the substrate-binding pockets of two new CaFOMTs responsible for flavonol metabolism in C. acuminata.

Plant-microbe interactions implicated in the production of camptothecin - An anticancer biometabolite from Phyllosticta elongata MH458897 a novel endophytic strain isolated from medicinal plant of Western Ghats of India

Endophytic wild fungal strain Phyllosticta elongata MH458897 isolated from medicinal plant Cipadessa baccifera from the Western Ghats region of Sathyamangalam Tiger Reserve Forest. This endophytic fungus has potential of effective anticancer drug Camptothecin (CPT). Endophytic fungi act as key symbionts in-between plants and ecosystem in the biosphere. This recently identified microbial population inside the plants produces many defence metabolites against plant pathogens. Among these defense metabolites, CPT gained much attention because of its effective anticancer activity. The maximum yield of CPT produced by optimizing the various factors like DEKM07 medium, pH 5.6, incubation time using Response Surface Methodology based on Central Composite Design. Extracted CPT is characterized using High Performance Liquid Chromatography and Electrospray ionization-Mass spectrometry. The highest yield of CPT was 0.747 mg/L was produced at optimized factors of dextrose - 50 g L^-1, peptone - 5.708 g L^-1, magnesium sulphate - 0.593 g L^-1, and incubation time - 14 days. In-vitro MTT assay revealed the CPT derivatives were cytotoxic to A-549 cancer cell line (IC₅₀ 58.28 μg/ml) as nearly compared to the (IC₅₀ 51.08 μg/ml) standard CPT. CPT producing strain P. elongata from C. baccifera has the potential of CPT biosynthesis, and could be an effective anticancer bio metabolite. This compound has been described in the literature to be an effective anticancer metabolite. Our findings support the novel lifesaving anticancer drug from endophytic fungus in forest ecosystem concludes effective utilization of key symbionts will safeguard the humans and forest ecosystem.

Bioproduction process of natural products and biopharmaceuticals: Biotechnological aspects

Decades of research have been put in place for developing sustainable routes of bioproduction of high commercial value natural products (NPs) on the global market. In the last few years alone, we have witnessed significant advances in the biotechnological production of NPs. The development of new methodologies has resulted in a better understanding of the metabolic flux within the organisms, which have driven manipulations to improve production of the target product. This was further realised due to the recent advances in the omics technologies such as genomics, transcriptomics, proteomics, metabolomics and secretomics, as well as systems and synthetic biology. Additionally, the combined application of novel engineering strategies has made possible avenues for enhancing the yield of these products in an efficient and economical way. Invention of high-throughput technologies such as next generation sequencing (NGS) and toolkits for genome editing Clustered Regularly Interspaced Short Palindromic Repeats/CRISPR-associated 9 (CRISPR/Cas9) have been the game changers and provided unprecedented opportunities to generate rationally designed synthetic circuits which can produce complex molecules. This review covers recent advances in the engineering of various hosts for the production of bioactive NPs and biopharmaceuticals. It also highlights general approaches and strategies to improve their biosynthesis with higher yields in a perspective of plants and microbes (bacteria, yeast and filamentous fungi). Although there are numerous reviews covering this topic on a selected species at a time, our approach herein is to give a comprehensive understanding about state-of-art technologies in different platforms of organisms.

Characterization of Camptotheca acuminata 10-hydroxygeraniol oxidoreductase and iridoid synthase and their application in biological preparation of nepetalactol in Escherichia coli featuring NADP+ - NADPH cofactors recycling

Nepetalactol, an iridoid with four chiral carbons, is a crucial component of aphid sex pheromones that have been employed with great success to control the insect-related diseases. Despite of agricultural usage as end products, iridoids are fundamental biosynthetic intermediates for pharmaceutically important monoterpenoid indole alkaloids such as camptothecin (CAM) and vinca alkaloids. Herein we characterized 10-hydroxygeraniol oxidoreductase (10HGO) and iridoid synthase (IS) from Camptotheca acuminata, a CAM-producing plant, and reported their application in biological preparation of nepetalactol. Ca10HGO and CaIS were respectively cloned from C. acuminata, overexpressed in Escherichia coli, and purified to homogeneity. Ca10HGO catalyzes the oxidation of 10-hydroxygeraniol into 10-oxogeranial, in which NADP⁺ was reduced to NADPH. CaIS catalyzes nepetalactol formation from 10-oxogeranial using NADPH cofactor. The net outcome of the two reactions generate nepetalactol from 10-hydroxygeraniol efficiently, indicating NADP⁺ - NADPH recycling. Ca10HGO and CaIS were co-overexpressed in E. coli under optimized fermentation conditions to prepare cell-based catalysts that catalyze the conversion of 10-hydroxygeraniol into nepetalactol. The present work shows the enzymatic conversion of 10-hydroxygeraniol into nepetalactol involved in CAM biosynthesis. Co-overexpression of Ca10HGO and CaIS in E. coli is an alternative valuable cell-based biotransformation process with regenerating recycling of NADP⁺ - NADPH cofactors for nepetalactol preparation.

An oxidatively stressful situation: a case of Artemisia annua L

Artemisinin (ART) is an antimalarial compound that possesses a variety of novel biological activities. Due to the low abundance of ART in natural sources, agricultural supply has been erratic, and prices are highly volatile. While heterologous biosynthesis and semi-synthesis are advantageous in certain aspects, these approaches remained disadvantageous in terms of productivity and cost-effectiveness. Therefore, further improvement in ART production calls for approaches that should supplement the agricultural production gap, while reducing production costs and stabilising supply. The present review offers a discussion on the elicitation of plants and/or in vitro cultures as an economically feasible yield enhancement strategy to address the global problem of access to affordable ART. Deemed critical for the manipulation of biosynthetic potential, the mechanism of ART biosynthesis is reviewed. It includes a discussion on the current biotechnological solutions to ART production, focusing on semi-synthesis and elicitation. A brief commentary on the possible aspects that influence elicitation efficiency and how oxidative stress modulates ART synthesis is also presented. Based on the critical analysis of current literature, a hypothesis is put forward to explain the possible involvement of enzymes in assisting the final non-enzymatic transformation step leading to ART formation. This review highlights the critical factors limiting the success of elicitor-induced modulation of ART metabolism, that will help inform strategies for future improvement of ART production. Additionally, new avenues for future research based on the proposed hypothesis will lead to exciting perspectives in this research area and continue to enhance our understanding of this intricate metabolic process.

Possible clues for camptothecin biosynthesis from the metabolites in camptothecin-producing plants

The plant derived camptothecin (CPT) is a pentacyclic pyrroloquinoline alkaloid with unique antitumor activity. Successive discoveries of new CPT-producing plants occurred in recent years due to market demands. The scattered distribution among angiosperms drew researchers' attention. The aim of this review is to appraise the literature available to date for CPT distribution and the phytochemistry of these CPT-producing plants. Metabolite comparative analyses between the plants were also conducted for tracking of possible clues for CPT biosynthesis. Forty-three plant species in total were reported to possess CPT-producing capability, and one hundred twenty-five alkaloids classified into three major categories are summarized herein. Metabolite comparative analysis between these plants suggests the probability that the formation of the central intermediate for CPT biosynthesis has multiple origins. A more complete biogenetic reasoning for CPT and its structural homolog was delineated based on this fragmentary phytochemical evidence from a chemical point of view. Furthermore, an in-house compound database was constructed for further metabolomic analysis.