Moroidin, a Cyclopeptide from the Seeds of Celosia cristata That Induces Apoptosis in A549 Human Lung Cancer Cells

Enzymatic crosslinking of histidine side chains in peptide natural products

Covering: 2019 to 2024Peptide macrocyclization stands as the pivotal step in the biosynthesis journey of bioactive cyclic peptide natural products, spanning both ribosomal and non-ribosomal origins. Beyond the enzymatic N- to C-terminus macrocyclization, natural cyclic peptides frequently display side chain-to-side chain crosslinks, which markedly bolster their stability and biological potency. Traditionally, histidine, with its imidazole side chain, has been regarded as chemically unreactive, leading to relatively sparse reports of histidine-containing crosslinks in cyclic peptide natural products. However, recent advancements in research have illuminated a novel perspective on the role of histidine (His) residues in peptide macrocyclization, revealing that His participation in this process is far more ubiquitous than previously envisioned. This highlight underscores the significance of His-containing crosslinks in natural cyclic peptides and delves into the enzymatic mechanisms underlying their formation.

The emergence and loss of cyclic peptides in Nicotiana illuminate dynamics and mechanisms of plant metabolic evolution

Specialized metabolism plays a central role in how plants cope with both biotic and abiotic stresses in order to survive and reproduce within dynamic and challenging environments. One recently described class of plant-specific, ribosomally synthesized, and posttranslationally modified peptides are the burpitides, which are characterized by the installation of distinct sidechain macrocycles by enzymes known as burpitide cyclases. While they are found across many plant families and exhibit diverse bioactivities, little is known about their evolution or how new variants arise. Here, we present the identification of a burpitide cyclase, resurrected from a defunct pseudogene from the model organism Nicotiana attenuata, the coyote tobacco. By repairing the pseudogene ΨNatBURP2 and expressing it heterologously in Nicotiana benthamiana, we successfully reconstituted its original enzymatic activity. As an autocatalytic peptide cyclase, it installs a unique C-C bond between the tyrosine side chain and a specific backbone α-carbon of a heptapeptide core motif, resulting in burpitides dubbed "nanamins." Despite its pseudogenization in N. attenuata, we found that the closely related species, Nicotiana clevelandii, retains the wild-type gene and produces nanamins. Phylogenetic analyses and targeted mutagenesis experiments reveal that this chemotype must have evolved from the duplication and neofunctionalization of a more promiscuous ancestral gene. This work highlights how novel peptide chemotypes may rapidly emerge and disappear in plants, while expanding the molecular toolkit for engineering novel peptides with applications in agriculture and drug discovery.

The Biarylitides: Understanding the Structure and Biosynthesis of a Fascinating Class of Cytochrome P450 Modified RiPP Natural Products

The biarylitides are a recently discovered class of RiPP natural products that are fascinating both from the small size of the core peptides as well as the diversity of peptide crosslinking exhibited by the cytochrome P450 enzymes found in these systems. In this review, we address the discovery and biosynthetic diversity of these systems and discuss the methods and challenges of analysing the structures of these constrained cyclic peptides. We also discuss the structures of the P450 enzymes involved in these pathways and address the potential for alternate catalytic outcomes and activities as seen most recently with the inclusion of biarylitide related enzymes within rufomycin biosynthesis.

Anticancer Ribosomally Synthesized and Post-Translationally Modified Peptides from Plants: Structures, Therapeutic Potential, and Future Directions

Cancer remains a significant medical challenge, necessitating the discovery of novel therapeutic agents. Ribosomally synthesized and post-translationally modified peptides (RiPPs) from plants have emerged as a promising source of anticancer compounds, offering unique structural diversity and potent biological activity. This review identifies and discusses cytotoxic RiPPs across various plant families, focusing on their absolute chemical structures and reported cytotoxic activities against cancer cell lines. Notably, plant-derived RiPPs such as rubipodanin A and mallotumides A-C demonstrated low nanomolar IC50 values against multiple cancer cell types, highlighting their therapeutic potential. By integrating traditional ethnobotanical knowledge with modern genomic and bioinformatic approaches, this study underscores the importance of plant RiPPs as a resource for developing innovative cancer treatments. These findings pave the way for further exploration of plant RiPPs, emphasizing their role in addressing the ongoing challenges in oncology and enhancing the repertoire of effective anticancer therapies.

Peptide Crosslinking by a Class of Plant Copper Enzymes

BURP domain peptide cyclases, or BpCs (an abbreviation we recommend in this opinion), are an emerging class of copper enzymes which catalyze the oxidative macrocyclization of peptides in plants. A close examination of their novel protein fold, along with the unique dicopper active site that meticulously controls crosslinking within peptides, highlights how nature exploits intricate mechanistic strategies to achieve diverse functionalities. Here, we summarize recent discoveries regarding the sequence, structure, function, and proposed chemistry of BpCs. We also present plausible mechanistic ideas and recommend important structural considerations that could advance investigations and discussions surrounding their reactivity and underlying mechanisms.

Histidine-bridged cyclic peptide natural products: isolation, biosynthesis and synthetic studies

The histidine bridge is a rare and often overlooked structural motif in macrocyclic peptide natural products, yet there are several examples in nature of cyclic peptides bearing this moiety that exhibit potent biological activity. These interesting compounds have been the focus of several studies reporting their isolation, biosynthesis and chemical synthesis over the last four decades. This review summarises the findings on the structure, biological activity and, where possible, proposed biosynthesis and progress towards the synthesis of histidine-bridged cyclic peptides.

Celosia cristata L.: A review of its traditional uses, phytochemistry, pharmacology, toxicology, and quality control, along with network pharmacological analysis of its components and targets

ETHNOPHARMACOLOGICAL RELEVANCE

Celosia cristata L. (C. cristata) is a widely used herb in China and has been used as a medicine for more than 1000 years. The herb has been clinically employed to treat various types of bleeding disorders including metrorrhagia, metrostaxis, and leukorrheal diseases, gastrointestinal infections.

AIM OF THE STUDY

This review provides a comprehensive analysis of C. cristata, encompassing its botany, traditional applications, phytochemistry, pharmacology, safety, and quality control. Additionally, it delves into the prevailing challenges and limitations with contemporary research concerning C. cristata, thus furnishing valuable insights for future investigations in this domain.

MATERIALS AND METHODS

Research data were gathered from authoritative sources including the Pharmacopoeia of China, the Flora of China, as well as various internet databases such as Web of Science, CAS CiFinder, PubMed, Science Direct, and CNKI, along with numerous ancient classics on Chinese herbal medicine.

RESULTS

Clinical applications of C. cristata demonstrate its efficacy in treating dysfunctional uterine bleeding, vaginitis, and pelvic inflammatory disease. Presently, seventy-seven compounds have been isolated, including flavonoids, triterpenoids, steroids, organic acids, phenylpropanoids, and alkaloids, with flavonoids and triterpenoids emerging as the primary bioactive constituents. Pharmacological studies reveal its diverse biological activities, such as haemostatic, antitrichomonal, antibacterial, antiviral, analgesic, immunoregulatory, anti-inflammatory, anticancer, hepatoprotective, and antioxidant effects. Leveraging network pharmacology, researchers have embarked on preliminary inquiries into the interplay among chemical constituents, molecular targets and pathological conditions.

CONCLUSIONS

C. cristata shows significant potential for use in hemostasis, anti-inflammatory, and antimicrobial treatments. Modern research has revealed its diverse chemical composition and pharmacological activities, making it highly valuable for further study. At the same time, it is necessary to find the characteristic components of C. cristata and establish better quality control standards to better explore its therapeutic potential.

Plant peptides - redefining an area of ribosomally synthesized and post-translationally modified peptides

Covering 1965 to February 2024Plants are prolific peptide chemists and are known to make thousands of different peptidic molecules. These peptides vary dramatically in their size, chemistry, and bioactivity. Despite their differences, all plant peptides to date are biosynthesized as ribosomally synthesized and post-translationally modified peptides (RiPPs). Decades of research in plant RiPP biosynthesis have extended the definition and scope of RiPPs from microbial sources, establishing paradigms and discovering new families of biosynthetic enzymes. The discovery and elucidation of plant peptide pathways is challenging due to repurposing and evolution of housekeeping genes as both precursor peptides and biosynthetic enzymes and due to the low rates of gene clustering in plants. In this review, we highlight the chemistry, biosynthesis, and function of the known RiPP classes from plants and recommend a nomenclature for the recent addition of BURP-domain-derived RiPPs termed burpitides. Burpitides are an emerging family of cyclic plant RiPPs characterized by macrocyclic crosslinks between tyrosine or tryptophan side chains and other amino acid side chains or their peptide backbone that are formed by copper-dependent BURP-domain-containing proteins termed burpitide cyclases. Finally, we review the discovery of plant RiPPs through bioactivity-guided, structure-guided, and gene-guided approaches.

Mining raw plant transcriptomic data for new cyclopeptide alkaloids

In recent years, genome and transcriptome mining have dramatically expanded the rate of discovering diverse natural products from bacteria and fungi. In plants, this approach is often more limited due to the lack of available annotated genomes and transcriptomes combined with a less consistent clustering of biosynthetic genes. The recently identified burpitide class of ribosomally synthesized and post-translationally modified peptide (RiPP) natural products offer a valuable opportunity for bioinformatics-guided discovery in plants due to their short biosynthetic pathways and gene encoded substrates. Using a high-throughput approach to assemble and analyze 700 publicly available raw transcriptomic data sets, we uncover the potential distribution of split burpitide precursor peptides in Streptophyta. Metabolomic analysis of target plants confirms our bioinformatic predictions of new cyclopeptide alkaloids from both known and new sources.

Cyclopeptide moroidin inhibits vasculogenic mimicry formed by glioblastoma cells via regulating β-catenin activation and EMT pathways

Glioblastoma (GBM) is a highly vascularized malignant brain tumor with poor clinical outcomes. Vasculogenic mimicry (VM) formed by aggressive GBM cells is an alternative approach for tumor blood supply and contributes to the failure of anti-angiogenic therapy. To date, there is still a lack of effective drugs that target VM formation in GBM. In the present study, we evaluated the effects of the plant cyclopeptide moroidin on VM formed by GBM cells and investigated its underlying molecular mechanisms. Moroidin significantly suppressed cell migration, tube formation, and the expression levels of α-smooth muscle actin and matrix metalloproteinase-9 in human GBM cell lines at sublethal concentrations. The RNA sequencing data suggested the involvement of the epithelial-mesenchymal transition (EMT) pathway in the mechanism of moroidin. Exposure to moroidin led to a concentration-dependent decrease in the expression levels of the EMT markers N-cadherin and vimentin in GBM cells. Moreover, moroidin significantly reduced the level of phosphorylated extracellular signal-regulated protein kinase (p-ERK) and inhibited the activation of β-catenin. Finally, we demonstrated that the plant cyclopeptide moroidin inhibited VM formation by GBM cells through inhibiting the ERK/β-catenin-mediated EMT. Therefore, our study indicates a potential application of moroidin as an anti-VM agent in the treatment of GBM.

plantMASST - Community-driven chemotaxonomic digitization of plants

Understanding the distribution of hundreds of thousands of plant metabolites across the plant kingdom presents a challenge. To address this, we curated publicly available LC-MS/MS data from 19,075 plant extracts and developed the plantMASST reference database encompassing 246 botanical families, 1,469 genera, and 2,793 species. This taxonomically focused database facilitates the exploration of plant-derived molecules using tandem mass spectrometry (MS/MS) spectra. This tool will aid in drug discovery, biosynthesis, (chemo)taxonomy, and the evolutionary ecology of herbivore interactions.

Seven lower toxicity celastrol derivatives by biotransformation of Pestalotiopsis sp. LGT-1

Biotransformation of toxic components by plant endophytes has become an effective method to reduce the toxicity of target compounds and discover lead compounds. In this context, an endophytic fungus, Pestalotiopsis sp. LGT-1, from Tripterygium wilfordii Hook F. (TwHF), was used to reduce the toxicity of celastrol which is also produced by TwHF and is considered an attractive molecule with a variety of biological activities. Seven celastrol derivatives (1-7) were isolated from the coculture fermentation broth of LGT-1 and celastrol. Their structures were elucidated by spectroscopic data analysis including 1D and 2D NMR, as well as HRESIMS. Their absolute configurations were determined by analysis of NOESY, ECD data and NMR calculations. In cell proliferation experiments, the toxicity of seven compounds was 10.11- to 1.24-fold lower in normal cells than the prototype compound celastrol. These derivatives serve as potential candidates for future pharmaceutical applications.