A new type 1 ribosome-inactivating protein from the seeds of Gypsophila elegans M.Bieb

In-silico analysis of ribosome inactivating protein (RIP) of the Cucurbitaceae family

Ribosome-inactivating proteins (RIPs) are highly active N-glycosidases that depurinate both bacterial and eukaryotic rRNAs, halting protein synthesis during translation. Found in a diverse spectrum of plant species and tissues, RIPs possess antifungal, antibacterial, antiviral, and insecticidal properties linked to plant defense. In this study, we investigated the physiochemical properties of RIP peptides from the Cucurbitaceae family through bioinformatics approaches. Molecular weight, isoelectric point, aliphatic index, extinction coefficient, and secondary structures were analyzed, revealing their hydrophobic nature. The novelty of this work lies in the comprehensive examination of RIPs from the Cucurbitaceae family and their potential therapeutic applications. The study also elucidated the binding interactions of Cucurbitaceae RIPs with key biological targets, including Interleukin-6 (IL-6). Strong hydrogen bond interactions between RIPs and these targets suggest potential for innovative insilico drug design and therapeutic applications, particularly in cancer treatment. Comprehensive analysis of bond lengths using Ligpolt + software provides insights for optimizing molecular interactions, offering a valuable tool for drug design and structural biology studies.

Mutational Analysis of RIP Type I Dianthin-30 Suggests a Role for Arg24 in Endocytosis

Saponin-mediated endosomal escape is a mechanism that increases the cytotoxicity of type I ribosome-inactivating proteins (type I RIPs). In order to actualize their cytotoxicity, type I RIPs must be released into the cytosol after endocytosis. Without release from the endosomes, type I RIPs are largely degraded and cannot exert their cytotoxic effects. Certain triterpene saponins are able to induce the endosomal escape of these type I RIPs, thus increasing their cytotoxicity. However, the molecular mechanism underlying the endosomal escape enhancement of type I RIPs by triterpene saponins has not been fully elucidated. In this report, we investigate the involvement of the basic amino acid residues of dianthin-30, a type I RIP isolated from the plant Dianthus caryophyllus L., in endosomal escape enhancement using alanine scanning. Therefore, we designed 19 alanine mutants of dianthin-30. Each mutant was combined with SO1861, a triterpene saponin isolated from the roots of Saponaria officinalis L., and subjected to a cytotoxicity screening in Neuro-2A cells. Cytotoxic screening revealed that dianthin-30 mutants with lysine substitutions did not impair the endosomal escape enhancement. There was one particular mutant dianthin, Arg24Ala, that exhibited significantly reduced synergistic cytotoxicity in three mammalian cell lines. However, this reduction was not based on an altered interaction with SO1861. It was, rather, due to the impaired endocytosis of dianthin Arg24Ala into the cells.

Sapovaccarin-S1 and -S2, Two Type I RIP Isoforms from the Seeds of Saponaria vaccaria L

Type I ribosome-inactivating proteins (RIPs) are plant toxins that inhibit protein synthesis by exerting rRNA N-glycosylase activity (EC 3.2.2.22). Due to the lack of a cell-binding domain, type I RIPs are not target cell-specific. However once linked to antibodies, so called immunotoxins, they are promising candidates for targeted anti-cancer therapy. In this study, sapovaccarin-S1 and -S2, two newly identified type I RIP isoforms differing in only one amino acid, were isolated from the seeds of Saponaria vaccaria L. Sapovaccarin-S1 and -S2 were purified using ammonium sulfate precipitation and subsequent cation exchange chromatography. The determined molecular masses of 28,763 Da and 28,793 Da are in the mass range typical for type I RIPs and the identified amino acid sequences are homologous to known type I RIPs such as dianthin 30 and saporin-S6 (79% sequence identity each). Sapovaccarin-S1 and -S2 showed adenine-releasing activity and induced cell death in Huh-7 cells. In comparison to other type I RIPs, sapovaccarin-S1 and -S2 exhibited a higher thermostability as shown by nano-differential scanning calorimetry. These results suggest that sapovaccarin-S1 and -S2 would be optimal candidates for targeted anti-cancer therapy.

Suicide nanoplasmids coding for ribosome-inactivating proteins

Conventional eukaryotic expression plasmids contain a DNA backbone that is dispensable for the cellular expression of the transgene. In order to reduce the vector size, minicircle DNA technology was introduced. A drawback of the minicircle technology are considerable production costs. Nanoplasmids are a relatively new class of mini-DNA constructs that are of tremendous potential for pharmaceutical applications. In this study we have designed novel suicide nanoplasmid constructs coding for plant derived ribosome-inactivating proteins. The suicide-nanoplasmids were formulated with a targeted K16-lysine domain, analyzed for size, and characterized by electron microscopy. The anti-proliferative activity of the suicide-nanoplasmids was investigated in vitro by real time microscopy and the expression kinetic was determined using an enhanced green fluorescent protein nanoplasmid variant. In an aggressive in vivo neuroblastoma tumor model, treated mice showed a reduced tumor growth whereby the therapy was well tolerated.

An unusual type I ribosome-inactivating protein from Agrostemma githago L

Agrostemma githago L. (corn cockle) is an herbaceous plant mainly growing in Europe. The seeds of the corn cockle are toxic and poisonings were widespread in the past by consuming contaminated flour. The toxic principle of Agrostemma seeds was attributed to triterpenoid secondary metabolites. Indeed, this is in part true. However Agrostemma githago L. is also a producer of ribosome-inactivating proteins (RIPs). RIPs are N-glycosylases that inactivate the ribosomal RNA, a process leading to an irreversible inhibition of protein synthesis and subsequent cell death. A widely known RIP is ricin from Ricinus communis L., which was used as a bioweapon in the past. In this study we isolated agrostin, a 27 kDa RIP from the seeds of Agrostemma githago L., and determined its full sequence. The toxicity of native agrostin was investigated by impedance-based live cell imaging. By RNAseq we identified 7 additional RIPs (agrostins) in the transcriptome of the corn cockle. Agrostin was recombinantly expressed in E. coli and characterized by MALDI-TOF–MS and adenine releasing assay. This study provides for the first time a comprehensive analysis of ribosome-inactivating proteins in the corn cockle and complements the current knowledge about the toxic principles of the plant.

Dianthin and Its Potential in Targeted Tumor Therapies

Dianthin enzymes belong to ribosome-inactivating proteins (RIPs) of type 1, i.e., they only consist of a catalytic domain and do not have a cell binding moiety. Dianthin-30 is very similar to saporin-S3 and saporin-S6, two RIPs often used to design targeted toxins for tumor therapy and already tested in some clinical trials. Nevertheless, dianthin enzymes also exhibit differences to saporin with regard to structure, efficacy, toxicity, immunogenicity and production by heterologous expression. Some of the distinctions might make dianthin more suitable for targeted tumor therapies than other RIPs. The present review provides an overview of the history of dianthin discovery and illuminates its structure, function and role in targeted toxins. It further discusses the option to increase the efficacy of dianthin by endosomal escape enhancers.