Exploiting Differential Signal Filtering (DSF) and Image Structure Filtering (ISF) Methods for Untargeted Mass Spectrometry Imaging of Bacterial Metabolites.

Matrix-assisted laser desorption/ionization (MALDI) mass spectrometry imaging (MSI) is a label-free technique, producing images where pixels contain mass spectra. The technique allows the visualization of the spatial distribution of (bio)molecules from metabolites to proteins, on surfaces such as tissues sections or bacteria culture media. One particularly exciting example of MALDI-MSI use rests on its potential to localize ionized compounds produced during microbial interactions and chemical communication, offering a molecular snapshot of metabolomes at a given time. The huge size and the complexity of generated MSI data make the processing of the data challenging, which requires the use of computational methods. Despite recent advances, currently available commercial software relies mainly on statistical tools to identify patterns, similarities, and differences within data sets. However, grouping m/z values unique to a given data set according to microbiological contexts, such as coculture experiments, still requires tedious manual analysis. Here we propose a nontargeted method exploiting the differential signals between negative controls and tested experimental conditions, i.e., differential signal filtering (DSF), and a scoring of the ion images using image structure filtering (ISF) coupled with a fold change score between the controls and the conditions of interest. These methods were first applied to coculture experiments involving Escherichia coli and Streptomyces coelicolor, revealing specific MS signals during bacterial interaction. Two case studies were also investigated: (i) cellobiose-mediated induction for the pathogenicity of Streptomyces scabiei, the causative agent of common scab on root and tuber crops, and (ii) iron-repressed production of siderophores of S. scabiei. This report proposes guidelines for MALDI-MSI data treatment applied in the case of microbiology contexts, with enhanced ion peak annotation in specific culture conditions. The strengths and weaknesses of the methods are discussed.

Investigation of Structure-Stabilizing Elements in Proteins by Ion Mobility Mass Spectrometry and Collision-Induced Unfolding.

A recently developed proteolytic reactor, designed for protein structural investigation, was coupled to ion mobility mass spectrometry to monitor collisional cross section (CCS) evolution of model proteins undergoing trypsin-mediated mono enzymatic digestion. As peptides are released during digestion, the CCS of the remaining protein structure may deviate from the classical 2/3 power of the CCS-mass relationship for spherical structures. The classical relationship between CCS and mass (CCS = A × M2/3) for spherical structures, assuming a globular shape in the gas phase, may deviate as stabilizing elements are lost during digestion. In addition, collision-induced unfolding (CIU) experiments on partially digested proteins provided insights into the CCS resilience in the gas phase to ion activation, potentially due to the presence of stabilizing elements. The study initially investigated a model peptide ModBea (3 kDa), assessing the impact of disulfide bridges on CCS resilience in both reduced and oxidized forms. Subsequently, ß-lactoglobulin (2 disulfide bridges), calmodulin (Ca2+ coordination cation), and cytochrome c (heme) were selected to investigate the influence of common structuring elements on CCS resilience. CIU experiments probed the unfolding process, evaluating the effect of losing specific peptides on the energy landscapes of partially digested proteins. Comparisons of the TWCCSN2→He to trend curves describing the CCS/mass relationship revealed that proteins with structure-stabilizing elements consistently exhibit TWCCSN2→He and greater resilience toward CIU compared to proteins lacking these elements. The integration of online digestion, ion mobility, and CIU provides a valuable tool for identifying structuring elements in biopolymers in the gas phase.

An engineered baculoviral protein and DNA co-delivery system for CRISPR-based mammalian genome editing.

CRISPR-based DNA editing technologies enable rapid and accessible genome engineering of eukaryotic cells. However, the delivery of genetically encoded CRISPR components remains challenging and sustained Cas9 expression correlates with higher off-target activities, which can be reduced via Cas9-protein delivery. Here we demonstrate that baculovirus, alongside its DNA cargo, can be used to package and deliver proteins to human cells. Using protein-loaded baculovirus (pBV), we demonstrate delivery of Cas9 or base editors proteins, leading to efficient genome and base editing in human cells. By implementing a reversible, chemically inducible heterodimerization system, we show that protein cargoes can selectively and more efficiently be loaded into pBVs (spBVs). Using spBVs we achieved high levels of multiplexed genome editing in a panel of human cell lines. Importantly, spBVs maintain high editing efficiencies in absence of detectable off-targets events. Finally, by exploiting Cas9 protein and template DNA co-delivery, we demonstrate up to 5% site-specific targeted integration of a 1.8 kb heterologous DNA payload using a single spBV in a panel of human cell lines. In summary, we demonstrate that spBVs represent a versatile, efficient and potentially safer alternative for CRISPR applications requiring co-delivery of DNA and protein cargoes.

Nitrogen sources enhance siderophore-mediated competition for iron between potato common scab and late blight causative agents.

How do pathogens affecting the same host interact with each other? We evaluated here the types of microbe-microbe interactions taking place between Streptomyces scabiei and Phytophthora infestans, the causative agents of common scab and late blight diseases in potato crops, respectively. Under most laboratory culture conditions tested, S. scabiei impaired or completely inhibited the growth of P. infestans by producing either soluble and/or volatile compounds. Increasing peptone levels correlated with increased inhibition of P. infestans. Comparative metabolomics showed that production of S. scabiei siderophores (desferrioxamines, pyochelin, scabichelin, and turgichelin) increased with the quantity of peptone, thereby suggesting that they participate in the inhibition of the oomycete growth. Mass spectrometry imaging further uncovered that the zones of secreted siderophores and of P. infestans growth inhibition coincided. Moreover, either the repression of siderophore production or the neutralization of their iron-chelating activity led to a resumption of P. infestans growth. Replacement of peptone by natural nitrogen sources such as ammonium nitrate, sodium nitrate, ammonium sulfate, and urea also triggered siderophore production in S. scabiei. Interestingly, nitrogen source-induced siderophore production also inhibited the growth of Alternaria solani, the causative agent of the potato early blight. Overall, our work further emphasizes the importance of competition for iron between microorganisms that colonize the same niche. As common scab never alters the vegetative propagation of tubers, we propose that S. scabiei, under certain conditions, could play a protective role for its hosts against much more destructive pathogens through exploitative iron competition and volatile compound production.

Lipopeptides as rhizosphere public goods for microbial cooperation.

IMPORTANCE: Here, we provide new insights into the possible fate of cyclic lipopeptides as prominent specialized metabolites from beneficial bacilli and pseudomonads once released in the soil. Our data illustrate how the B. velezensis lipopeptidome may be enzymatically remodeled by Streptomyces as important members of the soil bacterial community. The enzymatic arsenal of S. venezuelae enables an unsuspected extensive degradation of these compounds, allowing the bacterium to feed on these exogenous products via a mechanism going beyond linearization, which was previously reported as a detoxification strategy. As soils are carbon-rich and nitrogen-poor environments, we propose a new role for cyclic lipopeptides in interspecies interactions, which is to fuel the nitrogen metabolism of a part of the rhizosphere microbial community. Streptomyces and other actinomycetes, producing numerous peptidases and displaying several traits of beneficial bacteria, should be at the front line to directly benefit from these metabolites as "public goods" for microbial cooperation.

Bothrops snake venom L-amino acid oxidases impair biofilm formation of clinically relevant bacteria.

The present work addressed the abilities of two L-amino acid oxidases isolated from Bothrops moojeni (BmooLAAO-I) and Bothrops jararacussu (BjussuLAAO-II) snake venoms to control the growth and prevent the biofilm formation of clinically relevant bacterial pathogens. Upon S. aureus (ATCC BAA44) and S. aureus (clinical isolates), BmooLAAO-I (MIC = 0.12 and 0.24 µg/mL, respectively) and BjussuLAAO-II (MIC = 0.15 µg/mL) showed a potent bacteriostatic effect. Against E. coli (ATCC BAA198) and E. coli (clinical isolates), BmooLAAO-I (MIC = 15.6 and 62.5 µg/mL, respectively) and BjussuLAAO-II (MIC = 4.88 and 9.76 µg/mL, respectively) presented a lower extent effect. Also, BmooLAAO-I (MICB50 = 0.195 µg/mL) and BjussuLAAO-II (MICB50 = 0.39 µg/mL) inhibited the biofilm formation of S. aureus (clinical isolates) in 88% and 89%, respectively, and in 89% and 53% of E. coli (clinical isolates). Moreover, scanning electron microscopy confirmed that the toxins affected bacterial morphology by increasing the roughness of the cell surface and inhibited the biofilm formation. Furthermore, analysis of the tridimensional structures of the toxins showed that the surface-charge distribution presents a remarkable positive region close to the glycosylation motif, which is more pronounced in BmooLAAO-I than BjussuLAAO-II. This region may assist the interaction with bacterial and biofilm surfaces. Collectively, our findings propose that venom-derived antibiofilm agents are promising biotechnological tools which could provide novel strategies for biofilm-associated infections.

ADDovenom: Thermostable Protein-Based ADDomer Nanoparticles as New Therapeutics for Snakebite Envenoming.

Snakebite envenoming can be a life-threatening medical emergency that requires prompt medical intervention to neutralise the effects of venom toxins. Each year up to 138,000 people die from snakebites and threefold more victims suffer life-altering disabilities. The current treatment of snakebite relies solely on antivenom-polyclonal antibodies isolated from the plasma of hyperimmunised animals-which is associated with numerous deficiencies. The ADDovenom project seeks to deliver a novel snakebite therapy, through the use of an innovative protein-based scaffold as a next-generation antivenom. The ADDomer is a megadalton-sized, thermostable synthetic nanoparticle derived from the adenovirus penton base protein; it has 60 high-avidity binding sites to neutralise venom toxins. Here, we outline our experimental strategies to achieve this goal using state-of-the-art protein engineering, expression technology and mass spectrometry, as well as in vitro and in vivo venom neutralisation assays. We anticipate that the approaches described here will produce antivenom with unparalleled efficacy, safety and affordability.

Inhibition of bacterial biofilms by the snake venom proteome.

Snake venoms possess a range of pharmacological and toxicological activities. Here we evaluated the antibacterial and anti-biofilm activity against methicillin-susceptible and methicillin-resistant Staphylococcus aureus (MSSA and MRSA) of venoms from the Samar spitting cobra Naja samarensis and the Puff adder Bitis arietans. Both venoms prevented biofilm production by pathogenic S. aureus in a growth-independent manner, with the B. arietans venom being most potent. Fractionation showed the active molecule to be heat-labile and >10 kDa in size. Proteomic profiles of N. samarensis venom revealed neurotoxins and cytotoxins, as well as an abundance of serine proteases and three-finger toxins, while serine proteases, metalloproteinases and C-lectin types were abundant in B. arietans venom. These enzymes may have evolved to prevent bacteria colonising the snake venom gland. From a biomedical biotechnology perspective, they have valuable potential for anti-virulence therapy to fight antibiotic resistant microbes.

Exploring the Phytobeneficial and Biocontrol Capacities of Endophytic Bacteria Isolated from Hybrid Vanilla Pods.

In this study, 58 endophytic bacterial strains were isolated from pods of two hybrid vanilla plants from Madagascar, Manitra ampotony and Tsy taitra. They were genetically characterized and divided into four distinct phylotypes. Three were associated to genus Bacillus species, and the fourth to the genus Curtobacterium. A selection of twelve strains corresponding to the identified genetic diversity were tested in vitro for four phytobeneficial capacities: phosphate solubilisation, free nitrogen fixation, and phytohormone and siderophore production. They were also evaluated in vitro for their ability to biocontrol the growth of the vanilla pathogenic fungi, Fusarium oxysporum f. sp. radicis vanillae and Cholletotrichum orchidophilum. Three bacteria of phylotype 4, m62a, m64 and m65, showed a high nitrogen fixation capacity in vitro, similar to the Pseudomonas florescens F113 bacterium used as a control (phospate solubilizing efficiency respectively 0.50 ± 0.07, 0.43 ± 0.07 and 0.40 ± 0.06 against 0.48 ± 0.03). Strain t2 related to B. subtilis showed a higher siderophore production than F113 (respectively 1.40 ± 0.1 AU and 1.2 ± 0.1 AU). The strain m72, associated with phylotype 2, showed the highest rate of production of Indole-3-acetic acid (IAA) in vitro. Bacteria belonging to the pylotype 4 showed the best capacity to inhibit fungal growth, especially the strains m62b m64 and t24, which also induced a significant zone of inhibition, suggesting that they may be good candidates for controlling fungal diseases of vanilla. This competence was highlighted with spectral imaging showing the production of lipopeptides (Iturin A2 and A3, C16 and C15-Fengycin A and C14 and C15-Surfactin) by the bacterial strains m65 confronted with the pathogenic fungi of vanilla.

In vivo deglycosylation of recombinant glycoproteins in tobacco BY-2 cells.

Production of recombinant pharmaceutical glycoproteins has been carried out in multiple expression systems. However, N-glycosylation, which increases heterogeneity and raises safety concerns due to the presence of non-human residues, is usually not controlled. The presence and composition of N-glycans are also susceptible to affect protein stability, function and immunogenicity. To tackle these issues, we are developing glycoengineered Nicotiana tabacum Bright Yellow-2 (BY-2) cell lines through knock out and ectopic expression of genes involved in the N-glycosylation pathway. Here, we report on the generation of BY-2 cell lines producing deglycosylated proteins. To this end, endoglycosidase T was co-expressed with an immunoglobulin G or glycoprotein B of human cytomegalovirus in BY-2 cell lines producing only high mannose N-glycans. Endoglycosidase T cleaves high mannose N-glycans to generate single, asparagine-linked, N-acetylglucosamine residues. The N-glycosylation profile of the secreted antibody was determined by mass spectrometry analysis. More than 90% of the N-glycans at the conserved Asn297 site were deglycosylated. Likewise, extensive deglycosylation of glycoprotein B, which possesses 18 N-glycosylation sites, was observed. N-glycan composition of gB glycovariants was assessed by in vitro enzymatic mobility shift assay and proven to be consistent with the expected glycoforms. Comparison of IgG glycovariants by differential scanning fluorimetry revealed a significant impact of the N-glycosylation pattern on the thermal stability. Production of deglycosylated pharmaceutical proteins in BY-2 cells expands the set of glycoengineered BY-2 cell lines.

Next-Generation Sequencing for Venomics: Application of Multi-Enzymatic Limited Digestion for Inventorying the Snake Venom Arsenal.

To improve the characterization of snake venom protein profiles, we report the application of a new generation of proteomic methodology to deeply characterize complex protein mixtures. The new approach, combining a synergic multi-enzymatic and a time-limited digestion (MELD), is a versatile and straightforward protocol previously developed by our group. The higher number of overlapping peptides generated during MELD increases the quality of downstream peptide sequencing and of protein identification. In this context, this work aims at applying the MELD strategy to a venomics purpose for the first time, and especially for the characterization of snake venoms. We used four venoms as the test models for this proof of concept: two Elapidae (Dendroaspis polylepis and Naja naja) and two Viperidae (Bitis arietans and Echis ocellatus). Each venom was reduced and alkylated before being submitted to two different protocols: the classical bottom-up proteomics strategy including a digestion step with trypsin only, or MELD, which combines the activities of trypsin, Glu-C and chymotrypsin with a limited digestion approach. The resulting samples were then injected on an M-Class chromatographic system, and hyphenated to a Q-Exactive Mass Spectrometer. Toxins and protein identification were performed by Peaks Studio X+. The results show that MELD considerably improves the number of sequenced (de novo) peptides and identified peptides from protein databases, leading to the unambiguous identification of a greater number of toxins and proteins. For each venom, MELD was successful, not only in terms of the identification of the major toxins (increasing of sequence coverage), but also concerning the less abundant cellular components (identification of new groups of proteins). In light of these results, MELD represents a credible methodology to be applied as the next generation of proteomics approaches dedicated to venomic analysis. It may open new perspectives for the sequencing and inventorying of the venom arsenal and should expand global knowledge about venom composition.

Oxidative stress induced by Pollonein-LAAO, a new L-amino acid oxidase from Bothrops moojeni venom, prompts prostate tumor spheroid cell death and impairs the cellular invasion process in vitro.

Cancer cells produce abnormal levels of reactive oxygen species (ROS) that contribute to promote their malignant phenotype. In this framework, we hypothesized that the change in ROS concentration above threshold could impair key events of prostate cancer cells (PC-3) progression. Our results demonstrated that Pollonein-LAAO, a new L-amino acid oxidase obtained from Bothrops moojeni venom, was cytotoxic to PC-3 cells in two-dimensional and in tumor spheroid assays. Pollonein-LAAO was able to increase the intracellular ROS generation that culminates in cell death from apoptosis by both intrinsic and extrinsic pathways due to the up-regulation of TP53, BAX, BAD, TNFRSF10B and CASP8. Additionally, Pollonein-LAAO reduced mitochondrial membrane potential and caused G0/G1 phase to delay, due to the up-regulation of CDKN1A and the down-regulation of the expression of CDK2 and E2F. Interestingly, Pollonein-LAAO inhibited critical steps of the cellular invasion process (migration, invasion and adhesion), due to the down-regulation of SNAI1, VIM, MMP2, ITGA2, ITGAV and ITGB3. Furthermore, the Pollonein-LAAO effects were associated with the intracellular ROS production, since the presence of catalase restored the invasiveness of PC-3 cells. In this sense, this study contributes to the potential use of Pollonein-LAAO as ROS-based agent to enhance the current understanding of cancer treatment strategies.

Biochemical characterization and assessment of leishmanicidal effects of a new L-amino acid oxidase from Crotalus durissus collilineatus snake venom (CollinLA AO-I).

This study reports the isolation of CollinLAAO-I, a new L-amino acid oxidase from Crotalus durissus collilineatus snake venom, its biochemical characterization and leishmanicidal potential in Leishmania spp. CollinLAAO-I (63.1 kDa) was successfully isolated with high purity using two chromatographic steps and represents 2.5% of total venom proteins. CollinLAAO-I displayed high enzymatic activity (4262.83 U/mg/min), significantly reducing after 28 days. The enzymatic activity of CollinLAAO-I revealed higher affinity for hydrophobic amino acids such as L-leucine, high enzymatic activity in a wide pH range (6.0-10.0), at temperatures from 0 to 25 °C, and showed complete inhibition in the presence of Na+ and K+. Cytotoxicity assays revealed IC50 of 18.49 and 11.66 µg/mL for Leishmania (L.) amazonensis and Leishmania (L.) infantum, respectively, and the cytotoxicity was completely suppressed by catalase. CollinLAAO-I significantly increased the intracellular concentration of reactive oxygen species (ROS) and reduced the mitochondrial potential of both Leishmania species. Furthermore, CollinLAAO-I decreased the parasite capacity to infect macrophages by around 70%, indicating that even subtoxic concentrations of CollinLAAO-I can interfere with Leishmania vital processes. Thus, the results obtained for CollinLAAO-I provide important support for developing therapeutic strategies against leishmaniasis.

Isolation and characterization of the first phosphodiesterase (Bj-PDE) from the venom of Bothrops jararacussu snake.

Phosphodiesterases are exonucleases that sequentially hydrolyse phosphodiester bonds of polynucleotides from the 3'-end and release 5-mononucleotides. After more than one decade without any advance in the study of Bothropic phosphodiesterases, we described here the isolation of the first phosphodiesterase from Bothrops jararacussu, which we named Bj-PDE. A five-step column chromatography procedure (size exclusion, hydrophobic interaction, cation exchange, lentil lectin affinity, and blue sepharose affinity) enabled isolation of Bj-PDE with preserved and stable enzymatic activity (bis(p-nitrophenyl) phosphate substrate), Km = 6.9 mM (± 0.7 mM), kcat/Km = 1.7 × 104 M-1 s-1 (± 0.2 × 104 M-1 s-1), MW = 116 kDa (SDS-PAGE), optimum activity around 45 °C at pH 8.0, and stability for 81 days at different storage temperatures (8, -20, and - 80 °C). Ca2+ and Mg2+ ions positively influenced Bj-PDE activity, while EDTA had the opposite action. Zn2+ restored >50 % of enzyme activity after its inhibition by EDTA. The Bj-PDE partial sequence identified by mass spectrometry was very similar to the sequence of BATXPDE1 from Bothrops atrox, which was evolutionarily close to this new PDE. Therefore, our study represents an important progress on the isolation of this minor toxin and sheds new lights on the properties and bioprospection of bothropic phosphodiesterases.

Differential Kendrick's Plots as an Innovative Tool for Lipidomics in Complex Samples: Comparison of Liquid Chromatography and Infusion-Based Methods to Sample Differential Study.

Lipidomics has developed rapidly over the past decade. Nontargeted lipidomics from biological samples remains a challenge due to the high structural diversity, the concentration range of lipids, and the complexity of biological samples. We introduce here the use of differential Kendrick's plots as a rapid visualization tool for a qualitative nontargeted analysis of lipids categories and classes from data generated by either liquid chromatography-mass spectrometry (LC-MS) or direct infusion (nESI-MS). Each lipid class is easily identified by comparison with the theoretical Kendrick plot pattern constructed from exact mass measurements and by using MSKendrickFilter, an in-house Python software. The lipids are identified with the LIPID MAPS database. In addition, in LC-MS, the software based on the Kendrick plots returns the retention time from all the lipids belonging to the same series. Lipid extracts from a yeast (Saccharomyces cerevisiae) are used as a model. An on/off case comparing Kendrick plots from two cell lines (prostate cancer cell lines treated or not with a DGAT2 inhibition) clearly shows the effect of the inhibition. Our study demonstrates the good performance of direct infusion as a fast qualitative screening method as well as for the analysis of chromatograms. A fast screening semiquantitative approach is also possible, while the targeted mode remains the golden standard for precise quantitative analysis.

Grapevine leaf MALDI-MS imaging reveals the localisation of a putatively identified sucrose metabolite associated to Plasmopara viticola development.

Despite well-established pathways and metabolites involved in grapevine-Plasmopara viticola interaction, information on the molecules involved in the first moments of pathogen contact with the leaf surface and their specific location is still missing. To understand and localise these molecules, we analysed grapevine leaf discs infected with P. viticola with MSI. Plant material preparation was optimised, and different matrices and solvents were tested. Our data shows that trichomes hamper matrix deposition and the ion signal. Results show that putatively identified sucrose presents a higher accumulation and a non-homogeneous distribution in the infected leaf discs in comparison with the controls. This accumulation was mainly on the veins, leading to the hypothesis that sucrose metabolism is being manipulated by the development structures of P. viticola. Up to our knowledge this is the first time that the localisation of a putatively identified sucrose metabolite was shown to be associated to P. viticola infection sites.

RNAi of Mannosidase-Ia in the Colorado potato beetle and changes in the midgut and peritrophic membrane.

BACKGROUND: In addition to its role in the digestive system, the peritrophic membrane (PM) provides a physical barrier protecting the intestine from abrasion and against pathogens. Because of its sensitivity to RNA interference (RNAi), the notorious pest insect, the Colorado potato beetle (CPB, Leptinotarsa decemlineata), has become a model insect for functional studies. Previously, RNAi-mediated silencing of Mannosidase-Ia (ManIa), a key enzyme in the transition from high-mannose glycan moieties to paucimannose N-glycans, was shown to disrupt the transition from larva to pupa and the metamorphosis into adult beetles. While these effects at the organismal level were interesting in a pest control context, the effects at the organ or tissue level and also immune effects have not been investigated yet. To fill this knowledge gap, we performed an analysis of the midgut and PM in ManIa-silenced insects. RESULTS: As marked phenotype, the ManIaRNAi insects, the PM pore size was found to be decreased when compared to the control GFPRNAi insects. These smaller pores are related to the observation of thinner microvilli (Mv) on the epithelial cells of the midgut of ManIaRNAi insects. A midgut and PM proteome study and reverse transcription quantitative polymerase chain reaction (RT-qPCR) analysis with a selection of marker genes was performed to characterize the midgut cells and understand their response to the silencing of ManIa. In agreement with the loss of ManIa activity, an accumulation of high-mannose N-glycans was observed in the ManIa-silenced insects. As a pathogen-associated molecular pattern (PAMP), the presence of these glycan structures could trigger the activation of the immune pathways. CONCLUSION: The observed decrease in PM pore size could be a response to prevent potential pathogens to access the midgut epithelium. This hypothesis is supported by the strong increase in transcription levels of the anti-fungal peptide drosomycin-like in ManIaRNAi insects, although further research is required to elucidate this possibility. The potential immune response in the midgut and the smaller pore size in the PM shed a light on the function of the PM as a physical barrier and provide evidence for the relation between the Mv and PM. © 2022 Society of Chemical Industry.

FT-ICR Mass Spectrometry Imaging at Extreme Mass Resolving Power Using a Dynamically Harmonized ICR Cell with 1ω or 2ω Detection.

MALDI mass spectrometry imaging (MALDI MSI) is a powerful analytical method for achieving 2D localization of compounds from thin sections of typically but not exclusively biological samples. The dynamically harmonized ICR cell (ParaCell) was recently introduced to achieve extreme spectral resolution capable of providing the isotopic fine structure of ions detected in complex samples. The latest improvement in the ICR technology also includes 2ω detection, which significantly reduces the transient time while preserving the nominal mass resolving power of the ICR cell. High-resolution MS images acquired on FT-ICR instruments equipped with 7T and 9.4T superconducting magnets and the dynamically harmonized ICR cell operating at suboptimal parameters suffered severely from the pixel-to-pixel shifting of m/z peaks due to space-charge effects. The resulting profile average mass spectra have depreciated mass measurement accuracy and mass resolving power under the instrument specifications that affect the confidence level of the identified ions. Here, we propose an analytical workflow based on the monitoring of the total ion current to restrain the pixel-to-pixel m/z shift. Adjustment of the laser parameters is proposed to maintain high spectral resolution and mass accuracy measurement within the instrument specifications during MSI analyses. The optimized method has been successfully employed in replicates to perform high-quality MALDI MS images at resolving power (FWHM) above 1,000,000 in the lipid mass range across the whole image for superconducting magnets of 7T and 9.4T using 1 and 2ω detection. Our data also compare favorably with MALDI MSI experiments performed on higher-magnetic-field superconducting magnets, including the 21T MALDI FT-ICR prototype instrument of the NHMFL group at Tallahassee, Florida.

Cyclic Peptide Protomer Detection in the Gas Phase: Impact on CCS Measurement and Fragmentation Patterns.

With the recent improvements in ion mobility resolution, it is now possible to separate small protomeric tautomers, called protomers. In larger molecules above 1000 Da such as peptides, a few studies suggest that protomers do exist as well and may contribute to their gas-phase conformational heterogeneity. In this work, we observed a CCS distribution that can be explained by the presence of protomers of surfactin, a small lipopeptide with no basic site. Following preliminary density functional theoretical calculations, several protonation sites in the gas phase were energetically favorable in positive ionization mode. Experimentally, at least three near-resolved IM peaks were observed in positive ionization mode, while only one was detected in negative ionization mode. These results were in good agreement with the DFT predictions. CID breakdown curve analysis after IM separation showed different inflection points (CE50) suggesting that different intramolecular interactions were implied in the stabilization of the structures of surfactin. The fragment ratio observed after collision-induced fragmentation was also different, suggesting different ring-opening localizations. All these observations support the presence of protomers on the cyclic peptide moieties of the surfactin. These data strongly suggest that protomeric tautomerism can still be observed on molecules above 1000 Da if the IM resolving power is sufficient. It also supports that the proton localization involves a change in the 3D structure that can affect the experimental CCS and the fragmentation channels of such peptides.

A new Kunitz-type snake toxin family associated with an original mode of interaction with the vasopressin 2 receptor.

BACKGROUND AND PURPOSE: Venomous animals express numerous Kunitz-type peptides. The mambaquaretin-1 (MQ1) peptide identified from the Dendroaspis angusticeps venom is the most selective antagonist of the arginine-vasopressin V2 receptor (V2R) and the only unique Kunitz-type peptide active on a GPCR. We aimed to exploit other mamba venoms to enlarge the V2R-Kunitz peptide family and gain insight into the MQ1 molecular mode of action. EXPERIMENTAL APPROACH: We used a bio-guided screening assay to identify novel MQs and placed them phylogenetically. MQs were produced by solid-phase peptide synthesis and characterized in vitro by binding and functional tests and in vivo by diuresis measurement in rats. KEY RESULTS: Eight additional MQs were identified with nanomolar affinities for the V2R, all antagonists. MQs form a new subgroup in the Kunitz family, close to the V2R non-active dendrotoxins and to two V2R-active cobra toxins. Sequence comparison between active and non-active V2R Kunitz peptides highlighted five positions, among which four are involved in V2R interaction and belong to the two large MQ1 loops. We finally determined that eight positions, part of these two loops, interact with the V2R. The variant MQ1-K39A showed a higher affinity for the hV2R, but not for the rat V2R. CONCLUSIONS AND IMPLICATIONS: A new function and mode of action is associated with the Kunitz peptides. The number of MQ1 residues involved in V2R binding is large and may explain its absolute selectivity. MQ1-K39A represents the first step in the improvement of the MQ1 design from a medicinal perspective.