Peptide Mass Research Articles

Phlebotomine sand fly survey, blood meal source identification, and description of Sergentomyia imihra n. sp. in the central Sahara of Algeria

BackgroundPhlebotomine sand flies (Diptera: Psychodidae) are important vectors of various pathogens, mainly Leishmania parasites. In the Old World, the most important genus in term of pathogens transmission is the genus Phlebotomus, which includes many proven or suspected vectors of several Leishmania species, while the genus Sergentomyia remains so far unproven as a vector of human pathogens. Algeria is one of the most affected countries by human leishmaniasis.MethodsIn the present study, an entomological survey was carried out in two provinces, Ghardaïa and Illizi, located in the north and central Sahara, respectively, where cases of human leishmaniasis are recorded. Our goal was to understand the role of the local sand fly species in the transmission of Leishmania parasites and to analyze their blood meal preferences. Collected sand flies were identified by a combination of morphological and molecular approaches that included DNA-barcoding and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) protein profiling. In addition, female blood meals were analyzed by peptide mass mapping using MALDI-TOF MS.ResultsIn total, 640 sand fly specimens belonging to Phlebotomus and Sergentomyia genera were collected in the two provinces. Sergentomyia antennata and Se. fallax were most abundant species in Ghardaïa, and Ph. papatasi and Ph. alexandri in Illizi. In addition, a new sand fly species was described in Illizi named Sergentomyia (Sergentomyia) imihra n. sp. Blood meal analysis of the engorged females revealed various mammalian hosts, especially goats, but also humans for Phlebotomus papatasi and Ph. alexandri, suggesting that these vector species are opportunistic feeders.ConclusionsIntegrative approach that combined morphological analysis, sequencing of DNA markers, and protein profiling enabled the recognition and description of a new Sergentomyia species, raising the number of the Algerian sand fly fauna to 27 species. Further sand fly surveillance in the central Sahara is recommended to identify the thus-far unknown males of Se. imihra n. sp.Graphical

Multi-proxy investigations of Bronze Age diet and environment in the hyper-arid eastern Tarim Basin (Lop Nur), northwest China

Humans have a long history of occupying ecologically marginal regions, and the ancient cultural mechanisms of adaptation to these challenging environments remain poorly understood. We examine archaeological deposits from a Bronze Age settlement in the hyper-arid eastern Tarim Basin (Lop Nur), identifying well-preserved plant remains and bone fragments that shed light on the palaeodiet and past environmental setting. We use the newly developed peptide mass fingerprinting method of ZooMS (zooarchaeology by mass spectrometry) and TimsTOF MS (trapped ion mobility time of flight mass spectrometry) to identify fragments of ancient fish bones as Cyprinidae and possible Salmonidae, indicating both their consumption and the former presence of intra-settlement fresh water-bodies. Remains of littoral and aquatic plants attest to a marshy palaeo-delta at the confluence of the Tarim and Kongque rivers, testifying to a former biodiverse oasis in the Lop Desert when humans occupied the site. We conclude that the use of both aquatic and desert peripheral resources, combined with the intentional management of local environments, were all essential prehistoric adaptations. In addition, we show that radiocarbon dates of aquatic remains have an offset spanning hundreds to thousands of years, due to a freshwater reservoir effect, requiring careful consideration of ages for archaeological bones in the broader region.

Identification, Purification, and Characterization of Kunitz-Type Protease Inhibitors from White-Fleshed Dragon Fruit (Selenicereus undatus) and Red-Fleshed Dragon Fruit (Selenicereus costaricensis) Seeds as Novel Food Allergens.

There have been clinical reports of allergies to dragon fruits. However, little is known about the allergens that trigger these reactions. This study aimed to investigate novel allergens in dragon fruits. The peptide mass fingerprints of two purified natural allergens were identified by LC-MS/MS with chymotrypsin proteolysis. The complete amino acid sequences of the allergens were deduced from cDNA amplicon sequences. The coding sequences of two allergens were inserted in the expression vector pColdI, and recombinant allergens were produced in Escherichia coli. Circular dichroism was performed to analyze the secondary structures of natural and recombinant allergens. Our results identified two novel allergens as Kunitz-type protease inhibitors. Recombinant allergens exhibited well-folded structures, predominantly composed of β-sheets, similar to their natural counterparts. IgE reactivity analysis with sera from ten patients primarily sensitized to dragon fruit indicated that Kunitz-type protease inhibitors are major allergens in dragon fruits. These results improve our understanding of allergen sources and provide important insights into the allergenicity of proteins from different species.

A Thin Polymer Layer Enables Peptide-Polycation Complexes with Ultrahigh Efficient Encapsulation.

A monolayer encapsulation is a new opportunity for engineering a system with high drug loading, but immobilizing polymer molecules on the surface of individual peptide nanoparticles is still an ongoing challenge. Herein, an individual peptide nanoparticle encapsulation strategy is proposed via surface adsorption, in which peptide molecules undergo granulation and subsequently aggregate with polymer molecules, forming a network via electrostatic interactions. Under the water phase, surplus polymer molecules dissolve, leading to a single nanoparticle encapsulation with a core-shell structure. As expected, the dense interfacial layer on the peptide nanoparticle surface achieves a superior loading degree of up to 95.4%. What's more, once the core-shell structure is established, the peptide mass fraction in individual encapsulation always exceeds 90% even under fierce external force. Following the individual nanoparticle encapsulation, the insulin-polycation complex (InsNp@PEI) reduces the inflammation from polymer and displays an effective glycemic control in type 1 diabetes. Overall, the newly developed single surface decoration encapsulates peptides with ultrahigh efficiency and opens up the possibility for further encapsulation.

Alpha-1 antitrypsin inhibits pertussis toxin

Pertussis (whooping cough) is a vaccine-preventable but re-emerging, highly infectious respiratory disease caused by Bordetella pertussis. There are currently no effective treatments for pertussis, complicating care for non-vaccinated individuals, especially newborns. Disease manifestations are predominantly caused by pertussis toxin (PT), a pivotal virulence factor classified as an ADP-ribosylating AB-type protein toxin. In this work, an unbiased approach using peptide libraries, bioassay-guided fractionation and mass spectrometry revealed α1-antitrypsin (α1AT) as a potent PT inhibitor. Biochemistry-, cell culture- and molecular modeling-based in vitro experimentation demonstrated that the α1AT mode of action is based on blocking PT-binding to the host target cell surface. In the infant mouse model of severe pertussis, α1AT expression was reduced upon infection. Further, systemic administration of α1AT significantly reduced B. pertussis-induced leukocytosis, which is a hallmark of infant infection and major risk factor for fatal pertussis. Taken together our data demonstrates that α1AT is a novel PT inhibitor and that further evaluation and development of α1AT as a therapeutic agent for pertussis is warranted. Importantly, purified α1AT is already in use clinically as an intravenous augmentation therapy for those with genetic α1AT deficiency and could be repurposed to clinical management of pertussis.

A novel molecular target, superoxide dismutase 1, in ALK inhibitor-resistant lung cancer cells, detected through proteomic analysis

BackgroundsTo the best of our knowledge, there are no reports of proteomic analysis for the identification of unknown proteins involved in resistance to anaplastic lymphoma kinase (ALK) inhibitors. In this study, we investigated the proteins involved in resistance to alectinib, a representative ALK inhibitor, through proteomic analysis and the possibility of overcoming resistance. MethodsAn ALK-positive lung adenocarcinoma cell line (ABC-11) and the corresponding alectinib-resistant cell line (ABC-11/CHR2) were used. Two-dimensional difference gel electrophoresis (2D DIGE) was performed; the stained gel was scanned and the spots were analyzed using DeCyder TM2D 7.0. Mass spectrometry (MS) with the UltrafleXtreme matrix-assisted laser desorption ionization-tandem time-of-flight (MALDI-TOF/TOF) MS system was performed. For the MS/MS analysis, the samples were spotted on an AnchorChipTM 600 TF plate. The peptide masses obtained in the reflector positive mode were acquired at m/z of 400−6,000. MS/MS data were searched against the NCBI protein databases. Growth inhibition was measured using an MTT assay. The isobologram and combination index were calculated based on the median-effect analysis. Western blotting was performed using antibodies, including superoxide dismutase (SOD) 1, MET, ERK, PARP, AKT, and BRCA1. ResultsThe 2D DIGE for ABC-11 and ABC-11/CHR2 showed different expression levels in about 2,000 spots. SOD was identified from spots highly expressed in resistant strains. Western blotting also confirmed SOD1 overexpression in ABC-11/CHR2. siSOD1 enhanced the growth inhibitory effects of alectinib, increased cleaved PARP levels, and decreased pERK, pAKT, and BRCA1 levels with a combination of alectinib. In addition, the combination of LCS-1, an SOD1 inhibitor, and alectinib synergistically suppressed the growth in ABC-11/CHR2, but not in ABC-11. ConclusionsSOD1 overexpression is thought to be a mechanism for alectinib resistance, suggesting the possibility of overcoming resistance using SOD1 inhibitors.

Identification and Activity Study of an Impurity Band Observed in the nrSDS-PAGE of Aflibercept.

Aflibercept is a biopharmaceutical targeting vascular endothelial growth factor (VEGF) that has shown promise in the treatment of neovascular age-related macular degeneration (nAMD) and diabetic macular edema (DME) in adults. Quality control studies of aflibercept employing non-reduced SDS-PAGE (nrSDS-PAGE) have shown that a significant variant band (IM1) is consistently present below the main band. Considering the quality control strategy of biopharmaceuticals, structural elucidation and functional studies are required. In this study, the variant bands in nrSDS-PAGE were collected through electroelution and identified by peptide mass fingerprinting based on liquid chromatography-tandem MS (LC-MS/MS). This variant was expressed using knob-into-hole (KIH) design transient transfection for the detection of ligand affinity, binding activity and biological activity. The variant band was formed by C-terminal truncation at position N99 of one chain in the aflibercept homodimer. Then, this variant was successfully expressed using KIH design transient transfection. The ligand affinity of the IM1 truncated variant was reduced by 18-fold, and neither binding activity nor biological activity were detected. The efficacy of aflibercept is influenced by the loss of biological activity of the variant. Therefore, this study supports the development of a quality control strategy for aflibercept.

Amino Acid Composition Determination From the Fractional Mass of Peptides

ABSTRACTA peptide's fractional mass is directly associated with its elemental composition and thus amino acid composition. Here it is demonstrated that a peptide's fractional mass alone can be a useful identifier or indicator of that composition for small to mid‐sized peptides (5–7 amino acids) and can significantly reduce the number of viable amino acid compositions for larger peptides (> 8 residues) to include or exclude certain possibilities. Separate consideration of the integer portion of the peptide's mass helps to reduce the number of possibilities where many duplicate fractional mass values are found. Adoption of this fractional mass strategy should aid approaches that are presently employed for peptide identification, including in the use of mass map data to search protein databases for proteomics applications.

Phlebotomine sand flies (Diptera: Psychodidae) of Bosnia and Herzegovina: distribution, ecology and environmental preferences

Sand flies (Diptera: Phlebotominae) are the principal vectors for the protozoan parasites Leishmania spp. and for phleboviruses. The sand fly fauna on the Balkan Peninsula, including Bosnia and Herzegovina (BIH), is diverse and the circulation of Leishmania infantum as well as phleboviruses has been proven. However, recent data on the sand fly fauna in BIH are scarce. In this study, we surveyed understudied regions in central and northeastern BIH to update the sand fly distribution and gain insights into the ecological and environmental factors shaping their appearance. CDC light trapping was conducted in 2022 and 2023 and a combination of morphological and molecular methods (cytochrome oxidase I barcoding) was performed for species identifications. We mapped the currently known distribution, modelled climatic suitability patterns and performed environmental analyses by applying machine learning methods. In addition, we analyzed blood meals by host gene sequencing and MALDI-TOF peptide mass mapping and screened for Leishmania spp. DNA and Phlebovirus RNA.Altogether, 591 sand flies of four species were trapped, predominantly Phlebotomus neglectus (97 %), but also Ph. balcanicus, Ph. mascittii, and Ph. papatasi. Records of seven sand fly species known to be endemic were plotted onto distribution maps based on 101 datapoints, identifying Ph. neglectus as the overall predominant species. The environmental analyses of sand fly species indicated variation in altitudinal, thermal, and precipitation conditions across the sand fly-positive sites. Phlebotomus simici, Phlebotomus tobbi, and Sergentomyia minuta are typically found exclusively in Mediterranean and subtropical climate zones, whereas other species typically inhabit continental regions. The Inverse Distance Weighted (IDW) interpolation of sand fly species numbers and Shannon entropy values suggested the southeastern coastal region of BIH as a primary focus for sand fly occurrence. This finding was corroborated by modeled average climatic suitability patterns for sand flies, depicting four distinct meso-regions for sand fly occurrence. The results of the ensemble method highlight the importance of annual precipitation to distinguish between positive and negative sand fly trapping sites in BIH. In total, 55 blood meals of two sand fly species, Ph. neglectus and Ph. balcanicus, were analyzed and five host species identified.Our comprehensive assessment of ecological and environmental preferences of sand flies in BIH may support further entomological surveys and help to better understand and evaluate potential hot spots of disease transmission in the country.

Fixative or Finish? Identifying the Surface Coating on John Constable’s Drawings Using Peptide Mass Fingerprinting

ABSTRACT A survey of graphite drawings by the English painter John Constable revealed that in many cases the artist applied a coating overtop of the media. This thin, clear, glossy coating was characterized on over thirty drawings where it appeared to be the same material although employed in different ways. Several attempts were made to identify the material with minimal success until peptide mass fingerprinting (PMF) was used, and a minimally invasive sampling method involving vinyl eraser cubes proved to be a very easy and effective technique to collect sufficient sample material for the analysis. The results of testing samples from seven drawings conclusively identified the coating as isinglass, which Constable was using in other preparations of support materials for painting. As part of this work, putative markers for the identification of isinglass by PMF were developed.

Dear-PSM: A deep learning-based peptide search engine enables full database search for proteomics.

Peptide spectrum matching is the process of linking mass spectrometry data with peptide sequences. An experimental spectrum can match thousands of candidate peptides with variable modifications leading to an exponential increase in candidates. Completing the search within a limited time is a key challenge. Traditional searches expedite the process by restricting peptide mass errors and variable modifications, but this limits interpretive capability. To address this challenge, we propose Dear-PSM, a peptide search engine that supports full database searching. Dear-PSM does not restrict peptide mass errors, matching each spectrum to all peptides in the database and increasing the number of variable modifications per peptide from the conventional 3-20. Leveraging inverted index technology, Dear-PSM creates a high-performance index table of experimental spectra and utilizes deep learning algorithms for peptide validation. Through these techniques, Dear-PSM achieves a speed breakthrough 7 times faster than mainstream search engines on a regular desktop computer, with a remarkable 240-fold reduction in memory consumption. Benchmark test results demonstrate that Dear-PSM, in full database search mode, can reproduce over 90% of the results obtained by mainstream search engines when handling complex mass spectrometry data collected from different species using various instruments. Furthermore, it uncovers a substantial number of new peptides and proteins. Dear-PSM has been publicly released on the GitHub repository https://github.com/jianweishuai/Dear-PSM.

CPred: Charge State Prediction for Modified and Unmodified Peptides in Electrospray Ionization.

The mass-to-charge ratio serves as a critical parameter in peptide identification via mass spectrometry, enabling the precise determination of peptide masses and facilitating their differentiation based on unique charge characteristics, especially when peptides are ionized by tools like electrospray ionization, which produces multiply charged ions. We developed a neural network called CPred, which can accurately predict the charge state distribution from +1 to +7 for the modified and unmodified peptides. CPred was trained on the large-scale synthetic training data, consisting of tryptic and non-tryptic peptides, and various fragmentation methods. The model was further evaluated on independent, external test data sets. Results were evaluated through the Pearson correlation coefficient and showed high correlations of up to 0.9997117 between the predicted and acquired charge state distributions. The effect of specifying modifications in the neural network and feature importance was further investigated, revealing the value of modifications and vital peptide properties in holding on to protons. CPreds' accurate predictions of the charge state distribution can play an essential role in boosting confidence in peptide identifications during rescoring as a novel feature.

Innovations Toward Immunopeptidomics

Over the past 30 years, immunopeptidomics has grown alongside improvements in mass spectrometry technology, genomics, transcriptomics, T cell receptor sequencing, and immunological assays to identify and characterize the targets of activated T cells. Together, multiple research groups with expertise in immunology, biochemistry, chemistry, and peptide mass spectrometry have come together to enable the isolation and sequence identification of endogenous major histocompatibility complex (MHC)-bound peptides. The idea to apply highly sensitive mass spectrometry techniques to study the landscape of peptide antigens presented by cell surface MHCs was innovative and continues to be successfully used and improved upon to deepen our understanding of how peptide antigens are processed and presented to T cells. Multiple research groups were involved in this bringing immunopeptidomics to the forefront of translational research, and we will highlight the contributions of one of the earliest developers, Professor Donald F. Hunt, and his research group at the University of Virginia. The Hunt laboratory applied cutting edge mass spectroscopy–based immunopeptidomics to study cancer, autoimmunity, transplant rejection, and infectious diseases. Across these diverse research areas, the Hunt laboratory and collaborators would characterize previously unknown MHC peptide–binding motifs and identify immunologically active antigens using ultra sensitive mass spectrometry techniques. Amazingly, many of the MHC-bound peptide antigens discovered in collaborations with the Hunt laboratory were sequenced by mass spectrometry before the completion of the human genome using manual de novo sequencing. In this perspective article, we will chronicle the work of the Hunt laboratory and their many collaborators that would be a major part of the foundation for mass spectrometry–based immunopeptidomics and its application to immunology research.

Microfluidic Chip Coupled with MALDI-TOF MS for Multitarget Detection of Allergens in Crucian Carp (Carassius auratus).

The goal of the present study was to establish a rapid, simple method for simultaneous allergy testing of sera from multiple fish-allergic patients. Sera from fish-allergic patients were pooled and used for capturing allergens in fish muscle of crucian carp (Carassius auratus), which was studied as a fish model. Sarcoplasmic proteins of crucian carp (Carassius auratus) were extracted for the analysis of allergens. Anti-human IgE antibody-functionalized magnetic beads were utilized to collect IgE antibodies from human pooled sera. The isolation of allergenic proteins was immunomagnetically performed in microfluidic channels, and the elution of the captured allergenic proteins was done with 5% (v/v) acetic acid aqueous solution. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) and peptide mass fingerprinting were used for the analysis of tryptic digests of eluted proteins. Ten potential allergenic proteins were identified from crucian carp (Carassius auratus). The present protocol provides a rapid, efficient, and simple method for simultaneous detection of multiple allergens, based on multitargeted antibodies from pooled sera of allergic patients. The constructed multiple antibody-modified MBs can be applied for the deallergenicity of food matrices. The efficiency of allergen detection can be greatly improved, with promising application in allergen discovery and filtration for other muscle-based foods.

Characteristics of Umami Taste of Soy Sauce Using Electronic Tongue, Amino Acid Analyzer, and MALDI-TOF MS.

The objective of this study was to investigate the umami characteristics of soy sauce using electronic tongue evaluation and amino acid composition and matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) analysis. The soy sauce peptides were isolated from soy sauce using XAD-16 macroporous resin combined with ethanol solution. The results showed that the soy sauce peptide fraction eluted by 60% ethanol (SS-60%) exhibited a prominent umami taste, and the umami scores were highly positively correlated with the amino acid nitrogen contents of soy sauces. The umami scores of SS-60% were significantly positively correlated with the contents of free amino acids. Especially, Phe showed the highest positive correlation with the umami scores. In addition, five characteristic ion peaks with m/z at 499, 561, 643, 649, and 855 were identified in the peptide mass fingerprinting. Therefore, this study provides new insights into the umami characteristics for the taste evaluation and reality identification of soy sauce.

Plasma-based proteomic profiling identifies the distinct regulation of proteins in hyperplasia and endometrial cancer

BackgroundAmong gynaecological malignancies, endometrial cancer (EC) is the most prevalent type of uterine cancer affecting women. This study explored the proteomic profiles of plasma samples obtained from EC patients, those with hyperplasia (Hy), and a control group (CO). A combination of techniques, such as 2D-DIGE, mass spectrometry, and bioinformatics, including pathway analysis, was used to identify proteins with modified expression levels, biomarkers and their associated metabolic pathways in these groups.MethodsThirty-four patients, categorized into three groups—10 with EC, 12 with Hy, and 12 CO—between the ages of 46 and 75 years old were included in the study. Untargeted proteomic analysis was carried out using two-dimensional difference in gel electrophoresis (2D-DIGE) coupled with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS).ResultsIn all three groups, 114 proteins that were significantly (p ≤ 0.05 and fold change ≥ 1.5) altered were successfully identified using peptide mass fingerprints (PMFs). Compared with those in the control group (CO), the EC samples had 85 differentially expressed proteins (39 upregulated and 46 downregulated), and in the Hy group, 81 proteins were dysregulated (40 upregulated and 41 downregulated) compared to those in the CO group, while 33 proteins exhibited differential regulation (12 upregulated and 21 downregulated) in the EC plasma samples compared to those in the Hy group. Vitamin D binding protein and complement C3 distinguished Hy and EC from CO with the greatest changes in expression. Among the differentially expressed proteins identified, enzymes with catalytic activity represented the largest group (42.9%). In terms of biological processes, most of the proteins were involved in cellular processes (28.8%), followed by metabolic processes (16.7%). STRING analysis for protein interactions revealed that the significantly differentially abundant proteins in the three groups are involved in three main biological processes: signalling of complement and coagulation cascades, regulation of insulin-like growth factor (IGF) transport and uptake by insulin-like growth factor binding proteins (IGFBPs), and plasma lipoprotein assembly, remodelling, and clearance.ConclusionThe identified plasma protein markers have the potential to serve as biomarkers for differentiating between EC and Hy, as well as for early diagnosis and monitoring of cancer progression.

Finding the right plaice at the right time: Multi‐molecular analysis of flatfish reveals historical catch habitats

AbstractFlatfish are ecologically diverse species that commonly occur in marine environments, but also in estuarine and riverine habitats. This complicates the examination of the potential role of flatfish in the ‘marine fish event horizon’, an economic shift in human exploitation from freshwater to marine fish species during the 10–11th centuries CE around the southern North Sea. This study represents the first multi‐disciplinary investigation of flatfish remains to make species‐specific interpretations of flatfish exploitation. Peptide mass fingerprinting and multi‐isotope analysis of carbon (δ13C), nitrogen (δ15N) and sulphur (δ34S) was performed on collagen from 356 archaeological flatfish and 120 comparative archaeological marine or freshwater species to explore the catch habitat of individual flatfish species between 600 and 1600 CE from the North Sea area. European flounder show signals reflecting both freshwater and marine environments, while other flatfish show only those of marine habitats. A subtle shift towards more marine exploitation towards the end of the period is identified, corresponding to the observed transition in targeted species from flounder to plaice throughout the medieval period. Sites show slight differences in δ13C and δ34S within the same species, related to the local environments. Remarkable is the high abundance of marine plaice and flounder during the early medieval period, which shows clear marine or coastal exploitation of flatfish early on, well before the previously accepted onset of the marine fish event horizon. This indicates a gradual shift from coastal to open marine fish exploitation over the medieval period.

Non-prime- and prime-side profiling of Pro-Pro endopeptidase specificity using synthetic combinatorial peptide libraries and mass spectrometry.

A group of bacterial proteases, the Pro-Pro endopeptidases (PPEPs), possess the unique ability to hydrolyze proline-proline bonds in proteins. Since a protease's function is largely determined by its substrate specificity, methods that can extensively characterize substrate specificity are valuable tools for protease research. Previously, we achieved an in-depth characterization of PPEP prime-side specificity. However, PPEP specificity is also determined by the non-prime-side residues in the substrate. To gain a more complete insight into the determinants of PPEP specificity, we characterized the non-prime- and prime-side specificity of various PPEPs using a combination of synthetic combinatorial peptide libraries and mass spectrometry. With this approach, we deepened our understanding of the P3-P3' specificities of PPEP-1 and PPEP-2, while identifying the endogenous substrate of PPEP-2 as the most optimal substrate in our library data. Furthermore, by employing the library approach, we investigated the altered specificity of mutants of PPEP-1 and PPEP-2. Additionally, we characterized a novel PPEP from Anoxybacillus tepidamans, which we termed PPEP-4. Based on structural comparisons, we hypothesized that PPEP-4 displays a PPEP-1-like prime-side specificity, which was substantiated by the experimental data. Intriguingly, another putative PPEP from Clostridioides difficile, CD1597, did not display Pro-Pro endoproteolytic activity. Collectively, we characterized PPEP specificity in detail using our robust peptide library method and, together with additional structural information, provide more insight into the intricate mechanisms that govern protease specificity.

Proteome analysis, genetic characterization, and antibiotic resistance patterns of Klebsiella pneumoniae clinical isolates

Klebsiella pneumoniae (K. pneumoniae) is a member of the ESKAPE group and is responsible for severe community and healthcare-associated infections. Certain Klebsiella species have very similar phenotypes, which presents a challenge in identifying K. pneumoniae. Multidrug-resistant K. pneumoniae is also a serious global problem that needs to be addressed. A total of 190 isolates were isolated from urine (n = 69), respiratory (n = 52), wound (n = 48) and blood (n = 21) samples collected from various hospitals in the Al-Qassim, Saudi Arabia, between March 2021 and October 2022. Our study aimed to rapidly and accurately detect K. pneumoniae using the Peptide Mass Fingerprinting (PMF) technique, confirmed by real-time PCR. Additionally, screening for antibiotic susceptibility and resistance was conducted. The primary methods for identifying K. pneumoniae isolates were culture, Gram staining, and the Vitek® 2 ID Compact system. An automated MALDI Biotyper (MBT) instrument was used for proteome identification, which was subsequently confirmed using SYBR green real-time polymerase chain reaction (real-time PCR) and microfluidic electrophoresis assays. Vitek® 2 AST-GN66 cards were utilized to evaluate the antimicrobial sensitivity of K. pneumoniae isolates. According to our results, Vitek® 2 Compact accurately identified 178 out of 190 (93.68%) K. pneumoniae isolates, while the PMF technique correctly detected 188 out of 190 (98.95%) isolates with a score value of 2.00 or higher. Principal component analysis was conducted using MBT Compass software to classify K. pneumoniae isolates based on their structure. Based on the analysis of the single peak intensities generated by MBT, the highest peak values were found at 3444, 5022, 5525, 6847, and 7537 m/z. K. pneumoniae gene testing confirmed the PMF results, with 90.53% detecting entrobactin, 70% detecting 16 S rRNA, and 32.63% detecting ferric iron uptake. The resistance of the K. pneumoniae isolates to antibiotics was as follows: 64.75% for cefazolin, 62.63% for trimethoprim/sulfamethoxazole, 59.45% for ampicillin, 58.42% for cefoxitin, 57.37% for ceftriaxone, 53.68% for cefepime, 52.11% for ampicillin-sulbactam, 50.53% for ceftazidime, 52.11% for ertapenem, and 49.47% for imipenem. Based on the results of the double-disk synergy test, 93 out of 190 (48.95%) K. pneumoniae isolates were extended-spectrum beta-lactamase. In conclusion, PMF is a powerful analytical technique used to identify K. pneumoniae isolates from clinical samples based on their proteomic characteristics. K. pneumoniae isolates have shown increasing resistance to antibiotics from different classes, including carbapenem, which poses a significant threat to human health as these infections may become difficult to treat.

Reinvestigating the Correctness of Decoy-Based False Discovery Rate Control in Proteomics Tandem Mass Spectrometry.

Traditional database search methods for the analysis of bottom-up proteomics tandem mass spectrometry (MS/MS) data are limited in their ability to detect peptides with post-translational modifications (PTMs). Recently, "open modification" database search strategies, in which the requirement that the mass of the database peptide closely matches the observed precursor mass is relaxed, have become popular as ways to find a wider variety of types of PTMs. Indeed, in one study, Kong et al. reported that the open modification search tool MSFragger can achieve higher statistical power to detect peptides than a traditional "narrow window" database search. We investigated this claim empirically and, in the process, uncovered a potential general problem with false discovery rate (FDR) control in the machine learning postprocessors Percolator and PeptideProphet. This problem might have contributed to Kong et al.'s report that their empirical results suggest that false discovery (FDR) control in the narrow window setting might generally be compromised. Indeed, reanalyzing the same data while using a more standard form of target-decoy competition-based FDR control, we found that, after accounting for chimeric spectra as well as for the inherent difference in the number of candidates in open and narrow searches, the data does not provide sufficient evidence that FDR control in proteomics MS/MS database search is inherently problematic.