Journal of the American Society for Mass Spectrometry最新文献

In recent years, alternative enzymes with varied specificities have gained importance in MS-based bottom-up proteomics, offering orthogonal information about biological samples and advantages in certain applications. However, most mass spectrometric workflows are optimized for tryptic digests. This raises the questions of whether enzyme specificity impacts mass spectrometry and if current methods for nontryptic digests are suboptimal. The success of peptide and protein identifications relies on the information content of MS/MS spectra, influenced by collision energy in collision-induced dissociation. We investigated this by conducting LC-MS/MS measurements with different enzymes, including trypsin, Arg-C, Glu-C, Asp-N, and chymotrypsin, at varying collision energies. We analyzed peptide scores for thousands of peptides and determined optimal collision energy (CE) values. Our results showed a linear m/z dependence for all enzymes, with Glu-C, Asp-N, and chymotrypsin requiring significantly lower energies than trypsin and Arg-C. We proposed a tailored CE selection method for these alternative enzymes, applying ca. 20% lower energy compared to tryptic peptides. This would result in a 10-15 eV decrease on a Bruker QTof instrument and a 5-6 NCE% (normalized collision energy) difference on an Orbitrap. The optimized method improved bottom-up proteomics performance by 8-32%, as measured by peptide identification and sequence coverage. The different trends in fragmentation behavior were linked to the effects of C-terminal basic amino acids for Arg-C and trypsin, stabilizing y fragment ions. This optimized method boosts the performance and provides insight into the impact of enzyme specificity. Data sets are available in the MassIVE repository (MSV000095066).

Biobased poly(ethylene furanoate) (PEF)/poly(ε-caprolactone) (PCL) block copolymers have been synthesized using ring opening polymerization (ROP) of ε-caprolactone (ε-CL) in the presence of PEF in different mass ratios. An increase in intrinsic viscosity is observed for the block copolymers with higher ε-CL content due to the extension of their macromolecular chain. Matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MS) was employed to understand the composition and structure of the produced block copolymers. The MS analysis helped to confirm the formation of PEF-PCL copolymers in all cases. Furthermore, tandem mass spectrometry experiments were performed to analyze the intrinsic fragmentation mechanism of neat PEF and PCL (both linear and cyclic) and confirm the block structure and end-groups. Finally, nuclear magnetic resonance results confirmed the composition and microstructure of the block copolymers. The synthesized PEF-PCL block copolymers can be used as a replacement for petroleum derived plastics, especially in the field of food packaging.

Förster resonance energy transfer (FRET) is becoming a valuable technique in gas-phase structural biology for identifying local structural motifs and conformations of biological molecules, such as peptides and proteins. This method involves labeling the biomolecule with two dyes, a donor dye and an acceptor dye, that are commonly charged rhodamines. Here we examine how different amino acid (AA) methyl esters linked to the dye via amide linkages can influence the dye transition energy and, consequently, the energy-transfer efficiency, using cryogenic ion fluorescence spectroscopy. Absorption spectra were recorded for rhodamine B⁺-labeled AA esters (RB⁺-AA) through fluorescence-excitation experiments at the LUNA2 setup in Aarhus, which operates at cryogenic temperatures (down to approximately 100 K). The AAs studied include aliphatic ones (alanine (A), leucine (L), tert-leucine (tert-L), and methionine (M)), aromatic ones (phenylalanine (F) and tryptophan (W)), and two with polar side chains (serine (S) and threonine (T)). Results show that the band maximum either remains unchanged compared to RB⁺ or red shifts by over 3 nm in the case of RB⁺-M and RB⁺-F. While the spectra of RB⁺-A and RB⁺-L closely resemble that of RB⁺, RB⁺-tert-L shows a distinct red shift of about 1.4 nm. Spectral variations do not appear to be more influenced by the presence of aromatic AA side chains than other types, as differences observed between aliphatic AAs are comparable to those between the three groups. Instead, these variations appear to arise from differing conformations where the dihedral angle between the xanthene moiety and the pendant phenyl group varies, as influenced by the linked AA side chain. The angle determines the π-overlap between the two aromatic moieties, and according to TD-DFT calculations, an angle larger than 90° can easily account for red shifts due to larger delocalization of the π-electron cloud. Another factor is the polarizability of the side chain that could also contribute to the red shift. RB⁺-F and RB⁺-W spectra exhibit red-shifted, narrower absorption profiles, which is likely associated with the large aromatic side chains that limit the number of contributing structural configurations.

Reproducibility in untargeted metabolomics data processing remains a significant challenge due to software limitations and the complex series of steps required. To address these issues, we developed Nextflow4MS-DIAL, a reproducible workflow for liquid chromatography-mass spectrometry (LC-MS) metabolomics data processing, validated with publicly available data from MetaboLights (MTBLS733). Nextflow4MS-DIAL automates LC-MS data processing to minimize human errors from manual data handling. The workflow supports software containerization, ensuring computational reproducibility and enabling collaborative research. Nextflow4MS-DIAL is compatible with any Unix-like system and supports multiple job schedulers, offering flexibility and ease of use. The Nextflow4MS-DIAL workflow is available under the permissive MIT license: https://github.com/Nextflow4Metabolomics/nextflow4ms-dial.

In this study, we analyzed purine derivatives using multimatrix variation matrix-assisted laser desorption ionization mass spectrometry (MALDI MS) with α-cyano-4-hydroxycinnamic acid (CHCA), 1,5-diaminonaphtalene (DAN), 5-formylsalicylic acid (FSA), and 5-nitrosalicylic acid (NSA) as matrices. Further, we focused on the abstraction/attachment of hydrogen from/to analytes and detected [M - H]⁺, [M + 2H]^+• and/or [M + 3H]⁺ in MALDI MS spectra of compounds containing nitrogen and/or carbonyl oxygen. Although [M - H]⁺ generation of purine compounds in MALDI MS with conventional matrices was challenging, NSA-MALDI MS effectively yielded the [M - H]⁺species of purine derivatives compared with CHCA, FSA, and DAN, and the [M - H]⁺/[M + H]⁺ ratios reflected their structures, such as the substituting groups and positions. We speculated that the molecular ion [M]^+• generated and the subsequent hydrogen radical abstraction proceeded by NSA matrix from the α-carbon of the amine group. The nitro group (-NO₂) of NSA can withdraw hydrogen radicals in photochemical reactions. The [M - H]⁺ of adenosine, guanosine, and inosine suggested that hydrogen abstraction occurred in the ribose unit. The xanthine isomer of paraxanthine was distinguished from those of theophylline and theobromine using their [M - H]⁺/[M + H]⁺ ratios obtained with NSA-MALDI MS. Additionally, [M + 2H]^+• generated in DAN-MALDI MS of xanthine derivatives due to their carbonyl groups. The relative abundances of [M + 2H]^+• of xanthine derivatives were much higher than those of the other purine derivatives such as adenine derivatives which generated [M + 3H]⁺ in their DAN-MALDI MS. DAN induced the hydrogen attachment of purine compounds because the amine group (-NH₂) of DAN can give hydrogen radicals in photochemical reactions. NSA- and DAN-MALDI MS characterized purine derivatives and were useful for their structure categorization.

Phased structures for lossless ion manipulation offer significant improvements over the scanning second gate method for coupling with ion trap mass analyzers. With an experimental run time of under 1 min for select conditions and an average run time of less than 4 min, this approach significantly reduces experimental time while enhancing the temporal duty cycle. The outlined SLIM system connects to an ion trap mass analyzer via a PCB stacked ring ion guide, which replaces the commercial ion optics and capillary inlet. By applying a discrete and repeating injection pulse and solving a series of algebraic equations, the system reconstructs an arrival time distribution with a minimal degree of error with enhanced ion throughput. To demonstrate the feasibility of this approach, the 3.4-m SLIM system resolves gas-phase conformers for various small peptides and proteins. This system and methodology also enable direct implementation between SLIM and ion trap mass analyzers traditionally interfaced with front separation systems such as liquid chromatography.

The Mass Spectrometry Data Center (MSDC) has recently started improving existing libraries and creating new ones for identifying and analyzing plastics-related compounds (PRC) and materials (PRM) as part of the NIST circular economy program. PRC are small molecules of dissimilar chemical nature; hence, to increase coverage, we have used three types of ionizations: EI, ESI, and APCI. PRM are solids that include polymers, polymer mixtures, and commercial plastics, so we have used pyrolysis-gas chromatography (py-GC-MS) to create a new searchable library. First, we have increased the coverage of the existing libraries by including as many as possible commercially available PRC. Then, for testing the libraries and to deconvolute complex PRM mixtures, we have analyzed extractable and leachable (E&L) samples and pyrolysis products from one hundred standards of the most common polymers and some of their mixtures using LC-MS/MS, GC-MS, and py-GC-MS. In collaboration with the FDA, the EPA, and other non-government institutions, we are applying techniques, libraries, and tools to areas of interest to the circular economy of plastics, health risk assessments, and environmental challenges.

Post expression from the host cells, biotherapeutics undergo downstream processing steps before final formulation. Mass spectrometry and biophysical characterization methods are valuable for examining conformational and stoichiometric changes at these stages, although typically not used in biomanufacturing, where stability is assessed via bulk property studies. Here we apply hybrid MS methods to understand how solution condition changes impact the structural integrity of a biopharmaceutical across the processing pipeline. As an exemplar product, we use the model IgG1 antibody, mAb4. Flexibility, stability, aggregation propensity, and bulk properties are evaluated in relation to perfusion media, purification stages, and formulation solutions. Comparisons with Herceptin, an extensively studied IgG1 antibody, were conducted in a mass spectrometry-compatible solution. Despite presenting similar charge state distributions (CSD) in native MS, mAb4, and Herceptin show distinct unfolding patterns in activated ion mobility mass spectrometry (aIM-MS) and differential scanning fluorimetry (DSF). Herceptin's greater structural stability and aggregation onset temperature (T_agg) are attributed to heavier glycosylation and kappa-class light chains, unlike the lambda-class light chains in mAb4. Hydrogen-deuterium exchange mass spectrometry (HDX-MS) revealed that mAb4 undergoes substantial structural changes during purification, marked by high flexibility, low melting temperature (Tm), and prevalent repulsive protein-protein interactions but transitions to a compact and stable structure in high-salt and formulated environments. Notably, in formulation, the third constant domain (CH3) of the heavy chain retains flexibility and is a region of interest for aggregation. Future work could translate features of interest from comprehensive studies like this to targeted approaches that could be utilized early in the development stage to aid in decision-making regarding targeted mutations or to guide the design space of bioprocesses and formulation choices.

Leaves of tomato plants contain various glandular trichomes that produce a wide range of metabolic products including acylsugars, which may serve as a defense mechanism against various insect pests. Acylsugars exhibit significant structural diversity, differing in their sugar cores, acylated positions, and type of acyl chains. This work demonstrated a comprehensive approach using multidimensional separation techniques, specifically liquid chromatography-ion mobility-tandem mass spectrometry (LC-IM-MS/MS), for structural characterization, and the discrimination of different tomato plants (one cultivar and five accessions) was demonstrated using tomato leaf extracts; six genotypes from five species of Solanum were represented. As a result, we identified 16 acylsugars through their molecular formulas and annotations using LC and MS analyses. The incorporation of ion mobility (IM) analysis revealed an additional 9 isomeric forms, resulting in a comprehensive total of 25 isomeric acylsugars identified. Furthermore, the experimental collision cross section (CCS_exp) values agreed reasonably well with the corresponding predicted values (CCS_pred), with an overall estimated error of less than 2%. These findings pave the way for research into how the different structural isomers of acylsugars might influence the self-defense mechanism in plants. Moreover, this work demonstrated that the investigated cultivar and accessions of tomatoes can be distinguished from each other based on their metabolite profile, e.g., acylsugars, with principal component analysis (PCA) and linear discriminant analysis (LDA) statistical models, yielding a prediction rate of 98.3%.