Extending the Orbitrap Transient
A pulsed gas valve reduces ion loss and drift during long Orbitrap measurements, improving mass determination for viruses, plasmids, and antibodies.
A pulsed gas-delivery system has improved the stability of individual ions during long Orbitrap measurements, allowing charge-detection mass spectrometry (CDMS) to resolve large and fragile biomolecules with greater sensitivity, mass accuracy, and resolution.
The study, from a team including Albert Heck and Orbitrap inventor Alexander Makarov, tackles a longstanding pressure trade-off in native mass spectrometry. Elevated gas pressure in the higher-energy collisional dissociation (HCD) cell helps desolvate and cool large ions before analysis, but gas leaking into the Orbitrap can destabilize ion trajectories. The effect becomes particularly problematic during ultralong transients used to improve single-ion measurements.
The researchers fitted a Q Exactive UHMR with a pulsed gas valve that supplies higher pressure during ion injection and cooling, then shuts before mass analysis. This separates the conditions needed for transmission and desolvation from the lower-pressure environment required for stable Orbitrap recording.
For adeno-associated virus particles, pulsing the gas largely eliminated charge loss and signal drift during recordings approaching 20 seconds. The measured mass shifted from an erroneous 3.62 ± 0.07 MDa under continuous gas flow to 3.80 ± 0.05 MDa with pressure modulation, while longer transients also narrowed the mass distribution.
The improvement was particularly clear for fragile plasmid DNA. Without pressure modulation, only 50 of 3,100 ions remained stable for at least 12 seconds, preventing reliable mass determination. With the valve operating, 1,865 of 4,054 ions met the same criterion, yielding 2.72 ± 0.06 MDa for the intact plasmid, close to its theoretical 2.69 MDa.
Longer-lived ion signals also improved immunoglobulin measurements and allowed CDMS to distinguish an approximately 150 kDa antibody carrying different numbers of an 8.3 kDa binding domain. The pressure-control strategy therefore extends ultralong Orbitrap transients from more accurate mass measurements to finer resolution of heterogeneous complexes and binding stoichiometries.
Phosphorylation as a Phage Weapon
A single viral kinase drives widespread phosphorylation across infected cells, with nucleic-acid-associated proteins among its strongest targets.
Phosphoproteomics has uncovered an unusually broad strategy used by bacteriophage T7 to suppress bacterial defenses, with a single viral kinase rapidly modifying much of the host and phage proteomes while preferentially targeting nucleic-acid-associated proteins.
The study revisited T7 kinase (T7K), which has long been known to phosphorylate several Escherichia coli proteins during infection. Mass spectrometry instead revealed activity on a far broader scale, with wild-type T7 infection producing 19,532 phosphopeptides compared with only a few hundred when the kinase was deleted or rendered inactive.
Time-resolved phosphoproteomics captured how quickly that wave develops. Within five minutes, more than 15,000 phosphopeptides mapped to 2,093 host and 33 phage proteins, with T7K-dependent phosphorylation reaching around 70 percent of the expressed proteome. The kinase modified serine, threonine, and tyrosine residues without a clear sequence preference.
Quantitative mass spectrometry then estimated phosphorylation-site occupancy after phosphatase treatment, distinguishing the most heavily modified proteins from the broader phosphoproteomic background. The most heavily phosphorylated proteins were enriched for nucleic-acid-binding functions, while follow-up experiments linked that bias to a DNA-binding C-terminal domain in T7K.
The same pattern extended to bacterial defense systems. In Retron-Eco9, phosphoproteomics identified 17 sites on the RcaT toxin, including several near residues important for activity. Phosphomimetic mutations at selected positions abolished protection against T7, supporting a functional role for phosphorylation in weakening the defense response.
Screening 513 natural E. coli isolates extended the effect beyond the model systems, with T7K weakening defense in several genetically distinct strains. The authors argue that the kinase’s broad substrate range is not incidental, but central to how T7 counters diverse bacterial immune systems.
A Three-Protein Signature for Kidney Cancer
Targeted mass spectrometry validates a urinary protein signature that could offer a simpler route toward noninvasive kidney cancer detection.
A three-protein urine signature has distinguished clear cell renal cell carcinoma (ccRCC) from healthy controls in two independent cohorts, using targeted mass spectrometry to turn a broader multi-omics screen into a potentially more practical diagnostic assay.
The researchers first profiled urine from ccRCC patients and matched controls using proteomics, lipidomics, and metabolomics. The combined data pointed to altered lipid metabolism and mitochondrial activity in the urinary profile, alongside increased phosphatidylcholines, phosphatidylethanolamines, and coenzyme Q10.
Not all of those signals were equally useful for diagnostic development. Metabolomics mainly identified low-abundance compounds that were decreased in ccRCC, while adding lipid measurements did not substantially improve discrimination over proteins alone. Proteomics of urine supernatant therefore became the main route forward, identifying serum amyloid A1, haptoglobin, and lipocalin 15 as consistently elevated in ccRCC.
To move beyond discovery-scale proteomics, the team developed a parallel reaction monitoring mass spectrometry (PRM-MS) assay for the three proteins. Peptide signals were normalized against three relatively stable reference proteins and combined into a cumulative “UrineScore.”
The UrineScore performed strongly in the discovery cohort and showed similar accuracy in an independent Madrid cohort, with area-under-the-curve values of 0.96 and 0.95, respectively. It also showed some ability to distinguish ccRCC from other renal cell carcinoma subtypes, although that comparison involved fewer patients.
The authors now plan to validate the assay in larger, clinically representative cohorts, including patients with benign kidney disease and inflammatory or urological conditions that could alter urinary protein levels. If the three-protein signature retains its performance, they suggest it could eventually be adapted to simpler antibody-based formats for broader clinical use.
Exposures and Metabolites in One Run
A two-dimensional LC-MS workflow couples untargeted metabolomics with sensitive targeted exposure measurements from the same sample.
A column-switching LC–MS system has combined high-coverage metabolite profiling with targeted quantification of trace-level exposures in a single run.
The workflow addresses the large differences in polarity and concentration that usually force the two analyses into separate methods. It couples hydrophilic interaction liquid chromatography (HILIC) and reversed-phase liquid chromatography (RPLC) in sequence, separating polar and non-polar compounds across a broad chemical range.
The separated fractions are then split between high-resolution mass spectrometry (HRMS) for untargeted metabolite profiling and triple-quadrupole mass spectrometry (TQMS) for targeted quantification of 601 environmental and drug-related exposures. That division is important because many exposures circulate at concentrations two to three orders of magnitude below endogenous metabolites.
Compared with conventional one-dimensional LC–HRMS methods, the two-dimensional setup increased metabolite coverage across serum, tissue, and urine. In serum, 986 compounds were annotated, versus 652 with RPLC and 483 with HILIC alone. Targeted detection on the TQMS was also one to two orders of magnitude more sensitive than HRMS for the exposure panel.
The researchers then applied the workflow to 276 serum samples from people with lung adenocarcinoma and healthy controls. A single analysis yielded 853 annotated metabolites alongside quantitative measurements for 205 exposures, with the system remaining stable across more than 300 consecutive injections.
In an exploratory lung adenocarcinoma analysis, the workflow linked low-level chemical exposures with accompanying metabolic changes from the same serum samples. Several exposures were associated with disease status, while related metabolic shifts involved peptides, bile acids, and fatty acids.
Some mid-polarity compounds remained difficult to capture, while reliance on surrogate internal standards limited quantitative accuracy for certain exposures. The authors suggest that further refinement could support larger studies seeking to relate low-level environmental exposures directly to metabolic responses from the same sample.
(Mass) Spectacular and Strange
An Ambergris Appetizer
Ambergris has long been prized by perfumers. In activated sludge, however, one of its key fragrant molecules is treated less like perfume than provisions.
Researchers at Givaudan isolated two Sphingomonas strains from activated sewage sludge that could mineralize (−)-Ambrox, a key odor molecule in sperm-whale ambergris. The molecule does not look like an easy target: it is a saturated tricyclic terpenoid ether with multiple tertiary and quaternary carbon centers, structural features that usually make microbial degradation difficult.
To trace the pathway, the team combined HPLC-HRMS, preparative HPLC, 2D-NMR, genome sequencing, fosmid-library screening, and experiments with two ^13C-labeled Ambrox substrates. Seven metabolites were structurally assigned by 2D-NMR, while further intermediates were proposed from exact masses and isotope-labeling patterns.
The pathway began with methyl-group oxidation, followed by hydroxylation that helped open one ring through a retro-aldol reaction, before β-oxidation trimmed the structure further. The bacteria were selective: natural (−)-Ambrox and related labdanoids such as sclareol, manool, and drimanol were mineralized, but the opposite enantiomer and several stereoisomers were not.
Further work is still needed to identify the full gene set, but the pathway could help improve biodegradation models and guide the rational design of biodegradable fragrance ingredients.
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