The challenge of detecting USP is rooted in its biology. The protein is a bacterial nuclease, an enzyme that degrades nucleic acids, and it has been associated both with urinary tract infections and with genotoxicity, meaning it has the capacity to damage the genetic material of host cells. Scientists have been able to detect the usp gene in human samples using nucleic-acid-based methods, but demonstrating the presence of the encoded protein in those same samples proved far more difficult. Without antibodies that bind USP specifically, there was no way to confirm that the gene was actually being expressed into protein during infection, and no way to explore whether protein levels correlate with disease severity, treatment outcomes, or other clinical variables.

To close that gap, the research team turned to mouse hybridoma technology, a classical but powerful approach for generating monoclonal antibodies. Hybridomas are immortalized cell lines produced by fusing antibody-producing immune cells with myeloma cells, and each hybridoma clone secretes a single, uniform antibody. The investigators generated and screened a panel of 38 mouse hybridomas containing USP-specific antibodies, evaluating each candidate for its ability to bind the target protein. The screening method of choice was biolayer interferometry, an optical technique that measures real-time binding between an immobilized ligand and an analyte in solution by monitoring interference patterns of light reflected from the surface of a biosensor. This allowed the team to quantitatively compare the binding behavior of all 38 antibody candidates and select the strongest performers.

From that screen, two antibodies emerged as the winners: mAb-A10 and mAb-D5. After purification, these two monoclonals became the first antibodies ever reported to specifically recognize the USP protein. That distinction matters because polyclonal antibody preparations, which contain a heterogeneous mixture of antibodies, can suffer from batch-to-batch variability and cross-reactivity, whereas monoclonal antibodies provide a reproducible, well-defined reagent that can be manufactured consistently and shared between laboratories. The availability of these reagents transforms USP from a protein that could only be inferred from its gene into a measurable molecular entity.

With validated antibodies in hand, the team built a diagnostic-style assay around them: a single-antibody enzyme-linked immunosorbent assay, or ELISA. In an ELISA, an antibody is used to capture a target protein from a sample, and an enzymatic reaction generates a measurable signal proportional to the amount of target present. The researchers optimized the assay over a working range of 0.1 to 12.5 micrograms per milliliter of USP and rigorously characterized its analytical performance. The lower limit of quantification, the lowest concentration that can be measured with acceptable precision and accuracy, came out at 0.13 micrograms per milliliter. The lower limit of detection, the lowest concentration that can be reliably distinguished from background, was even lower, at 0.04 micrograms per milliliter. These figures define the practical boundaries within which the assay can yield trustworthy quantitative results.

The true test of any immunoassay intended for clinical research is whether it works in real biological matrices, which are far messier than purified protein solutions. Urine contains salts, urea, host proteins, and variable pH, all of which can interfere with antibody binding or enzymatic signal generation. The Puerto Rico team implemented their ELISA for the detection of USP in human urine samples obtained from consenting participants in a study conducted at Auxilio BioLabs under institutional review board protocol IRB1083505. Two of the urine samples registered a statistically significant response in the assay, providing proof of concept that the method can pick up a signal attributable to USP in a clinical matrix.

That encouraging result comes with an important caveat that the authors themselves emphasize: although the responses in those two samples were statistically significant, the protein levels fell below the lower limit of quantification. In other words, the assay detected something, but the concentration was too low to assign a reliable numerical value. This is a common situation in the early development of biomarker assays, and it points to the next phase of work: refining sample preparation, concentrating analytes from larger urine volumes, or further optimizing the assay format to push the effective quantification limit down. Even in its current form, the assay provides a foundation that did not previously exist.

The significance of the work extends beyond the immediate technical achievement. The usp gene has been implicated in several human diseases, and a nuclease toxin that damages host DNA raises questions about its possible role in the pathology of urinary tract infections and potentially other conditions. Researchers studying bacterial genotoxins have long noted that toxins capable of damaging host cell DNA can influence inflammation, cell death, and tissue damage at sites of infection. Being able to measure the actual protein in patient samples will allow investigators to ask whether USP expression varies between patients, whether it tracks with symptoms or antibiotic response, and whether it could serve as a biomarker for particular types of infection. None of these questions could be addressed rigorously without protein-level detection.

The study also illustrates the value of sustained investment in research infrastructure at institutions that have historically been underrepresented in biomedical science. The project was supported by the National Institutes of Health through Grant 1R16GM153691-01 to Abel Baerga-Ortiz and Grant R25GM061838 to Rachell Martinez-Ramirez, the latter being part of a program that supports undergraduate research training. An additional NIH grant, 1S10OD025143-01A1, enabled the purchase of the MALDI-ToF mass spectrometry equipment used in the work. The collaboration spanned academic laboratories at the University of Puerto Rico and the Molecular Sciences Research Center, the biotechnology company CDI Laboratories in Mayaguez, and the clinical laboratory Auxilio BioLab at Hospital Auxilio Mutuo in San Juan, combining antibody discovery expertise, analytical instrumentation, and access to clinical samples.

One practical detail worth noting for the research community is that some of the authors are affiliated with CDI Laboratories, which sells the two antibodies reported in the work. That commercial availability means other laboratories will not need to repeat the hybridoma generation and screening process to obtain these reagents, which should accelerate adoption. The article itself is published open access under a Creative Commons license, and the authors note that the version shared early is citable and carries a permanent DOI, subject to further editorial edits before the final version of record. As the first monoclonal antibodies against USP and the first immunoassay for the protein, the tools described in this study are likely to become standard reagents in the growing effort to understand how this bacterial nuclease contributes to urinary tract disease, and whether detecting it in urine could one day inform how clinicians diagnose, monitor, or treat infections caused by USP-producing uropathogens.

Subject of Research: Development of monoclonal antibodies and an ELISA for detecting the bacterial nuclease toxin uropathogenic specific protein in biological samples

Article Title: Antibody-based detection of the bacterial nuclease toxin uropathogenic specific protein (USP)

Article References: Martinez-Ramirez, R., Toro-Diaz, V., Akamine, P., Gonzalez-Feliciano, J. A., Capo-Velez, C., Ruiz-Rosado, K., Pino, I., Eichinger, D., Canto, E., & Baerga-Ortiz, A. (2026). Antibody-based detection of the bacterial nuclease toxin uropathogenic specific protein (USP). Applied Microbiology and Biotechnology. https://doi.org/10.1007/s00253-026-14066-8

Image Credits: AI Generated

DOI: 10.1007/s00253-026-14066-8

Keywords: uropathogenic specific protein, USP, monoclonal antibodies, ELISA, bacterial nuclease, urinary tract infection, biolayer interferometry, bacterial toxin, biomarker, immunoassay, Escherichia coli, genotoxicity

The modification in question is an N-linked glycosylation at asparagine residue 153 of the viral envelope protein, a carbohydrate chain that decorates the outer surface of the virion. Glycosylation is a common strategy employed by enveloped viruses to shield vulnerable protein surfaces from immune surveillance, since the bulky, flexible sugar chains can physically obstruct antibody access to epitopes that would otherwise be exposed. In the case of dengue virus, the N153 glycan sits in a region of the envelope protein landscape that overlaps with binding sites targeted by well-characterized human monoclonal antibodies. The research team reasoned that if this glycan were removed, the underlying protein surface would become more accessible, and antibodies that struggle to engage the glycosylated wild-type virus might bind the mutant far more effectively.

To test this hypothesis, the investigators constructed a mutant dengue virus 2 in which asparagine 153 was replaced by glutamine, a substitution designated N153Q that eliminates the glycosylation consensus sequence without otherwise altering the envelope protein sequence. Previous work had already shown that this deglycosylated mutant displays attenuated infection in a mouse model, and importantly, that attenuation appears to be driven mainly by the mutant’s increased susceptibility to antibodies rather than by an intrinsic defect in viral fitness. This distinction matters for vaccine design, because an attenuated candidate whose weakness lies in antibody sensitivity is precisely the kind of candidate that could stimulate strong protective responses while remaining controllable by the immune system.

The heart of the new study lies in its structural comparison of wild-type and N153Q mutant viruses in complex with two human monoclonal antibodies, 2D22 and C10, both of which are known to neutralize dengue virus 2 with high potency. Using cryo-electron microscopy at physiological temperature, the team determined structures of the antibody fragment-antigen complexes bound to intact virions at resolutions ranging from 2.7 to 3.2 angstroms. These near-atomic maps allowed the researchers to visualize, across the entire icosahedral viral surface, exactly where the antibody fragments docked and, crucially, how many of the available binding sites were actually occupied on each virus particle. Such whole-virion structural analysis is essential for dengue, because the virus presents its envelope proteins in a herringbone arrangement with multiple distinct epitope environments, and antibody occupancy patterns can differ dramatically depending on the accessibility of each site.

The cryo-EM analysis revealed a clear and consistent difference between the two viruses. Both 2D22 and C10 showed increased occupancies on the N153Q mutant compared with the wild-type virus, meaning that a larger fraction of the antibody binding sites on the mutant virion surface were engaged by antibody fragments. This finding directly supports the interpretation that the glycan at position 153 had been physically blocking access to epitopes on the wild-type virus, and that its removal unveiled additional binding sites. In neutralization assays, the same pattern held: the human monoclonal antibodies 2D22 and C10 were more potent against the mutant than against the wild-type virus, consistent with the idea that a greater number of accessible epitopes allows antibodies to coat the virion more completely and thereby block infection more efficiently.

To complement the structural work, the researchers turned to biolayer interferometry, a technique that measures the real-time kinetics of antibody binding to and dissociation from the virus particles. At 30 degrees Celsius, an interesting nuance emerged: both antibodies exhibited a slower binding rate with the mutant than with the wild-type virus, but they also displayed a slower dissociation rate, meaning that once attached, they held on more tightly. The slower on-rate may reflect subtle conformational or dynamic differences in the mutant’s surface, while the slower off-rate indicates a net gain in binding stability. Overall affinity, which reflects the balance between these two rates, was thus shaped by competing kinetic effects at the lower temperature.

At 37 degrees Celsius, however, the picture became unambiguous. When the experiments were repeated at physiological temperature, the affinities of both 2D22 and C10 for the dengue virus 2 particles increased significantly for both the wild-type and the N153Q mutant. This temperature dependence underscores an important methodological point for the field: structural and biophysical measurements performed at reduced temperatures may not fully capture the behavior of virus-antibody interactions in the human body, where fever-range and core temperatures prevail. By conducting their cryo-EM imaging and binding assays at 37 degrees Celsius, the team ensured that their observations of enhanced antibody engagement on the deglycosylated mutant reflect conditions closer to those encountered during an actual infection.

The implications of these findings extend beyond basic virology into practical vaccine development. A live attenuated vaccine candidate works by replicating sufficiently to stimulate immunity while causing minimal disease, and the safety margin of such candidates often depends on how readily the immune system can control them. The N153Q mutant’s attenuation in mice, attributable to heightened antibody susceptibility, combined with the demonstration that key neutralizing epitopes become more accessible when the glycan is absent, suggests a dual advantage. The mutant should be easier for the immune system to clear during immunization, reducing the risk of uncontrolled replication, while simultaneously presenting its most vulnerable surfaces to the antibody-producing machinery, potentially eliciting highly potent neutralizing responses. As the authors note, the N153Q mutant might therefore serve as a good vaccine candidate precisely because important epitopes are made more accessible for stimulating potent antibodies.

More broadly, the study adds to a growing appreciation that viral glycans are not merely passive decorations but active modulators of antigenicity whose manipulation can be exploited rationally. Similar strategies of glycan removal or repositioning have informed vaccine design efforts for other enveloped viruses, and the dengue work demonstrates that the approach can be validated at the level of intact virion structure and single-molecule binding kinetics. The technical achievement of resolving Fab-decorated dengue virions at 2.7 to 3.2 angstrom resolution at physiological temperature also sets a benchmark for future structural studies of flavivirus-antibody complexes. As dengue continues to expand its geographic range under the pressures of urbanization, climate change, and mosquito vector spread, every additional tool for designing better vaccines carries real public health weight. This study’s demonstration that a single point mutation can strip away a molecular shield and lay bare the virus’s most vulnerable surfaces offers a conceptually elegant step toward that goal, and it will likely encourage further exploration of glycan engineering in next-generation dengue vaccine candidates.

Subject of Research: Structural and biophysical analysis of how loss of N153 glycosylation on dengue virus 2 enhances recognition by neutralizing antibodies

Article Title: Dengue virus 2 lacking N153 glycosylation displayed enhanced recognition by neutralizing antibodies

Article References: Fibriansah, G., Ng, T.-S., Lim, X.-N., Ng, J. W. S., Tan, A. W. K., Ting, D. H. R., Screaton, G. R., Crowe, J. E., Alonso, S., & Lok, S.-M. (2026). Dengue virus 2 lacking N153 glycosylation displayed enhanced recognition by neutralizing antibodies. npj Viruses. https://doi.org/10.1038/s44298-026-00241-1

Image Credits: AI Generated

DOI: 10.1038/s44298-026-00241-1

Keywords: dengue virus 2, N153 glycosylation, N153Q mutant, neutralizing antibodies, cryo-electron microscopy, monoclonal antibody 2D22, monoclonal antibody C10, biolayer interferometry, epitope accessibility, live attenuated vaccine, flavivirus, vaccine design

Nanobodies, the single-domain antibody fragments originally derived from camelids, have become indispensable instruments across modern biology. Because they are compact, remarkably stable, and easy to engineer, they serve as conformational stabilizers, crystallization chaperones, biosensors, intracellular targeting agents, and imaging probes. Clinically, the class has already produced approved drugs such as caplacizumab, and nanobody-based therapeutics are advancing against cancer, autoimmune disorders, and infectious disease. In structural biology, their most celebrated role has been locking fragile membrane proteins into defined functional states, a strategy that made high-resolution structures of G-protein-coupled receptors possible more than a decade ago.

Traditionally, these binders are obtained by immunizing llamas or other animals with the protein of interest, an approach that fails when antigens are toxic, unstable, or require trapping in artificial conditions such as extreme pH or fully liganded states. Synthetic libraries sidestep these constraints entirely. Instead of an immune system, researchers use combinatorial gene libraries encoding billions of randomized antibody fragments, then select binders in vitro. Among the display technologies available, ribosome display is uniquely powerful because it couples each protein to its encoding messenger RNA without any cells, allowing theoretical diversities of 10^12 to 10^13 to be explored in a test tube, far beyond what phage or yeast display can practically achieve.

The existing benchmark, the Seeger concave sybody library, has enabled countless selections, including binders that trap membrane proteins in specific conformations. However, it carries a hidden incompatibility. Its nanobody constructs lack the C-terminal histidine tag that the Legobody system requires to recognize its target. Legobody, an approximately 120-kilodalton scaffold assembled from a sybody, an engineered maltose-binding protein, and a nanobody-binding antibody fragment, dramatically enlarges small protein complexes so that cryo-EM image alignment becomes feasible. Without the tag, every sybody recovered from the established libraries must be subcloned and re-engineered before it can be used, adding days of work and eroding throughput precisely where speed matters most.

The new S1.0 library eliminates that detour by embedding the required C-terminal histidine tag and a short Legobody-compatible linker directly into the library scaffold. But the redesign went beyond a simple tagging exercise. Drawing on structural analyses of published concave sybody-antigen complexes, the team noticed that these synthetic binders engage their targets mainly through the CDR1 and CDR2 loops, unlike natural nanobodies, which typically lean heavily on CDR3. In the concave library, the short seven-residue CDR3 and the largely fixed CDR1 had constrained where binding could occur. The researchers therefore extended CDR3 by one residue, raised the number of randomized positions in CDR3 and CDR1 to seven each, and deliberately reduced variability at one CDR2 position, restricting it to serine, tyrosine, arginine, and glutamate to tune surface chemistry while preserving the concave paratope architecture.

The mathematics of library design dictated careful restraint. Nineteen fully randomized positions would imply a theoretical diversity of roughly 5.2 × 10^24, unreachable by any physical display system. Instead, the team employed semi-randomization, enriching bulky aromatic and charged residues at positions likely to contact antigen while weighting choices according to amino-acid frequencies observed in natural nanobody interfaces, yielding a practical theoretical diversity of 10^18. The gene library itself was assembled through overlapping polymerase chain reactions, Type IIS restriction digestion, and T4 ligation, then transcribed into messenger RNA and stored in aliquots at minus 80 degrees Celsius.

Quality control came from deep sequencing. Approximately 9 × 10^7 reads of the naive library revealed that 98 percent of sequences were unique, and most designed amino-acid compositions at randomized positions matched expectations closely, particularly in CDR1, where 23 of 32 compositions showed discrepancies below 10 percent. Some positions, especially in CDR3, deviated more substantially, a caveat the authors acknowledge, though the overall fidelity confirmed that the construction strategy had faithfully captured the intended chemical space.

Functional validation proceeded against two test proteins. In head-to-head selections against calmodulin, performed in parallel with the benchmark concave library, S1.0 produced 45 positive clones from 96 screened, compared with 61 for the established library, but the S1.0 binders showed statistically significantly stronger calcium-dependent ELISA signals. Selections against thermostable green fluorescent protein, enzymatically biotinylated for magnetic bead capture, were even more striking: after one round of ribosome display and two rounds of phage display with off-rate selection, an enrichment factor of 427 was recorded, and ten unique sybody sequences emerged from twelve colonies analyzed. Fluorescence-detection size-exclusion chromatography showed that all ten shifted the elution profile of the fluorescent target, and biolayer interferometry confirmed nanomolar binding, with the best binder, named SH2, achieving a dissociation constant of 1.9 nanomolar.

The decisive experiment came next. When sybodies SH1 and SH2 were mixed with TGP and Legobody components, both assembled into stable complexes that could be pulled down through the maltose-binding protein’s affinity for amylose resin, detected directly by gel electrophoresis with no re-engineering of any kind. That intrinsic compatibility transforms the workflow for structural studies: a selection campaign that once ended with weeks of subcloning can now feed binders straight into Legobody assembly and cryo-EM grid preparation.

The authors are candid about remaining limitations. Validation covered only two soluble targets, and performance against the small membrane proteins that motivate the entire endeavor remains to be demonstrated. Sequencing also revealed instructive surprises, such as the strong underrepresentation of isoleucine at position 29 among functional binders despite its 20 percent abundance in the design, evidence that effective functional diversity, not raw theoretical diversity, ultimately governs library success. The team argues that accumulating sequencing data from naive and enriched libraries, mined with machine-learning approaches and shared through public repositories, should guide the next generation of synthetic nanobody libraries, turning empirical selection outcomes into ever-smarter designs.

Subject of Research: Design and validation of a ribosome display library for synthetic nanobody selection

Article Title: Design and validation of a ribosome display library for synthetic nanobody selection

Article References: Design and validation of a ribosome display library for synthetic nanobody selection. (n.d.). https://doi.org/10.1007/s44307-026-00112-z

Image Credits: AI Generated

DOI: 10.1007/s44307-026-00112-z

Keywords: nanobodies, sybodies, ribosome display, synthetic antibody library, Legobody, cryo-EM, structural biology, membrane proteins, CDR randomization, biolayer interferometry, phage display, protein engineering