Search

Despite their high clinical relevance, obtaining structural and biophysical data on transmembrane proteins has been hindered by challenges involved in their expression and extraction in a homogeneous, functionally-active form. The inherent enzymatic activity of receptor tyrosine kinases (RTKs) presents additional challenges. Oncogenic fusions of RTKs with heterologous partners represent a particularly difficult-to-express protein subtype due to their high flexibility, aggregation propensity and the lack of a known method for extraction within the native lipid environment. One such protein is the fibroblast growth factor receptor 3 fused with transforming acidic coiled-coil-containing protein 3 (FGFR3-TACC3), which has failed to express to sufficient quality or functionality in traditional expression systems. Cell-free protein expression (CFPE) is a burgeoning arm of synthetic biology, enabling the rapid and efficient generation of recombinant proteins. This platform is characterised by utilising an optimised solution of cellular machinery to facilitate protein synthesis in vitro. In doing so, CFPE can act as a surrogate system for a range of proteins that are otherwise difficult to express through traditional host cell-based approaches. Here, functional FGFR3-TACC3 was expressed through a novel cell-free expression system in under 48 h. The resultant protein was reconstituted using SMA copolymers with a specific yield of 300 µg/mL of lysate. Functionally, the protein demonstrated significant kinase domain phosphorylation (t < 0.0001). Currently, there is no published, high-resolution structure of any full-length RTK. These findings form a promising foundation for future research on oncogenic RTKs and the application of cell-free systems for synthesising functional membrane proteins., Competing Interests: Declarations. Competing interests: The authors declare no competing interests., (© 2025. The Author(s).)

Lectins are produced in almost all life forms, can interact with targets (glycans) in a cross-kingdom manner and have served as valuable tools for studying glycobiology. Previously, a bacterial lectin, named Streptomyces hemagglutinin (SHA), was found to agglutinate human type B erythrocytes. However, the binding of SHA to mammalian cell types other than human erythrocytes has not been explored. To address this, we produced a recombinant fusion protein, with the mCherry reporter protein proceeding the SHA protein (referred to as mCherry-SHA), and performed co-immunofluorescence staining analysis. We focused on the normal pancreas in this study because glycans on pancreatic cells have been associated with initiation and progression of pancreatic cancer, a deadly disease. We found that only acinar, but not ductal or endocrine cells were stained positively with mCherry-SHA from embryonic day (E) 18.5 to 35 weeks old mice; in contrast, E12.5 and E15.5 pancreas display minimal mCherry-SHA binding. In adult humans, mCherry-SHA also targeted acinar cells specifically; however, only tissue from blood type B donors, but not type A or O donors, showed positivity. Together, these results demonstrate that SHA can bind to normal murine and human pancreatic acinar cells and that SHA-binding glycans are developmentally regulated., Competing Interests: Declarations. Competing interests: M.K., Y.F-Y, and K.B. declare holder for United States Patent No. US11,767,351 B2. Date of Patent: Sept. 26, 2023. Other authors declare no conflicts of interest with the contents of this article., (© 2025. The Author(s).)

Keratinases are valuable enzymes for converting feather keratin waste into bioactive products but often suffer from poor substrate specificity and low catalytic efficiency. This study reported the creating of a novel keratinase with targeted adherence and specific degradation on feather keratins by fusing prepeptidase C-Terminal (PPC) domain. A PPC domain of metalloprotease E423 specifically adsorbed feather keratins by hydrogen bonds and hydrophobic interactions in a time- and temperature-dependent manner. Stepwise N-/C-terminal truncations disclosed the essential core sequence composed of 21 amino acid residues determining the keratin-targeted adherence. Fusion of the core fragment with a flexible linker (GGGGS) 1 achieved the optimal secretion, and improved the catalytic efficiency of a representative keratinase 4-3 Ker -MAV by 0.97-fold. Moreover, the feather degradation rate increased from 65 to 82%, representing the highest reported performance for a keratinase. This PPC-fusion strategy opens new horizons in enzyme engineering, promising not only to revolutionize keratin waste valorization but also to inspire the design of substrate-specific biocatalysts across diverse industrial applications.

Background: Iduronate-2-sulfatase (IDS) deficiency (MPS II; Hunter syndrome) is a disorder that exhibits peripheral and CNS pathology. The blood brain barrier (BBB) prevents systemic enzyme replacement therapy (ERT) from alleviating CNS pathology. We aimed to enable brain delivery of systemic ERT by using molecular BBB-Trojans targeting endothelial transcytosis receptors., Methods: Single-domain antibody (sdAb)-enzyme fusion protein constructs were prepared in Yarrowia lipolytica. sdAb affinity and BBB permeability were characterized using SPR and an in vitro rodent BBB assay, respectively. In vivo pharmacokinetic (PK) analysis was performed in rats. Quantification of fusion protein amounts were performed using LC-MS., Results: Fusion proteins consisting of IDS and BBB-transmigrating sdAbs, albumin binding sdAbs or human serum albumin (HSA) were evaluated for their in vitro BBB permeability. IGF1R3H5-IDS was selected for in vivo PK analysis in rats. IDS and IGF1R3H5-IDS exhibited very short (< 10 min) serum half-life (t 1/2α ), while constructs containing either HSA or anti-serum albumin sdAbs (R28 or M79) showed 8-11 fold increases in the area under the curve (AUC) in serum. CSF analysis indicated that IGF1R3H5 increased brain exposure by 9 fold (AUC) and constructs containing HSA or R28 exhibited 42-52 fold increases. Quantitation of brain levels confirmed the increased and sustained delivery of IDS to the brain of HSA- and R28-containing constructs. Lastly, analysis of brain fractions demonstrated that the increases in brain tissue were due to parenchymal delivery without fusion protein accumulation in brain vessels., Conclusions: These results demonstrate the utility of IGF1R-targeting sdAbs to effect brain delivery of lysosomal enzymes, as well as the utility of serum albumin-targeting sdAbs in t 1/2 extension, to increase brain delivery of rapidly cleared enzymes., Competing Interests: Declarations. Ethical approval: All animal experiments were conduced at the National Research Council and prior ethical approval for the studies was obtained from the NRC Animal Care Committee. The NRC maintains active certification by the Canadian Council on Animal Care (CCAC) and conforms to their guidelines pertaining to research ethics involving rats. All studies described herein comply with the ARRIVE guidelines. Competing interests: The authors declare no competing interests., (© 2024. Crown.)

SARS-CoV-2 has continued spreading around the world in recent years since the initial outbreak in 2019, frequently developing into new variants with greater human infectious capacity. SARS-CoV-2 and its mutants use the angiotensin-converting enzyme 2 (ACE2) as a cellular entry receptor, which has triggered several therapeutic strategies against COVID-19 relying on the use of ACE2 recombinant proteins as decoy receptors. In this work, we propose an ACE2 silent Fc fusion protein (ACE2-hFcLALA) as a candidate therapy against COVID-19. This fusion protein was able to block the binding of SARS-CoV-2 RBD to ACE2 receptor as measured by ELISA and flow cytometry inhibition assays. Moreover, we used classical neutralization assays and a progeny neutralization assay to show that the ACE2-hFcLALA fusion protein is capable of neutralizing the authentic virus. Additionally, we found that this fusion protein was more effective in preventing in vitro infection with different variants of interest (alpha, beta, delta, and omicron) compared to the D614G strain. Our results suggest the potential of this molecule to be used in both therapeutic and preventive settings against current and emerging mutants that use ACE2 as a gateway to human cells., Competing Interests: The authors have declared that no competing interests exist., (Copyright: © 2025 Bermúdez-Abreut et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

A distinctive feature of both type 1 and type 2 diabetes is the waning of insulin-secreting beta cells in the pancreas. New methods for direct and specific targeting of the beta cells could provide platforms for delivery of pharmaceutical reagents. Imaging techniques such as Positron Emission Tomography (PET) rely on the efficient and specific delivery of imaging reagents, and could greatly improve our understanding of diabetes etiology as well as providing biomarkers for viable beta-cell mass in tissue, in both pancreas and in islet grafts.The DiGeorge Syndrome Critical Region Gene 2 (DGCR2) protein has been suggested as a beta-cell specific protein in the pancreas, but so far there has been a lack of available high-affinity binders suitable for targeted drug delivery or molecular imaging. Affibody molecules belong to a class of small affinity proteins with excellent properties for molecular imaging. Here, we further validate the presence of DGCR2 in pancreatic and stem cell (SC)-derived beta cells, and then describe the generation and selection of several Affibody molecules candidates that target human DGCR2. Using an in-house developed directed evolution method, new DGCR2-binding Affibody molecules were generated and evaluated for thermal stability and affinity. The Affibody molecules variants were further developed as targeting agents for delivering imaging reagents to beta cell. The Affibody molecule Z DGCR2:AM106 displayed nanomolar affinity, suitable stability and biodistribution, with negligible toxicity to islets, qualifying it as a suitable lead candidate for further development as a tool for specific delivery of drugs and imaging reagents to beta cells., Competing Interests: Declarations. Competing interests: O.E. is an employee of Antaros Tracer. O.E. and O.K. are minority shareholders of Antaros Tracer AB, which hold patents related to DGCR2 binding peptides. Otherwise, the authors declare no competing interests. Ethics approval and consent to participate: All the performed procedures were in accordance with the ARRIVE guidelines for animal research. The animal experiments were ethically reviewed, authorized by the Animal Ethics Committee of the Swedish Animal Welfare Agency and carried out in accordance with the European Directive 2010/63/EEC and the institutional guidelines at Uppsala University (UFV 2007/724)., (© 2024. The Author(s).)

Cleavage Under Targets and Release Using Nuclease (CUT&RUN) is a chromatin profiling strategy that releases specific DNA-protein complexes from in situ chromatin to the supernatant. CUT&RUN employs the hybrid protein pAG-MNase, composed of IgG binding proteins A and G, followed by micrococcal nuclease. Here, I describe the expression and purification of recombinant pAG-MNase as well as the assessment of its enzymatic activity. Purified pAG-MNase is hyperactive and enables large-scale analyses., (© 2025. The Author(s), under exclusive license to Springer Science+Business Media, LLC, part of Springer Nature.)

The fusion of the exonuclease Trex2 with the Cas9 protein significantly enhanced the efficiency of genome editing in hexaploid common wheat, particularly for the simultaneous editing of multiple favorable alleles within a single generation, thereby facilitating genome editing-assisted breeding in polyploid crops., (© 2024 The Author(s). Journal of Integrative Plant Biology published by John Wiley & Sons Australia, Ltd on behalf of Institute of Botany, Chinese Academy of Sciences.)

The ability to add bioactivities, such as cell signaling or ligand recognition, to biomaterials has generated the potential to include multiple bioactivities into a single material. In some cases, it is desirable to localize these activities to different areas of the biomaterial, creating functional patterns. While photolithography and 3D printing have been effective techniques for patterning functions in many materials, patterning remains a challenge in materials composed of protein, in part due to how these materials are artificially assembled. Protein fibers are often produced from protein films that co-acervate at the air-water interface. This chapter describes methods to leverage this coacervation process to pattern materials, using the Drosophila melanogaster Hox protein Ultrabithorax (Ubx) as a model self-assembling protein. Through gene fusion, Ubx and a functional protein are produced as a single polypeptide, capable of both forming materials and performing the activity of interest. This functionality is retained in the final materials. In this chapter, we describe how to use multiple Ubx fusion proteins to not only imbue the final materials with multiple functions, but also to create macroscale patterns of the appended proteins in fibrous protein-based materials. These patterned materials include striped fibers, bifunctional-faced fibers, gradient fibers, and core-shell fibers., (© 2025. The Author(s), under exclusive license to Springer Science+Business Media, LLC, part of Springer Nature.)

Recombinant protein production is pivotal in molecular biology, enabling profound insights into cellular processes through biophysical, biochemical, and structural analyses of the purified samples. The demand for substantial biomolecule quantities often presents challenges, particularly for eukaryotic proteins. Escherichia coli expression systems have evolved to address these issues, offering advanced features such as solubility tags, posttranslational modification capabilities, and modular plasmid libraries. Nevertheless, existing tools are often complex, which limits their accessibility and necessitate streamlined systems for rapid screening under standardized conditions. Based on the Golden Gate cloning method, we have developed a simple "one-pot" approach for the generation of expression constructs using strategically chosen protein purification tags like hexahistidine, SUMO, MBP, GST, and GB1 to enhance solubility and expression. The system allows visual candidate screening through mScarlet fluorescence and solubility tags are removable via TEV protease cleavage. We provide a comprehensive protocol encompassing oligonucleotide design, cloning, expression, His-tag affinity chromatography, and size-exclusion chromatography. This method, therefore, streamlines prokaryotic and eukaryotic protein production, rendering it accessible to standard molecular biology laboratories with basic protein biochemical equipment., (© 2025. The Author(s), under exclusive license to Springer Science+Business Media, LLC, part of Springer Nature.)

Saccharomyces boulardii and Saccharomyces cerevisiae share over 99 % genetic similarity yet exhibit distinct metabolic traits. While the cell surface display system of S. cerevisiae is well-documented, the equivalent system in S. boulardii has yet to be fully characterized. This study investigates the cell surface display system of S. boulardii for the expression of a heterologous protein using different anchor proteins. Six strains expressing the enhanced green fluorescent protein (Egfp) and an anchor protein as a fusion protein were constructed to visualize the cell surface display system. Then a heterologous endo-inulinase protein was expressed with selected anchor proteins through fluorescence intensity comparison. Analysis by fluorescence microscopy revealed that the anchor protein Sed1 exhibited the highest fluorescence intensity. Furthermore, expressed selected anchor proteins and heterologous protein, endo-inulinase, the engineered strain could degrade and consume almost inulin in 72 h. Through endo-inulinase expression, we confirmed that not only Egfp but also heterologous protein is well expressed, and we successfully built an S. boulardii cell surface display system., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Dynamic interactions between transcription factors govern changes in gene expression that mediate changes in cell state accompanying injury response and regeneration. Transcription factors frequently function as obligate dimers whose activity is often modulated by post-translational modifications. These critical and often transient interactions are not easily detected by traditional methods to investigate protein-protein interactions. This chapter discusses the design and validation of a fusion protein involving a transcription factor tethered to a proximity labeling ligase, APEX2. In this technique, proteins are biotinylated within a small radius of the transcription factor of interest, regardless of time of interaction. Here we discuss the validations required to ensure proper functioning of the transcription factor proximity labeling tool and the sample preparation of biotinylated proteins for mass spectrometry analysis of putative protein interactors., (© 2025. The Author(s), under exclusive license to Springer Science+Business Media, LLC, part of Springer Nature.)

Cell division is a fundamental biological process, essential for sustaining life on Earth. Accurate replication followed by uniform segregation of the genome is required to ensure cell division is sustainable and reduces the likelihood of aneuploidy. The cell cycle has various checkpoints to safeguard proper replication, for example, the spindle assembly checkpoint (SAC) which ensures that all chromosomes are correctly aligned and attached to the spindle, before the transition to anaphase. The precise function of the SAC and SAC components in plants is so far unclear. First, the high level of polyploidy in plants raises concerns about the efficacy of the SAC. Second, many plant SAC components are implicated in other cellular processes, such as MAD1, which has been implicated in the reproductive transition of Arabidopsis thaliana. Overexpression of GFP fusions of core SAC components provides a key route to establish the functions of the different SAC components in plants. Here we describe two methods for agrobacterium-mediated transformation of plants., (© 2025. The Author(s), under exclusive license to Springer Science+Business Media, LLC, part of Springer Nature.)

After overexpression in a suitable host, recombinant protein purification often relies on affinity (e.g., poly-histidine) and solubility-enhancing (e.g., small ubiquitin-like-modifier [SUMO]) tags. Following purification, these tags are removed to avoid their interference with target protein structure and function. The wide use of N-terminal His 6 -SUMO fusions is partly due to efficient cleavage of the SUMO tag's C-terminal Gly-Gly motif by the Ulp1 SUMO protease and generation of the native N-terminus of the target protein. While adopting this system to purify the Salmonella homodimeric FraB deglycase, we discovered that Shine-Dalgarno (SD) sequences in the eukaryotic SUMO tag resulted in truncated proteins. This finding has precedents for synthesis of partial proteins in Escherichia coli from cryptic ribosome-binding sites within eukaryotic coding sequences. The SUMO open reading frame has two "GGNGGN" motifs that resemble SD sequences, one of which encodes the Gly-Gly motif required for Ulp1 cleavage. By mutating these SD sequences, we generated SUMO NIT (no internal translation), a variant that eliminated production of the truncated proteins without affecting the levels of full-length His 6 -SUMO-FraB or Ulp1 cleavage. SUMO NIT should be part of the toolkit for enhancing SUMO fusion protein yield, purity, and homogeneity (especially for homo-oligomers). Moreover, we showcase the value of native mass spectrometry in revealing the complications that arise from generation of truncated proteins, as well as oxidation events and protease inhibitor adducts, which are indiscernible by commonly employed lower resolution methods., (© 2024 The Author(s). Protein Science published by Wiley Periodicals LLC on behalf of The Protein Society.)

Cryptococcus gattii and its medical implications have been extensively studied. There is, however, a significant knowledge gap regarding cryptococcal survival in its environmental niche, namely woody material, which is glaring given that infection is linked to environmental populations. A gene from C. gattii (WM276), the predominant global molecular type (VGI), has been sequenced and annotated as a putative cellulase. It is therefore, of both medical and industrial intertest to delineate the structure and function of this enzyme. A homology model of the enzyme was constructed as a fusion protein to a maltose binding protein (MBP). The CGB&#95;E4160W gene was overexpressed as an MBP fusion enzyme in Escherichia coli T7 cells and purified to homogeneity using amylose affinity chromatography. The structural and functional character of the enzyme was investigated using fluorescence spectroscopy and enzyme activity assays, respectively. The optimal enzyme pH and temperature were found to be 6.0 and 50 °C, respectively, with an optimal salt concentration of 500 mM. Secondary structure analysis using Far-UV CD reveals that the MBP fusion protein is primarily α-helical with some β-sheets. Intrinsic tryptophan fluorescence illustrates that the MBP-cellulase undergoes a conformational change in the presence of its substrate, CMC-Na + . The thermotolerant and halotolerant nature of this particular cellulase, makes it useful for industrial applications, and adds to our understanding of the pathogen's environmental physiology., Competing Interests: Declaration of competing interest The authors have no competing interests to declare that are relevant to the content of this article., (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)

The aim of the present study was to assess systemic circulatory and tissue activities of both the classical arm and of the alternative arm of the renin-angiotensin system (RAS) in a new transgenic rat line (TG7371) that expresses angiotensin-(1-7) (ANG 1-7)-producing fusion protein; the results were compared with the activities measured in control transgene-negative Hannover Sprague-Dawley (HanSD) rats. Plasma and tissue concentrations of angiotensin II (ANG II) and ANG 1-7, and kidney mRNA expressions of receptors responsible for biological actions of ANG II and ANG 1-7 [i.e. ANG II type 1 and type 2 (AT 1 and AT 2 ) and Mas receptors] were assessed in TG7371 transgene-positive and in HanSD rats. We found that male TG7371 transgene-positive rats exhibited significantly elevated plasma, kidney, heart and lung ANG 1-7 concentrations as compared with control male HanSD rats; by contrast, there was no significant difference in ANG II concentrations and no significant differences in mRNA expression of AT 1 , AT 2 and Mas receptors. In addition, we found that in male TG7371 transgene-positive rats blood pressure was lower than in male HanSD rats. These data indicate that the balance between the classical arm and the alternative arm of the RAS was in male TGR7371 transgene-positive rats markedly shifted in favor of the latter. In conclusion, TG7371 transgene-positive rats represent a new powerful tool to study the long-term role of the alternative arm of the RAS in the pathophysiology and potentially in the treatment of cardio-renal diseases., Competing Interests: Compliance with ethical standards. Conflict of interest: The authors declare no competing interests., (© 2024. The Author(s).)

One of the promising drug delivery tools is ferritin, which features high stability at a wide range of conditions and protects cargo by its spherical protein shell. We studied the self-assembly into homoglobules of ferritin from H. pylori and a chimeric protein ferritin-SUMO. We exposed the globules to pH-driven dis/reassembly and in both cases we observed two fractions during size exclusion chromatography (SEC) procedure. The higher molecular weight fraction contained fully assembled globules of ferritin and ferritin-SUMO that well coincides with literature. Interestingly, the lower molecular weight fraction contained intermediate subglobular oligomers that also formed globules, but on a time scale of hours, while being under physiological conditions. We performed biochemical characterization of this fraction and found that, in the case of ferritin, it contained almost the whole range of intermediate oligomers with different stoichiometry. In contrast, the ferritin-SUMO fraction contained only two distinct states: dimers and globules, without any other ferritin-SUMO intermediate oligomers. We built AlphaFold-derived schemes of ferritin and ferritin-SUMO self-assembly which also indicated differences in their assembly pathways. Our results could potentially open the possibility of cargo loading into ferritins at physiological conditions and improved purification of ferritin-based products if using a ferritin-SUMO modification with following cleavage of the SUMO-tag by the SUMO protease., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Inc. All rights reserved.)

Expression of GRF3-GIF1 chimera significantly enhanced regeneration and transformation efficiency in soybean, increasing the number of transformable cultivars. Moreover, GmGRF3-GIF1 can be combined with CRISPR/Cas9 for highly effective gene editing., (© 2024 The Author(s). Journal of Integrative Plant Biology published by John Wiley & Sons Australia, Ltd on behalf of Institute of Botany, Chinese Academy of Sciences.)

Fusion proteins are valuable molecules to meet different demands related to the development of biopharmaceuticals and bioprocesses. In human therapy, they are used to improve the half-life of biologics by modifying the biophysical properties of the proteins. In biotechnology, the design of fusion proteins can standardize the establishment of production clones and the purification process. Analytical detection capabilities of the fusion partner and binding to affinity ligands play a crucial role. For the generation of the recombinant cell line, the maturation of the protein and the secretion are also crucial factors, which can be significantly influenced by the fusion partner and can determine the final yield of the bioprocess. Here we present a protocol to recombine the human extracellular domain of CD19 with the human serum albumin domain 2 resulting in a fusion protein CD19-AD2 including a flexible linker sequence in the interface between the C-terminus of CD19 and the N-terminus of HSA-D2 and a terminal His12-tag. The two fragments are independently amplified with primers allowing to genetically connect the two fragments in the next step by overlap extension PCR. By this strategy, the linker sequence as well as the albumin fragment can be chosen individually to be flexible in the fine-tuning of the final protein. The amplified product is then cloned into a mammalian expression vector suitable to generate a recombinant transient or stable cell culture. This workflow can be applied to any protein sequence by adapting the specific primer sequences., (© 2025. The Author(s), under exclusive license to Springer Science+Business Media, LLC, part of Springer Nature.)

Purpose: Accuracy in in vivo assessment of human epidermal growth factor receptor type 2 (HER2) status is crucial for predicting the response to HER2-targeted therapies in breast cancer. This study assessed the safety, feasibility, and diagnostic accuracy of 99mTc-ABH2, a reengineered affibody molecule with radionuclide labeling, for HER2 expression in breast cancer using SPECT/CT imaging, compared with 18F-FDG PET/CT., Patients and Methods: Thirty-six patients suspected of primary breast cancer were enrolled in this prospective, single-center study from March to July in 2023. Each participant underwent SPECT/CT imaging with 99mTc-ABH2 SPECT/CT and 18F-FDG PET/CT. The imaging results were validated against immunohistochemistry and fluorescence in situ hybridization, employing visual scores and quantitative values for analysis., Results: Optimal imaging contrast was observed around 2 hours postinjection of 99mTc-ABH2. Among the evaluated 27 patients with immunohistochemistry and fluorescence in situ hybridization findings, the 99mTc-ABH2 SPECT/CT visual evaluation displayed a sensitivity of 71.4%, specificity of 72.2%, and accuracy of 71.9%. Using an SUVmax cutoff of 2.32, the sensitivity, specificity, and accuracy for detecting HER2 status were 92.86%, 72.22%, and 81.25%, respectively. Notably, 99mTc-ABH2 precisely identified all immunohistochemistry (3+) tumors and showed increased uptake in bone and lymph node metastases. Meanwhile, 18F-FDG PET/CT showed no significant difference in uptake between HER2 (2+/3+) and HER2 (0/1+) tumors (P = 0.81)., Conclusions: This study validated 99mTc-ABH2 SPECT/CT as a promising diagnostic tool for precise HER2 assessment. The robust sensitivity for immunohistochemistry (3+) tumors and the visualization of metastases highlight its diagnostic significance, potentially impacting patient outcomes positively., Competing Interests: Conflicts of interest and sources of funding: The authors declare that they have no conflict of interest. This study was supported by National High Level Hospital Clinical Research Funding (grant number: 2022-PUMCH-B-071), National High Level Hospital Clinical Research Funding (grant number: 2022-PUMCH-C-003), and Chinese Academy of Medical Sciences Innovation Fund for Medical Sciences (grant number: CF 2021-I2M-1-2-2022564)., (Copyright © 2024 Wolters Kluwer Health, Inc. All rights reserved.)