Inosine Monophosphate Dehydrogenase Research Articles

The IMPDH cytoophidium couples metabolism and fetal development in mice

The cytoophidium is an evolutionarily conserved subcellular structure formed by filamentous polymers of metabolic enzymes. In vertebrates, inosine monophosphate dehydrogenase (IMPDH), which catalyses the rate-limiting step in guanosine triphosphate (GTP) biosynthesis, is one of the best-known cytoophidium-forming enzymes. Formation of the cytoophidium has been proposed to alleviate the inhibition of IMPDH, thereby facilitating GTP production to support the rapid proliferation of certain cell types such as lymphocytes, cancer cells and pluripotent stem cells (PSCs). However, past studies lacked appropriate models to elucidate the significance of IMPDH cytoophidium under normal physiological conditions. In this study, we demonstrate that the presence of IMPDH cytoophidium in mouse PSCs correlates with their metabolic status rather than pluripotency. By introducing IMPDH2 Y12C point mutation through genome editing, we established mouse embryonic stem cell (ESC) lines incapable of forming IMPDH polymers and the cytoophidium. Our data indicate an important role of IMPDH cytoophidium in sustaining a positive feedback loop that couples nucleotide biosynthesis with upstream metabolic pathways. Additionally, we find that IMPDH2 Y12C mutation leads to decreased cell proliferation and increased DNA damage in teratomas, as well as impaired embryo development following blastocoel injection. Further analysis shows that IMPDH cytoophidium assembly in mouse embryonic development begins after implantation and gradually increases throughout fetal development. These findings provide insights into the regulation of IMPDH polymerisation in embryogenesis and its significance in coordinating cell metabolism and development.

In vitro and in vivo antiviral effects of CLEVir-X against porcine reproductive and respiratory syndrome virus

The aim of this study was to investigate the in vitro and in vivo antiviral effects of CLEVir-X, against porcine reproductive and respiratory syndrome virus (PRRSV). CLEVir-X is a nucleoside analogue and a dialdehyde form of xanthosine. CLEVir-X demonstrated antiviral action during the in vitro portion of this experiment with its inosine monophosphate dehydrogenase (IMPDH) inhibition against PRRSV. The anti-PRRSV effect of CLEVir-X was recovered through supplementation with guanosine. This suggests that PRRSV replication may be regulated through IMPDH and its guanosine biosynthetic pathway. CLEVir-X treatment in cultures resulted in mutation frequency increase of up to 7.8-fold within the viral genomes (e.g. ORF6) compared to their parallel, untreated cultures. The incorporation of CLEVir-X into the viral genome causes lethal mutagenesis and subsequent decrease in specific infectivity. During the in vivo antiviral experiment, 21-day-old pigs began oral administration of 5 mL of phosphate buffered saline containing CLEVir-X (with purity of 68 % and dosage of 40 mg/kg body weight). This treatment was provided twice daily at 9:00AM and 5:00PM for 14 days. Pigs were simultaneously intranasally inoculated with PRRSV at the beginning of CLEVir-X treatment (21 days of age). Several beneficial effects from the oral administration of CLEVir-X were observed including reduction of body temperature, alleviation of respiratory clinical signs, decreased PRRSV load in both blood and lung tissues, and mitigation of lung interstitial pneumonia lesions. The results of the present study demonstrated that CLEVir-X has mutagenic and nonmutagenic modes of antiviral action against PRRSV based on both in vitro and in vivo antiviral experiments.

Abstract 1789: Machine learning-based method to analyze metabolic fluxes of patient tumors

Abstract Personalized oncology must overcome the complex challenge of distinct cancer phenotypes in each patient, formed in part in response to unique metabolic crosstalk among cells in the tumor microenvironment which can be a determining factor in therapeutic response. Although isotope tracing sheds light on differences of metabolite enrichments in tumor and normal tissues, quantifying the metabolic fluxes in patients remains elusive. The conventional metabolic flux analysis tools are unable to estimate patient metabolic fluxes because we are limited to a single time point enrichment datapoint from each patient’s in-vivo measurement at isotopic non-steady state. We overcame this challenge by generating training data from the limited patient data and implementing a machine learning model to predict fluxes. To generate training data, we first simulated constrained random fluxes and enrichment patterns at different time points using patient circulating metabolites enrichment via an isotopic non-stationary metabolic flux analysis framework. Using this data, we trained a convolutional neural network to predict flux ratios. To validate our model, we compared predicted flux ratios to the experimental data from mouse models for two different treatments. Our recent findings from a glioblastoma (GBM) mouse model study using conventional metabolic flux analysis revealed higher de novo guanosine monophosphate (GMP) synthesis in GBM than normal cortex. These tumors can be sensitive to mycophenolate mofetil (MMF) which inhibits inosine monophosphate dehydrogenase, but only if the major source of GMP production is de novo synthesis and not salvage. Our machine learning model can discriminate between sources of GMP synthesis in patients, thus enabling prediction of potential responders. Furthermore, we previously showed that serine uptake is higher in GBM than normal cortex, and a serine- and glycine-restricted diet slows tumor growth in mice. While both circulating serine and microenvironment-derived serine could account for serine uptake in GBM, we hypothesized that the circulating serine dependence would better predict response to dietary serine depletion. Hence, we combined patient scRNA-seq and metabolomics data to feed our neural network framework to estimate microenvironmental and circulating serine uptake in six patients with brain cancer. Thus, we have shown that our model can identify patients who will benefit from MMF treatment or a serine- and glycine-restricted diet, enabling administration of highly effective personalized treatments for GBM patients. Citation Format: Baharan Meghdadi, Anjali Mittal, Andrew J. Scott, Sravya Palavalasa, Daniel R. Wahl, Deepak Nagrath. Machine learning-based method to analyze metabolic fluxes of patient tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1789.

IMPDH2 Positively Impacts the Proliferation Potential of Hepatoblastoma Cells by Activating JunB Signaling Pathway.

Amplification of inosine monophosphate dehydrogenase II, EC 1,1,1,205 (IMPDH2) has been reported in various cancers, which results in transformation and tumorigenicity. In our current work, we have explored the oncogenic properties and the underlying pathophysiology of IMPDH2 in hepatoblastoma (HB). To investigate IMPDH2 expression in HB tissues and prognostic significance in HB patients, gene expression profiling interactive analysis (GEPIA) has been adopted. Immunohistochemistry has also helped to validate the protein expression of IMPDH2 in HB tissues. The effect of IMPDH2 overexpression or depletion on the proliferation of Hepatoblastoma cells in vitro has been evaluated by CCK8 assays and colony formation assays. Xenograft tumor growth of mice has been detected. Luciferase reporter assays have been conducted to determine the interaction of IMPDH2 and JunB, which was further asserted by pharmacological inhibition of JunB. IMPDH2 was highly expressed in HB tissues. Experimentally, the proliferation and colony formation of HuH6 cells were increased by IMPDH2 overexpression. Conversely, genetic inactivation of IMPDH2 impaired the proliferative efficiency and colony-forming rate of HepG2 cells. Besides, the luciferase reporter assay validated IMPDH2 overexpression to be associated with enhanced JunB transcriptional activity, while its activity was diminished in the case of IMPDH2 depletion. JunB inhibitor neutralized the IMPDH2-mediated increased phosphorylation of JunB. Our findings, thus, suggest that IMPDH2 exhibits its oncogenic role in HB partially via JunB-dependent proliferation.

A journey into the regulatory secrets of the de novo purine nucleotide biosynthesis.

De novo purine nucleotide biosynthesis (DNPNB) consists of sequential reactions that are majorly conserved in living organisms. Several regulation events take place to maintain physiological concentrations of adenylate and guanylate nucleotides in cells and to fine-tune the production of purine nucleotides in response to changing cellular demands. Recent years have seen a renewed interest in the DNPNB enzymes, with some being highlighted as promising targets for therapeutic molecules. Herein, a review of two newly revealed modes of regulation of the DNPNB pathway has been carried out: i) the unprecedent allosteric regulation of one of the limiting enzymes of the pathway named inosine 5'-monophosphate dehydrogenase (IMPDH), and ii) the supramolecular assembly of DNPNB enzymes. Moreover, recent advances that revealed the therapeutic potential of DNPNB enzymes in bacteria could open the road for the pharmacological development of novel antibiotics.

Light-sensitive phosphorylation regulates retinal IMPDH1 activity and filament assembly.

Inosine monophosphate dehydrogenase (IMPDH) is the rate-limiting enzyme in guanosine triphosphate (GTP) synthesis and assembles into filaments in cells, which desensitizes the enzyme to feedback inhibition and boosts nucleotide production. The vertebrate retina expresses two splice variants IMPDH1(546) and IMPDH1(595). In bovine retinas, residue S477 is preferentially phosphorylated in the dark, but the effects on IMPDH1 activity and regulation are unclear. Here, we generated phosphomimetic mutants to investigate structural and functional consequences of S477 phosphorylation. The S477D mutation resensitized both variants to GTP inhibition but only blocked assembly of IMPDH1(595) filaments. Cryo-EM structures of both variants showed that S477D specifically blocks assembly of a high-activity assembly interface, still allowing assembly of low-activity IMPDH1(546) filaments. Finally, we discovered that S477D exerts a dominant-negative effect in cells, preventing endogenous IMPDH filament assembly. By modulating the structure and higher-order assembly of IMPDH, S477 phosphorylation acts as a mechanism for downregulating retinal GTP synthesis in the dark when nucleotide turnover is decreased.

Cytoophidia: a conserved yet promising mode of enzyme regulation in nucleotide metabolism.

Nucleotide biosynthesis encompasses both de novo and salvage synthesis pathways, each characterized by significant material and procedural distinctions. Despite these differences, cells with elevated nucleotide demands exhibit a preference for the more intricate de novo synthesis pathway, intricately linked to modes of enzyme regulation. In this study, we primarily scrutinize the biological importance of a conserved yet promising mode of enzyme regulation in nucleotide metabolism-cytoophidia. Cytoophidia, comprising cytidine triphosphate synthase or inosine monophosphate dehydrogenase, is explored across diverse biological models, including yeasts, Drosophila, mice, and human cancer cell lines. Additionally, we delineate potential biomedical applications of cytoophidia. As our understanding of cytoophidia deepens, the roles of enzyme compartmentalization and polymerization in various biochemical processes will unveil, promising profound impacts on both research and the treatment of metabolism-related diseases.

N6-methyladenosine modification of the mRNA for a key gene in purine nucleotide metabolism regulates virus proliferation in an insect vector

The titer of viruses that persist and propagate in their insect vector must be high enough for transmission yet not harm the insect, but the mechanism of this dynamic balance is unclear. Here, expression of inosine monophosphate dehydrogenase (LsIMPDH), a rate-limiting enzyme for guanosine triphosphate (GTP) synthesis, is shown to be downregulated by increased levels of N6-methyladenosine (m6A) on LsIMPDH mRNA in rice stripe virus (RSV)-infected small brown planthoppers (SBPHs; Laodelphax striatellus), the RSV vector, which decreases GTP content, thus limiting viral proliferation. Moreover, planthopper methyltransferase-like protein 3 (LsMETTL3) and m6A reader protein LsYTHDF3 are found to catalyze and recognize the m6A on LsIMPDH mRNA, respectively, and cooperate in destabilizing LsIMPDH transcripts. Co-silencing assays show that negative regulation of viral proliferation by both LsMETTL3 and LsYTHDF3 is partially dependent on LsIMPDH. This distinct mechanism limits virus replication in an insect vector, providing a potential gene target to block viral transmission.

Structural, morphological, and modeling studies of N-(benzoyloxy)benzamide as a specific inhibitor of Type II inosine monophosphate dehydrogenase

For decades now, computational chemistry has allowed us to shorten experimental times to meet the needs of humanity in finding solutions. In this regard, we tried to exploit tools such as molecular modeling and scaffold hopping to find possible inhibitors for the enzyme Type II inosine monophosphate dehydrogenase (IMPDH). The mechanism of the interactions has been studied, and a scaffold hopping replacement was used to optimize the structure of N-(Benzoyloxy)benzamide (BOBA) for its inhibition activity in this regard. A crystal morphology study was then performed to check a visual comparison between the already reported crystal forms of BOBA. Type I IMPDH predominates in normal resting cells compared with Type II, which is found in rapidly proliferating cells. The discovery of agents which would selectively target IMPDH found in proliferating cells should eliminate any antineoplastic therapeutic toxic effects in normal cells of the body.

Catalytic isoforms of AMP-activated protein kinase differentially regulate IMPDH activity and photoreceptor neuron function.

AMP-activated protein kinase (AMPK) plays a crucial role in maintaining ATP homeostasis in photoreceptor neurons. AMPK is a heterotrimeric protein consisting of α, β, and γ subunits. The independent functions of the 2 isoforms of the catalytic α subunit, PRKAA1 and PRKAA2, are uncharacterized in specialized neurons, such as photoreceptors. Here, we demonstrate in mice that rod photoreceptors lacking PRKAA2, but not PRKAA1, showed altered levels of cGMP, GTP, and ATP, suggesting isoform-specific regulation of photoreceptor metabolism. Furthermore, PRKAA2-deficient mice displayed visual functional deficits on electroretinography and photoreceptor outer segment structural abnormalities on transmission electron microscopy consistent with neuronal dysfunction, but not neurodegeneration. Phosphoproteomics identified inosine monophosphate dehydrogenase (IMPDH) as a molecular driver of PRKAA2-specific photoreceptor dysfunction, and inhibition of IMPDH improved visual function in Prkaa2 rod photoreceptor-knockout mice. These findings highlight a therapeutically targetable PRKAA2 isoform-specific function of AMPK in regulating photoreceptor metabolism and function through a potentially previously uncharacterized mechanism affecting IMPDH activity.

Update on monkeypox virus infection: Focusing current treatment and prevention approaches.

While the world is still facing the global pandemic COVID-19, another zoonosis monkeypox (Mpox) has emerged posing a great threat to society. Insight into the pathogenesis, symptoms, and management strategies will aid in the development of potent therapeutics for the treatment of monkeypox virus infection. To get insight into the current treatment and prevention strategies will aid in effectively coping with the disease. For obtaining information regarding the ongoing treatment and prevention strategies and the drugs under pipeline, we referred to Google Scholar, Pub Med, Pub Chem, and WHO official site. There are a few drugs that came out to be effective for the treatment of Mpox. Tecovirimat acts by inhibiting viral replication and viral wrapping. Another drug is cidofovir, which hinders the activity of viral DNA polymerase but has the drawback of nephrotoxicity. To overcome this, a conjugate of cidofovir is being used-known as brincidofovir-which has a similar mechanism as cidofovir but lesser toxicity. Ribavirin acts via inhibiting inosine monophosphate dehydrogenase (IMPDPH) thus disrupting viral translation. It also interferes with helicase activity. Tiazofurin, Adenosine N1 oxide, and HPMPA have shown efficacy in in-vitro studies by inhibiting IMPDH, DNA polymerase, and viral mRNA translation respectively. In-silico studies have proven the effect of nilotinib, simeprevir, and dihydroergotamine for Mpox treatment. They have shown binding affinity for proteins required for the growth and release of MPXV. Vaccines have also been employed for the prevention of Mpox, which includes JYNNEOS, ACAM2000, and VIGIV. This review highlights the pathogenesis of the virus, disease manifestations, drugs, and vaccines that are being used and those under pipeline for the treatment and prevention of Mpox.

Inhibition of nucleotide metabolism with dual-template epitope imprinted nanoparticles for targeted HER2+ tumor therapy

Nucleotide metabolism therapeutics, aimed at disrupting nucleic acid production, have proven to be an effective strategy against cancers. Traditionally, these therapies rely on classical antimetabolites such as fluorouracil and mercaptopurine; however, they suffer from the drawback of high biotoxicity. In this study, we introduced a novel approach using dual-template epitope molecularly imprinted polymers (D-EMIPs), designed with the nucleotide metabolism therapy strategy in mind for precise targeting and cancer treatment. The imprinting process comprised two key template peptides: the active center peptide of inosine 5′-monophosphate dehydrogenase (IMPDH) and epitope of the human epidermal growth factor receptor-2 (HER2). The D-EMIPs could selectively bind to IMPDH and occupy its catalytic active sites, thereby suppressing enzymatic reactions and inhibiting DNA and RNA synthesis, ultimately impeding tumor growth. Furthermore, by specifically targeting HER2, an overexpressed protein in certain cancer types, D-EMIPs enhanced the therapeutic efficacy for HER2-positive (HER2+) cancers. In vitro experiments suggested that D-EMIPs could selectively target HER2+ tumor cells, leading to a substantial 41% reduction in cell proliferation. In vivo experiments further confirmed the tumor-specific targeting capability of D-EMIPs, resulting in smaller tumor volumes compared to the control group treated with phosphate-buffered saline (PBS). These findings emphasize the promise of combining nucleotide metabolism therapeutics with the dual-template imprinted technique as a comprehensive strategy to establish an integrated platform for cancer diagnosis and treatment.

Triple in silico targeting of IMPDH enzyme and RNA-dependent RNA polymerase of both SARS-CoV-2 and Rhizopus oryzae.

Aim: Mucormycosis has been associated with SARS-CoV-2 infections during the last year. The aim of this study was to triple-hit viral and fungal RNA-dependent RNA polymerases (RdRps) and human inosine monophosphate dehydrogenase (IMPDH). Materials & methods: Molecular docking and molecular dynamics simulationwere usedto test nucleotide inhibitors (NIs) against the RdRps of SARS-CoV-2 and Rhizopus oryzae RdRp. These same inhibitors targeted IMPDH. Results: Four NIs revealed a comparable binding affinity to the two drugs, remdesivir and sofosbuvir. Binding energies were calculated using the most abundant conformations of the RdRps after 100-ns molecular dynamics simulation. Conclusion: We suggest the triple-inhibition potential of four NIs against pathogenic RdRps and IMPDH, which is worth experimental validation.

Chronic GVHD: review advances in prevention, novel endpoints, and targeted strategies.

Allogeneic hematopoietic cell transplantation (allo-HCT) is a curative therapy for many malignant and non-malignant hematologic disorders. Chronic graft-versus-host (cGVHD) disease remains a significant hurdle for long-term survival in patients post allo-HCT, and it remains the leading cause of late non-relapse mortality. The risk factors for development of cGVHD include degree of human leukocyte antigen (HLA) disparity, increasing recipient age, use of peripheral blood stem cells as a source, myeloablative conditioning regimens, prior acute GVHD (aGVHD), and female donor to male recipient. Our biological understanding of cGVHD is mostly derived from transplantation mouse models and patient data. There are three distinct phases in the development of cGVHD. Approaches to prevent GVHD include pharmacologic strategies such as calcineurin inhibitors (cyclosporine, tacrolimus) combined with methotrexate or mTOR inhibitors (sirolimus), and IMP dehydrogenase inhibitors (mycophenolate mofetil). Increasingly, posttransplant cyclophosphamide is emerging as a promising strategy for GVCHD prevention especially in a setting of reduced intensity conditioning. Other approaches include serotherapy (ATG, Campath) and graft manipulation strategies. A significant obstacle to evaluating the response of novel GVHD-directed therapies has been standardized response assessments. This has functioned as a barrier to designing and interpreting clinical trials that are structured around the treatment of cGVHD. Novel endpoints including failure-free survival, Graft-versus-host disease-free, relapse-free survival (GRFS), and current GVHD-free, relapse-free survival (CGRFS) may create a clearer picture for post-HCT outcomes. Targeted therapies including Bruton's tyrosine kinase inhibition, JAK1/2 inhibition, and ROCK2 inhibitors have improved cGVHD therapy, especially in the steroid refractory setting. Continued improvement in prophylactic strategies for cGVHD, identification of accurate cGVHD treatment endpoints, and access to novel therapeutic agents are expected to improve cGVHD outcomes.

IMPDH2 forms spots at branching sites and distal ends of astrocyte stem processes.

Inosine monophosphate dehydrogenase (IMPDH) is a rate-limiting enzyme in the de novo GTP biosynthesis pathway. Recent studies suggest that IMPDH2, an isoform of IMPDH, can localize to specific subcellular compartments under certain conditions and regulate site-specific GTP availability and small GTPase activity in invasive cancer cells. However, it is unclear whether IMPDH2 plays a site-specific regulatory role in subcellular functions in healthy cells. In this study, we focused on brain cells and examined the localization pattern of IMPDH2. We discovered that IMPDH2 forms localized spots in the astrocytes of the adult mouse hippocampus. Further analysis of spot distribution in primary astrocyte cultures revealed that IMPDH2 spots are predominantly localized on branching sites and distal ends of astrocyte stem processes. Our findings suggest a potential unidentified role for IMPDH2 and GTP synthesis specifically at specialized nodes of astrocyte branches.

Inosine monophosphate dehydrogenase intranuclear inclusions are markers of aging and neuronal stress in the human substantia nigra

We explored mechanisms involved in the age-dependent degeneration of human substantia nigra (SN) dopamine (DA) neurons. Owing to its important metabolic functions in post-mitotic neurons, we investigated the developmental and age-associated changes in the purine biosynthetic enzyme inosine monophosphate dehydrogenase (IMPDH). Tissue microarrays prepared from post-mortem samples of SN from 85 neurologically intact participants humans spanning the age spectrum were immunostained for IMPDH combined with other proteins. SN DA neurons contained two types of IMPDH structures: cytoplasmic IMPDH filaments and intranuclear IMPDH inclusions. The former were not age-restricted and may represent functional units involved in sustaining purine nucleotide supply in these highly metabolically active cells. The latter showed age-associated changes, including crystallization, features reminiscent of pathological inclusion bodies, and spatial associations with Marinesco bodies; structures previously associated with SN neuron dysfunction and death. We postulate dichotomous roles for these two subcellularly distinct IMPDH structures and propose a nucleus-based model for a novel mechanism of SN senescence that is independent of previously known neurodegeneration-associated proteins.

Mycophenolate mofetil in giant cell arteritis.

Giant cell arteritis (GCA) is a systemic granulomatous vasculitis affecting the large arteries. Abnormal lymphocyte function has been noted as a pathogenic factor in GCA. Mycophenolate mofetil (MMF) inhibits inosine monophosphate dehydrogenase and is therefore a highly lymphocyte-specific immunosuppressive therapy. We aimed to assess the efficacy of MMF for inducing remission in GCA. Seven patients (5 female, 2 male) with GCA under therapy with MMF and who were treated at the outpatient clinic for rare inflammatory systemic diseases at Hannover Medical School between 2010 and 2023 were retrospectively included in the study. All patients underwent duplex sonography, 18F-fluorodeoxyglucose positron emission tomography (18F-FDG PET), magnetic resonance imaging (MRI), and/or biopsy to confirm the diagnosis. The primary endpoints were the number of recurrences, CRP levels at 3-6 and 6-12 months, and the period of remission. All patients in this case series showed inflammatory activity of the arterial vessels in at least one of the imaging modalities: duplex sonography (n = 5), 18F-FDG PET (n = 5), MRI (n = 6), and/or biopsy (n = 5). CRP levels of all patients decreased at the measurement time points 3-6 months, and 6-9 months after initiation of therapy with MMF compared with CRP levels before MMF therapy. All patients with GCA in this case series achieved disease remission. The results of the present case series indicate that MMF is an effective therapy in controlling disease activity in GCA, which should be investigated in future randomized controlled trials.

Molecular Mechanisms for Changing Brain Connectivity in Mice and Humans.

The goal of this study was to examine commonalities in the molecular basis of learning in mice and humans. In previous work we have demonstrated that the anterior cingulate cortex (ACC) and hippocampus (HC) are involved in learning a two-choice visuospatial discrimination task. Here, we began by looking for candidate genes upregulated in mouse ACC and HC with learning. We then determined which of these were also upregulated in mouse blood. Finally, we used RT-PCR to compare candidate gene expression in mouse blood with that from humans following one of two forms of learning: a working memory task (network training) or meditation (a generalized training shown to change many networks). Two genes were upregulated in mice following learning: caspase recruitment domain-containing protein 6 (Card6) and inosine monophosphate dehydrogenase 2 (Impdh2). The Impdh2 gene product catalyzes the first committed step of guanine nucleotide synthesis and is tightly linked to cell proliferation. The Card6 gene product positively modulates signal transduction. In humans, Card6 was significantly upregulated, and Impdh2 trended toward upregulation with training. These genes have been shown to regulate pathways that influence nuclear factor kappa B (NF-κB), a factor previously found to be related to enhanced synaptic function and learning.

GuaB3, an overlooked enzyme in cyanobacteria's toolbox that sheds light on IMP dehydrogenase evolution

IMP dehydrogenase and GMP reductase are enzymes from the same protein family with analogous structures and catalytic mechanisms that have gained attention because of their essential roles in nucleotide metabolism and as potential drug targets. This study focusses on GuaB3, a less-explored enzyme within this family. Phylogenetic analysis uncovers GuaB3's independent evolution from other members of the family and it predominantly occurs in Cyanobacteria. Within this group, GuaB3 functions as a unique IMP dehydrogenase, while its counterpart in Actinobacteria has a yet unknown function. Synechocystis sp. PCC6803 GuaB3 structures demonstrate differences in the active site compared to canonical IMP dehydrogenases, despite shared catalytic mechanisms. These findings highlight the essential role of GuaB3 in Cyanobacteria, provide insights into the diversity and evolution of the IMP dehydrogenase protein family, and reveal a distinctive characteristic in nucleotide metabolism, potentially aiding in combating harmful cyanobacterial blooms-a growing concern for humans and wildlife.

Berberrubine is a novel and selective IMPDH2 inhibitor that impairs the growth of colorectal cancer

Inosine monophosphate dehydrogenase (IMPDH) catalyzes the rate-limiting reaction in the de novo synthesis pathway of guanine nucleotides that is highly required for cancer cell outgrowth. Herein, we found that IMPDH isoform 2 (IMPDH2) is highly expressed in colorectal cancer (CRC) and is correlated with poor patient prognosis. Via structure-based virtual screening, we identified berberrubine, a critical ingredient of the medical plant Coptis chinensis, as a novel, selective, and competitive inhibitor of IMPDH2, which demonstrated over 15-fold selectivity to IMPDH2 than IMPDH1. Besides, we also confirmed the interaction between berberrubine and IMPDH2. Of note, berberrubine treatment significantly impairs the growth of human CRC cells in a dose-dependent manner, which can be rescued by supplementing with guanosine. Furthermore, oral administration of berberrubine remarkably reduced tumor volume and weight in a human cell line-derived xenograft model. Importantly, the anti-cancer activity of berberrubine was also confirmed by using the azoxymethane (AOM) / dextran sulfate sodium (DSS)-induced spontaneous CRC mouse model. Taken together, our study highlights that berberrubine acts as a novel IMPDH2 inhibitor, suppressing the growth of CRC in vitro and in vivo, providing a fresh perspective for its potential application in the treatment of CRC.