Search Results (418)

Trypsin is one of the most extensively studied enzymes in biochemistry. However, little information is available on the role of the disulfide bonds to establish the correct conformation and enzyme activity during molecular evolution. To obtain this information, two additional disulfide bonds corresponding to those found in human trypsin were individually or simultaneously introduced into the trypsin-like protease cocoonase (Bombyx mori), which contains three consensus disulfide bonds, and structural effects were analyzed. Enzyme assays of the mutant proteins revealed that, during molecular evolution, the Cys19–Cys154 bond contributed to improving substrate recognition (K_m), whereas the Cys134–Cys199 bond contributed to enhancing catalytic turnover (k_cat). In addition, the Cys134–Cys199 disulfide bond significantly increased the structural stability, whereas the Cys19–Cys154 disulfide bond promoted a more compact folded ensemble. Interestingly, when both disulfide bridges were introduced together, their effects acted synergistically, yielding the highest catalytic activity toward the substrate BAEE (k_cat/K_m). Taken together, these findings suggest that trypsin-like proteases evolved through a two-step adaptive process: an initial phase in which the catalytic efficiency (k_cat) and structural stability were enhanced, followed by a second phase in which the fold became more compact, thereby improving the overall enzymatic activity. Full article

This research utilized the CRISPR/Cas9 editing method to generate six mutant strains of Escherichia coli (E. coli) DH5α targeting specific genes. The functional characterization and phenotypic analysis confirmed the regulatory roles of these genes in modifying membrane permeability. The variations in membrane permeability among the mutant strains were assessed by measuring electrical conductivity, ortho-nitrophenyl-β-D-galactopyranoside (ONPG) hydrolysis, and propidium iodide (PI) fluorescence, with E. coli DH5α:ompA′ exhibiting the most pronounced increase in membrane permeability. The function of these genes in transformation was analyzed from physicochemical and microscopic perspectives. Assays of plasmid transformation efficiency revealed a significant enhancement in the E. coli DH5α:ompA′ mutant strain, underscoring the critical function of outer membrane proteins in DNA acquisition. Permeability simulations were performed utilizing the E. coli DH5α:ompA′ mutant strain, grounded in a previously established model. The quantitative correlation between transformation efficiency and membrane permeability in this mutant conformed to the equation T = aP + c. Full article

Terminal deoxynucleotidyl transferase (TdT) is a unique DNA polymerase that catalyzes template-independent nucleotide addition at the 3′-end of DNA, playing a critical role in generating immune receptor diversity. While the structural importance of Loop1 in blocking template strand binding and enabling this activity is established, the precise molecular contribution of hydrophobic interactions within Loop1 to the catalytic mechanism of human TdT remains unclear. In the present study, we aim to elucidate the roles of hydrophobic Loop1 residues (L397, F400, F404) in the structural organization and catalytic function of TdT. We engineered alanine and tryptophan substitutions at these positions and systematically analyzed the resulting mutant forms using molecular dynamics simulations and pre-steady-state kinetic measurements. Our results show that substitutions L397A and F400A increase Loop1 flexibility and significantly reduce catalytic activity, particularly for purine nucleotide incorporation, while F404A completely abolishes enzymatic function. The F404W mutant largely preserves activity. All mutant forms retain the ability to bind single-stranded DNA and dNTP, but in some cases, their affinity and thermal stability were reduced. These findings demonstrate that hydrophobic interactions in Loop1 are essential for maintaining the catalytically competent conformation of TdT, ensuring precise substrate positioning and active site stability. Full article

Alginate lyases are commonly employed for producing alginate oligosaccharides (AOS), but their industrial application is often constrained by low thermal stability and catalytic efficiency. This study engineered mutants of alginate lyase Alyw203 from marine Vibrio based on B-factor values and negative ΔΔG values. The L172V mutant exhibited a 2.43-fold increase in half-life at 40 °C, reduced K_m (from 107 to 65 mg/mL), and enhanced k_cat/K_m (from 0.07 to 0.35 mL/mg/s), indicating improved thermal stability, substrate affinity, and catalytic efficiency. Molecular dynamics simulations revealed that these improvements originated from reconstructed hydrogen bond networks, which stabilized enzyme–substrate interactions and reduced conformational flexibility. These results demonstrate that rational design focused on strengthening hydrogen bonding can simultaneously improve both stability and activity, offering a promising strategy for industrial AOS production. Full article

γ-Aminobutyric acid type A receptors (GABA_ARs) are pentameric ligand-gated ion channels mediating fast inhibitory neurotransmission in the mammalian brain. Although recent structural and kinetic studies have advanced understandings regarding their activation mechanisms, the molecular determinants coupling agonist binding to channel gating remain unclear. We investigated the contribution of the β₂E153 residue, located on loop B of the extracellular domain, to the activation of α₁β₂γ₂ GABA_ARs. Macroscopic and single-channel patch clamp recordings were used to characterize two β₂E153-mutants: charge reversal (β₂E153K) and hydrophobic substitution (β₂E153A). Both substitutions disrupted normal receptor kinetics, with β₂E153K selectively accelerating deactivation and β₂E153A affecting both deactivation and desensitization. Single-channel analysis showed that β₂E153A reduced open probability and mean open times, consistent with altered gating transitions inferred from kinetic modeling. Structural inspection suggested that β₂E153 forms electrostatic interactions with β₂K196 and β₂R207 to stabilize loop C and maintain the agonist-bound conformation. The disruption of this interaction likely destabilizes loop C, leading to weakened agonist binding and modified gating. Overall, our results identify β₂E153 as a key element in the long-range allosteric network linking the binding site to the channel gate in GABA_ARs. Full article

While there is a consensus that the cytochrome b₆f complex (cytb₆f) in algae and plants is involved in the regulatory mechanism of oxygenic photosynthesis known as light-induced state transitions (STs), no such consensus exists for cyanobacteria. Here, we provide the first direct functional evidence for cytb₆f using single-point mutation data. We introduced a PetD-Phe124Ala substitution in the cyanobacterium Synechocystis sp. PCC 6803 to test the key predictions of the hydrophobic-mismatch (HMM) model for cytb₆f-driven STs in all oxygenic photosynthetic species. These predictions concern the role of the Phe/Tyr124^fg-loop-PetD and the extent and kinetic characteristics of STs. The effects of PetD-F124A mutation on STs were monitored using 77K and Pulse-Amplitude-Modulated (PAM) fluorescence. For comparison, we employed a phycobilisome (PBS)-less Synechocystis mutant and wild-type (WT) strain, as well as the stn7 mutant and WT of Arabidopsis plant. The PetD-F124A mutation reduced the extent of STs and selectively affected the two-exponential kinetics components of the transitions. Under State 1 conditions, the mutant exhibited ~60% less energetic decoupling of PBS from photosystem I (PSI) compared to the WT. It is explainable by the HMM model with the inability of the PetD-F124A mutant, during the induction phase of the State 2→State 1 transition to adopt the cytb₆f conformation with minimal hydrophobic thickness. PAM-derived parameters indicated that PSII electron transport function is not inhibited, and no detectable effect on cyclic electron transport around PSI was observed under low-light conditions. Circular dichroism and differential scanning calorimetry confirmed that both the PSI trimer/monomer ratio and the structural integrity of the PBSs are preserved in the mutant. The compensatory response to the mutation includes decreased PSI content and an increase in PBS rod size. In conclusion, (1) cytb₆f is involved in cyanobacterial STs; (2) evidence is provided supporting the HMM model; (3) the electron transfer and signal transduction functions of cytb₆f are separated into distinct domains; and (4) the signaling pathway regulating STs and pigment-protein composition in Synechocystis involves PetD-Phe124. Full article

Background/Objectives: The emergence of drug-resistant HIV-1 strains challenges the long-term efficacy of current antiretroviral therapies. Non-nucleoside reverse transcriptase inhibitors (NNRTIs) are critical in HIV-1 treatment; however, the need for new candidates with improved resistance profiles and pharmacokinetics remains. This study aims to design and evaluate novel NNRTIs targeting both wild-type (WT) and mutant-type (MT) HIV-1 reverse transcriptase (RT) using integrated computational strategies. Methods: We conducted a 3D-QSAR study on 33 naphthyl-diarylpyrimidine derivatives using CoMFA and CoMSIA models. We designed thirty-five novel molecules based on contour map insights. We applied ADMET and drug-likeness filters to prioritize ten candidates. Molecular docking was performed on WT (PDB: 3HVT) and MT (PDB: 4PUO) RT structures. The top candidates underwent 100 ns molecular dynamics (MD) simulations. We analyzed structural stability via RMSD, RMSF, and Rg, while we used SASA and MolSA to assess solvent exposure and surface compactness. Results: The CoMFA and CoMSIA models demonstrated robust predictivity (R² = 0.979/0.920, Q² = 0.643/0.546, R²_test = 0.747/0.603). P14 and P43 showed higher binding affinities than nevirapine and favorable ADMET profiles. MD simulations confirmed stable binding in WT-RT and adaptive flexibility in MT-RT. SASA and MolSA analysis revealed favorable conformational compaction. Drug-likeness profiles indicated optimal log P, strong hydrogen bonding, and acceptable bioavailability. Conclusions: P14 and P43 demonstrate strong potential as NNRTI leads, combining binding affinity, structural stability, and favorable pharmacokinetics, supporting further experimental development. Full article

GABA transporter 1 (GAT1), encoded by the SLC6A1 gene, is essential for maintaining inhibitory neurotransmission by mediating the reuptake of GABA from the synaptic cleft. Dysfunction of GAT1 has been linked to several neurological and neurodevelopmental disorders, including epilepsy and Alzheimer’s disease. In this study, we performed a comprehensive computational investigation of reported GAT1 mutations to understand their structural and functional implications. Seven mutations (G63S, Y140C, Q291Δ, F294Δ, N310I, D451G, and G457H) were analyzed using homology modeling, structural validation tools, molecular dynamics (MD) simulation triplicates, and binding free energy calculations via the gmx_MMPBSA method. The wild-type consistently exhibited the most favorable interaction energy (−59.89 kcal/mol), the strongest binding free energy (ΔG = −28.29 kcal/mol), and the most stable hydrogen-bonding network. While all mutants displayed elevated RMSD and energy fluctuations relative to the wild-type, these changes predominantly reflected local conformational disturbances rather than global unfolding, indicating that the overall structural framework of GAT1 remains largely preserved. Among the mutants, G63S exerted the mildest effect on ligand stabilization, whereas Y140C, G457H, Q291Δ, and D451G produced substantial reductions in protein–ligand stability, weakened hydrogen bonding, and increased ligand mobility within the binding pocket. Free-energy analysis further highlighted the pronounced destabilizing influence of N310I, Q291Δ, and G457H on tiagabine binding. These findings provide mechanistic insights into how specific GAT1 mutations may alter transporter stability and function, offering a structural framework for future studies on GABAergic dysfunction and therapeutic development. Full article

Background/Objectives: Approximately 20% of familial ALS (fALS) cases are linked to mutations in Cu/Zn superoxide dismutase (SOD1). Through a gain function, SOD1 misfolding exerts a toxic effect on motor neurons, leading to their degradation and ALS symptomology in both fALS cases and sporadic ALS (sALS) cases with no known genetic cause. To further our understanding of SOD1-ALS etiology, identifying motor neuron-specific SOD1 post-translational modifications (PTMs) and studying their structural influence is necessary. To this end, we have conducted a study on the influence of the deamidation of Asn53, a PTM proximal to key stabilizing motifs in SOD1, which has scarcely been addressed in the literature to date. Methods: Deamidation to N53 was identified by tandem mass spectrometry of SOD1 immunoprecipitated from motor neuron (MN) cultures derived from wild-type (WT) human induced pluripotent stem cells (iPSCs). WT SOD1 and N53D SOD1, a mutant mimicking the deamidation, were expressed in Escherichia coli and purified for in vitro analyses. Differences between species were measured by experiments probing metal cofactors, relative monomer populations, and aggregation propensity. Furthermore, molecular dynamics experiments were conducted to model and determine the influence of the PTM on SOD1 structure. Results: In contrast to WT, N53D SOD1 showed non-native incorporation of metal cofactors, coordinating more Zn²⁺ cofactors than total Zn-binding sites, and more readily adopted monomeric forms, unfolded, and aggregated with heating, possibly while releasing coordinated metals. Conclusions: Deamidation to N53 in SOD1 encourages the adoption of non-native conformers, and its detection in WT MN cultures suggests relevance to sALS pathophysiology. Full article

Huntingtin (HTT) is a large, ubiquitously expressed scaffold protein that participates in multiple cellular processes, including vesicular transport, transcriptional regulation, and energy metabolism. The mutant form of HTT (mHTT), characterized by an abnormal polyglutamine (polyQ) expansion in its N-terminal region, is the causative agent of Huntington’s disease (HD), a progressive neurodegenerative disorder. Current therapeutic efforts for HD have primarily focused on lowering HTT levels through gene silencing or promoting mHTT degradation. However, accumulating evidence suggests that post-translational modifications (PTMs) of HTT—such as phosphorylation, ubiquitination, acetylation, and SUMOylation—play pivotal roles in modulating HTT’s conformation, aggregation propensity, subcellular localization, and degradation pathways. These modifications regulate the balance between HTT’s physiological functions and pathological toxicity. Importantly, dysregulation of PTMs has been linked to mHTT accumulation and selective neuronal vulnerability, highlighting their relevance as potential therapeutic targets. A deeper understanding of how individual PTMs and their crosstalk regulate HTT homeostasis may not only provide mechanistic insights into HD pathogenesis but also uncover novel, more specific strategies for intervention. In this review, we summarize recent understanding on HTT PTMs, discuss their implications for disease modification, and outline critical knowledge gaps that remain to be addressed. Full article

Aspergillus flavus is both an agricultural and clinical pathogen, notable for its ability to contaminate crops with aflatoxins and cause invasive aspergillosis. The increasing emergence of azole resistance in A. flavus poses a serious challenge to food safety and human health. Although mutations in ergosterol biosynthesis genes have been reported in resistant isolates, their functional contributions remain largely unvalidated. In this study, we investigated the role of the CYP51A Y119F mutation in azole resistance. Site-directed mutants were generated using PCR-based gene editing, and their susceptibility to antifungal agents was assessed through Clinical and Laboratory Standards Institute broth microdilution and agar diffusion assays. The Y119F mutation reduced susceptibility specifically to voriconazole and isavuconazole, while susceptibility to itraconazole and posaconazole remained unchanged. To explore the structural basis of this phenotype, molecular dynamics simulations were performed. The mutant protein exhibited greater fluctuations and reduced conformational stability compared to the wild-type enzyme. Tunnel analysis further indicated that the Y119F substitution caused narrowing and shortening of the main access tunnels to the heme-binding pocket, likely impairing azole access and binding. The combined biochemical and structural analyses suggest that Y119F represents a primary resistance-conferring mutation that modifies the structural dynamics of CYP51A. Full article

Background: Acute myeloid leukemia (AML) is a heterogeneous hematologic malignancy characterized by impaired differentiation, apoptosis resistance, and metabolic reprogramming, which collectively contribute to therapeutic resistance and poor clinical outcomes. While targeted agents—such as LSD1 inhibitors, the BCL-2 inhibitor venetoclax, and IDH1 inhibitors—have provided clinical benefit, their efficacy is often limited by compensatory signaling and clonal evolution. This study aimed to identify FDA-approved compounds with multitarget potential to simultaneously modulate key epigenetic, apoptotic, and metabolic pathways in AML. Methods: Structure-based virtual screening of 3957 FDA-approved molecules was performed against three AML-relevant targets: lysine-specific demethylase 1 (LSD1), BCL-2, and mutant IDH1 (R132H). Top-ranked hits were evaluated using ADMET prediction and molecular dynamics (MD) simulations to assess pharmacokinetic properties, toxicity, and ligand–protein complex stability over 100 ns trajectories. Results: Three compounds—DB16703, DB08512, and DB16047—exhibited high binding affinities across all three targets with favorable pharmacokinetic and safety profiles. MD simulations confirmed the structural stability of the ligand–protein complexes, revealing persistent hydrogen bonding and minimal conformational deviation. These findings suggest that these repurposed drugs possess a promising multitarget profile capable of addressing AML’s multifactorial pathophysiology. Conclusions: This computational study supports the feasibility of a polypharmacology-based strategy for AML therapy by integrating epigenetic modulation, apoptotic reactivation, and metabolic correction within single molecular scaffolds. However, the identified compounds (Belumosudil, DB08512, and Elraglusib) have not yet demonstrated efficacy in AML models; further preclinical validation is warranted to substantiate these predictions and advance translational development. Full article

The antimalarial combination of sulfadoxine–pyrimethamine is used as a preventive treatment in pregnant women and children in Africa. Sulfadoxine inhibits the Plasmodium falciparum dihydropteroate synthase (PfDHPS), but resistance has emerged through point mutations in this enzyme. In this study, we investigate the impact of mutations on the structural and dynamic properties of PfDHPS using molecular dynamics simulations. Our results show that PfDHPS maintains overall structural integrity across various combinations of resistance-associated mutations. However, significant differences emerge in ligand binding. Sulfadoxine binding is particularly impacted and shows reduced stability in the mutant systems compared to the wild-type enzyme, while the natural substrate generally maintains stable or even enhanced binding affinity. A key finding is the critical role of the D2 loop, whose conformational flexibility influences ligand retention. In mutant enzymes, the disruption of interactions between the D2 loop and the natural substrate correlates with decreased affinity. In contrast, specific mutations in the loop are associated with an increased affinity. Conversely, sulfadoxine binding is associated with an open D2 loop conformation, facilitating its release from the active site. Finally, the intrinsic flexibility of sulfadoxine emerges as an important determinant of this process. Together, these results provide molecular-level insights into the mechanisms of resistance in PfDHPS and establish a structural and dynamic framework for future investigations into its catalytic function and inhibitor design. Full article

The antigenic relationship between Eurasian avian-like H1N1 swine influenza viruses (EA H1N1) and human pandemic 2009 H1N1 viruses (2009/H1N1) remains a critical question for influenza surveillance and vaccine efficacy. This study systematically investigated the antigenic differences between strains A/swine/Tianjin/312/2016 (TJ312, EA H1N1) and A/Guangdong-Maonan/SWL1536/2019 (GD1536, 2009/H1N1). Cross-hemagglutination inhibition (HI) assays revealed a significant antigenic disparity, with a 16-fold reduction in heterologous versus homologous HI titers. Comparative sequence analysis identified 22 amino acid differences across the five major antigenic sites (Sa, Sb, Ca1, Ca2, and Cb) of the HA1 subunit. Using reverse genetics, a panel of mutant viruses was generated. This study revealed that a single histidine (H)-to-asparagine (N) substitution at residue 128 (H3 numbering) in the Sa antigenic site acts as a primary determinant of antigenic variation, sufficient to cause a four-fold change in HI titers and a measurable drift in antigenic distance. Structural modeling via AlphaFold3 and PyMOL software suggests that the H128N mutation may alter the local conformation of the antigenic site. It is plausible that H at position 128 could exert electrostatic repulsion with adjacent amino acids, whereas N might facilitate hydrogen bond formation with neighboring residues. These interactions would potentially lead to structural changes in the antigenic site. Our findings confirm that residue 128 is a critical molecular marker for the antigenic differentiation of EA H1N1 and 2009/H1N1 viruses. The study underscores the necessity of monitoring specific HA mutations that could reduce cross-reactivity and provides valuable insights for refining vaccine strain selection and pandemic preparedness strategies. Full article

The inactivation of thrombin by antithrombin is highly enhanced by the presence of heparin chains forming “bridges” between the two proteins. X-ray structures for such ternary complexes have been published, but the molecular background of the lower efficiency of smaller heparinoids on thrombin inhibition remains poorly understood. Antithrombin-resistant prothrombin mutants (mutations affecting Arg596 in prothrombin) have been reported that cause severe thrombophilia. Our aim was to study the interactions in the antithrombin–thrombin Michaelis complex both in the presence and the absence of a heparinoid chain and in the presence of pentasaccharide by using molecular dynamics. We also intended to study the complexes of thrombin mutants as well as a known alternative antithrombin conformation at the “hinge” region built using docking. The binding between the proteins was investigated by Gaussian Accelerated Molecular Dynamics (GaMD). We compared the contribution of several amino acids at the binding “exosites” between AT and the wild type and mutant thrombins and between systems containing or not containing a heparinoid. In the docking-based simulations, several of the analyzed amino acid pairs no longer contributed to the interaction, suggesting that the open “hinge” conformation has limited biological relevance. We could identify multiple conformational types using clustering, revealing high flexibility in mutants and systems without heparinoid, probably indicating lower stability. We were also able to detect the allosteric effects of the ligands on the bound thrombin. In summary, we were able to obtain conformations using GaMD that can explain the better protein–protein interactions in the ternary complexes and the impaired AT binding of the thrombin Arg596 mutants at an atomic level. Full article