Wild-type Complex Research Articles

Molecular investigation of TSHR gene in Bangladeshi congenital hypothyroid patients.

The disorder of thyroid gland development or thyroid dysgenesis accounts for 80-85% of congenital hypothyroidism (CH) cases. Mutations in the TSHR gene are mostly associated with thyroid dysgenesis, and prevent or disrupt normal development of the gland. There is limited data available on the genetic spectrum of congenital hypothyroid children in Bangladesh. Thus, an understanding of the molecular aetiology of thyroid dysgenesis is a prerequisite. The aim of the study was to investigate the effect of mutations in the TSHR gene on the small molecule thyrogenic drug-binding site of the protein. We identified two nonsynonymous mutations (p.Ser508Leu, p.Glu727Asp) in the exon 10 of the TSHR gene in 21 patients with dysgenesis by sequencing-based analysis. Later, the TSHR368-764 protein was modeled by the I-TASSER server for wild-type and mutant structures. The model proteins were targeted by thyrogenic drugs, MS437 and MS438 to perceive the effect of mutations. The damaging effect in drug-protein complexes of mutants was explored by molecular docking and molecular dynamics simulations. The binding affinity of wild-type protein was much higher than the mutant cases for both of the drug ligands (MS437 and MS438). Molecular dynamics simulates the dynamic behavior of wild-type and mutant complexes. MS437-TSHR368-764MT2 and MS438-TSHR368-764MT1 showed stable conformations in biological environments. Finally, Principle Component Analysis revealed structural and energy profile discrepancies. TSHR368-764MT1 exhibited much more variations than TSHR368-764WT and TSHR368-764MT2, emphasizing a more damaging pattern in TSHR368-764MT1. This genetic study might be helpful to explore the mutational impact on drug binding sites of TSHR protein which is important for future drug design and selection for the treatment of congenital hypothyroid children with dysgenesis.

Aptamer-, heparin- or cocktail-based inhibition of S1-ACE2 protein complexes

The Spike protein (S1) from the Severe acute respiratory syndrome 2 virus binds to angiotensin converting enzyme 2 (ACE2) receptor to initiate infection. Hence, antiviral therapeutic targeting the S1-ACE2 interface is of interest. Herein, we compare the inhibition efficacy of an aptamer to heparin or their cocktail, against wild-type (WT), Omicron, Delta, and Lambda S1-ACE2 complexes. The aptamer-protein complexes had the dissociation constant KD values in the 2–13 nM range. The aptamer half-maximal inhibitory concentration against WT S1-ACE was 17 nM, with the % inhibition in the 12–35% range. Several aptamer-S1 protein complexes were also stable at low pH with 60% inhibition. Despite the similarity in S1 sequences, the extent of inhibition (2–27%) with heparin was highly dependent on the type of S1 protein. More importantly, heparin did not inhibit the WT S1-ACE2 complex but was effective with mutants. The aptamer-heparin cocktail was less effective compared to aptamer or heparin, individually. Modelling data show that either a direct or proximal binding to RBD sites by aptamer or heparin prevents the ACE2 binding. Overall, heparin was as an effective inhibitor as aptamer against certain variants, and represents the more cost-effective neutralizing agent against emerging coronaviruses.

An In Silico Study Investigating Camptothecin-Analog Interaction with Human Protein Tyrosine Phosphatase, SHP2 (PTPN11).

The human PTPN11 gene encodes for the src tyrosine phosphatase protein (SHP2) is now gaining much attention in many disorders, particularly its oncogenic involvement in many types of cancer. Efforts in developing molecules targeting SHP2 with high efficacy are the future of drug discovery and chemotherapy. However, the interaction of a new camptothecin analog with the catalytic domain of SHP2 protein remains unknown. Therefore, this study aims to provide in silico rationale for the recognition and binding of FL118 and irinotecan with the catalytic domain of human protein tyrosine phosphatase-SHP2 (PTPc-SH2-SHP2, chain A). The docking interaction of the human SHP2 protein's catalytic domain as well as Y279C and R465G mutants with FL118 and irinotecan ligands were calculated and analyzed using the Autodock 4.2 programme, setting the docking grid to target the protein's active site. The camptothecin analog FL118 had the best lowest negative affinity energies with PTPc-SHP2 wildtype and SHP2-Y279C mutant model (-7.54 Kcal/mol and -6.94 Kcal/mol, respectively). Moreover, the protein-ligand complexes revealed several hydrogen bond interactions reflecting the degree of stability that each structure possesses, with the FL118-SHP2-wildtype forming the most stable complex among the structures. In addition, the FL118-SHP2 wildtype complex was validated for RMSD, RMSF, hydrogen bonds, and salt bridges. This revealed that the complex generated became stable over time. This in silico rationale identifies the novel FL118 camptothecin analog as a potent selective inhibitor of PTPc-SH2 domain of SHP2 protein, paving way for further in vitro investigations into the interactions and binding activity of analogs with SHP2 for potential therapeutic applications in PTPN11-associated disorders.

Analysis of the binding modes and resistance mechanism of four methyl benzimidazole carbamates inhibitors fungicides with Monilinia fructicola β2-tubulin protein

Monilinia fructicola can infest plants during fruit flowering and during fruit storage and transportation, causing serious economic losses. The resistance problem of methyl benzimidazole carbamates inhibitors fungicide is becoming more and more prominent as the use time increases. By exploring the molecular binding mode, we studied the changes of the binding mode of the main amino acid residues between the four MBCs fungicides and the wild type and mutant Monilinia fructicoloa beta-tubulin protein constructed by homologous modeling. Constructing homology related models through sequence alignment based on sequence information from Monilinia fructicola beta-tubulin protein. Molecular docking and molecular dynamics simulations were then used to identify the optimum binding mode of benomyl, carbendazim, thiabendazole and thiophanate-methyl with Monilinia fructicola beta-tubulin protein. Furthermore, we calculated the binding free energy of four wild-type and mutant protein-ligand complexes using MM/PBSA. The result shows that when E198A was mutated, the hydrogen bonding force of thiophanate-methyl binding to the protein was reduced. The possible underlying cause of the resistance is the disappearance of the π-π stacking interaction with Phe200. When E198Q was mutated, all three fungicides, excluding carbendazim, interacted with Gln198 of the protein through hydrogen bonding. However, the binding pattern of carbendazim, thiophanate-methyl were least affected. When F200Y was mutated, the binding pocket of benomyl is slightly altered concerning the binding pattern between the wild-type protein and the fungicide concerning the amino acid residues. The resistance mechanism of M. fructicola beta-tubulin protein to MBCs fungicides and the mechanism of cross-resistance between MBCs fungicides were initially elucidated by computer simulation.

In silico investigation on the mutational analysis of BRCA1-BARD1 RING domains and its effect on nucleosome recognition and ubiquitination

The BRCA1-BARD1 complex is a crucial tumor suppressor E3 ubiquitin ligase involved in DNA double-stranded break repair. The BRCA1-BARD1 RING domains interact with UBE2D3 through the BRCA1 interface and this complex flexibly tether to the nucleosome core particle (NCP), where BRCA1 and BARD1 interacts with histone H2A and H2B of NCP. Mutations in the BRCA1-BARD1 RING domains have been linked to familial breast and ovarian cancer. Seven mutations were analyzed to understand their effect on the binding interface of protein partners and changes in conformational dynamics. Molecular dynamics simulations revealed that mutant complexes were less conformationally flexible than the wildtype complex. Protein-protein interaction profiling showed the importance of specific molecular interactions, hotspot and hub residues, and some of these were lost in the mutant complexes. Two mutations (BRCA1L51W-K65R and BARD1C53W) hindered significant interaction between protein partners and may prevent signaling for ubiquitination of histones in NCP and other cellular targets. The structural compactness and reduced significant interaction in mutant complexes may be the possible reason of preventing ubiquitination and hinder DNA repair, resulting cancer.

A mutation-induced drug resistance database (MdrDB)

Mutation-induced drug resistance is a significant challenge to the clinical treatment of many diseases, as structural changes in proteins can diminish drug efficacy. Understanding how mutations affect protein-ligand binding affinities is crucial for developing new drugs and therapies. However, the lack of a large-scale and high-quality database has hindered the research progresses in this area. To address this issue, we have developed MdrDB, a database that integrates data from seven publicly available datasets, which is the largest database of its kind. By integrating information on drug sensitivity and cell line mutations from Genomics of Drug Sensitivity in Cancer and DepMap, MdrDB has substantially expanded the existing drug resistance data. MdrDB is comprised of 100,537 samples of 240 proteins (which encompass 5119 total PDB structures), 2503 mutations, and 440 drugs. Each sample brings together 3D structures of wild type and mutant protein-ligand complexes, binding affinity changes upon mutation (ΔΔG), and biochemical features. Experimental results with MdrDB demonstrate its effectiveness in significantly enhancing the performance of commonly used machine learning models when predicting ΔΔG in three standard benchmarking scenarios. In conclusion, MdrDB is a comprehensive database that can advance the understanding of mutation-induced drug resistance, and accelerate the discovery of novel chemicals.

Molecular dynamics simulations corroborate recombinant expression studies carried out on three αIIb β-propeller mutations reported in Indian Glanzmann thrombasthenia patients.

Mutations in the αIIb β-propeller domain have long been known to disrupt heterodimerization and intracellular trafficking of αIIbβ3 complexes leading to diminished surface expression and/or function, resulting in Glanzmann thrombasthenia. Our previous study on three β-propeller mutations, namely G128S, S287L, and G357S, showed variable defects in protein transport correlated with the patient's clinical phenotypes. Pulse-chase experiments revealed differences in αIIbβ3 complex maturation among the three mutations. Hence, the current study aims to correlate conformational changes caused by each one of them. Evolutionary conservation analysis, stability analysis, and molecular dynamics simulations of the three mutant structures were carried out. Stability analysis revealed that, while G128S and G357S mutations destabilized the β-propeller structure, S287L retained the stability. Wild-type and mutant β-propeller structures, when subjected to molecular dynamics simulations, confirmed that G128S and G357S were both destabilizing in nature when compared with the wild-type and S287L based on several parameters studied, like RMSD, RMSF, Rg, FEL, PCA, secondary structure, and hydrogen bonds. In our previous study, we demonstrated that mutant S287L αIIbβ3 complexes were more stable than the wild-type αIIbβ3 complexes, as evidenced in pulse-chase experiments. These findings corroborate variable intracellular fates of mutant αIIbβ3 complexes as a result of these β-propeller mutations.

Predicting the effects of rare genetic variants on oncogenic signaling pathways: A computational analysis of HRAS protein function.

The HRAS gene plays a crucial role in regulating essential cellular processes for life, and this gene's misregulation is linked to the development of various types of cancers. Nonsynonymous single nucleotide polymorphisms (nsSNPs) within the coding region of HRAS can cause detrimental mutations that disrupt wild-type protein function. In the current investigation, we have employed in-silico methodologies to anticipate the consequences of infrequent genetic variations on the functional properties of the HRAS protein. We have discovered a total of 50 nsSNPs, of which 23 were located in the exon region of the HRAS gene and denoting that they were expected to cause harm or be deleterious. Out of these 23, 10 nsSNPs ([G60V], [G60D], [R123P], [D38H], [I46T], [G115R], [R123G], [P11OL], [A59L], and [G13R]) were identified as having the most delterious effect based on results of SIFT analysis and PolyPhen2 scores ranging from 0.53 to 69. The DDG values -3.21 kcal/mol to 0.87 kcal/mol represent the free energy change associated with protein stability upon mutation. Interestingly, we identified that the three mutations (Y4C, T58I, and Y12E) were found to improve the structural stability of the protein. We performed molecular dynamics (MD) simulations to investigate the structural and dynamic effects of HRAS mutations. Our results showed that the stable model of HRAS had a significantly lower energy value of -18756 kj/mol compared to the initial model of -108915 kj/mol. The RMSD value for the wild-type complex was 4.40 Å, and the binding energies for the G60V, G60D, and D38H mutants were -107.09 kcal/mol, -109.42 kcal/mol, and -107.18 kcal/mol, respectively as compared to wild-type HRAS protein had -105.85 kcal/mol. The result of our investigation presents convincing corroboration for the potential functional significance of nsSNPs in augmenting HRAS expression and adding to the activation of malignant oncogenic signalling pathways.

Effect of Single-Residue Mutations on CTCF Binding to DNA: Insights from Molecular Dynamics Simulations.

In humans and other eukaryotes, DNA is condensed into chromatin fibers that are further wound into chromosomes. This organization allows regulatory elements in the genome, often distant from each other in the linear DNA, to interact and facilitate gene expression through regions known as topologically associating domains (TADs). CCCTC-binding factor (CTCF) is one of the major components of TAD formation and is responsible for recruiting a partner protein, cohesin, to perform loop extrusion and facilitate proper gene expression within TADs. Because single-residue CTCF mutations have been linked to the development of a variety of cancers in humans, we aim to better understand how these mutations affect the CTCF structure and its interaction with DNA. To this end, we compare all-atom molecular dynamics simulations of a wildtype CTCF-DNA complex to those of eight different cancer-linked CTCF mutant sequences. We find that most mutants have lower binding energies compared to the wildtype protein, leading to the formation of less stable complexes. Depending on the type and position of the mutation, this loss of stability can be attributed to major changes in the electrostatic potential, loss of hydrogen bonds between the CTCF and DNA, and/or destabilization of specific zinc fingers. Interestingly, certain mutations in specific fingers can affect the interaction with the DNA of other fingers, explaining why mere single mutations can impair CTCF function. Overall, these results shed mechanistic insights into experimental observations and further underscore CTCF's importance in the regulation of chromatin architecture and gene expression.

Conformational and binding mode assessment of the human IL-3 recognition by its alpha receptor.

Protein-protein interactions (PPIs) are attractive targets as they are critical in a variety of biological processes and pathologies. As an illustration, the interleukin 3 (IL-3) and its α subunit receptor (IL-3Rα) are two proteins belonging to the cytokine or receptor βc family and are involved in several disorders like inflammatory diseases or hematological malignancies. This PPI exhibits a low binding affinity and a complex formed by a mutant form of IL-3 (superkine) and IL-3Rα have emerged from the literature, with an increase of the affinity. Therefore, in this study, we performed molecular dynamics simulations and binding energy calculation in order to evaluate protein dynamics and to characterize the main interactions between IL-3 and IL-3Rα, considering both wild-type and mutant. First, in the case of IL-3Rα/IL-3 wild-type complex, IL-3Rα can adopt three different conformations essentially driven by NTD domain, including the open and closed conformations, previously observed in crystal structures. Additionally, our results reveal a third conformation that has a distinct interaction profile that the others. Interestingly, these conformational changes are attenuated in IL-3Rα/IL-3 mutant complex. Then, we highlighted the contribution of different residues which interact principally with IL-3 or IL-3Rα conserved region. As for the mutated residue at position 135 of IL-3, other residues such as IL-3 E138, IL-3 D40, IL-3Rα Y279, IL-3Rα K235, or IL-3Rα R277 seem important for a low or a high binding affinity. Altogether these findings yield new information that could be exploited in a drug discovery process.

Neutron Reflectometry and Molecular Simulations Demonstrate HIV-1 Nef Homodimer Formation on Model Lipid Bilayers

The HIV-1 Nef protein plays a critical role in viral infectivity, high-titer replication in vivo, and immune escape of HIV-infected cells. Nef lacks intrinsic biochemical activity, functioning instead through interactions with diverse host cell signaling proteins and intracellular trafficking pathways. Previous studies have established an essential role for Nef homodimer formation at the plasma membrane for most if not all its functions. Here we combined neutron reflectometry of full-length myristoylated Nef bound to model lipid bilayers with molecular simulations based on previous X-ray crystal structures of Nef homodimers. This integrated approach provides direct evidence that Nef associates with the membrane as a homodimer with its structured core region displaced from the membrane for partner protein engagement. Parallel studies of a dimerization-defective mutant, Nef-L112D, demonstrate that the helical dimerization interface present in previous crystal structures stabilizes the membrane-bound dimer. X-ray crystallography of the Nef-L112D mutant in complex with the SH3 domain of the Nef-associated host cell kinase Hck revealed a monomeric 1:1 complex instead of the 2:2 dimer complex formed with wild-type Nef. Importantly, the crystal structure of the Nef-L112D core and SH3 interface are virtually identical to the wild-type complex, indicating that this mutation does not affect the overall Nef fold. These findings support the intrinsic capacity of Nef to homodimerize at lipid bilayers using structural features present in X-ray crystal structures of dimeric complexes.

Ternary complex dissociation kinetics contribute to mutant-selective EGFR degradation

Targeted degradation of proteins by chimeric heterobifunctional degraders has emerged as a major drug discovery paradigm. Despite the increased interest in this approach, the criteria dictating target protein degradation by a degrader remain poorly understood, and potent target engagement by a degrader does not strongly correlate with target degradation. In this study, we present the biochemical characterization of an epidermal growth factor receptor (EGFR) degrader that potently binds both wild-type and mutant EGFR, but only degrades EGFR mutant variants. Mechanistic studies reveal that ternary complex half-life strongly correlates with processive ubiquitination with purified components and mutant-selective degradation in cells. We present cryoelectron microscopy and hydrogen-deuterium exchange mass spectroscopy data on wild-type and mutant EGFR ternary complexes, which demonstrate that potent target degradation can be achieved in the absence of stable compound-induced protein-protein interactions. These results highlight the importance of considering target conformation during degrader development as well as leveraging heterobifunctional ligand binding kinetics to achieve robust target degradation.

Complementary in vitro functional studies and in silico alchemical free energy simulations of the sarco-endoplasmic reticulum calcium pump (SERCA) and phospholamban (PLN) complex.

SERCA is ubiquitously expressed in all eukaryotic cells and is responsible for actively transporting calcium ions from the cytoplasm into the SR/ER lumen. PLN is a small transmembrane peptide that regulates SERCA's calcium transport activity in cardiac muscle. Human genetic variants of PLN have been implicated in cardiomyopathies. PLN is a 52 amino acid peptide with an N-terminal cytoplasmic helix (residues 1-17), a short linker region (residues 18-27) and a C-terminal transmembrane helix (residues 28-52). Previous structural studies have identified the binding groove for PLN formed by transmembrane segments M2, M6, and M9 of SERCA (PDB: 4KYT). The structure of the SERCA-PLN complex consists of SERCA in a calcium-free, E1-like state and includes the linker region and transmembrane helix of PLN (residues 20-52). Here, we carry out in vitro functional studies and in silico free energy calculations to examine the effects of alanine scanning mutations in PLN (residues 20-52) on SERCA regulation. From the functional studies, changes in kinetics parameters such as calcium affinity (KCa) and maximal activity (VMax) of SERCA are determined for each of the alanine substitutions. From the in silico alchemical free energy simulations (using Compute Canada supercomputing resources), each of the residues in PLN are alchemically transformed to alanine to determine the change in Gibbs free energy (Δ;Δ;G) relative to the wild-type SERCA-PLN complex. Together, the complementary in vitro and in silico mutational studies provide novel insights into a membrane protein-peptide complex. The PLN variants are quantified in terms of their physiological significance – gain-of-function, loss-of-function, or neutral – and the molecular determinants that control binding specificity.

A nucleotide binding-independent role for γ-tubulin in microtubule capping and cell division.

The γ-tubulin ring complex (γ-TuRC) has essential roles in centrosomal and non-centrosomal microtubule organization during vertebrate mitosis. While there have been important advances in understanding γ-TuRC-dependent microtubule nucleation, γ-TuRC capping of microtubule minus-ends remains poorly characterized. Here, we utilized biochemical reconstitutions and cellular assays to characterize the human γ-TuRC's capping activity. Single filament assays showed that the γ-TuRC remained associated with a nucleated microtubule for tens of minutes. In contrast, caps at dynamic microtubule minus-ends displayed lifetimes of ∼1 min. Reconstituted γ-TuRCs with nucleotide-binding deficient γ-tubulin (γ-tubulinΔGTP) formed ring-shaped complexes that did not nucleate microtubules but capped microtubule minus-ends with lifetimes similar to those measured for wild-type complexes. In dividing cells, microtubule regrowth assays revealed that while knockdown of γ-tubulin suppressed non-centrosomal microtubule formation, add-back of γ-tubulinΔGTP could substantially restore this process. Our results suggest that γ-TuRC capping is a nucleotide-binding-independent activity that plays a role in non-centrosomal microtubule organization during cell division.

The role of the γ subunit in the photosystem of the lowest-energy phototrophs

Purple phototrophic bacteria use a 'photosystem' consisting of light harvesting complex 1 (LH1) surrounding the reaction centre (RC) that absorbs far-red-near-infrared light and converts it to chemical energy. Blastochloris species, which harvest light >1000 nm, use bacteriochlorophyll b rather than the more common bacteriochlorophyll a as their major photopigment, and assemble LH1 with an additional polypeptide subunit, LH1γ, encoded by multiple genes. To assign a role to γ, we deleted the four encoding genes in the model Blastochloris viridis. Interestingly, growth under halogen bulbs routinely used for cultivation yielded cells displaying an absorption maximum of 825 nm, similar to that of the RC only, but growth under white light yielded cells with an absorption maximum at 972 nm. HPLC analysis of pigment composition and sucrose gradient fractionation demonstrate that the white light-grown mutant assembles RC-LH1, albeit with an absorption maximum blue-shifted by 46 nm. Wavelengths between 900-1000 nm transmit poorly through the atmosphere due to absorption by water, so our results provide an evolutionary rationale for incorporation of γ; this polypeptide red-shifts absorption of RC-LH1 to a spectral range in which photons are of lower energy but are more abundant. Finally, we transformed the mutant with plasmids encoding natural LH1γ variants and demonstrate that the polypeptide found in the wild type complex red-shifts absorption back to 1018 nm, but incorporation of a distantly related variant results in only a moderate shift. This result suggests that tuning the absorption of RC-LH1 is possible and may permit photosynthesis past its current low-energy limit.

Computational Prediction of Resistance Induced Alanine-Mutation in ATP Site of Epidermal Growth Factor Receptor.

Epidermal growth factor receptor (EGFR) resistance to tyrosine kinase inhibitors can cause low survival rates in mutation-positive non-small cell lung cancer patients. It is necessary to predict new mutations in the development of more potent EGFR inhibitors since classical and rare mutations observed were known to affect the effectiveness of the therapy. Therefore, this research aimed to perform alanine mutagenesis scanning on ATP binding site residues without COSMIC data, followed by molecular dynamic simulations to determine their molecular interactions with ATP and erlotinib compared to wild-type complexes. Based on the result, eight mutations were found to cause changes in the binding energy of the ATP analogue to become more negative. These included G779A, Q791A, L792A, R841A, N842A, V843A, I853A, and D855A, which were predicted to enhance the affinity of ATP and reduce the binding ability of inhibitors with the same interaction site. Erlotinib showed more positive energy among G779A, Q791A, I853A, and D855A, due to their weaker binding energy than ATP. These four mutations could be anticipated in the development of the next inhibitor to overcome the incidence of resistance in lung cancer patients.

Clinicopathologic and Molecular Features of Pancreatic Ductal Adenocarcinomas Harboring Alterations in COMPASS-like Complex Genes.

Recent genome-wide sequencing studies have identified a subset of pancreatic ductal adenocarcinomas (PDACs) harboring significant alterations in epigenetic regulation genes, including the COMPASS-like complex genes. Whether this subset of PDACs has specific histologic characteristics or carries prognostic or therapeutic implications is unknown. To determine the specific clinicopathologic and molecular features of PDACs carrying mutations in COMPASS-like complex genes. We analyzed a series of 103 primary and metastatic PDACs with comprehensive molecular profiling, including 13 PDACs carrying loss-of-function COMPASS-like complex gene alterations (study cohort). Another 45 patients carrying PDACs with wild-type COMPASS-like complex genes were used as the control group. PDACs within the study cohort were smaller, harboring frequent areas of poor differentiation and concurrent alterations in KRAS, TP53, SMAD4, and CDKN2A. A subset of metastatic PDACs from the study cohort showed squamous differentiation. There was a trend toward decreased survival in the study group. We further interrogated 2 public data sets and found that PDACs with COMPASS-like complex gene alterations have increased rates of TP53 mutation, body-tail location, poor differentiation or undifferentiated histology, and a higher death rate. COMPASS-like complex gene alterations likely represent a subset of more aggressive PDACs with poor or squamous differentiation histologically and increased concurrent TP53 mutations. These findings may have potential prognostic and therapeutic implications.

Electrostatic Interactions Are the Primary Determinant of the Binding Affinity of SARS-CoV-2 Spike RBD to ACE2: A Computational Case Study of Omicron Variants.

To explore the mechanistic origin that determines the binding affinity of SARS-CoV-2 spike receptor binding domain (RBD) to human angiotensin converting enzyme 2 (ACE2), we constructed the homology models of RBD-ACE2 complexes of four Omicron subvariants (BA.1, BA.2, BA.3 and BA.4/5), and compared them with wild type complex (RBDWT-ACE2) in terms of various structural dynamic properties by molecular dynamics (MD) simulations and binding free energy (BFE) calculations. The results of MD simulations suggest that the RBDs of all the Omicron subvariants (RBDOMIs) feature increased global structural fluctuations when compared with RBDWT. Detailed comparison of BFE components reveals that the enhanced electrostatic attractive interactions are the main determinant of the higher ACE2-binding affinity of RBDOMIs than RBDWT, while the weakened electrostatic attractive interactions determine RBD of BA.4/5 subvariant (RBDBA.4/5) lowest ACE2-binding affinity among all Omicron subvariants. The per-residue BFE decompositions and the hydrogen bond (HB) networks analyses indicate that the enhanced electrostatic attractive interactions are mainly through gain/loss of the positively/negatively charged residues, and the formation or destruction of the interfacial HBs and salt bridges can also largely affect the ACE2-binding affinity of RBD. It is worth pointing out that since Q493R plays the most important positive contribution in enhancing binding affinity, the absence of this mutation in RBDBA.4/5 results in a significantly weaker binding affinity to ACE2 than other Omicron subvariants. Our results provide insight into the role of electrostatic interactions in determining of the binding affinity of SARS-CoV-2 RBD to human ACE2.

Molecular basis of ssDNA recognition by RBM45 protein of neurodegenerative disease from multiple molecular dynamics simulations and energy predictions

Neurodegenerative diseases (NDD) are a group of cognitive and behavioral disorders characterized by progressive loss of neuronal structure and function. As the population ages, the incidence is getting higher and higher, but there is currently no effective treatment. The details of RNA/DNA recognition by the RNA-binding protein RBM45 closely related to neurodegenerative diseases through its two tandem RNA-recognition domains at its N-terminus have important implications for structure-based drug discovery against degenerative diseases. To explore the key characteristics of interaction between ssDNA and RBM45, we performed multiple molecular dynamics (MD) simulations along with MM-PBSA energy prediction on the complexes of wild type (WT) and three mutant RBM45s (K100A, F124A/Y165A, and F29A/F70A/F124A/Y165A) with ssDNA, respectively. The findings suggest that these mutated residues of RBM45 modify the interaction of their surrounding residues with ssDNA, thereby affecting RBM45 protein binding to ssDNA. In contrast with WT RBM45 protein, variations in van der Waals and electrostatic interactions with ssDNA caused by these three RBM45 mutants are critical to affect binding between them. In addition, energy analysis showed that RBM45 is a specific ssDNA-binding protein. The results of our work provide valuable theoretical guidance for the design effective drugs of NDD.

Intramolecular charge-transfer enhances energy transfer efficiency in carotenoid-reconstituted light-harvesting 1 complex of purple photosynthetic bacteria

In bacterial photosynthesis, the excitation energy transfer (EET) from carotenoids to bacteriochlorophyll a has a significant impact on the overall efficiency of the primary photosynthetic process. This efficiency can be enhanced when the involved carotenoid has intramolecular charge-transfer (ICT) character, as found in light-harvesting systems of marine alga and diatoms. Here, we provide insights into the significance of ICT excited states following the incorporation of a higher plant carotenoid, β-apo-8′-carotenal, into the carotenoidless light-harvesting 1 (LH1) complex of the purple photosynthetic bacterium Rhodospirillum rubrum strain G9+. β-apo-8′-carotenal generates the ICT excited state in the reconstituted LH1 complex, achieving an efficiency of EET of up to 79%, which exceeds that found in the wild-type LH1 complex.