Secondary Structure Elements Research Articles

Interaction of Antimalarial Drug, Pyrimethamine and Sulphadoxine with Sickle Haemoglobin at pH 5.0 and pH 7.2: A Fourier Transform Infrared (FTIR) Study

Aggregation of sickle haemoglobin (HbS), upon deoxygenation, is responsible for an inherited genetic disorder in the human red blood cells (RBCs) known as Sickle cell disease (SCD). On the suggestion that this phenomenon could arise from some form of conformational changes in the structure of HbS arising from a pH-induced rearrangement of secondary structural elements of the haemoglobin, Fourier Transform Infrared (FTIR) spectroscopy (in the mid-infrared region) was used to measure the amino acid side chain absorbance and also, the secondary structural transitions in the protein. A comparative study between the interaction of HbS with Pyrimethamine and sulphadoxine at pH 5.0, (the acidic pH of malarial parasites’ digestive vacuole during the intra-erythrocytic development and proliferation), and the body’s physiological pH of 7.2 was carried out. The amide I region (1700 – 1600 cm-1) comprising the amino acids side-chains absorbance and the proteins secondary structural components (α-helix, β-sheets, random and turn structures) showed that at pH 5.0 for Pyrimethamine-sulphadoxine combination therapy, there were significant changes in absorbance for HbS while at pH 7.2, little or no significant absorbance changes were observed. The results suggest that HbS is easily destabilized at pH 5.0 than pH 7.2 on interaction with Pyrimethamine and sulphadoxine. These interactions may hinder the development of the Plasmodium falciparum at the intra-erythrocytic stage and may account for the novel strategies of monitoring HbS aggregation during malarial infection as well as improvements in administering effective antimalarial treatment.

Molecular characterization of a 42 kDa subunit pili protein of Salmonella typhi causes typhoid fever

Abstract. Darmawati S, Ethica SN, Prastiyanto ME, Depamede SN, Putri EO, Kamaruddin M. 2022. Molecular characterization of a 42 kDa subunit pili protein of Salmonella typhi causes typhoid fever. Biodiversitas 23: 962-968. Blood culture is the gold standard for diagnosing typhoid fever, but it has limitations such as media and laboratory equipment, specimen volume, and examination time. However, the Academy of Pediatrics does not recommend serology due to its low sensitivity.The purpose of this study was to determine the molecular properties of the protein pilli of Salmonella typhi(S. typhi) that the findings can be used to develop a typhoid fever diagnostic reagent. The SDS-PAGE method was used, as well sequence analysis with ProtParam, ProtScale, and PSIPRED. The SDS-PAGE profile reveals one major protein (42 kDa) and fourteen minor proteins. The pili protein subunit 42 kDa had an amino acid (AA) sequence with a length of 390 AA, according to bioinformatics analysis. According to the ProtParam results, the pili protein subunit 42 kDa has good stability with a value of 40 and is a hydrophilic protein with an average GRAVY value of -0.950. PSIPRED results show that among the secondary structural elements, coil strand predominates, followed by -helix and -strand. It is concluded that this protein is immunogenic and that it can be used to develop a more specific and sensitive diagnostic reagent for typhoid fever.

An End-to-End Deep Learning Pipeline for Assigning Secondary Structure in Proteins

Protein secondary structure assignment, a subdiscipline of computational chemistry, is yet to be explored using deep learning techniques. Protein secondary structure elements are assigned to support structural analysis and prediction. Algorithms like DSSP, generally regarded as the gold standard for assigning the secondary structure of proteins, need full atom information to label protein coordinates. The PDB database has been the major repository for data on the 3D structures of proteins, nucleic acids, and other complex assemblies since 1971. However, a significant fraction of protein structures contains missing atoms. As a result, new approaches to reliably and consistently assigning secondary structures based on coarse-grained atomic coordinates are needed. While deep learning architectures have an unparalleled track record in applications such as protein structure prediction, there are only a few known deep learning solutions for structure assignment problems. While the gold standard methods are based on bonding information and other geometric characteristics, deep learning methods extract features themselves without human intervention. The benefit that standardised datasets provide to the effectiveness of deep learning systems in multiple domains motivated us to create a labeled dataset for protein structure assignment tasks. Additionally, a deep learning model, named PSSADL, solely based on [Formula: see text] coordinates was trained on the generated dataset to validate its potency. The proposed method, which combines Convolutional Neural Networks (CNN) and Long Short Term Memory (LSTM)/Bidirectional LSTM networks, has been compared to the established standards and more recent techniques. The model achieved an accuracy of [Formula: see text] on the benchmark and individual test sets. The results show that deep learning techniques have a promising future in protein structure analysis, implying that the dataset developed as part of our work will be a valuable resource for further protein structure research.

A bipartite chromatophore transit peptide and N-terminal protein processing in the Paulinella chromatophore.

The amoeba Paulinella chromatophora contains photosynthetic organelles, termed chromatophores, which evolved independently from plastids in plants and algae. At least one-third of the chromatophore proteome consists of nucleus-encoded (NE) proteins that are imported across the chromatophore double envelope membranes. Chromatophore-targeted proteins exceeding 250 amino acids (aa) carry a conserved N-terminal extension presumably involved in protein targeting, termed the chromatophore transit peptide (crTP). Short imported proteins do not carry discernable targeting signals. To explore whether the import of proteins is accompanied by their N-terminal processing, here we identified N-termini of 208 chromatophore-localized proteins by a mass spectrometry-based approach. Our study revealed extensive N-terminal acetylation and proteolytic processing in both NE and chromatophore-encoded (CE) fractions of the chromatophore proteome. Mature N-termini of 37 crTP-carrying proteins were identified, of which 30 were cleaved in a common processing region. Surprisingly, only the N-terminal ∼50 aa (part 1) become cleaved upon import. This part contains a conserved adaptor protein-1 complex-binding motif known to mediate protein sorting at the trans-Golgi network followed by a predicted transmembrane helix, implying that part 1 anchors the protein co-translationally in the endoplasmic reticulum and mediates trafficking to the chromatophore via the Golgi. The C-terminal part 2 contains conserved secondary structural elements, remains attached to the mature proteins, and might mediate translocation across the chromatophore inner membrane. Short imported proteins remain largely unprocessed. Finally, this work illuminates N-terminal processing of proteins encoded in an evolutionary-early-stage organelle and suggests host-derived posttranslationally acting factors involved in regulation of the CE chromatophore proteome.

Ligand pathways in estrogen-related receptors

The three subtypes of estrogen-related receptors ERRα, ERRβ, and ERRγ are nuclear receptors mediating metabolic processes in various tissues such as the skeletal muscle, fat tissue, bone, and liver. Although the knowledge on their physiological ligands is limited, they have been implicated as drug targets for important indications including diabetes, cardiovascular diseases, and osteoporosis. As in other nuclear receptors, their ligand binding pocket is buried within the core of the receptor and connected to its surrounding by ligand pathways. Here, we investigated these pathways with conventional molecular dynamics as well as metadynamics simulations to reveal their distribution and their capability to facilitate ligand translocation. Dependent on the ERR subtype and the conformational state of the receptor, we could detect different pathways to be favored. Overall, the results suggested pathways IIIa and IIIb to be favored in the agonistic conformation, while antagonists preferred pathways I, II, and V. Along the pathways, the ligands passed different gating mechanisms of the receptor, including groups of protein residues as well as whole secondary structure elements, to leave the binding site. Even though these pathways are suggested to influence ligand specificity of the receptors and their elucidation might advance rational drug design, they have not yet been studied in ERRs. Communicated by Ramaswamy H. Sarma

Identification of natural products against enoyl-acyl-carrier-protein reductase in malaria via combined pharmacophore modeling, molecular docking and simulations studies

Plasmodium falciparum is counted as one of the deadly species causing malaria. In that respect, enoyl acyl carrier protein reductase is recognized as one of the attractive druggable targets for the identification of antimalarials. Thus, from the structural proteome of ENR, common feature pharmacophores were constructed. To identify the representative models, all the hypotheses were subjected to validation methods, like, test set, enrichment factor, and Güner-Henry method, and the selected representative hypotheses were used to screen out the drug-like natural products. Further, the screened candidates were advanced to molecular docking calculations. Based on the docking score criteria and presence of essential interaction with Tyr277, seven candidates were shortlisted to conduct the HYDE and QSAR assessment. Further, the stability of these complexes was evaluated by employing molecular dynamics simulations, molecular mechanics‐generalized born surface area approach‐based free binding energy calculations with the residue-wise contribution of PfENR to the total binding free energy of the complex. On comparing the root mean square deviation, and fluctuation plots of the docked candidates with the reference, all the candidates displayed stable behavior, and the same outcome was depicted from the secondary structure element. However, from the free energy calculations, and residue-wise contribution conducted after dynamics, it was observed that out of seven, only five candidates sustain the binding with Tyr277 and cofactor of PfENR. Therefore, in the current work, the hybrid study of screening and stability lead to the identification of five structurally diverse candidates that can be employed for the design of novel antimalarials. Communicated by Ramaswamy H. Sarma

Hydrophobic core formation and secondary structure elements in uranyl(VI)-binding peptides.

Cyclic peptides as well as a modified EF-hand motif of calmodulin have been newly designed to achieve high affinity towards uranyl(VI). Cyclic peptides may be engineered to bind uranyl(VI) to its backbone under acidic conditions, which may enhance its selectivity. For the modified EF-hand motif of calmodulin, strong electrostatic interactions between uranyl(VI) and negatively charged side chains play an important role in achieving high affinity; however, it is also essential to have a secondary structure element and formation of hydrophobic cores in the metal-bound state of the peptide.

Secondary Structure Transitions for a Family of Amyloidogenic, Antimicrobial Uperin 3 Peptides in Contact with Sodium Dodecyl Sulfate.

Secondary structure changes are an inherent part of antimicrobial (AMP) and amyloidogenic peptide activity, especially in close proximity to membranes, and impact the peptides' function and dysfunction roles. The formation, and stability of α-helical components are regarded as essential 'intermediates' for both these functions. To illuminate the conformational transitions leading to amyloid formation we use short cationic AMPs, from an Australian toadlet, Uperoleia mjobergii, (Uperin 3 family, U3) and assess the impact on secondary structural elements in the presence of a membrane mimetic surfactant, sodium dodecyl sulfate (SDS). Specifically, Uperin 3.x, where x=4, 5, 6 wild-type peptides and position seven variants for each, R7A or K7A, were investigated using a combination of experimental and simulation approaches. In water, U3 peptides remain largely unstructured as random coils, with the addition of salts initiating structural transitions leading to assembly towards amyloid. Solution NMR data show that an unstructured U3.5 wt peptide transitions in the presence of SDS to a well-defined α-helical structure that spans nearly the entire sequence. Circular dichroism (CD) and ThT fluorescence studies show that all six U3 peptides aggregate in solution, albeit with vastly varying rates, and a dynamic equilibrium between soluble aggregates rich in either α-helices or β-sheets may exist in solution. However, the addition of SDS leads to a rapid disaggregation for all peptides and stabilisation of predominantly α-helical content in all the U3 peptides. Molecular dynamics (MD) simulations show that the adsorption of U3.5 wt/R7A peptides onto the SDS micelle is driven by Coulombic attraction between peptide cationic residues and the negatively charged sulfate head-groups on SDS. Simulating the interactions of various kinds of β-sheet dimers (of both U3.5 wt and its variant U3.5 R7A) with SDS micelles confirmed β-sheet content decreases in the dimers after their attachment to the SDS micelle. Adsorbed peptides interact favourably with the hydrophobic core of the micelle, promoting intramolecular hydrogen bonds leading to stabilisation of the α-helical structure in peptides, and resulting in a corresponding decrease in intermolecular hydrogen bonds responsible for β-sheets.

Structural Analysis of Hybrid Ro-Pax Ferry

With the aim of improving the environmental sustainability in the field of maritime transport and with special reference to multimodality and 'green' solutions for coastal transport, within the METRO project (Maritime Environment-friendly TRanspOrt systems), funded under the Interreg VA CBC Programme Italy-Croatia, a project of a hybrid Ro-Pax medium range ferry for coastal navigation in the Adriatic area is developed. The paper presents a part of the conceptual design for the assessment of the global hull structure strength, which is not common for this phase of the project, and that is the structural analysis of the complete ship. For this purpose, a detailed computer model of the geometry of the whole ship was made, which includes all primary and basic secondary structural elements, with the aim that such a model can serve later as a good basis for classification and workshop documentation production during contract phase. Additionally, a preliminary calculation of the scantlings of the complete ship was performed according to BV rules and regulations using the MARS2000 software package, with regard to bending and buckling. Loads were modeled according to real conditions for two unfavorable loading conditions, and static linear analysis was performed using the LS-DYNA software package. The global analysis of bending strength in still water could reveal problematic areas in the structure.

SAA fibrils involved in AA amyloidosis are similar in bulk and by single particle reconstitution: A MAS solid-state NMR study

AA amyloidosis is one of the most prevalent forms of systemic amyloidosis and affects both humans and other vertebrates. In this study, we compare MAS solid-state NMR data with a recent cryo-EM study of fibrils involving full-length murine SAA1.1. We address the question whether the specific requirements for the reconstitution of an amyloid fibril structure by cryo-EM can potentially yield a bias towards a particular fibril polymorph. We employ fibril seeds extracted from in to vivo material to imprint the fibril structure onto the biochemically produced protein. Sequential assignments yield the secondary structure elements in the fibril state. Long-range DARR and PAR experiments confirm largely the topology observed in the ex-vivo cryo-EM study. We find that the β-sheets identified in the NMR experiments are similar to the β-sheets found in the cryo-EM study, with the exception of amino acids 33–42. These residues cannot be assigned by solid-state NMR, while they adopt a stable β-sheet in the cryo-EM structure. We suggest that the differences between MAS solid-state NMR and cryo-EM data are a consequence of a second conformer involving residues 33–42. Moreover, we were able to characterize the dynamic C-terminal tail of SAA in the fibril state. The C-terminus is flexible, remains detached from the fibrils, and does not affect the SAA fibril structure as confirmed further by molecular dynamics simulations. As the C-terminus can potentially interact with other cellular components, binding to cellular targets can affect its accessibility for protease digestion.

Knowledge-Based Atomic Polarizabilities Used to Model Circular Dichroism Spectra of Proteins.

We present a model of circular dichroism for proteins, which is mainly based on both the classical theory of optical activity and a series of effective atomic polarizabilities. Such polarizabilities are extracted from the analysis of a set of synchrotron radiation circular dichroism spectra and their corresponding three-dimensional structures from the Protein Data Bank. Each modeled spectrum is obtained from the protein atomic coordinates and the identification of its secondary structure elements. The resulting spectra are in good agreement with additional experimental data and also with the predictions of some other models. Among them, only our approach is able to describe the effect of d-amino acids. Moreover, our model is also utilized to evaluate protein reconstructions as well as structural changes.

Control over Multiple Nano- and Secondary Structures in Peptide Self-Assembly.

Herein, we report the rich morphological and conformational versatility of a biologically active peptide (PEP‐1), which follows diverse self‐assembly pathways to form up to six distinct nanostructures and up to four different secondary structures through subtle modulation in pH, concentration and temperature. PEP‐1 forms twisted β‐sheet secondary structures and nanofibers at pH 7.4, which transform into fractal‐like structures with strong β‐sheet conformations at pH 13.0 or short disorganized elliptical aggregates at pH 5.5. Upon dilution at pH 7.4, the nanofibers with twisted β‐sheet secondary structural elements convert into nanoparticles with random coil conformations. Interestingly, these two self‐assembled states at pH 7.4 and room temperature are kinetically controlled and undergo a further transformation into thermodynamically stable states upon thermal annealing: whereas the twisted β‐sheet structures and corresponding nanofibers transform into 2D sheets with well‐defined β‐sheet domains, the nanoparticles with random coil structures convert into short nanorods with α‐helix conformations. Notably, PEP‐1 also showed high biocompatibility, low hemolytic activity and marked antibacterial activity, rendering our system a promising candidate for multiple bio‐applications.

Control over Multiple Nano‐ and Secondary Structures in Peptide Self‐Assembly

AbstractHerein, we report the rich morphological and conformational versatility of a biologically active peptide (PEP‐1), which follows diverse self‐assembly pathways to form up to six distinct nanostructures and up to four different secondary structures through subtle modulation in pH, concentration and temperature. PEP‐1 forms twisted β‐sheet secondary structures and nanofibers at pH 7.4, which transform into fractal‐like structures with strong β‐sheet conformations at pH 13.0 or short disorganized elliptical aggregates at pH 5.5. Upon dilution at pH 7.4, the nanofibers with twisted β‐sheet secondary structural elements convert into nanoparticles with random coil conformations. Interestingly, these two self‐assembled states at pH 7.4 and room temperature are kinetically controlled and undergo a further transformation into thermodynamically stable states upon thermal annealing: whereas the twisted β‐sheet structures and corresponding nanofibers transform into 2D sheets with well‐defined β‐sheet domains, the nanoparticles with random coil structures convert into short nanorods with α‐helix conformations. Notably, PEP‐1 also showed high biocompatibility, low hemolytic activity and marked antibacterial activity, rendering our system a promising candidate for multiple bio‐applications.

NMR Analysis of Protein Folding Interaction Networks.

Theory and experimental evidence unequivocally indicate that protein folding is far more complex than the two-state (all-or-none) model that is usually assumed in the analysis of folding experiments. Proteins tend to fold hierarchically by forming secondary structure elements, followed by supersecondary arrangements, and other intermediate states that ultimately adopt the native tertiary fold as a result of a delicate balance between interatomic interactions and entropic contributions. However, small proteins with simple folds typically follow downhill folding, characterized by very small energetic barriers (<3RT) that allow multiple protein conformations to be populated along the folding path down the free energy landscape, reaching the native fold at the lowest energy level.Here we describe the use of solution-state nuclear magnetic resonance (NMR) for the analysis of protein folding interaction networks at atomic resolution. The assignment of NMR spectra acquired at different unfolding conditions provides hundreds of atomic unfolding curves that are analyzed to infer the network of folding interactions. The method is particularly useful to study small proteins that fold autonomously in the sub-millisecond timescale. The information obtained from the application of this method can potentially unveil the basic relationships between protein structure and folding.

Three-Dimensional Graph Matching to Identify Secondary Structure Correspondence of Medium-Resolution Cryo-EM Density Maps.

Cryo-electron microscopy (cryo-EM) is a structural technique that has played a significant role in protein structure determination in recent years. Compared to the traditional methods of X-ray crystallography and NMR spectroscopy, cryo-EM is capable of producing images of much larger protein complexes. However, cryo-EM reconstructions are limited to medium-resolution (~4–10 Å) for some cases. At this resolution range, a cryo-EM density map can hardly be used to directly determine the structure of proteins at atomic level resolutions, or even at their amino acid residue backbones. At such a resolution, only the position and orientation of secondary structure elements (SSEs) such as α-helices and β-sheets are observable. Consequently, finding the mapping of the secondary structures of the modeled structure (SSEs-A) to the cryo-EM map (SSEs-C) is one of the primary concerns in cryo-EM modeling. To address this issue, this study proposes a novel automatic computational method to identify SSEs correspondence in three-dimensional (3D) space. Initially, through a modeling of the target sequence with the aid of extracting highly reliable features from a generated 3D model and map, the SSEs matching problem is formulated as a 3D vector matching problem. Afterward, the 3D vector matching problem is transformed into a 3D graph matching problem. Finally, a similarity-based voting algorithm combined with the principle of least conflict (PLC) concept is developed to obtain the SSEs correspondence. To evaluate the accuracy of the method, a testing set of 25 experimental and simulated maps with a maximum of 65 SSEs is selected. Comparative studies are also conducted to demonstrate the superiority of the proposed method over some state-of-the-art techniques. The results demonstrate that the method is efficient, robust, and works well in the presence of errors in the predicted secondary structures of the cryo-EM images.

NMR study of macro domains (MDs) from betacoronavirus: backbone resonance assignments of SARS-CoV and MERS-CoV MDs in the free and the ADPr-bound state.

SARS-CoV and MERS-CoV Macro Domains (MDs) exhibit topological and conformational features that resemble the nsP3b macro (or “X”) domain of SARS-CoV-2. Indeed, all the three domains (SARS-CoV-2, SARS-CoV and MERS-CoV MDs) fold in a three-layer α/β/α sandwich structure, as reported by crystallographic structural investigation of SARS-CoV MD and MERS-CoV MD. These viral MDs are able to bind ADP-ribose as many other MDs from different kingdoms. They have been characterized also as de-ADP-ribosylating enzymes. For this reason, these viral macrodomains recently emerged as important drug targets since they can counteract antiviral ADP-ribosylation mediated by poly-ADP-ribose polymerase (PARPs). Even in presence of the 3D structures of SARS-CoV MD and of MERS-CoV MD, we report herein the almost complete NMR backbone (1H, 13C, 15N) of SARS-CoV MD and MERS-CoV proteins in the free and ADPr bound forms, and the NMR chemical shift-based prediction of their secondary structure elements. These NMR data will help to further understanding of the atomic-level conformational dynamics of these proteins and will allow an extensive screening of small molecules as potential antiviral drugs.

Structural and functional insights of GSU0105, a unique multiheme cytochrome from G. sulfurreducens

Geobacter sulfurreducens possesses over 100 cytochromes that assure an effective electron transfer to the cell exterior. The most abundant group of cytochromes in this microorganism is the PpcA family, composed of five periplasmic triheme cytochromes with high structural homology and identical heme coordination (His-His). GSU0105 is a periplasmic triheme cytochrome synthetized by G. sulfurreducens in Fe(III)-reducing conditions but is not present in cultures grown on fumarate. This cytochrome has a low sequence identity with the PpcA family cytochromes and a different heme coordination, based on the analysis of its amino acid sequence. In this work, amino acid sequence analysis, site-directed mutagenesis, and complementary biophysical techniques, including ultraviolet-visible, circular dichroism, electron paramagnetic resonance, and nuclear magnetic resonance spectroscopies, were used to characterize GSU0105. The cytochrome has a low percentage of secondary structural elements, with features of α-helices and β-sheets. Nuclear magnetic resonance shows that the protein contains three low-spin hemes (Fe(II), S = 0) in the reduced state. Electron paramagnetic resonance shows that, in the oxidized state, one of the hemes becomes high-spin (Fe(III), S = 5/2), whereas the two others remain low-spin (Fe(III), S = 1/2). The data obtained also indicate that the heme groups have distinct axial coordination. The apparent midpoint reduction potential of GSU0105 (−154 mV) is pH independent in the physiological range. However, the pH modulates the reduction potential of the heme that undergoes the low- to high-spin interconversion. The reduction potential values of cytochrome GSU0105 are more distinct compared to those of the PpcA family members, providing the protein with a larger functional working redox potential range. Overall, the results obtained, together with an amino acid sequence analysis of different multiheme cytochrome families, indicate that GSU0105 is a member of a new group of triheme cytochromes.

The RNA chaperone StpA enables fast RNA refolding by destabilization of mutually exclusive base pairs within competing secondary structure elements.

In bacteria RNA gene regulatory elements refold dependent on environmental clues between two or more long-lived conformational states each associated with a distinct regulatory state. The refolding kinetics are strongly temperature-dependent and especially at lower temperatures they reach timescales that are biologically not accessible. To overcome this problem, RNA chaperones have evolved. However, the precise molecular mechanism of how these proteins accelerate RNA refolding reactions remains enigmatic. Here we show how the RNA chaperone StpA of Escherichia coli leads to an acceleration of a bistable RNA’s refolding kinetics through the selective destabilization of key base pairing interactions. We find in laser assisted real-time NMR experiments on photocaged bistable RNAs that the RNA chaperone leads to a two-fold increase in refolding rates at low temperatures due to reduced stability of ground state conformations. Further, we can show that upon interaction with StpA, base pairing interactions in the bistable RNA are modulated to favor refolding through the dominant pseudoknotted transition pathway. Our results shed light on the molecular mechanism of the interaction between RNA chaperones and bistable RNAs and are the first step into a functional classification of chaperones dependent on their biophysical mode of operation.

The ubiquitous buried water in the beta-trefoil architecture contributes to the folding nucleus and ~20% of the folding enthalpy.

The beta-trefoil protein architecture is characterized by three repeating "trefoil" motifs related by rotational symmetry and postulated to have evolved via gene duplication and fusion events. Despite this apparent structural symmetry, the primary and secondary structural elements typically exhibit pronounced asymmetric features. A survey of this family of proteins has revealed that among the most conserved symmetric structural elements is a ubiquitous buried solvent which participates in a bridging H-bond with three different beta-strands in each of the trefoil motifs. A computational analysis reported that these waters are likely associated with a substantial enthalpic contribution to overall stability. In this report, a Pro mutation is used to disrupt one of the water H-bond interactions to a main chain amide, and the effects upon stability and folding kinetics are determined. Combined with Ala mutations, the separate effects upon side chain truncation and H-bond deletion are analyzed in terms of stability and folding kinetics. The results show that these buried waters act to assemble a central folding nucleus, and are responsible for ~20% of the overall favorable enthalpy of folding.

Impact of Mutation on the Structural Stability and the Conformational Landscape of Inhibitor-Resistant TEM β-Lactamase: A High-Performance Molecular Dynamics Simulation Study.

Gain-of-function mutations and structural adjustment toward β-lactamase inhibitors in the TEM-type β-lactamases among the uropathogenic E. coli (UPEC) culminate in treatment complications and demands detailed investigation. In this study, uncharacterized amino acid substitutions, M69L/I84V/W165G/V184A/V262I/N276S, in inhibitor-resistant TEM (IRT) β-lactamase isolated from clinical UPEC were subjected to extensive molecular dynamics (EMD) simulations for 100 ns to estimate parameters such as root-mean-square deviation (RMSD), root-mean-square fluctuation (RMSF), the radius of gyration (Rg), contour plot (Rg/RMSD), secondary structure element (SSE), etc. Residue interaction networks, principal component analysis (PCA), and correlation heatmaps were generated to predict the relation between functionally important atomic motions to uncover the structural stability of the mutants. To avoid the false positive conclusion of the simulation study, we performed three identically parameterize replicas of 100 ns each. Alterations in hydrophobic interactions resulted in conformation changes exhibited as comparable residue interaction networks. Besides, PCA and porcupine plot analysis based on the ensemble of structure from molecular dynamics trajectories revealed the collective atomic motions of the IRT variants that impart structural flexibility to their active site loop. This study conducted on IRT mutants that delineate intricate protein motions contributes to their stability and folding, which is an absolute necessity for designing candidate molecules owing to the clinical threat of emerging resistance against potent β-lactam antibiotics.