Biology subjects

Maroli, N.

Publications and source records attributed to Maroli, N..

6 recordsLinked to original sources

bioRxiv2023

Riding the Wave: Unveiling the Conformational Waves from RBD to ACE2

The binding affinity between angiotensin-converting enzyme 2 (ACE2) and the receptor-binding domain (RBD) plays a crucial role in the transmission and re-infection of SARS-CoV2. Here, microsecond molecular dynamics simulations revealed that point mutations in the RBD domain induced conformational transitions that determined the binding affinity between ACE2 and RBD. These structural changes propagate through the RBD domain, altering the orientation of both ACE2 and RBD residues at the binding site. ACE2 receptor shows significant structural heterogeneity, whereas its binding to the RBD domain indicates a much greater degree of structural homogeneity. The receptor was more flexible in its unbound state, with the binding of RBD domains inducing structural transitions. The structural heterogeneity observed in the ACE2 unbound form plays a role in the promiscuity of viral entry as it may allow the receptor to interact with various related and unrelated ligands. Furthermore, rigidity may be important for stabilizing the complex and ensuring the proper orientation of the RBD-binding interface with ACE2. The greater structural homogeneity observed in the ACE2-RBD complex revealed the effectiveness of neutralizing antibodies and vaccines that are primarily directed towards the RBD-binding interface. The binding of the B38 monoclonal antibody revealed restricted conformational transitions in the RBD and ACE2 receptor, attributed to its potent binding interaction.

biophysics↗

bioRxiv2023

Aquaporin-4 mediated aggregation of Alzheimer amyloid beta-peptide

Clearance of Alzheimers amyloid oligomers from the brain is crucial for preventing cell toxicity. Dementia complications arise as a result of apoptosis, which is caused by peptide plaques on the lipid surface of cells. Here, we employed all-atom and coarse-grained molecular dynamics simulations to investigate the aggregation of amyloid peptides at the lipid surface and the role of the Aquaporin-4 (AQP4) in facilitating peptide clearance from astrocytes. The network of protein-protein interactions through text mining revealed that the expression of AQP4 and amyloid aggregation were strongly correlated. It has also been revealed that the role of aquaporins in the etiology of Alzheimers involves several interconnected proteins and pathways. The nature of aggregation at the surface of the 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) lipid bilayer was revealed by the interaction of amyloid oligomers. The membrane-bound pore region of AQP4 interacts with the peptide and slows its aggregation. This interaction maintains the helical content of the peptide while lowering its toxicity at the lipid surface. The hydrophobicity of the peptide also decreased because of these interactions, which may help in the removal of the peptide from astrocytes. Long-term coarse-grained MD simulations demonstrated different features of oligomer aggregation at the surface and strong oligomer attraction to AQP4, which inhibited aggregation. Additionally, the water dynamics of aquaporins demonstrate how the selectivity filter is broken to disrupt water flow. Our findings also provide insight into the physiological alterations in brain tissue associated with Alzheimers disease, including water retention and increased water flow in the CSF. Furthermore, in vitro thioflavin fluorescence spectroscopy revealed a slower aggregation of the peptide in the presence of AQP4.

biophysics↗

bioRxiv2022

Molecular Dynamics Simulations Show How Antibodies May Rescue HIV-1 Mutants Incapable of Infecting Host Cells

High mutation and replication rates of HIV-1 result in the continuous generation of variants, allowing it to adapt to changing host environments. Mutations often have deleterious effects, but variants carrying them are rapidly purged. Surprisingly, a particular variant incapable of entering host cells was found to be rescued by host antibodies targeting HIV-1. Understanding the molecular mechanism of this rescue is important to develop and improve antibody-based therapies. To unravel the underlying mechanisms, we performed fully atomistic molecular dynamics simulations of the HIV-1 gp41 trimer responsible for viral entry into host cells, its entry-deficient variant, and its complex with the rescuing antibody. We find that the Q563R mutation, which the entry-deficient variant carries, prevents the native conformation of the gp41 6-helix bundle required for entry and stabilizes an alternative conformation instead. This is the consequence of substantial changes in the secondary structure and interactions between the domains of gp41. Binding of the antibody F240 to gp41 reverses these changes and re-establishes the native conformation, resulting in rescue. To test the generality of this mechanism, we performed simulations with the entry-deficient L565A variant and antibody 3D6. We find that 3D6 binding was able to reverse structural and interaction changes introduced by the mutation and restore the native gp41 conformation. Viral variants may not only escape antibodies but be aided by them in their survival, potentially compromising antibody-based therapies, including vaccination and passive immunization. Our simulation framework could serve as a tool to assess the likelihood of such resistance against specific antibodies.

biophysics↗

bioRxiv2021

Mechanistic Insights into the Effects of Key Mutations on SARS-CoV-2 RBD-ACE2 Binding

Some recent SARS-CoV-2 variants appear to have increased transmissibility than the original strain. An underlying mechanism could be the improved ability of the variants to bind receptors on target cells and infect them. In this study, we provide atomic-level insight into the binding of the receptor binding domain (RBD) of the wild-type SARS-CoV-2 spike protein and its single (N501Y), double (E484Q, L452R) and triple (N501Y, E484Q, L452R) mutated variants to the human ACE2 receptor. Using extensive all-atom molecular dynamics simulations and advanced free energy calculations, we estimate the associated binding affinities and binding hotspots. We observe significant secondary structural changes in the RBD of the mutants, which lead to different binding affinities. We find higher binding affinities of the double (E484Q, L452R) and triple (N501Y, E484Q, L452R) mutated variants than the wild type and the N501Y variant, which could contribute to the higher transmissibility of recent variants containing these mutations.

biophysics↗

bioRxiv2020

FRET based aptamer assay for sensitive detection of Salmonella paratyphi A and revealing its molecular interaction with DNA gyrase: An in silico accessment

Rapid pathogen detection and identification of its serovars are crucial to provide essential treatment during pandemic circumstances. Herein, we developed a facile and versatile FRET-based aptasensor for rapid Salmonella paratyphi A detection. The ssDNA aptamers specific towards pathogenic Salmonella paratyphi A were generated via whole-cell SELEX. The aptamer was conjugated onto quantum dot (QD) that served as the molecular beacon and graphene oxide (GO) was used as fluorescence quencher. The detection of Salmonella paratyphi A leads to the quenching of QD fluorescence due to the non-covalent interaction between GO and CdTe quantum dot. The assay shows a detection limit up to 10 cfu{middle dot}mL-1 with no cross-reactivity towards closely related species. The spiking analysis demonstrated an inter-assay coefficient of variance less than 8 % and recovery rate between 85%-102% mitigates assay reliability. Further analysis with commercially available ELISA kit validated the reliability of the developed aptasensor. Furthermore, molecular dynamics simulation was used to establish the mechanism of action of generated aptamer against bacterial DNA gyrase protein. The strong non-bonded interaction energies along with hydrogen bonds between the aptamer and protein inhibit the function of the bacteria.

synthetic biology↗

bioRxiv2020

Melatonin Protects T-2 toxin-induced neuronal stress through Acetylcholinesterase & Cytochrome P450 receptor-mediated signaling

T-2 toxin is one of the potent mycotoxins responsible for several pathological conditions in humans and animals. This nonvolatile low molecular weight toxin compound shows strong resistance to degradation at room temperature as well as at autoclaving temperature. The inhibition of acetylcholinesterase and cytochrome P450 receptor by T-2 toxin leads to many pathological conditions as these two receptors involved in many pathways. Here, we have used melatonin as a protection agent against T-2 toxin in both receptor systems. Using molecular docking, molecular dynamics simulation and free energy calculations we have shown that melatonin can act as a potent inhibitor of T-2 toxin in acetylcholinesterase and cytochrome P450.

biophysics↗