Biology subjects

Islam, B.

Publications and source records attributed to Islam, B..

5 recordsLinked to original sources

bioRxiv2025

A missense mutation in Muc2 promotes gut microbiome- and metabolome-dependent colitis-associated tumorigenesis.

Colitis-associated cancer (CAC) arises from a complex interplay between host and environmental factors, including the gut microbiome. Since ulcerative colitis (UC), a significant risk factor for CAC, is rising in prevalence worldwide, an integrative approach is essential to identify potential triggers linking inflammation to cancer. In the present study, we investigated the role of the gut microbiome using Winnie mice, a UC-like model with a relevant missense mutation in the Muc2 gene. Upon transfer from a conventional (CONV) to a specific-pathogen-free (SPF) facility, Winnie mice exhibited a more severe colitis phenotype, and notably, spontaneous CAC as early as four weeks of age, which progressively worsened over time. In contrast, CONV Winnie developed only mild colitis but with no overt signs of tumorigenesis. Notably, when rederived into germ-free (GF) conditions, SPF Winnie mice were protected from colitis or colon tumor development, indicating an essential role for the gut microbiome in the initiation and progression of CAC in these mice. Using shotgun metagenomics, metabolomics, and lipidomics, we identified a distinct pro-inflammatory microbial and metabolic signature that potentially drives the transition from colitis to CAC. Fecal microbiota transplantation (FMT), using either SPF Winnie or WT (Bl/6) donors into GF Winnie recipients, demonstrated that while colitis developed regardless of donor, only FMT from SPF Winnie donors resulted in CAC, revealing a microbiota-driven, host-specific susceptibility to tumorigenesis in Winnie mice. Our studies present a novel and relevant model of CAC, providing further evidence that the microbiome plays a key role in the pathogenesis of CAC, thereby challenging the concept of colon cancer as a strictly non-transmissible disease. Lay summaryThis study reveals a distinct metagenomic, metabolomic, and lipidomic profile associated with tumorigenesis in a murine model of ulcerative colitis, highlighting the risks of specific intestinal dysbiosis in genetically predisposed subjects. What you need to knowO_ST_ABSBackground and contextC_ST_ABSColitis-associated colorectal cancer arises from complex host-environment interactions, including gut microbiome influences, driving chronic inflammation, with the intestinal lumen environment remaining a largely unexplored potential risk factor in cancer development. New findingsWinnie mice in specific pathogen-free conditions developed severe colitis, and a novel juvenile colon dysplasia and cancer, with gut microbiome changes driving colitis-associated cancer initiation and progression. LimitationsWe identified a pro-inflammatory microbial/metabolic signature promoting colitis-to-CAC transition in Winnie mice, with FMT confirming microbiota-driven tumor susceptibility. However, further research is needed to pinpoint the key bacteria-metabolite-lipid combination driving CAC. Clinical research relevanceThis newly characterized microbiota-metabolome-based model of CAC, challenges the dogma of cancer as a non-transmittable disease, providing a foundation for developing microbiota-based strategies for CAC prevention and treatment. Basic research relevanceUnlike genetic or chemically induced models, the Winnie mouse model uniquely serves as a dual model for spontaneous colitis and juvenile CAC, offering a fast, 100% penetrant phenotype that enhances reliability, accelerates research, and provides valuable insights into IBD and CAC.

cancer biology↗

bioRxiv2021

Ligand-induced unfolding mechanism of an RNA G-quadruplex

The cationic porphyrin, TMPyP4, is a well-established DNA G-quadruplex (G4) binding ligand that can stabilize different topologies via multiple binding modes. However, TMPyP4 has completely opposite destabilizing and unwinding effect on RNA G4 structures. The structural mechanisms that mediate RNA G4 unfolding remains unknown. Here, we report on the TMPyP4-induced RNA G4 unfolding mechanism studied by well-tempered metadynamics (WT-MetaD) with supporting biophysical experiments. The simulations predict a two-state mechanism of TMPyP4 interaction via a groove-bound and a top-face bound conformation. The dynamics of TMPyP4 stacking on the top tetrad disrupts Hoogsteen H-bonds between guanine bases resulting in the consecutive TMPyP4 intercalation from top-to-bottom G-tetrads. The results reveal a striking correlation between computational and experimental approaches and validate WT-MetaD simulations as a powerful tool for studying RNA G4-ligand interactions.

biophysics↗

bioRxiv2021

Structural dynamics of the β-coronavirus Mpro protease ligand binding sites

{beta}-coronaviruses alone have been responsible for three major global outbreaks in the 21st century. The current crisis has led to an urgent requirement to develop therapeutics. Even though a number of vaccines are available, alternative strategies targeting essential viral components are required as a back-up against the emergence of lethal viral variants. One such target is the main protease (Mpro) that plays an indispensible role in viral replication. The availability of over 270 Mpro X-ray structures in complex with inhibitors provides unique insights into ligand-protein interactions. Herein, we provide a comprehensive comparison of all non-redundant ligand-binding sites available for SARS-CoV2, SARS-CoV and MERS-CoV Mpro. Extensive adaptive sampling has been used to explore conformational dynamics employing convolutional variational auto encoder-based deep learning, and investigates structural conservation of the ligand binding sites using Markov state models across {beta}-coronavirus homologs. Our results indicate that not all ligand-binding sites are dynamically conserved despite high sequence and structural conservation across {beta}-coronavirus homologs. This highlights the complexity in targeting all three Mpro enzymes with a single pan inhibitor.

biophysics↗

bioRxiv2020

Insights into G-Quadruplex-Hemin Dynamics Using Atomistic Simulations: Implications for Reactivity and Folding

Guanine quadruplex nucleic acids (G4s) are involved in key biological processes such as replication or transcription. Beyond their biological relevance, G4s find applications as biotechnological tools since they readily bind hemin and enhance its peroxidase activity, creating a G4-DNAzyme. The biocatalytic properties of G4-DNAzymes have been thoroughly studied and used for biosensing purposes. Despite hundreds of applications and massive experimental efforts, the atomistic details of the reaction mechanism remain unclear. To help select between the different hypotheses currently under investigation, we use extended explicit-solvent molecular dynamics (MD) simulations to scrutinize the G4/hemin interaction. We find that besides the dominant conformation in which hemin is stacked atop the external G-quartets, hemin can also transiently bind to the loops and be brought to the external G-quartets through diverse delivery mechanisms. The simulations do not support the catalytic mechanism relying on a wobbling guanine. Similarly, catalytic role of the iron-bound water molecule is not in line with our results, however, given the simulation limitations, this observation should be considered with some caution. The simulations rather suggest tentative mechanisms in which the external G-quartet itself could be responsible for the unique H2O2-promoted biocatalytic properties of the G4/hemin complexes. Once stacked atop a terminal G-quartet, hemin rotates about its vertical axis while readily sampling shifted geometries where the iron transiently contacts oxygen atoms of the adjacent G-quartet. This dynamics is not apparent from the ensemble-averaged structure. We also visualize transient interactions between the stacked hemin and the G4 loops. Finally, we investigated interactions between hemin and on-pathway folding intermediates of the parallel-stranded G4 fold. The simulations suggest that hemin drives the folding of parallel-stranded G4s from slip-stranded intermediates, acting as a G4 chaperone. Limitations of the MD technique are briefly discussed. For Table of Contents Only O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=77 SRC="FIGDIR/small/375691v2_ufig1.gif" ALT="Figure 1"> View larger version (20K): org.highwire.dtl.DTLVardef@384380org.highwire.dtl.DTLVardef@1d7c730org.highwire.dtl.DTLVardef@1562248org.highwire.dtl.DTLVardef@1e4cb9c_HPS_FORMAT_FIGEXP M_FIG C_FIG

biophysics↗

bioRxiv2019

Stability of Two-quartet G-quadruplexes and Their Dimers in Atomistic Simulations

G-quadruplexes (GQs) are four-stranded non-canonical DNA and RNA architectures that can be formed by guanine-rich sequences. The stability of GQs increases with the number of G-quartets and three G-quartets generally form stable GQs. However, the stability of two-quartet GQs is an open issue. To understand the intrinsic stability of two-quartet GQ stems, we have carried out a series of unbiased molecular dynamics (MD) simulations ([~]505 {micro}s in total) of two- and four-quartet DNA and RNA GQs, with attention paid mainly to parallel-stranded arrangements. We used AMBER DNA parmOL15 and RNA parmOL3 force fields and tested different ion and water models. DNA two-quartet parallel-stranded GQs unfolded in all the simulations while the equivalent RNA GQ was stable in most of the simulations. GQs composed of two stacked units of two-quartet GQs were stable for both DNA and RNA. The simulations suggest that a minimum of three quartets are needed to form an intrinsically stable all-anti parallel-stranded DNA GQ. Parallel two-quartet DNA GQ may exist if substantially stabilized by another molecule or structural element, including multimerisation. On the other hand, we predict that isolated RNA two-quartet parallel GQs may form, albeit being weakly stable. We also show that ionic parameters and water models should be chosen with caution because some parameter combinations can cause spurious instability of GQ stems. Some in-so-far unnoticed limitations of force-field description of multiple ions inside the GQs are discussed, which compromise capability of simulations to fully capture the effect of increase of the number of quartets on the GQ stability.

biophysics↗