Biology subjects

Osman, M. M.

Publications and source records attributed to Osman, M. M..

6 recordsLinked to original sources

bioRxiv2026

Functional Differentiation of GH172 Arabinofuranosidases Through Divergent Quaternary Structures

Mycobacteria synthesise the unusual glycan [x1D05]-arabinan as a major component of the cell wall glycoconjugates arabinogalactan (AG) and lipoarabinomannan (LAM). We previously identified Dysgonomonas gadei, a member of the Bacteroidota, as capable of complete [x1D05]-arabinan degradation through the concerted action of endo- and exo-acting enzymes. Among these are three glycoside hydrolase family 172 (GH172) enzymes with exo--[x1D05]-arabinofuranosidase activity against AG and LAM, although their linkage specificities were unknown. Here, using defined synthetic substrates, we show that the three enzymes possess distinct linkage preferences. We also develop -[x1D05]-arabinofuranosyl cyclophellitol aziridines as covalent inhibitors and activity-based probes for GH172 enzymes. X-ray crystallography and cryo-EM to reveal strikingly different quaternary assemblies across the three homologues, while a 1.5 [A] cryo-EM structure of dodecameric Dg67 covalently modified by an aziridine inhibitor identifies the catalytic nucleophile and provides direct structural support for a retaining mechanism. A BODIPY-tagged aziridine probe selectively labelled the three GH172 enzymes in D. gadei cell lysates. Together, these findings define functional and structural diversity within GH172 and establish chemical probes for profiling -[x1D05]-arabinofuranosidase activity in complex biological samples.

biochemistry↗

bioRxiv2024

Remission spectroscopy resolves the mode of action of bedaquiline within living mycobacteria

Bedaquiline, an ATP synthase inhibitor, is the spearhead of transformative therapies against drug-resistant Mycobacterium tuberculosis. Here, remission spectroscopy is used to measures the energy-transducing cytochromes within unperturbed, respiring suspensions of mycobacterial and human cells, allowing spectroscopic measurements of electron transport chains as they power living cells and respond to bedaquiline. No evidence is found for protonophoric or ionophoric uncoupling. Rather, by directly inhibiting ATP synthase, bedaquiline slows the respiratory supercomplex (Qcr:Cta; bcc:aa3) by increasing the proton-motive force, causing sub-second redirection of electron flux through the cytochrome bd oxidase (Cyd) to O2. Electron flux redirection explains the idiosyncratic bedaquiline-induced increase in O2 consumption rates previously observed. Redirection occurs as Cyd is present even in cells grown in plentiful O2. Applying the same approach to human cells did not detect bedaquiline-induced inhibition of mitochondrial function despite such inhibition being seen in isolated systems. Overall, we clarify how bedaquiline works, why different models for its action developed, and the mechanisms underlying the synergy of bedaquiline in combination regimes.

biophysics↗

bioRxiv2022

The C terminus of the mycobacterium ESX-1 secretion system substrate ESAT-6 is required for phagosomal membrane damage and virulence

Mycobacterium tuberculosis and its close relative Mycobacterium marinum infect macrophages and induce the formation of granulomas, organized macrophage-rich immune aggregates. These mycobacterial pathogens can accelerate and co-opt granuloma formation for their benefit, using the specialized secretion system ESX-1, a key virulence determinant. ESX-1-mediated virulence is attributed to the damage it causes to the membranes of macrophage phagosomal compartments, within which the bacteria reside. This phagosomal damage, in turn, has been attributed to the membranolytic activity of ESAT-6, the major secreted substrate of ESX-1. However, mutations that perturb ESAT- 6s membranolytic activity often result in global impairment of ESX-1 secretion. This has precluded an understanding of the causal and mechanistic relationships between ESAT-6 membranolysis and ESX-1-mediated virulence. Here, we identify two conserved residues in the unstructured C-terminal tail of ESAT-6 required for phagosomal damage, granuloma formation and virulence. Importantly, these ESAT-6 mutants have near- normal levels of secretion, far higher than the minimal threshold we establish is needed for ESX-1-mediated virulence early in infection. Unexpectedly, these loss-of-function ESAT-6 mutants retain the ability to lyse acidified liposomes. Thus, ESAT-6s virulence functions in vivo can be uncoupled from this in vitro surrogate assay. These uncoupling mutants highlight an enigmatic functional domain of ESAT-6 and provide key tools to investigate the mechanism of phagosomal damage and virulence. Significance StatementTuberculosis (TB), an ancient disease of humanity, continues to be a major cause of worldwide death. The causative agent of TB, Mycobacterium tuberculosis, and its close pathogenic relative Mycobacterium marinum, initially infect, evade, and exploit macrophages, a major host defense against invading pathogens. Within macrophages, mycobacteria reside within host membrane-bound compartments called phagosomes. Mycobacterium-induced damage of the phagosomal membranes is integral to pathogenesis, and this activity has been attributed the specialized mycobacterial secretion system ESX-1, and particularly to ESAT-6, its major secreted protein. Here, we show that the integrity of the unstructured ESAT-6 C-terminus is required for macrophage phagosomal damage, granuloma formation, and virulence.

microbiology↗

bioRxiv2020

Mycobacterium marinum phthiocerol dimycocerosates enhance macrophage phagosomal permeabilization and membrane damage

Phthiocerol dimycocerosates (PDIMs) are a class of mycobacterial lipids that promote virulence in Mycobacterium tuberculosis and Mycobacterium marinum. It has recently been shown that PDIMs work in concert with the M. tuberculosis Type VII secretion system ESX-1 to permeabilize the phagosomal membranes of infected macrophages. As the zebrafish-M. marinum model of infection has revealed the critical role of PDIM at the host-pathogen interface, we set to determine if PDIMs contributed to phagosomal permeabilization in M. marinum. Using an{Delta} mmpL7 mutant defective in PDIM transport, we find the PDIM-ESX-1 interaction to be conserved in an M. marinum macrophage infection model. However, we find PDIM and ESX-1 mutants differ in their degree of defect, with the PDIM mutant retaining more membrane damaging activity. Using an in vitro hemolysis assay-- a common surrogate for cytolytic activity, we find that PDIM and ESX-1 differ in their contributions: the ESX-1 mutant loses hemolytic activity while PDIM retains it. Our observations confirm the involvement of PDIMs in phagosomal permeabilization in M. marinum infection and suggest that PDIM enhances the membrane disrupting activity of pathogenic mycobacteria and indicates that the role they play in damaging phagosomal and red blood cell membranes may differ.

microbiology↗

bioRxiv2019

Ebselen inhibits mycobacterial ESX-1 secretion through modification of EccA1

The type VII secretion system ESX-1 mediates virulence in Mycobacterium tuberculosis and Mycobacterium marinum. We find that in M. marinum, the synthetic organoselenium compound ebselen inhibits secretion of ESAT-6, a major ESX-1 substrate. We find that ebselen inhibits the in vitro activity of the ESX-1 AAA+ ATPase EccA1, which potentiates ESX-1 substrate secretion and function. Ebselen modifies a cysteine in its N-terminal tetratricopeptide repeat domain that is required for EccA1s in vitro ATPase activity. Surprisingly, mutational analyses show this this cysteine is not required for ESX-1 secretion or ebselens activity, showing that ebselen inhibits ESX-1 secretion independently of inhibiting EccA1 activity in vitro. While the mechanism by which ebselen inhibits ESX-1 secretion remains elusive, we show that it attenuates ESX-1-mediated damage of M. marinum-containing macrophage phagosomes and inhibits intramacrophage growth. Extending our studies to M. tuberculosis, we find that ebselen inhibits ESX-1 secretion and phagosomal membrane damage in this organism. This work provides insight into EccA1 biology. Ebselen is an orally active drug in clinical trials for other conditions and this work suggests its potential in tuberculosis therapy.

microbiology↗

bioRxiv2019

Thirty two novel nsSNPs May effect on HEXA protein Leading to Tay-Sachs disease (TSD) Using a Computational Approach

BackgroundGenetic polymorphisms in the HEXA gene are associated with a neurodegenerative disorder called Tay-Sachs disease (TSD) (GM2 gangliosidosis type 1). This study aimed to predict the possible pathogenic SNPs of this gene and their impact on the protein using different bioinformatics tools.\n\nMethodsSNPs retrieved from the NCBI database were analyzed using several bioinformatics tools. The different algorithms collectively predicted the effect of single nucleotide substitution on both structure and function of the hexosaminidase A protein.\n\nResultsFifty nine mutations were found to be highly damaging to the structure and function of the HEXA gene protein.\n\nConclusionAccording to this study, thirty two novel nsSNP in HEXA are predicted to have possible role in Tay-Saches Disease using different bioinformatics tools. Our findings could help in genetic study and diagnosis of Tay-Saches Disease.

bioinformatics↗