Biology subjects

Besra, G. S.

Publications and source records attributed to Besra, G. S..

7 recordsLinked to original sources

bioRxiv2026

Polyketide synthase 12 is an in vivo essential source of novel mycolyl lipids in Mycobacterium tuberculosis

Mycobacterium tuberculosis (Mtb) is a major pathogen worldwide that infects and transmits only among humans, yet nearly all in vivo virulence research occurs in non-human hosts. To overcome this central challenge in tuberculosis research, we leveraged a dataset of more than 50,000 sequenced isolates to identify Mtb genes that that are functionally preserved during natural infection, disease causation, and transmission between humans. This whole-genome ranking identified polyketide synthase 12 (pks12 ) as an exceptionally in vivo essential gene in human tuberculosis, which we validated in zebrafish and mouse models. Though Pks12 produces a mycoketide lipid in only trace amounts, pks12 deletion severely altered the host-facing surface and arabinoglycan architecture of Mtb. This amplified effect was explained through the discovery of mannosyl-{beta}-1-phosphomycoketide monomycolate (MPMMM), which is synthesized from the known Pks12 product at higher abundance by antigen 85 mycolyltransferases. Thus, we used a new host-facing genomic-metabolomic-phenotypic approach to discover the functions of an in vivo essential Mtb gene, which controls the physical structure of the Mtb-host interface.

microbiology↗

bioRxiv2023

The mycobacterial glycoside hydrolase LamH enables capsular arabinomannan release and stimulates growth

Mycobacterial glycolipids are important cell envelope structures that drive host-pathogen interactions. Arguably, the most important amongst these are lipoarabinomannan (LAM) and its precursor, lipomannan (LM), which are both trafficked out of the bacterium to the host via unknown mechanisms. An important class of exported LM/LAM is the capsular derivative of these molecules which is devoid of its lipid anchor. Here, we describe the identification of a glycoside hydrolase family 76 enzyme that we term LamH which specifically cleaves -1,6-mannoside linkages within LM and LAM, driving its export to the capsule releasing its phosphatidyl-myo-inositol mannoside lipid anchor. Unexpectedly, we found that the catalytic activity of this enzyme is important for efficient exit from stationary phase cultures where arabinomannan acts as a signal for growth phase transition. Finally, we demonstrate that LamH is important for Mycobacterium tuberculosis survival in macrophages. These data provide a new framework for understanding the biological role of LAM in mycobacteria.

microbiology↗

bioRxiv2023

Conserved allomorphs of MR1 drive specificity of MR1-restricted TCRs

Major histocompatibility complex class-1-related protein (MR1), unlike human leukocyte antigen (HLA) class-1, has until recently been reported to be monomorphic. Tumor cell-specific MR1 restricted T cell receptors (TCRs) have been described, offering potential therapeutic application for cancer treatment. We show that human T cells expressing a TCR derived from an MR1-restricted T cell clone, termed MC.7.G5 (7G5.TCRT), retain MR1-directed cytotoxicity. However, activity is not pan-cancer, as initially reported with the clone MC.7.G5. Recognition is restricted by an allelic variant of MR1 (MR1*04) which is present at approximately 1% of the population at the heterozygote level. The 7G5 TCR is not cancer specific, as 7G5.TCRT and 7G5.TCRT-like TCRs react to both cancer and healthy cells expressing MR1*04 alleles. These data demonstrate that healthy individuals can harbor T cells reactive to an MR1 variant displaying self-ligands expressed in cancer and benign tissues. Targeting MR1 in cancer will require identification of cancer-specific presented ligands, and careful confirmation of cancer specificity of TCRs. MR1*04 may behave as an alloantigen warranting further study.

cancer biology↗

bioRxiv2022

Repurposing Vanoxerine as a new antimycobacterial drug and its impact on the mycobacterial membrane

Mycobacterium tuberculosis is a deadly pathogen, currently the leading cause of death worldwide from a single infectious agent through tuberculosis infections. If the End TB 2030 strategy is to be achieved, additional drugs need to be identified and made available to supplement the current treatment regimen. In addition, drug resistance is a growing issue, leading to significantly lower treatment success rates, necessitating further drug development. Vanoxerine (GBR12909), a dopamine re-uptake inhibitor, was recently identified as having anti-mycobacterial activity. Repurposing vanoxerine or its analogues to treat tuberculosis infections may allow a faster route to clinical use than novel drug discovery. However, its effects on Mycobacteria were not well characterised. Herein, we report vanoxerine as a disruptor of the membrane potential, inhibiting mycobacterial efflux and survival, with an undetectable level of resistance. This study suggests a mechanism of action for vanoxerine, which will allow for its continued development and optimisation for pre-clinical testing.

microbiology↗

bioRxiv2019

African Salmonella Typhimurium sequence type 313 lineage 2 evades MAIT cell recognition by overexpressing RibB

Mucosal-associated invariant T (MAIT) cells are a subset of innate T lymphocytes activated by bacteria that produce vitamin B2 metabolites. Mouse models of infection have demonstrated a role for MAIT cells in antimicrobial defence. However, proposed protective roles of MAIT cells in human infections remain unproven and clinical conditions associated with a selective absence of MAIT cells have not been identified. We report that typhoidal and non-typhoidal S. enterica strains generally activate MAIT cells. However, African invasive disease-associated multidrug-resistant S. Typhimurium sequence type 313 lineage 2 strains escape MAIT cell recognition through overexpression of ribB, a bacterial gene that encodes the 4-dihydroxy-2-butanone 4-phosphate synthase enzyme of the riboflavin biosynthetic pathway. This MAIT cell-specific phenotype did not extend to other innate lymphocytes. We propose that ribB overexpression is an evolved trait that facilitates evasion from immune recognition by MAIT cells and contributes to the invasive pathogenesis of S. Typhimurium sequence type 313 lineage 2 in vivo.

immunology↗

bioRxiv2018

A novel mutation alters the stability of PapA2 resulting in the complete abrogation of sulfolipids in clinical mycobacterial strains

The analysis of whole genome has revealed specific geographical distribution of Mycobacterium tuberculosis (Mtb) strains across the globe suggestive of unique host dependent adaptive mechanisms in Mtb evolved out of selective pressures. We provide an important correlation of a genome-based mutation to a molecular phenotype across two predominant clinical Mtb lineages of the Indian subcontinent. We have identified a distinct lineage specific mutation-G247C, translating into an alanine to proline conversion in the papA2 gene of Indo oceanic lineage 1 [L1] Mtb strains; restoration of cell wall sulfolipids by simple genetic complementation of papA2 from lineage 3 [L3] or from H37Rv (Lineage 4-L4) attributed the loss of this glycolipid to this specific mutation in Indo oceanic L1 Mtb. Investigation into the structure of Mtb PapA2 revealed a distinct non-ribosomal peptide synthetase (NRPS) C domain conformation with an unconventional presence of Zinc binding motif. Surprisingly, the A83P mutation did not map to either the catalytic centre in the N-terminal subdomain or any of the substrate binding region of the protein. On the contrary, the inherent ability of mutant PapA2 to form insoluble aggregates and molecular simulations with the Wt/ mut PapA2 purports an important role for the surface associated 83rd residue in protein conformation. The present study demonstrates the importance of a critical structural residue in the papA2 protein of Mtb and helps establish a link between observed genomic alteration and its molecular consequence in the successful human pathogen Mtb.

molecular biology↗

bioRxiv2018

Mycobacteria recycle their peptidoglycan via a novel pathway which influences antimicrobial resistance and limits proliferation in macrophages.

Growth and division by most bacteria requires remodeling and cleavage of their cell wall. A byproduct of this process is the generation of free peptidoglycan (PG) fragments known as muropeptides. These muropeptides are recycled in many model organisms, where the bacteria can harness their unique nature as a signal for cell wall damage. These molecules also serve as important signals for hosts where binding to specific receptors reports on the presence of intracellular bacteria. Despite this critical role for muropeptides, it has long been thought that pathogenic mycobacteria such as Mycobacterium tuberculosis do not recycle their PG. Herein we show for the first time that M. tuberculosis and Mycobacterium bovis BCG are able to recycle components of their PG. We demonstrate that the core-mycobacterial gene lpqI, encodes an authentic NagZ {beta}-N-acetylglucosaminidase and that it is essential for PG-derived amino sugar recycling via an unusual pathway. By characterizing an M. bovis BCG strain lacking lpqI we are also able to show that stem-peptide recycling proceeds independent of amino sugar recovery and loss of lpqI leads to antimicrobial resistance in vitro. Together these data provide a critical first step in understanding how mycobacteria recycle their peptidoglycan.

microbiology↗