Biology subjects

Mendum, T. A.

Publications and source records attributed to Mendum, T. A..

7 recordsLinked to original sources

bioRxiv2026

Phosphoserine aminotransferase SerC is a central metabolic checkpoint and druggable vulnerability in Mycobacterium tuberculosis

Serine metabolism is fundamental to the pathogenicity of Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis (TB), yet its full metabolic scope and therapeutic potential remain unclear. Here we show that the phosphoserine aminotransferase serC is an essential metabolic node that coordinates central carbon and nitrogen flux and enables intracellular survival in the host. Deletion of serC caused severe growth defects across macrophage and murine infection models and rewired central carbon metabolism, reducing glycolytic, tricarboxylic-acid-cycle, and methylcitrate-cycle fluxes while altering one-carbon, branched-chain, and amino-acid biosynthetic pathways. Transposon sequencing identified sdaA-dependent serine deamination and the glycine cleavage system as key determinants of serine-based nitrogen assimilation, while revealing redundancy in serine transport. Our findings validate serine biosynthesis as a vulnerable, druggable metabolic target in Mtb and highlight it as a promising route for the development of urgently needed therapies against TB, which continues to kill millions of people each year.

microbiology↗

bioRxiv2025

Mosquito NF-κB-mediated innate immunity exerts arbovirus-specific antiviral effects at multiple stages of the viral life cycle

One third of all emerging infectious diseases are vector-borne, with the vectors ecology and physiology playing key roles in determining whether viruses can access new vertebrate host species and spread globally. Innate immunity is a known barrier to virus replication in mosquito vectors that influences arboviral vector tropism. We here generated novel CRISPR-Cas9-mediated knockouts of the NF-{kappa}B family transcription factor Rel2 in Aedes aegypti-derived Aag2 cells and tested the impact on the replication of a diverse range of arboviruses in the Flaviviridae and Togaviridae families and the class Bunyaviricetes. We found that NF-{kappa}B-mediated innate immunity has broad antiviral activity against the Ae. aegypti-borne orthoflaviviruses dengue virus (DENV), yellow fever virus (YFV) and Zika virus (ZIKV) in mosquito cells. In contrast, little impact of NF-{kappa}B-loss-of-function was observed for the alphavirus chikungunya virus (CHIKV) or phlebovirus Rift Valley fever virus (RVFV), indicating specificity in the antiviral effects of NF-{kappa}B-mediated immunity. By comparing orthoflaviviruses with different transmission routes (mosquito-borne, tick-borne, no known vector), we demonstrated that NF-{kappa}B-mediated immunity exerts its antiviral effects both early and late in the viral replication cycle, and that NF-{kappa}B-mediated immunity is not the only molecular barrier influencing the ability of orthoflaviviruses to replicate in Ae. aegypti cells. Overall, our work demonstrates the importance of mosquito NF-{kappa}B-mediated innate immunity in suppressing arbovirus replication, and shows that the barriers for arboviruses to adapt to new vector species are multifactorial and virus-specific. Our findings increase our understanding of the molecular barriers influencing arboviral emergence, and could inform the development of refractory mosquitoes incapable of transmitting human pathogens. Author SummaryMosquito-borne viruses are causing an increasing global disease burden due to urbanisation, globalisation, changing land use and the climate change-driven invasion of mosquitoes into new locations. Few vaccines and no medicines for mosquito-borne viral infections are licensed for human use. Historically, the most effective way to reduce human disease has been to kill mosquitoes using insecticides, which also harms beneficial insects and is leading to resistance. Newer technologies with lower ecological impacts are being developed, including genetically modified mosquitoes with a reduced ability to transmit viruses. Like humans, mosquitoes have an immune system that protects against viral infections, and strengthening this immune system through genetic modification has shown promise for reducing virus transmission. We here expand our understanding of the ways in which mosquito immunity could be harnessed by demonstrating that a gene called "Rel2" helps the mosquito fight mosquito-borne virus infection. Unlike previously studied mosquito immune responses, Rel2 has a very broad (but not universal) protective capacity against viruses. Our work also indicates that Rel2 works in concert with other arms of the mosquito immune system, highlighting a need for further research to fully realise the potential of genetically modifying mosquito immune responses for the prevention of human disease.

microbiology↗

bioRxiv2025

VadK, a Non-Canonical Kinase that Regulates the Methylcitrate Cycle and is Essential for Mycobacterium tuberculosis Virulence

The evolution of new enzymatic functions is constrained and guided by the architecture of an organisms metabolic and regulatory networks as well as by environmental constraints. Here, we identify a previously uncharacterized kinase that has evolved from pyruvate phosphate dikinase (PPDK). Through biochemical and systems-level analyses, we show that this enzyme, encoded by Rv1127c in Mycobacterium tuberculosis (Mtb), has diverged from its ancestral role in central carbon metabolism to function as a histidine kinase in pathogenic mycobacteria and related species. We designate this enzyme Virulence Associated DiKinase (VadK), reflecting its ability to autophosphorylate and role in coordinating metabolism and virulence. VadK is essential for the utilization of exogenous carbon sources critical for survival within the host and is required for Mtb pathogenicity in murine models of tuberculosis. Furthermore, VadK interacts with key enzymes of the methylcitrate cycle, and 13C-metabolic flux analysis indicates that it fine-tunes flux through this pathway, with elevated flux proving growth limiting. Together, these findings identify VadK as a previously unrecognized regulatory kinase that integrates metabolic control with virulence in Mtb, revealing a new facet of metabolic regulation in bacterial pathogenesis and a potential target for therapeutic intervention.

microbiology↗

bioRxiv2023

Temporal genome-wide fitness analysis of Mycobacterium marinum during infection reveals genetic requirement for virulence and survival in amoebae and microglial cells

Tuberculosis remains the most pervasive infectious disease and the recent emergence of multiple or even fully drug-resistant strains increases the risk and emphasizes the need for more efficient and better drug treatments. A key feature of mycobacteria pathogenesis is the metabolic switch during infection and expression of virulence genes is often adapted to specific infection conditions. This study aims to identify genes that are involved in the establishment and maintenance of the infection. To answer these questions, we have applied Transposon Sequencing (Tn-Seq) in M. marinum, an unbiased genome-wide strategy that combines saturation insertional mutagenesis and high throughput sequencing. This approach allowed us to precisely identify the localization and relative abundance of insertions in pools of Tn mutants. The essentiality and fitness cost, in terms of growth advantage and disadvantage of over 105 mutants were quantitatively compared between in vitro and different stages of infection in two evolutionary distinct hosts, D. discoideum and BV2 microglial cells. We found that 57% of TA sites in the M. marinum genome were disrupted and that 568 genes (10.2%) are essential for M. marinum, which is comparable to previous Tn-Seq studies on M. tuberculosis. The major pathways involved in the survival of M. marinum during infection of D. discoideum were related to vitamin metabolism, the esx-1 operon, as well as the mce1 operon.

microbiology↗

bioRxiv2023

Mycolactone causes catastrophic Sec61-dependent loss of the endothelial glycocalyx and basement membrane: a new indirect mechanism driving tissue necrosis in Mycobacterium ulcerans infection

The drivers of tissue necrosis in Mycobacterium ulcerans infection (Buruli ulcer disease) have historically been ascribed solely to the directly cytotoxic action of the diffusible exotoxin, mycolactone. However, its role in the clinically-evident vascular component of disease aetiology remains poorly explained. We have now dissected mycolactones effects on primary vascular endothelial cells in vitro and in vivo. We show that mycolactone-induced changes in endothelial morphology, adhesion, migration, and permeability are dependent on its action at the Sec61 translocon. Unbiased quantitative proteomics identified a profound effect on proteoglycans, driven by rapid loss of type II transmembrane proteins of the Golgi, including enzymes required for glycosaminoglycan (GAG) synthesis, combined with a reduction in the core proteins themselves. Loss of the glycocalyx is likely to be of particular mechanistic importance, since knockdown of galactosyltransferase II (beta-1,3-galactotransferase 6; B3GALT6), the GAG linker-building enzyme, phenocopied the permeability and phenotypic changes induced by mycolactone. Additionally, mycolactone depleted many secreted basement membrane components and microvascular basement membranes were disrupted in vivo. Remarkably, exogenous addition of laminin-511 reduced endothelial cell rounding, restored cell attachment and reversed the defective migration caused by mycolactone. Hence supplementing mycolactone-depleted extracellular matrix may be a future therapeutic avenue, to improve wound healing rates.

microbiology↗

bioRxiv2021

Metabolic flux partitioning between the TCA cycle and glyoxylate shunt combined with a reversible methyl citrate cycle provide nutritional flexibility for Mycobacterium tuberculosis

The utilisation of multiple host-derived carbon substrates is required by Mycobacterium tuberculosis (Mtb) to successfully sustain a tuberculosis infection thereby identifying the Mtb specific metabolic pathways and enzymes required for carbon co-metabolism as potential drug targets. Metabolic flux represents the final integrative outcome of many different levels of cellular regulation that contribute to the flow of metabolites through the metabolic network. It is therefore critical that we have an in-depth understanding of the rewiring of metabolic fluxes in different conditions. Here, we employed 13C-metabolic flux analysis using stable isotope tracers (13C and 2H) and lipid fingerprinting to investigate the metabolic network of Mtb growing slowly on physiologically relevant carbon sources in a steady state chemostat. We demonstrate that Mtb is able to efficiently co-metabolise combinations of either cholesterol or glycerol along with C2 generating carbon substrates. The uniform assimilation of the carbon sources by Mtb throughout the network indicated no compartmentalization of metabolism in these conditions however there were substrate specific differences in metabolic fluxes. This work identified that partitioning of flux between the TCA cycle and the glyoxylate shunt combined with a reversible methyl citrate cycle as the critical metabolic nodes which underlie the nutritional flexibility of Mtb. These findings provide new insights into the metabolic architecture that affords adaptability of Mtb to divergent carbon substrates. ImportanceEach year more than 1 million people die of tuberculosis (TB). Many more are infected but successfully diagnosed and treated with antibiotics, however antibiotic-resistant TB isolates are becoming ever more prevalent and so novel therapies are urgently needed that can effectively kill the causative agent. Mtb specific metabolic pathways have been identified as an important drug target in TB. However the apparent metabolic plasticity of this pathogen presents a major obstacle to efficient targeting of Mtb specific vulnerabilities and therefore it is critical to define the metabolic fluxes that Mtb utilises in different conditions. Here, we used 13C-metabolic flux analysis to measure the metabolic fluxes that Mtb uses whilst growing on potential in vivo nutrients. Our analysis identified selective use of the metabolic network that included the TCA cycle, glyoxylate shunt and methyl citrate cycle. The metabolic flux phenotypes determined in this study improves our understanding about the co-metabolism of multiple carbon substrates by Mtb identifying a reversible methyl citrate cycle and the glyoxylate shunt as the critical metabolic nodes which underlie the nutritional flexibility of Mtb.

systems biology↗

bioRxiv2019

A systematic evaluation of Mycobacterium tuberculosis Genome-Scale Metabolic Networks

The metabolism of the causative agent of TB, Mycobacterium tuberculosis (Mtb) has recently re-emerged as an attractive drug target. A powerful approach to study Mtb metabolism is to use a systems biology framework, such as a Genome-Scale Metabolic Network (GSMN) that allows the dynamic interactions of the many individual components of metabolism to be interrogated together. Several GSMNs networks have been constructed for Mtb and used to study the complex relationship between Mtb genotype and phenotype. However, their utility is hampered by the existence of multiple models of varying properties and performances. Here we systematically evaluate eight recently published metabolic models of Mtb-H37Rv to facilitate model choice. The best performing models, sMtb2018 and iEK1011, were refined and improved for use in future studies by the TB research community.

systems biology↗