Biology subjects

Grundner, C.

Publications and source records attributed to Grundner, C..

6 recordsLinked to original sources

bioRxiv2026

Inorganic sulfate transport by the Mycobacterium tuberculosis PE22/PPE36 complex

Mycobacterium tuberculosis (Mtb) encodes two multigene families with 169 members that are exclusive to mycobacteria, the pe and ppe genes. These genes have unusual sequences including low-complexity repeat regions, but their functions--and whether they share a common function--have long been unclear. Recently, several members of the pe/ppe family were shown to transport nutrients across the outer Mtb membrane, a role for which no other proteins have yet been identified. Whether nutrient transport is a family-wide function and the range of nutrients transported by the PE/PPEs remains unclear. Sulfur is an essential nutrient for Mtb physiology and pathogenesis. To test whether PE/PPE transporters contribute to sulfur acquisition, we analyzed the transcriptional response of Mtb to sulfate by RNA sequencing. The pe22/ppe36 genes were induced in sulfate-limiting conditions. Deletion of pe22/ppe36 impaired growth in low-sulfate media and reduced intracellular sulfate levels, effects that were reversed by heterologous expression of the Mycobacterium smegmatis porin MspA. The response of sulfur-responsive genes to sulfur was muted in the pe22/ppe36 deletion strain, and mass spectrometry showed lower sulfolipid and sulfur metabolite levels in the deletion strain. These findings identify PE22/PPE36 as a specific sulfate uptake system and supports the emerging idea of PE/PPE proteins as nutrient uptake systems across the Mtb outer membrane. Significance statementThe mechanism of nutrient transport across the porin-less mycobacterial outer membrane and the function of the large pe/ppe gene family have been longstanding questions in mycobacterial biology. This study shows that the Mycobacterium tuberculosis PE22/PPE36 complex serves as a selective conduit for inorganic sulfate. Deletion of this complex disrupts intracellular sulfur homeostasis and triggers a metabolic seesaw that depletes cell-surface sulfolipids. Our findings expand the PE/PPE transport paradigm and suggest a direct link between nutrient acquisition and TB transmission.

microbiology↗

bioRxiv2025

PE/PPE proteins contribute to Mycobacterium tuberculosis drug resistance

The outer membrane (OM) of mycobacteria is a formidable permeability barrier that confers drug tolerance, and whether drugs traverse the OM by mechanisms beyond passive diffusion remains unclear. The proline-glutamic acid (PE) and proline-proline-glutamic acid (PPE) proteins of pathogenic mycobacteria include several OM transporters. Here, we tested the role of PE/PPE proteins in Mycobacterium tuberculosis (Mtb) drug transport and resistance. Mutations in multiple pe/ppe genes were strongly associated with drug resistance in a genetic association study, and mutations in ppe42 and ppe51 also conferred increased resistance in vitro. Deletion of a pe/ppe pair transcriptionally responsive to drug exposure, pe25/ppe41, led to elevated resistance to isoniazid (INH) across all major Mtb lineages and accelerated INH resistance emergence in vitro. These data identify a role for Mtb PE/PPE proteins in drug resistance consistent with the PE/PPE transporter paradigm, suggest a broader contribution of this large protein family, and a new factor of Mtb clinical drug resistance.

microbiology↗

bioRxiv2022

Calcium transport by the Mycobacterium tuberculosis PE15/PPE20 proteins

Many aspects of eukaryotic physiology are regulated by calcium ions (Ca2+). Whether bacteria have similar Ca2+ systems for transport, storage, binding, and response to Ca2+ is not well understood. To identify components of Ca2+ signaling in Mycobacterium tuberculosis, we determined its transcriptional response to Ca2+. Overall, only few genes changed expression, suggesting a limited role of Ca2+ as a transcriptional regulator. However, two of the most strongly downregulated genes were the pe15 and ppe20 genes that code for members of a large family of proteins that localizes to the outer membrane. PE15 and PPE20 formed a complex and PPE20 directly bound Ca2+. Ca2+-associated phenotypes such as an increase in ATP consumption and increase in biofilm formation were reversed in a pe15/ppe20 knockout strain, suggesting a direct role in Ca2+ homeostasis. To test whether the complex has a role in Ca2+ transport across the outer membrane, we created a fluorescence resonance energy transfer (FRET)-based Ca2+ reporter strain. A pe15/ppe20 knockout in the FRET background showed a specific and selective loss of Ca2+ influx that was dependent on the presence of an intact outer cell wall. These data show that PE15/PPE20 form a Ca2+-binding protein complex that selectively imports Ca2+ and support the emerging idea of a general family-wide role of PE/PPE proteins in transport across the outer membrane.

microbiology↗

bioRxiv2022

The Mycobacterium tuberculosis protein O-phosphorylation landscape

Bacterial phosphosignaling has long been synonymous with the histidine kinases of the two component systems, but many bacteria, including Mycobacterium tuberculosis (Mtb), also code for Ser/Thr protein kinases (STPKs). STPKs are the main phosphosignaling enzymes in eukaryotes, but the full extent of phosphorylation on protein Ser/Thr and Tyr (O-phosphorylation) in bacteria remains unclear. Here, we explored the global signaling capacity of the STPKs in Mtb. We generated STPK loss-and gain-of-function strains and measured the resulting O-phosphorylation and transcriptional changes. This deep phosphoproteome shows that O-phosphorylation in Mtb is an underexplored protein modification that affects >70% of the proteome. The substrate-STPK interactions show an extensive interface with the transcriptional machinery, resulting in regulation of gene expression of [~]30% of Mtb genes. Mtb O-phosphorylation gives rise to an expansive, distributed, and cooperative network of a complexity that has previously only been associated with eukaryotic phosphosignaling networks.

microbiology↗

bioRxiv2021

An Alternative, Cas12a-based CRISPR Interference System for Mycobacteria

The introduction of CRISPR interference (CRISPRi) has made gene repression in mycobacteria much more efficient, but technical challenges of the prototypical Cas9-based platform, for example in multigene regulation, remain. Here, we introduce an alternative CRSPRi platform that uses the minimal Cas12a enzyme in combination with synthetic CRISPR arrays. This system is simple, tunable, and can regulate multiple genes simultaneously, providing a new tool to probe higher-order genetic interactions in mycobacteria including Mycobacterium tuberculosis (Mtb).

genetics↗

bioRxiv2019

Anti-tubercular activity of novel 4-anilinoquinolines and 4-anilinoquinazolines

We screened a series of 4-anilinoquinolines and 4-anilinoquinazolines and identified novel inhibitors of Mycobacterium tuberculosis (Mtb). The focused 4-anilinoquinoline/quinazoline scaffold arrays yielded compounds with high potency and the identification of 6,7-dimethoxy-N-(4-((4-methylbenzyl)oxy)phenyl)quinolin-4-amine (34) with an MIC90 value of 0.63-1.25 M. We also defined a series of key structural features, including the benzyloxy aniline and the 6,7-dimethoxy quinoline ring, that are important for Mtb inhibition. Importantly the compounds showed very limited toxicity and scope for further improvement by iterative medicinal chemistry.

pharmacology and toxicology↗