IPBS-Toulouse

Mycobacterial Envelopes and Therapeutic Targets

Picture of Hedia Marrakchi
Hedia Marrakchi

Group Leader

 

The main objective of our research group is the characterization of potential drug targets, from their identification to deciphering their mechanisms of action and roles in physiology and infection, for application in the context of improving anti-tuberculosis therapy. Our research includes better understanding of metabolic pathways and enzymes involved in cell envelope lipid biogenesis in Mycobacterium tuberculosis.

Our team focuses on metabolic pathways of mycobacterial envelope lipids in order to characterize new targets and design innovative therapeutic agents to face antibiotic resistance in tuberculosis.

Tuberculosis (TB), caused by Mycobacterium tuberculosis (Mtb), is one of the leading causes of death worldwide. The rise in drug resistance highlights the urgent need for novel anti-TB drug development. We use interdisciplinary approaches to develop various aspects of early-stage drug discovery, ranging from identification to exploitation of promising anti-TB targets with significant pharmaceutical interest to develop novel molecules with unexplored modes of action. Our expertise relies on complementary approaches in structural and quantitative biochemistry of lipids and glycoconjugates, microbiology, molecular biology, protein biotechnology and enzymology, enzyme assay development and target validation.

In this context, our main findings include:

The characterization and inhibition of enzymes involved in cell envelope biogenesis

Mycobacterial envelope is unique in the bacterial world, both in terms of composition, consisting of structurally exotic compounds, and their arrangement, including the occurrence of an outer and inner membranes. Targeting enzymes involved in cell envelope biosynthesis has been of major interest for anti-TB drug discovery. Our approach is illustrated here through the study of FAAL32, a fatty acyl-AMP ligase and a potential target, involved in the biosynthesis of the cell wall very long-chain fatty acids called mycolic acids. To validate this protein as a druggable target, we initiated a drug repurposing campaign and screened a collection of 1280 approved drugs (Prestwick Chemical Library) using a biochemical assay that reads out FAAL32 inhibition. These efforts led to discovery of salicylanilide closantel, and some of its derivatives as inhibitors with potent in vitro activity against Mtb. These results suggest that salicylanilide represent a potentially promising pharmacophore for the conception of novel anti-tubercular candidates that would open new targeting opportunities.

The structural and functional characterization of antibiotic-activating enzymes

Many anti-TB drugs require bioactivation, notably by Baeyer-Villiger monooxygenases (BVMOs). Despite their emerging importance, BVMO structural and functional features remain enigmatic. Combining in silico characterization with in vitro protein activity validation, we recently outlined structural framework and substrate preference of Mtb BVMO enzymes. These features ground the molecular basis for structure-function comprehension of the specificity in these enzymes and open for expansion of the repertoire of BVMO substrates, including prodrugs.
We also investigate the physiological roles and the functional relevance of the BVMO proteins in Mtb adaptation and resistance to stress conditions. We use genetically-modified mycobacteria and phenotypic and lipidomics characterizations to asses induced changes and cell envelope remodeling under stress conditions.

The development of bioinspired molecules for antituberculosis drug development

The increasing emergence of multi- and extremely-drug resistant Mtb to current treatment calls for the urgent need to develop novel chemical series of anti-TB drugs acting on original targets. Building on recent evidence, we propose that bioinspired lipids – based on compounds isolated from medicinal plants – represent a new class of anti-TB molecules with new mechanisms of action. In collaboration with chemistry groups, we are developing an inter-disciplinary approach to improve their activity against Mtb as well as other pathogenic mycobacteria, including Mycobacterium abscessus, and their pharmacokinetic properties while decreasing their cytotoxicity.

Team members

Research Scientists

Anne Lemassu (University)
Hedia Marrakchi (CNRS)

Research Engineer

Patricia Constant (CNRS)
Léa Masson

PhD Students

Martin Campoy

Dimitri Leonelli

Chloé Garcia

Chérine Mehalla

Rathies Ravindra

Our research projects

Characterization and inhibition of enzymes involved in cell envelope biogenesis

Structural and functional characterization of antibiotic-activating enzymes

Bioinspired molecules for antituberculosis drug development

Tomas*, Leonelli* et al. (2022) Bioinformatic Mining and Structure-Activity Profiling of Baeyer-Villiger Monooxygenases from Mycobacterium tuberculosis. mSphere

Le et al. (2022) Drug screening approach against mycobacterial fatty acyl-AMP ligase FAAL32 renews the interest of the salicylanilide pharmacophore in the fight against tuberculosis. Bioorg Med Chem

Lanéelle et al. (2021) Lipid and Lipoarabinomannan Isolation and Characterization. Methods Mol Biol

Le et al. (2020) The protein kinase PknB negatively regulates biosynthesis and trafficking of mycolic acids in mycobacteria. J Lipid Res

Daffé, Marrakchi (2019) Unraveling the Structure of the Mycobacterial Envelope. Microbiol Spectr

Chiaradia et al. (2017) Dissecting the mycobacterial cell envelope and defining the composition of the native mycomembrane. Sci Rep

 

Organization of the mycobacterial envelope. AG, arabinogalactan; PG, peptidoglycan; GL, granular layer; PM, plasma membrane.